This truck was purchased at auction with no start. There is 50 psi after fuel filter while cranking. When trying to read codes through OBD 2 port under dash, it says " communication error". Corrosion has been found on some major connections of main harness that goes to firewall. I would like a source of support like Mitchell or Identifix where I can pay a fee for a month of wiring diagrams, theory of operation and diagnostic procedures without signing up for 179 bucks a month. Is there such a thing? Thanks
Do you have an engine Serial Number..?
That's a HEUI engine, so first thing I would be checking is the high pressure oil pump. Is this in a GM truck? I don't know if Mitchell is going to help you a whole lot. You need Cat info.
http://www.catengine.info/workshop/...nes-problem-engine-cranks-will-not-start.html
7AS42121
There are many times in my business where I wish for some support without paying a big monthly subscription. Are there any pay per use websites for medium n heavy duty?
I think heymccalls's reply above is spot on. This is a HEUI engine and IMHO in the case of an engine that cranks but fails to start you need Cat information regarding the engine, and specifically the injection system, rather than OEM information. One question - do you get smoke out of the chimney when it is cranking...? I'm not sure you can connect with a generic scanner to the OBD2 port, AFAIK it needs Cat ET to run diagnostics on the engine. I see you are a master tech. Do you have any previous experience with the HEUI injection system..? I have the System Operation for the fuel injection system if it's any use to you. Attached is the Electrical Schematic for the engine.
I have worked on many variations of electronic injection but so far have not been successful to magically visualize what's going on inside "a box that runs on smoke put in by the factory." I would be as excited as a kid in a candy store to read up on the nitty gritty of how the system works. Please send theory of op.
No problem - attached here. The reason I was asking about smoke (or not) out of the chimney is that this system is very dependent on 2 major parameters: - Desired Injection Actuation Pressure - a value of the hydraulic pressure in the system that is calculated by the ECM based on engine speed, load, coolant temperature, inlet air temperature, and probably a host of other factors too. Actual Injection Actuation Pressure - the actual hydraulic pressure measured by the IAP sensor in the hydraulic system, it's usually mounted at the back of the cylinder head. When cranking if the Actual IAP does not reach the Desired IAP then the electrons will refuse to come out to play and therefore no fuel - and no smoke from the chimney. That's why it really needs Cat ET connected to the system to watch the two pressures when cranking to see if the command to light the fires is there or not. Low hydraulic pressure in the system can be down to two reasons, wear in the hydraulic pump or leaks in the hydraulic actuation side of the fuel injectors - or a combination of both. Another tidbit is that these engines like to crank pretty rapid, around 150 RPM, bad batteries and/or starter motor can be contributing factors to an engine not starting. However I would suspect that a truck that was sold at auction as a non-starter had more wrong with it than simply bad batteries. When the engine is running the hydraulic pump produces more oil than the injection system requires so the IAP Control Valve dumps excess oil to drain to match Desired and Actual IAP values to one another.
Finally got chance to proceed. Oil pressure out of a galley plug just above intake , takes Allen key...200 psi. Guess I'll remove valve cover and see if oil flowing by injectors? No there is no smoke out of the chimney. There is not a check engine light but it does say "check gauges" Thank you.
Not sure about a 3126 but from memory on other larger model engines the hydraulic pressure at the cylinder head should be around 2500-3000psi on an engine that's working correctly, so give or take you're off by a factor of about 10.
Dead headed a pressure gauge right at outlet line from HEUI pump to head. 200 psi. Should be minimum 850 psi to fire injectors. Any other cause than a worn out HEUI pump?
Nope it's just like on the 7.3 HEUI systems.
Certainly on that diagnosis the HEUI pump would be the place to start. Here's the parts breakdown for it. Both the pump and the IAPC valve are available Reman which will be significantly cheaper than new. Even money you'll be putting a new set of injectors in it as well.........
Supplied battery voltage n ground to IPR. That poor 5k gauge pegged out so the wife immediately released the starter switch for me. Will be ordering IPR tomorrow.
IPR?
Injector Pressure Regulator
IAPC Valve
Stupid question BUT> did u check your voltage coming TO the valve, on the engine harness side?? I didn't see that anywhere in the thread..
Very valid question not dumb at all if op supplied external voltage to it to make it work , how come the truck side isnt doing it?
Please share the troubleshooting for this. I have no info. Not sure how many millivolts to look for Thank you
Dont qoute me exactly cuz i dont have the time at the moment to look it up , i believe one of the wires should have 12 Volts key on , the other wire is the ground which is pulse width modulated by the ecm to control the valve . There are also 2 speed sensors under the huei pump in the back of the front cover that should be ohm checked and compared to spec i dont remember if the ecm will let the huei pump make pressure if iy doesnt see both speed sensors or not .
I can think of a few things that might cause the ECM not to give a signal to the IAPC Valve solenoid, including the IACP pressure sensor, engine oil pressure sensor, and others. The problem in this case is that there are no specifications on the Electrical Schematic for solenoids, sensors, etc, which is usually the case. Much though I hate to say it, I reckon this one needs Cat ET hooked up to the diagnostic port to see what Diagnostic Codes are Active. You could try this diagnostic procedure, but without confirmation of Codes from ET, it's a bit of a shot in the dark. The lack of power to the IAPC valve solenoid could easily be as a result of a lack of signal into the ECM from somewhere else.
Hey, if nothing else, I'm sure I'm providing entertainment for dealership techs, I've been there, I know, I know..... On a hunch I decided to pull the cam sensors, one has 143 ohms, other is completely OL ..(the lower one with grey connector) Will it start with one good and one open?
Suppoedly they will but i know how that usually works for me i would replace the bad one, check its ohms before putting it in to see if it compares with the maybe still good one and give it a whirl , just be sure to plug everything back in first, ask me how i know lol
Here's what the manual says about the speed/timing sensors. There is a lot more but I think this is the relevant bit ... The engine will start and run when only one sensor signal is present from either of the sensors. The loss of the signal from both of the sensors during engine operation will result in the termination of injection and the shutting down the engine by the ECM. The loss of the signal from both of the sensors during start-up will prevent the engine from starting. Both sensors are magnetic sensors. The two sensors are not interchangeable. Do not switch the positions of the sensors. The two sensors must be replaced as a pair . If the sensors are replaced, a timing calibration is not necessary for the engine. Timing calibration is only necessary after replacing an ECM that will not communicate. The two sensors are actually one Part Number (245-4630), so they cannot be replaced individually. So the sensor is not the root cause of your problem, but if one is failed then I guess the assembly ought to be replaced anyway.
I agree woth you on this truck needing cat et rather then throwing parts at it,, timing speed sensor thoughts are yeah its supposed to run on one but so are mack etechs they say they will start and run on only one of the speed sensors but i have run into several that wont when the flywheel sensor has crapped out but the. Cam sensor is still fine .
Have not purchased anything except the pressure regulating valve at back of head, which fixed fuel pursue pressure supply problem, 100 bucks only. I'm investing some time and now understand a lot about these engines. To get a Cat tech out here to the country or haul it to town would be cost prohibitive. Eventually I'd buy my own tool to connect if I saw it worth my while. Is there a connector dangling near the ECM for a Cat connection, not sure what I'm looking for if I did want to connect directly and not through GMC
If you refer back to the schematic the Diagnostic Connector appears just to the right of the ECM. On most on-highway trucks I've seen that connector physically located under the dash, or clipped somewhere right next to the engine ECM. It's a 9-pin circular Deutsch HD-10 connector, the ET cable connector that mates with it is identical to the illustration below. Without seeing it I'm not even sure there is a specific OEM diagnostic connector as I assume the engine is the only electronic thing on the truck.
Cool. I am talking as we speak to a tool dealer about a scan tool with capability to pull codes and do basic testing