Thanks for the add! I came here because most of the useful information I have found in my internet searches so far have come from this forum but I haven't figured out a few last details and hoping someone can contribute that on this thread since I haven't been able to find it in any other searches. I just acquired a Chevy T7500 containing the apparently rare Cat 3116 engine with HEUI injection system and it has the hard starting issue that seems typical of these engines. Engine fuel filter has been changed and primed, I'll check the fuel lines from the tank for pinholes on the suction side to make sure its not sucking air and fuel pressure to the injectors. Does anyone know what fuel pressure specs are for the HEUI system? I have found some info that suggests 4-9psi for MUI and 25psi for HEUI, can anyone confirm or correct that? Secondly, if I do end up taking out the injectors what tooling do I need to reinstall? It looks like the 173-1530 injector seating tooling is applicable to both MUI and HEUI, how about the injector seat reamer tooling, is that applicable to HEUI and which group? Any chance there is tooling available to rent rather than purchase for a (hopefully) 1 time use. I haven't tried the local Cat place yet but other heavy equipment/diesel shops and mobile repair trucks in the area do not have anything.
There's two parts to this video. Edit this is a mui, not heui
If you post an engine Serial Number I'm sure someone will be able to look up some specs for you.
I can't answer any of the questions, curious though. How similar is the 3116 Heui to the common 3126 Heui system? I'm not sure the injector pressure is relevant, not anything you'll measure or do anything about, is it? The oil pressure is typically important, right? Does that have a Delco direct drive 37MT or a gear reduction 39MT or Denso GR starter? If it's direct drive, that's the first thing I'd replace with a gear reduction.
This may be dated information, but when I was in college in 1999, our Cat engine guy told us the only difference then was a 3126 was only used in GM trucks, the 3116 was used in everything else, engines were identical.
Thanks! I have watched both parts and am thankful that I don't have to invest in the tooling or spend the time on synching the rack and setting injector timing manually. As you mentioned it does show the injector cup reaming process and seating process for MUI but I can't figure out if it's the exact same thing for HEUI or not?
I'll try to get the engine s/n tomorrow.
Yeah, I don't know how important or critical fuel pressure is to those injectors, seems like they would just need enough to fill em back up between injections but I did find one comment that indicated the HEUI needs more pressure than MUI so that's why I ask. Admittedly the only other HEUI system I am familiar with is on DT444Es aka Ford/Navistar 7.3 on those it's all about the oil pressure. I think the 3116 HEUI system might be the same as the 3126 HEUI but would like a little more confirmation so I know what I'm getting into before tearing into it. For the starter, I'll check it out next time I'm in the shop. At a quick first glance it did look like it was newer than surrounding parts and had nice new clean connections and spins the engine over quite nicely but didn't look any closer to know what kind.
I've seen a few other comments eluding to the roughly the same thing, at least that the 3116 HEUI is the same as the 3126 (I don't know if they had a MUI version?) I think I ended up with one of the rare versions where Cat developed the 3116 to be HEUI instead of MUI for GM trucks which then became the 3126 used in subsequent GM trucks? I am kinda leaning towards proceeding with the assumption that they might be the same and use the tooling and procedures recommended for the 3126.
Sorry, I completely misread that, I thought you were talking about the actual injector pressure, and my mind put a k in those pressures. The fuel supply pressure is relevant.
Fuel pressure is probably pretty important. I know about the 6.0 heui which needs 60+ psi and will have wot problems when you get around 50. Put a fuse on it tape it to the windshield and check it driving
engine s/n is 8WL02879. Couldn't see starter brand just a black label with red stripe through it but looks newer and appears to be gear reduction. It does not seem to struggle to turn the engine over or turn it slowly.
Easy with a Serial Number. From the Service Manual..... "Fuel pressure at the inlet to the secondary fuel filter should be between 58 and 76 psi during normal operating conditions under load. At low idle, fuel pressure at the filter inlet should be between 58 and 63 psi. Fuel pressure to the cylinder head fuel gallery should be similar to the above, less the pressure drop across the secondary fuel filter. Pressure drop across the secondary fuel filter is typically at least 5 psi with a new filter. As the filter accumulates deposits, the pressure differential will increase. If fuel pressure in the fuel gallery at the injectors decreases to approximately 10 psi misfiring may occur."
Thanks much! Now if only I could get it started to check fuel pressure during normal operating conditions... Previous owner and shop I picked it up from said it will start on a warm day, been seeing highs in the 30s here recently and hasn't quite been enough to get it to take off. I do need to verify no air in fuel still and maybe check intake heater too.
Air in any of these unit injector engines is a automatic fail. I haven't seen you mention anything about a primer pump. If it has one, you need to bleed, bleed, bleed. If it doesn't, your life just got way more complicated. Until you have full transfer pump pressure to the fuel rail, that engine isn't even going to try and fire. Once you've established good fuel to the transfer pump, and see fuel pressure at the head, it's a matter of cranking until it starts. Some of these can be a real mother-fer.
Thanks for the information, oh boy this sounds like fun..?! I haven't had a chance to familiarize myself much with this truck/engine yet, charged batteries, cranked it over a few times, and rolled around underneath it in the snow just long enough to cage the breaks so I could winch it on the trailer. I'll look for a primer pump next time I get a chance to mess with this (maybe this weekend?) Where is the transfer pump located and is it mechanical or electric? It will hit on one cylinder after about 5-8 seconds of cracking then once again every 5-8 seconds thereafter. Light colored smoke out the stack while cranking with a corresponding puff on each hit. Sure seems to be some kind of fuel delivery/atomization issue out of the injectors.
Still has air in it.
Update on this. No priming pump on this engine, we went through many cranking campaigns cracking lines and trying to bleed air with no change in wanting to start. Went through all the fuel lines from tank to engine and back and didn't find any issues in them and no evidence of sucking air when line was cracked going to the fuel galley. I don't have the fancy little clear line section to count bubbles going back to the tank but I'm thinking I have some injectors/injector sleeves leaking compression air into the fuel galley. I went ahead and pulled the injectors and will send them off for testing just to make sure they are good which leads me to my next hang-up. Apparently I have some really oddball HEUI injectors (sorry for the redundancy on the I, struggling to figure out how to write that correctly for those that read the acronym in their head...) They have the solenoid on the side and oil is fed to the top of the injectors through a short steel line from the oil galley to the injector top, the injector body looks identical to the 3116 MUI with just a single o-ring at the top. So now I'm searching for a local diesel shop with a test bench that can test these injectors... This of course sends me down the path of probably needing to ream the sleeves and reinstall injectors using the 'seating method' that Cat requires. Local Cat mobile service is $190/hr (travel and labor) and by my estimation will likely exceed 6 hours of travel and labor (1.5hrs each direction) if they even have the correct tooling to do this (I'm waiting for a call to confirm that). Looks like I can get the 143-2099 tool group that will do reaming and injector installation plus sleeve removal and reinstallation tooling (which I hope I don't need to do) for about $2500 on ebay, Freedom Racing does not have the set in stock that does just reaming and injector installation for $1300 but it looks like I can piece together the bare minimum necessary ream tooling and injector installation tooling (173-1530) for about $1000. Can anyone confirm I am looking for the right stuff with the 143-2099 and/or 173-1530 tooling sets for this application as described above or from the engine S/N provided earlier? Also I'm interested in suggestions or thoughts on how to proceed: just pay Cat service tech $1000-$2000 to do this, invest in ebay tooling at about $2500 and get the ability to remove and install injector sleeves, or invest in Freedom Racing tooling at about $1000. Note this is more of a personal project so I'm not figuring in my labor as a cost and have no reservations about being able to perform the work correctly myself.
I wouldn't waste your time. Even Cat dealers don't have the equipment to test them. Reman or replace with new - YMMV. If that's yours in the illustration below it's a pretty standard design of HEUI injector.
In that video I posted they were having trouble finding the tooling to adjust the rack, I imagine they might struggle to find the tooling to do the sleeves, I think it's also in the video. Might be best to do your self.
If no smoke comes out of the exhaust during cranking my bet would be on a hydraulic leak on the HP side of the injection system. The HEUI pump takes engine oil and jacks the pressure up to around 3000psi then sends it to the cylinder head top operate the injectors. The electronics simply control the flow of HP oil into the injectors to push the plungers. It's a bit late now but you could have put a pressure gauge on to the cyloinder head, either where the pressure sensor fits or one of the plugs in the oil gallery, and measured the HP oil pressure while cranking. If it wasn't making well over 2500+psi the electronics are not going to come out to play. See the attached for a bit of homework on how the engine operates.
Thanks for the homework and more good information. We were getting smoke out the exhaust just as I would expect from your description and the info provided. Nothing for the first second of cranking while it built oil pressure presumably then consistently from then on and would fire on a single cylinder every now and then. I meant to put a pressure gauge on both fuel and oil but got ahead of myself when I pulled the valve cover and kept on doing some dissection exploration. It does have the injectors you provided a picture of in a previous reply. I think I got the impression they were oddball because as you mentioned nobody would even consider them or had tooling to test them. I did find one guy that does 3126 HEUI and he is checking to see if he can get an injector holder or has one for his test stand that will work. At only 67k miles I wouldn't think all the injectors would need replaced at this time?
That's because there are no serviceable parts inside any model of HEUI injector, so what would anyone do if they got one apart and found worn parts in it.? No parts availability makes it not repairable. Also to test the injector requires about 3000psi on the HP oil side PLUS the electronic ability to fire the solenoid, duplicating the function of the ECM on a single cylinder if you will. Some HEUI injectors actually fire twice, a kind of pre-injection then a main injection. The type of test bench required to simulate that is AFAIK only available in the Cat Fuel Injection System facility in Pontiac IL.
Interestingly enough I am waiting for someone to come back from vacation to get the information if he thinks they have the tooling to do this. I'll probably invest in the tooling and do it myself. Might even get me a specialty side gig doing this if there are more of these engines around? Do you know if I might be on the right track with the tooling group part numbers I listed for this?
Are you talking about Cat HEUI injectors? I have had several sets of International/Navistar HEUI mostly DT444E injectors tested and remanufactured including both split shots (pre-ignition small pulse and then main fuel delivery pulse) and single shots. It is quite common to my knowledge. I'm not sure the brand but those test benches are capable of producing the high pressure oil needed (500psi - 3000ish), delivering the fuel, and electric signals to fire the solenoid. These Cat HEUIs appear to have the same solenoids (albeit mounted on the side rather than the top) and nozzles on them as the other HEUIs I have worked with and seems like they would have all the same internal parts (plunger and barrel assemblies, etc.) as others. A previous response suggested getting a set of reman injectors for this indicating they must be serviceable? I believe there could be value in testing injectors even if they are not serviceable. It should indicate if 1 or more has failed or are performing below spec or out of sync with each other. This could be corrected by just replacing the afflicted injector(s) rather than all of them.
Just because it doesn’t have a primer pump doesn’t mean you can’t prime it. Irked me that GM and Freightliner both didn’t spec these with primer pumps. That’s fine, I made money installing primer pumps and performing many service calls when customers couldn’t start them after a filter change or prolonged storage. Like someone else on this forum mentioned the other day, I liked the 3116 because I made lots of money working on them. I would connect a primer pump and try that before pulling injectors. Cylinder 5&6 will have you hating life.
$2000 for a Cat tech? Good luck You’ll spend way more than that. The 25 YO fella that shows up from the dealer, will be in awe of the first 3116 he has probably ever seen, and now gets to practice working on your rig at $190@ hr. Very few Techs, still in the workforce, are knowledgeable, tooled and capable of efficiently repairing the 1.1 & 1.2 family. You are kinda on your own.
I'm not a cat man at all I just watch that guy's videos. I don't think there are very many around and I don't truck very many mechanics to do the job right. Looking at that video I posted to you really think it will be $2000 at a dealer....and done right?
That response was mine and in my experience with other models of Cat HEUI injector what comes out of the OEM Reman-labelled box is a brand-new injector with a Reman Part Number stamped/etched on it. This was a while ago though. Even if OEM injectors are now genuine Reman products (reworked in other words) it still doesn't mean that OEM internal parts are freely available over the counter to customers. I have no idea about the availability of aftermarket internals.
A lot would depend on the quality of oil/filters used in the engine during its life and whether or not the oil change intervals had been strictly adhered to. HEUI injectors don't like dirty oil if you want them to live a long life. The same result can be obtained with a cylinder cutout test using ET without even removing the injectors. For injector installation the following tools are called out: - 164-5927 Wire Brush 9U-6862 Tapered Brush 4C-5552 Large Bore Brush 9U-6102 Reamer 173-1530 Injector Seating Tool For cylinder head injector sleeve installation the 143-2099 Unit Injector Tool Gp is required.
I really appreciate the line questioning guys. I have been my own service department my entire life except the early years of employment as an aircraft mechanic for yours and Uncle Sam's war fighting machines and therefore probably a bit naïve to the ways of current mainstream dealership/tech services. I would hope they would not quote a rate, or entertain a job if they did not have the resources (technicians) that know how to perform it and how long they expected but your input seems legit based on what I have seen with the new workforce and business practices in general. With this feedback I'm just planning on doing it myself and then I only have me to blame and pay for making it right if needed. Good advice but I jumped the gun and pulled them and now have accepted my fate of hating life sometime in the future when I put this back together and unknowingly added a new headache of trying to find someone with a test bench to check these buggers. I could be wrong but we cracked lines and cranked and had clear fuel everywhere we could check and went through more cranking campaigns than I have ever done to get any of the Perkins, other Cat, or DT engines going with no improvement in wanting to start. I would have bet a 30 rack that it would have been thoroughly purged and primed by then unless it was getting more air in. It would consistently produce smoke during cranking and it would hit on one cylinder repeatably but never more than that, it sure seemed like it was getting air in somewhere after the fuel enters the head fuel galley (presumably the sleeve to injector connection?) and that kept it from being able to fire on any downstream cylinders towards the back of the block. You mentioned installing aftermarket primer pumps on these engines. Do you have a link or information to share on what you used and where you put it? I'm considering adding such a thing for the same reasons, to get it primed after injector reinstall and when filters are changed or when it sits in storage for most the winter when I don't need it. Assuming this pans out to be worthy of adding to my fleet of inexpensive to purchase yet mentally and maintenance-ly taxing farm trucks. Good point. I picked it up with relatively new filters (maybe Napa brand if I recall correctly), used but good looking oil at the right level, and clean fuel with no water that came out the separator drain. This was just one recent snapshot in its life that suggested at least recent maintenance but I agree doesn't really speak to the full history of regular and good quality maintenance. What is ET? I am familiar with an injector "buzz" test I've done on DT444E injectors with engine off. I did the poor mans version of this when we were cranking with the valve cover off and listened and felt for each injector solenoid actuating and all seemed to be functioning. Plus the evidence of smoke and an occasional fire while cranking indicated injectors were functional and delivering some fuel but probably not at the right quantity, timing, atomization (air in fuel), or heat (compression) to combust. With the scan tool I have it does a cutout test/cylinder contribution test but only with the engine running. Not having anything to connect to this Cat EDM or IDM and with a non-running engine I didn't think I would be able to perform that test. Thanks much for the information on the tooling required! I'm going shopping now. With everyone's input and suggestions I am currently planning on purchasing the tooling to ream sleeves and reinstall injectors and avoid the costs, potential incompetency, and being at the 'mercy' of expensive dealer techs. I appreciate everyone's contributions thus far and spending the time to research and provide information to help me out. I do have a lead on someone who thinks he might be able to get an injector holder for his test bench to check these (he does 3126 HEUI injectors already). If not I'll ream the sleeves, reinstall and seat the existing injectors and try again hoping for the best in at least getting to run.
Caterpillar Electronic Technician, the OEM diagnostic software if you will. On a running engine with ET you can cut one cylinder out at a time and see the values for the other cylinders regarding fuel injection quantity & injection duration, etc. It's relatively easy to spot a cylinder that's not performing. TBH I wouldn't suggest using anything other than Cat filters on it along with a good branded major oil company (in other words not something picked up off the bargain shelf at Joe Blow's Gas & Groceries) product in the oil pan.
Not aftermarket primer pump. It’s fairly easy to look at a different AAR# of engine that came with the pump already installed and just order those part numbers you need. Some ARR#’s already have the boss needed to bolt on the factory primer pump.
Tell you what, all this 3116 talk got me jazzed up. Now, I’m on the Kenai, working on a Kodiak with a 3116. She’s a helluva a rig. Ol’e TT-103. She’s got Caterpillar Power, rolling coal by the hour! She’s been delivering the mail since 19 and 94. She’s wired, on fire, full of diesel and ready for hire. 2800 gallons filled to the top. Can pass anything but the chicken coop, with that single screw.
In case anyone ends up searching this thread or has any interest in knowing how it is going I thought I would post a follow up. I found a place to test the injectors, Bitteroot Diesel Performance in Montana, they did have to order some adapters to mount these side solenoid injectors with oil supply jumper tubes in their test stand which took several weeks. Injectors had a fairly wide variation in flow at various test points (up to 20% difference if I recall correctly) from each other and recommendation was to replace with new or reman. Found a place online, Dales Diesel Superstore in Florida, that rebuilds these and sent mine in for reman. Received them back a couple weeks later and since then I've been busy with haying and such all summer so finally had a chance to get back to this project last weekend. I also purchased the injector sleeve reaming tools and injector installation tools online from Freedom Racing over the summer. I just mention these sources in case anyone is looking in the future, not necessarily endorsing but I didn't experience any major issues from any of them. Two minor things: the reaming tool set did not include the shim washers for setting sleeve reaming depth so I had to manufacture my own; the injectors were remanufactured with the solenoid electric connection on the opposite side as they were originally so I had to reconfigure and re-route the electrical harness into and throughout the head to accommodate that (this was kind of a pain in the butt). Changed oil and after several rounds of cranking to prime fuel and oil side of injectors, it fired up and ran for the first time since I've owned it. After burning out all of the assembly lubes and such smoke went away and it ran smooth. Idled and test drove for about 1/2 hour to continue purging air from systems and check things out, ran smooth as glass. Returned home and shut off, tried to restart immediately after shutdown while still hot and it would not restart, no smoke at all from the exhaust. Something is prohibiting firing the injectors when it is hot. I let it sit 24 hours and tried the next day it fired right up, tried a shutdown immediately and restarted no problem. Warmed it up and test drove again and when I returned and shut it off it would not restart again. Waited an hour or so and it fired right back up. So now I seem to have some electrical or injection oil pressure issue preventing restart (firing injectors) when it is hot. Next step is to plumb an injection oil pressure gauge in to see what it looks like starting cold vs. hot. Seems like it could be either injection oil pressure sensor is reading low or a weak injection oil pump where either culprit might be able to read or output just enough pressure with cold oil to enable injectors to fire but not when it is warm? Any other theories, similar experiences, or ideas?
On the 6.0 Powerstroke you can have a no start hot from weak o rings, they seal when the oil is thick and when it heats up it can't seal anymore, but it will run till you shut it off. Definitely check oil pressure cold and hot and see if you have similar
I think what you have is a situation where the actual Injection Actuation Pressure (IAP) measured by the sensor on the cylinder head is not reaching the desired IAP required by the ECM. If this is the case the inectors will not be fired and no smoke from the chimney. Hook a 5000psi gauge into the IAP sensor #10 in the cylinder head. Crank the starter with the engine cold and record the maximum pressure. Then refit the sensor and run the engine until it's up to temperature and will not restart. Do the same test again and post the numbers. Don't rule out the rebuilt injectors as a potential source of internal HP oil leakage when the oil is hot.
Finally found some fittings and time to plumb a gauge in. Cranked dead cold engine, started firing at 1000-1500psi and when it started it ran at about 4500-5000psi at cold idle. Every restart when cold it climbed to 1500psi pretty much immediately during cranking then fired and jumped right up to 4500psi at idle. Removed gauge (interferes with the cab closing on this cabover truck) and test drove to warm it up. Of note during test drive holding the accelerator at rpms over 2000 would cause the check engine light to come on and no response or limited response like in limp mode from the accelerator. It would just coast down or idle for a few seconds then the check engine light would go out and accelerator would work again. Also same thing would happen upon deceleration most the time. Returned home shut the truck off and tried a restart. As usual no start and no smoke. Reinstalled the gauge, it cranks only up to 500psi and that's it. Tried with the injection oil pressure sensor connected and disconnected with same result. So mechanically the injection oil pump seems sufficient as it produces 4500-5000 at idle (probably shouldn't be that high) something must be not be sensing what pressure actually is or failing to regulate the pressure and it's just running full out. Does this sound like a faulty injection pressure sensor? Anyone know how to check this, i.e how many volts, mA, or ohms on which pins at say 500 or 5000psi? Or possibly the injection pressure regulator?
Sounds more like worn out injectors and/or pump to me. Typical symptoms, the system makes adequate pressure with cold oil but when the oil gets hot and thins out the pressure will not get high enough for starting. I’d be interested to know what others think. The ideal thing would be to get ET hooked up to it and monitor the desired versus actual pressures starting right from cold and watching the changes as the engine warms up.
I've been trying to find someone around here with Cat ET with no luck, except Cat service tech from a couple hours away for about $1000. Plenty of heavy equipment shops willing to look at it for less but none of them with ET so that doesn't help me. Was hoping I could at least electronically monitor with a multimeter or an o-scope the IAP sensor part to know if the system is getting feedback that corresponds with the mechanical gauge and possibly even the commanded output signal to the Injection Pressure Regulator (IPR) but of course neither tell me desired IAP which is critical to knowing exactly which piece of this puzzle isn't fitting right. Just would like to rule out the quick and simple and inexpensive electronic pieces being IAP sensor and IPR if possible before dropping another $1000 on this questionable engine/truck for a HPOP. It makes sense that it could be a worn pump by these symptoms. I'm putting injector leaks on the back burner for now since I just put in a remanufactured and tested set with new o-rings of course and sleeve seats freshly reamed. With this change the truck went from never starting (in my possession) to it at least starts and runs now so there must have been some injector oil side leakage that got corrected. Plus the fuel delivery in the original injectors was a bit variable across the set. Do you think a worn pump also fits with the check engine light and corresponding no power/accelerator response? I'm thinking that if the computer sees a large difference between desired IAP and actual IAP and also runs out of IPR command output span (is at max) then it could be throwing a code and kicking out. Then as the engine returns to idle the desirable IAP (which is now low due to seeking idle) and actual IAP (which is now high enough to meet conditions to keep up with idle) come back into close enough correspondence for check engine state to clear and accelerator response is restored? Until the next time the weak pump can't keep up with desired IAP again... I suppose a faulty IPR could cause these things too though. Tried to start the truck again yesterday on a fairly cold morning and it would not quite start. IAP would get to 1000psi per the gauge while cranking and it would fire on about 2-3 cylinders and climb to almost 1500psi but the next few cylinders weren't hitting so then it fell back to around 1000psi. From this I've learned that 500psi is not enough for electronics to fire injectors (from my hot restarting attempts) but 1000psi is, somewhere I read that 870psi is what it needs to see while cranking to fire which corresponds to my experience with the gauge installed. I suspect that with the firing of 2-3 cylinders this could have caused a short term drop in IAP below 870psi that the pump could not keep up with at cranking rpm so electronics prevented firing subsequent injectors until pressure built back up to over 870psi again and then would fire on 2-3 cylinders again. The glycerin filled mechanical gauge I'm using probably wouldn't catch those instantaneous pressure drops. And honestly my limited visibility to the gauge and ability to visually capture max and min values while cranking probably has a 100-200psi error in it. The cycle repeated for as long as I cranked the engine but it never started. Tried a few times with the same results. This also would support a worn injection oil pump. Builds just enough pressure with cold oil but not enough volume at that pressure once it starts using some to fire injectors to keep that pressure up and also not enough pressure while cranking with hot oil.
Rebuilt HPOP is installed. It now will restart when hot reliably, quickly builds to 1000+ psi when cranking cold or hot oil. So I'm getting closer with the hot restart issued now resolved but it still struggles a lot to start on cool/cold mornings. Fitted a fuel pressure gauge on it and only 4 psi when cranking. When it finally starts at idle it flutters quickly between 44-48psi, climbs to 63 and holds there smoothly when accelerated. The only fuel pump I can find on this is the one on the back of the HPOP, that came on the rebuilt HPOP. This is a long way from the tank and has to suck fuel through the primary fuel filter/water separator and quite a distance through small fuel lines, it then pushes fuel through the secondary fuel filter and into the head fuel galley and finally out the other end through the fuel pressure regulator. Seems like there should be an electric lift pump to supply fuel for better starting and less suction work for the mechanical pump but I can't find one that is obvious. I also can't hear one running with ignition on/engine off so if it is present it does not seem to be operating. Does anyone know if there is (or should be) an electric lift pump tucked away in the mess of wire looms, brake lines, air tanks and dryers, fuel tanks, and everything else somewhere along the frame rail that I can't see? A quick internet search for 1997 T7500 with CAT 3116 shows an electric fuel pump but I'm not sure if that is for this truck with the MUI version CAT 3116 or the HEUI version I have? Also wondering if this issue could be fuel pressure related too? Anytime it coasts or decelerates the engine cuts out; the signal to fire injectors completely shuts off, no fueling at all, not just reduced fueling. At low speeds/rpms it cuts out for just a second or less and comes back on immediately with more throttle. At higher speeds/rpms it cuts out, the SES light comes on and no response from the throttle for acceleration, after it coasts for about 5-10 seconds the engine comes back on, throttle response is restored and SES light goes out. It runs good and pulls hard accelerating and under load but anytime a coast or deceleration condition is encountered it cuts out. Other thoughts might be cam timing sensors or even injection actuation pressure sensor, not sure if any of those could be missing or sending some faulty feedback or input signals?
Having a Cummins M11 (ECM) that would lose prime driving me nuts I wonder if a check valve so fuel can't drain back might help and also if a different fuel filter may help? I know it's a completely different system but putting a shorter filter that wasn't listed as a fuel/water separator solved the problem for me. I don't know if a fuel/water separator filter requires more suction or has different media but going to a short standard filter did the trick. Truck would start right up and die 30 seconds later requiring cranking for 20 seconds to pick up fuel. The time between how long it could sit shut off and start back up and keep running went from several hours to about half an hour. Truck has a check valve but it didn't prevent the engine dying after 30 seconds nor did a filter specifically designed to fix the loss of prime. Read an old post from Truck Shop about a short filter and problem solved. Apparently on a Cummins the cam position sensor can cause starting/running problems too. Wonder if your Cat engine has something similar?
I think you're onto something here. The more times I try it the more it seems to be losing its fuel prime when sitting. Anything more than overnight seems to do it. Sometimes it fires up and slowly dies in a few a few seconds running out of fuel before it primes back up, it will do this many times in a row before finally starting. There is a fuel pressure regulator at the end of the fuel galley on the head of this engine that regulates pressure to the injectors and relieves excess back to the tank. This would logically have a check valve feature in it that I'm thinking is slowly letting fuel leak out of the head. I think I'll try to replace that and I have a new primary fuel filter coming that is not also a water separator. I'll see how these do for starting reliability and see if the cutout on deceleration continues or goes away too.
Put a clear line on the return fuel or plumb it into a bottle to see if you have air in the fuel while running. The fuel regulator in the head should also have a check valve in it.
Thanks for everyone's help and input on this, I think I might have the hard starting issues finally licked. I had a little bit of everything contributing to it. First off the injectors and the seats/cups needed replaced, reamed, and seated properly because initially there was some compression/combustion gasses making its way past the injector to cup mechanical seal and into the fuel in the head so the rear injectors were being starved of fuel even if the oil pressure was there to fire them and the engine never could quite get started. Plus when I had them tested they were quite variable from one another in fuel flow so would not have performed the best. Then this engine did need a new HPOP or HEUI pump (whatever you like to call it) as it was producing enough pressure while cranking to start with cold oil but not with warm so it would not restart after warmed up. The last thing I think I just resolved was the fuel check valve letting the engine lose is fuel prime when sitting for a day or so. I ordered the parts for the fuel check valve straight from cat parts for this engine S/N, when I pulled it apart I found the the OEM valve/regulator housing has been gutted and is just being used as a straight length of fuel line. There was a separate check valve inserted below it and the fuel pressure regulating orifice in a fitting below that. They look OEM but obviously don't line up with what the cat parts diagram was showing. Sure enough that check valve had a piece of the o-ring from the OEM original check valve stuck in it holding it open and letting the fuel drain out of the head when sitting. I am hopeful that finally resolves the last of my difficult starting issues and that it fires up readily after I let it sit for a few days. I still have the fuel pressure gauge fitted to monitor this and will know later this week. After breaking into the fuel system several times for all these things and changing filters (secondary filter to the OEM Cat one) I really wish this engine had a manual fuel prime pump on it! As Coaldust pointed out my life really sucked every time I had to re-prime this system. The issue with it cutting out on deceleration and throwing the SES light still persists. It will run at 65mph for as long as the throttle doesn't let up but as soon as it does it cuts out and coasts down to about 47 mph and then it will run again. Below 45 mph I can decelerate slowly (let off the throttle gradually) and it seems fine or at lower speeds/rpms it does it more rapidly cutting out and kicking back on within a second, even loping on and off at idle sometimes. First I have some new cam timing sensors coming to try (oh good the HPOP is coming off again and I get to re-prime both oil and fuel systems again...) then I might have to take it in to a cat tech for some diagnostic scanning. Since this doesn't seem to be linked to any of the hard starting solutions for my issue I will start a different thread where appropriate if I need to.
Hoping you have it figured out. Problems like this are so frustrating.
Vehicle speed sensor can also set SES light.