MBN02738 O2 t800 dump truck Middle of last week this truck started running rough and sputtering. The client decided to replace the fuel filters. He called me in the afternoon to ask how to prime it to get it started again. Friday morning they were pulling it out of my yard to move another piece of equipment. I don't know how far it got, but then someone came to get their peterbuilt to swap it out and send the kenworth back to my yard. Well, they didn't make it. Ended up about 4 or 5 miles and a couple of heavy grades north. I went to check it out and it would start and idle but just couldn't pull itself up the first hill. Since it was barely off of the road with bad drivers speeding past my backside I decided that my roadside trouble shooting was done and took the driver back to the yard, called a tow truck. I got it to run enough to fill up the air tanks while I was waiting and got it back to the yard. Barely got it running enough to get it parked out of the way and let it sit for a bit. I tapped a Guage into the filter housing and got it started again and read 75psi at idle and 95psi at throttle and those were the numbers I was expecting, still it died in about a minute or two. Had to stop there because it was pretty late in the day and we were expecting another hurricane over the weekend. Believing that I had ruled out the lift pump I moved on to fuel supply. Ran a hose to the first fuel filter from a clean source, primed everything up and got it started this morning it ran for about 4 minutes and died again. After a really long and frustrating time I decided to put the Guage back on (really wish I had done that first thing this morning) now it is fully primed from the hand pump to the return line by the regulator and it will not start and reads 0psi while cranking. I can't think of anything it could be but the lift pump. Who has better ideas?
Fuel pressure regulator may have taken a dump. I’ve seen trucks with the regulator separate from the check valve and have seen some where they are combined. It’s on the return side of the fuel filter head.
Thanks. I wrote the first post while I had someone out picking up stuff for more testing. One of those things was the fuel regulator. I don't know how often you are supposed to change them, but on this unit it has been about 13 years and I didn't remember thinking that they were pricey. I was surprised, I thought it would be about $100, I was $200 off. The other was some clear tubing to connect to the pump inlet. Took a lot of priming but it started and ran for over 4 minutes (today's record) had about 80 psi at idle but died before we could get it to 1000 rpm. The owner thought that we might still be losing prime because I only had the tubing pushed on to the inlet fitting ( I doubted that, 3/4" id tubing on a #10 jic fitting is pretty snug). And none of us had a hose clamp the right size so I sent him out for one. I had a couple of other ideas I wanted to try while he was gone. The first was that there is a line teed into the pump inlet that I don't remember seeing on any of the other of these engines that I work with. It runs from the feed side of the pump to the return to tank after the fuel regulator. So I capped that off. And then I saw all of the fuel in my tubing flow back to its bucket, aargh! Now I have to prime it again! Then I started to think about how ridiculously hard it has been to prime this thing all day and then decided to pull the hand primer check valve. I found a little piece of rubber that was keeping the check ball from seating. Cleaned that out and reinstalled the check valve and then primed it really fast. Like 4 or 5 pumps and it pulled the fuel through 6 feet of 3/4" id tubing straight to the pump. Started the truck again and now have 90 psi at idle, and honestly think that it would idle forever at this point. But it still dies around 1000rpm. So... I have isolated the entire suction side of the fuel system. I know that does not mean that there isn't a problem there, it could have been sucking air from either the hose from the fuel tank to the primary filter or the hose from the fuel filter to the lift pump. And perhaps a problem with the pick up in the tank. But what I have to focus on now is "c15 dies on acceleration".
Do you have a laptop or something that can do a click test or cutout test? I ask because I’ve run into similar issues and it ended up being in either the engine harness or the injector harness. One test I figured out by accident was to do the click test with the injector harness unplugged. Obviously it should not have any injectors pass. Believe it or not I’ve had some pass which has led me to issues in the engine harness. I’ve also recently had issues with the throttle, I was fortunate enough to have another truck I could borrow the pedal from the isolate it. Does the cab leak? Almost all of our dump trucks do or have at one time or another. The throttle connector often ends up laying right where it can get corroded. Yet another could be cam and crank sensor which would also give you a hard start like it’s losing prime because the engine can’t verify where it’s at. I chased a C12 with that issue and did everything I knew to do. Called an old friend who’s worked at Cat since the days of the 1693 and we finally decided tone ring on crank somehow moved and timing was off. Might be time to plug in and see if there are codes and do a little digging for bad connectors etc.
Have you checked inside tank for debris? I had a very similar issue with a 6TS about eight/nine years ago. It had good fuel pressure, replaced regulator, replaced old primer pump {leaked}. Would idle along fine for a few minutes then die or run rpm up to 1000/1100 run a few minutes and die, all the while with pressure gauge hooked up. Pressure would suddenly drop. Tank looked clean from where it could be viewed. Had to reprime each time. Then I noticed something odd in bottom of tank, a long piece of hard like plastic substance. Removed tank, Rolling it around was able to move object towards cap opening, using a thin grabber tool I removed what was the 1.25" X 22" piece of circuit board that is inside of a tube type fuel sending unit. It was getting sucked up covering pickup tube, engine would die it would float away, reprime and start it would be drawn right back to pickup tube. Note--it had the fuel sending unit changed about two months before.
My first thought was debris in the tank blocking the pickup. But last night I was running fuel straight to the pump with fuel from a bucket so that (i think) eliminates the tank and all of the suction side of the fuel circuit.
Junkyard, I don't have a way to scan it, but I agree. If I can't figure it out today I have someone coming tomorrow. The injector harness if fairly new, think I replaced it a couple of years ago when I ran the overhead, ecu was replaced around the same time. But now that you mention it the plug going into the head is grimed up. Could be oil in the plug, I will check that out. As far as the cab leaking... This may be the only truck that I take care of that I am sure doesn't have a cab leak. But that doesn't mean that one of the drivers didn't leave a window open last week so I will also look at the throttle pedal and wiring.
Cab doesn't have to leak to cause issue, boots tracking in water will do the same.