Truck dies randomly, screen shot attached

[thunder550]

Started having this problem after a 400 mile trip from Phoenix to Albuquerque. My truck will randomly die on me now. From what I can see it seems to happen on when at zero throttle, and it's only intermittent. All that I can see so far is that everything leans way out. I finally caught it in a log file. In this case it happens right before it went into DFCO. You can see how the AFR goes to full lean just before DFCO is enabled, which is not normal. I have looked at other log files and generally spark cuts first, then I see IDC go to zero, then I see AFR lean out. In this case, AFR leans out first, even though IDC is still at 2%.

Does this seem like a fuel pump issue? After I pull over I shut the ignition off, then turn it back to run and check fuel pressure, and it's fine. I have not yet looked at fuel pressure right when the truck dies, but I would think that if the pump quit working that it wouldn't start again. It usually takes me 2-3 tries cranking, turning off the ignition, turning to run, then cranking again to get it to start. Once it starts, everything seems normal. This issue seems to happen once or twice a day.

I have also attached the log file, this issue starts at frame 988. Tune file is also attached.

http://i217.photobucket.com/albums/cc22/thunder550/MiscCrap/truckdies.jpg

[thunder550]

It's also been getting increasingly difficult to start after sitting for awhile. Took me about 5 tries leaving work this morning, and about the same number leaving work to go to lunch. Fuel pressure is good when this happens. Just sits and cranks with no fire.

[thunder550]

Well it intermittently idles like shit now too, feels like it has a miss. Looks to be rich, but not rich enough to make it feel like it has a miss. Only in the 12.5:1 or so range. I'll mess around with the idle tuning a little bit. I decided to try and disable DFCO also and see if it changes anything. This is extremely frustrating.

[joecar]

Questions:
- are all spark plugs firing during cranking...?
- what is fuel pressure when this happens...?
- how long is fuel pressure held KOEO, or does it drop...?
- does fuel pump prime for ~2 seconds when going KO...?
- can you smell gas during cranking...?
- pull the MAP-reference hose from the FPR, is it wet with gas...?
- are all injectors firing during cranking...?
- does the ECT pid show the correct temperature...?
- does scantool show correct RPM value during cranking...?
- are crank and cam sensors both producing correct waveforms...?
- any DTC's...?

[joecar]

If it started doing this for no reason, then the problem may be outside the tune file...

[thunder550]

I'm thinking it's an electrical issue, maybe somewhere in the injector circuit. I messed around a little bit doing some testing and it seems to have stopped.

Cranking fuel pressure and pressure when the engine dies is about 50 psi
Fuel pressure holds at 50 psi for at least 30 seconds KOEO (I didn't try longer)
Fuel pump primes on KOEO for 2 seconds
I can not smell gas during cranking, but I have not gotten out and tried to find the gas smell
MAP vacuum line does not have fuel in it. FPR is aftermarket Edelbrock.
Did an injector balance test with the engine running and all injectors are working properly
ECT is showing correctly
Put a test light on injector #1 and got no flashes during cranking, but flashes after engine start
Scan tool shows roughly 130-150 RPM when cranking
No DTC's

I do not know if all spark plugs are firing during cranking, but I do not believe that this is a spark issue.

I do not have the proper equipment to check the waveform on the crank and cam sensors

I hope this helps a little bit...I'm leaning towards an intermittent short in the injector circuit somewhere. Seems to do it a lot less when the engine is warm than cold.

[thunder550]

Whatever the problem was seems to have fixed itself. Truck is running great now, starts on the first try, and even from cold start doesn't die. I have no idea what was wrong. I'm sure it will rear it's head again, but for now the problem seems to have healed itself.

[joecar]

It may have been an intermittent connection which got fixed up when you probed around... the act of probing has fixed it...:cheers:

(Try to remember what you touched in case the problem comes back.)

Some cheap tools that are good to have:
- spark tester (looks like a spark plug with a grounding clamp);
- noid light (plugs into injector connector).

[thunder550]

Well I only messed with a handful of things:

1) Injector driver box
2) Ignition relay
3) Fuel pump relay

If it comes back, I think it's gotta be in one of those somewhere.

I'll see if I can get a spark tester...borrowed a noid light from my neighbor.

[SSpdDmon]

If you look at the screen shot - it goes VERY lean according to your WBO2. Maybe when you futzed with the injector box, you fixed it.?.?.?


Edit - n/m

<<< (way to read the original post numbnuts) http://www.motownmuscle.com/forums/images/smilies/shake.gif

[thunder550]

Problem finally got bad enough that the truck quit starting all together. Traced it back to the injector driver box. Bypass box and truck starts. Put box back in and it doesn't.

[hquick]

Glad you found it. Anticipation of the problem is ALOT worse than the problem itself (ie...waiting for it to happen again).

[thunder550]

Yep, I have been afraid to drive it for the past week. I'm happy to have finally figured out what the problem is, and I am EXTREMELY happy to know that it's not a problem with my wiring :D

[joecar]

T550, good job...:cheers:

How did you trace the problem... (the process may help someone)...?

[thunder550]

I knew with crank but no start it had to be air, spark, or fuel.

I eliminated air easily by opening the throttle slightly while cranking, just in case the IAC valve was sticking shut.

I tested spark by putting my multimeter on one of the spark plug wires while cranking and watching the voltage jump.

So it had to be fuel.....cranking fuel pressure was good, and I could hear the fuel pump running while cranking and for two seconds after, so the problem was not in the pump. That leaves one possibility: injectors.


Because of the way that the injectors work with the common +12V leads and switched grounds, I knew that if the truck wouldn't start AT ALL it had to be all of the injectors. If only one had an intermittent short, the truck would still start and run just fine with the other 7 cylinders. I tested the positive lead on the injectors to make sure that it had 12V while cranking. When that tested ok, I knew it had to be in the ground system, and it had to be ALL of the grounds. That pointed directly to the injector driver box. Bypassed the box, and the truck started right up. Put the box back in, and no start. Bypassed it again, started right up. Put it back in, no start. The only wiring for the injector box is the 8 injector leads (which couldn't ALL be bad) and a power and ground. Tested power and ground while cranking, they are good, so the problem has to be inside the driver box.

Just used process of elimination to figure out what was wrong. The biggest deal was getting it to the point where it stopped being an intermittent problem and started being a consistent problem. It would have been next to impossible to trace this problem if it was still intermittent.

[kbracing96]

You talk to much :laugh: Nice writeup of the diagnosis, :)

[Sparky8370]

It would have been next to impossible to trace this problem if it was still intermittent.
This is a problem I run into all the time as an electrician. And the comparison that is always made (by either myself or the customer)is to a vehicle problem that doesn't exist when brought to the mechanic.

[thunder550]

Got the new driver box put in today, all is well in Truckville once again :D