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IP failure? Very hard starting

F

fastline

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Very frustrated with this issue. Problem is truck runs fine otherwise. Hard to start regardless of ambient temp, PMD replaced, lift pump good, etc. truck will take 2-4 attempts of approx 10 sec each. truck will blow gray smoke and stumble along just like when you have to reprime after running out of fuel.

Once truck "catches", it will make the nice "rhaap" sound and all cylinders are lit. There might be some very slight "fish biting" stumbles for up to a min and then all is clear. No abnormal smokes issues once running, accels ok (I guess, its a turd), smooth idle, very (maybe too) quiet when running down the road. I have always thought it was "real smooth".

I have tried about every trick in the book but I would bet a nut that for one reason or another, I am loosing prime somehow. truck just is not getting fuel. truck will hot start fine. Have had some recent PMD type stalling symptoms but rare. This is a 94, OBDi, no abnormal codes.

I have heard from a couple people that had similar issues and resolved them with a new pump. However, I have heard that you might be able to juice them with an additive to get them back some times. I just want to know where the problem is..

Oh, glow plugs are good. In many circumstances, the truck actually starts better on cold days than warmer days. I have unplugged the CTS to get full fuel/advance and it helps but certainly does not cure the problem.
 
How old ls all the rubber fuel line? Do you positively have power to all the glow plugs? Have you tried starting with the fuel cap loose? Will it pass the 2000 rpm test? Is you lift pump working?
 
Sounds like LP not working. LP is run by OPS so check the LP and make sure OPS runs the LP.

There are a lot of info in the Technical Library about testing LP.
 
Lift pump and fuel shut off solenoid have been bypassed to switched 12V. Truck will run all day with T valve open dumping approx 1 gal/min. The only thing I have not tested is the actual pressure from the lift pump. I guess it could be that the lift pump cannot build pressure but can move volume of fluid. What is the easiest way to check this? Wish I could just use the vent on the filter housing but it always leaks on the sides when the vent is open..
 
Use the water drain to check pressure.

X2 on clear line above from the IP to check for air. You may also want to disconnect the injector return lines and check for air - an indication that the injectors are sticking open.

You may need to set the timing as it may be retarded with the white smoke.
 
I am going to upload or link a vid in a few. I decided to go check codes on the truck. I have unplugged the EGR and turbo boost control circuits. I use a mechanical boost spring so I am used to seeing the EGR and boost codes. Also, I unhooked the boost sensor last night so that code should reset. The throttle code is new and the glow relay fault has always come up though I can "absolutely" confirm the glow relay operates fine. Even with the lower voltage of the batts, it showed 90A of current for the glows yesterday.
Codes
29
32
33
34
35
36
45
49
57
62
I will reset them and see what comes back. I expect the pulse width errors to be coming from a junk PMD where the ECM was hunting trying to get it to lite.
 
VIDEO
http://www.youtube.com/watch?v=P541tZHUKto

Please note, the truck started a bit easier because the CTS was unplugged forcing more timing and fuel. Usually takes 3-4 attempts with the stumbling you see in the first attempt and usually dies once or twice. You will see in the second attempt how it just "catches" and it is up and running. The smoke during start and rev up is a little excessive due to the CTS being unplugged. I ramped up the RPMs to 2K. I will admit that sometimes it seems that you get certain RPMs with the peddle, then they fall slightly and you have to apply more pedal but I am able to hold any rpm.

Also note, the truck just straight died and would not restart. No smoke which is what points me to a PMD issue there. I first tried to start with the "new" PMD that I think is junk as well, then went back to a known bad one so I am pretty sure that was the issue there. My PMD is in front of the LH batt with a heat sink on it. I think I am fighting several issues here.. HELP!!!!!

OH, I should point out the truck was dead cold, sitting all night. Ambient was about 80*F.
 
I reset codes and ran the truck. Code 29 always immediately comes up. I did not see other EGR codes but they are common and should not cause this.

The ones that are concerning me at this time are 35, 36. At least 36 seems to be coming right back when the truck is running. I am using GMTDscan basic and when watching the DTC count, it will bounce around from 0 to 2. I am not sure what would be causing a pulse width error but I commonly see in it gassers if the fuel pressure is not up to snuff and the pulse is well off the programmed mark, usually wide.

With both short and long codes, I am not sure what to make of it. Could be more PMD BS. Really wish I could get a known good one locally to test. I have 4 of them and all do the same thing. Even the one I just bought.

I should mention again though, all 4 of these PMDs do the exact same thing when starting so I really doubt my starting issue is the PMD.
 
35 and 36 are generic codes. They can be set by most any other code. With as many codes as you saw before, I'd be thinking ECM. That many sensors don't go bad at the same time. Check for 5 volt reference signal at all sensors. The ECM has 2 reference signal outputs. The ECM also has 2 power supplies. Check all fuses. Have you cleaned ALL grounds especially those on the rear of the intake manifold? Poor grounds can really foul things up. One shorted out sensor can disable all the rest on that reference signal.
 
Tested several sensor plugs for 5V reference. 5.01-5.04VDC. I have cleaned the bat grounds to the engine and such. Not aware of any others that would cause this but I am all ears.
 
IIRC with gmtdscan basic you should be able to monitor if the ect read by the ecm is accurate. Grounds you need to look at in particular are the ones at the back pass side of the engine on the trans dipstick tube. Should be 3 of them. also check your fuel shut off selenoid for proper operation
 
I think what you are saying is checking the actual coolant temp compared to the ECM perceived data? I have looked at that a bit, even tested the resistance on the CTS and all seems in check. Dash gauge is a bit off but who cares...

I did find the ground in question and I think I have "blessed" that one many months ago but I will take another look at it. that seems the be the ground for the glows but I don't think glowing is where my problem is.

In reading some more threads online, it sure seems like I really need to do more testing on the LP pressure and ensure no air. Now, common sense would say if I am getting air in, I am likely leaking fuel out and there is nothing dripping but....

I was jacking with the truck trying to find the actual return line to the tank from the IP and I pulled the one that is next to the fuel shut off valve and goes rearward. The other is the injector return to the pump. Anyway, when testing that with a clear tube on it, I noticed the fuel moved VERY slow from there going back to the pump. Or maybe it was going to the IP, can't remember. Either way, LP was running, truck was not, fuel not not moving much.

I could not find a fuel pressure gauge but I put my finger over the T valve hose and it will build pressure and spray a bit there. I will have to get a gauge on it. Kind of scratching on that return flow though...

OH, after messing with the return line and checking pressure at the T valve, the trucked fired right up without issue and went for a 10 mile drive, no problem. I am really wondering if we have a slight fuel system issues causing major repair concerns... I further wonder if some of the pulse width errors are from air in the system for lack of fuel for that matter. That is certainly what my gut is saying..
 
air leak pre LP will suck air and not leak any fuel. Those 3 grounds at the back of the engine are the life blood of the ecm and are better relocated to a intake manifold bolt
 
To admit my ignorance due to a lack of info, it would seem what I actually tapped into was the fuel supply line to the IP. Here is how I see the system, please critique as needed. fuel comes from tank, through LP, to bottom of filter housing, has to be a regulator somewhere and fuel return is also build onto the filter housing going back to tank. Fuel is taken from there to the IP where there should just be a set pressure of fuel delivered to the IP. The fuel "return" is only fuel coming back frok injectors in which I do not understand yet. In any case, there is no way for the IP to drain down once primed unless there is an issue with the pump or if there is air coming back from the return lines from the injectors.

I have been all over just trying to find a diagram of the DS4 pump to figure out how this all works. Once I know all the little pieces, I should be more able to pin down this issue. From this, I can certainly see why the IP pressure would be so important since it probably is required to keep fuel "loaded" in the IP. Otherwise it might pull a vacuum and further fail to inject properly. I just do not understand why there is a fuel return to the IP from the injectors. I rebuilt the damn things and I am sure it made sense then. Probably all part of holding them at the perfect pop off pressure.
 
Um, here is a dumb ass question but I have NEVER had a fuel tank cap on this truck. I know there is no water in it because it just sits in the shop but something worth mentioning... I would be PISSED to learn that is all this is...lol
 
IP uses fuel and calibrated pressure for timing and fuel delivery control. The transfer pump needs some pressure or it draws a vacuum. As a vacuum at the IP inlet is the other side of the case pressure regulator you are already down 5 PSI or more in pump housing pressure. This is why a working lift pump is important. Providing a prime to the system is also critical of the lift pump. Long crank times result when the lift pump fails.

Air in the fuel system cause many issues. You can compress air thus getting the 1800 PSI pressure is difficult with air in the fuel. Common sources of air would be the inlet of the lift pump and the fuel pickup assembly in the tank rusting pinholes in the lines.

You are checking the IP return line for air bubbles with clear tubing to diagnose the above air leaks.

The injector return lines will bubble air if an injector is sticking open and allowing the 400 PSI compression into the fuel lines. This is why I suggested this test for them.

Fuel cap is irrelevant to your issue. (Other than dirt, water esp from condensation, and algae in the tank plugging filters and socks.)

The IP will drain down with any air leaks - air leaks may not leak fuel. The return from the IP will allow fuel to drain off. So will leaky valves in the lift pump. The 6.2 fuel filter housing was known for air leaks and hard starting as well as throttle shaft seals in the IP - a design you do not have.
 
Guess I have some questions.

1. is there any way for the IP to purge air from itself once air is in?

2. As I understand you, the return lines back to the IP come from the injectors and if they do not seal correctly, it is possible for the cylinder to ram air back into the injector return line? how is that possible if the injector is injecting at 1800psi while the piston is coming up?

3. Would this air really cause an instant issue in the IP? Remember, there are no other issues than starting.

4. Were you referring to the "inlet" line for air concerns from the LP? I could see how it would be hard to maintain good line pressure if there is air in there but I would also think we would have problems elsewhere, not just starting. If it was pulling air, would it not pull air all the time thus causing a constant issue?
 
Had a similar problem hard starts ect. Would start fine when warmed up, put the clear return line on it and check each morning and had air in the clear tube. Started checking like you did but finally noticed weeping on the return injector lines. If you are smelling alot of diesel fuel in the engine bay or standing beside the front of the truck I would check those return lines. Ordered some new return lines on ebay and it solved my problem.
 
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