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Old 07-13-2011, 05:57 PM   #1 (permalink)
jhs123
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LB7 mystery stall

I was hoping some of the LB7 guru's can help me with this.
I've searched this site as well as others, but can't seem to fix this random stalling.
It stalls randomly regardless of temp, grade, fuel level, speed. I've had it into 2 different dealers, they couldn't find anything, since it didn't stall for them and there wasn't anything in memory when it did.

I've replaced the FPR and all injectors (not a job I want to do twice), NSBU switch and installed an Airdog 150 thinking it was air being sucked in to the stock fuel pump. The only code it ever threw was the P0090 a few times and only that when it stalled and didn't immediately start back up again.
It always starts back up, sometimes goes into limp mode. Only a few times did I need to bleed the filter housing to get it to start again. The only other thing is the idle will hunt a little before it stalls. And occasionally the idle just bumps a few hundred and doesn't actually stall. When that happens I know a stall is coming.
I've re-grounded my batteries thinking it could be a FICM or ECM issue. shook all wires and connectors, I cannot get it to miss or stall.

It's a '02 HD2500, engine stock, 4" exhaust no other mods other than the cut back spring on the Air Dog to only give me 3 PSI instead of the stock 10 PSI spring. The stock spring was sending my idle all over the place and had to keep two feet on the brakes at stop signs.
I've lived with this problem for several years now and it seems to be getting worse. It didn't do this the first 2 years I owned the truck. It just happened one day and I've been chasing it ever since. I like the truck too much to get rid of it. The dealer wants me to replace the ECM(s) and fuel pump as per the GM troubleshooting chart.

Any ideas, I'd love to hear'em.

Thanks
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Old 07-19-2011, 06:55 PM   #2 (permalink)
jhs123
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ttt
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Old 07-19-2011, 07:09 PM   #3 (permalink)
DuraTitus
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No idea...... Maybe try a new ECM and see if that fixes it. - I have never dealt with a problem like you are describing.

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Old 07-25-2011, 06:29 PM   #4 (permalink)
jhs123
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Thanks anyway Dura...
I don't want to take it far from home now.
I hate buying parts I don't need.
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Old 07-25-2011, 06:38 PM   #5 (permalink)
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Yea, I know what you mean.
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Old 07-26-2011, 12:16 PM   #6 (permalink)
403turbo
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The erratic idle before a stall leads me to think that it is fuel related. Electronic issues tend to be very sudden and without warning. I used to have an edge that would dump the truck randomly, never had any warning on that.

My first instinct when trouble shooting a mystery is to simplify everything I can. I would check the whole fuel system with a fine tooth comb. It's an older truck and like me, you live in the lovely northeast, the winter salt capital of the world. I wouldn't be at all surprised to find little wet spots on the fuel lines directly behind the clamps that hold them to the frame. Mine did that, and began acting like it had a plugged fuel filter. But in fact it was sucking air in, never stalled just ran like crap.

The next thing would be to remove the airdog from the system, their might not be anything wrong with it but try it and then check it off the list.

Troubleshooting is a PITA but just go slowly and logically and don't ever change more than one thing at a time and you will track it down.

Good Luck!
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Old 07-27-2011, 12:00 PM   #7 (permalink)
autotek
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Stalling

I have almost the same problem stalling o2 2500 hd 4x4 the truck will stall when driving mostly in the rain i suspect it is the connector at ecm but have not ever had it store a code i thought it was the edge juice but removed it and same problem tach goes wacky when it stalls also any info would help i believe it is electronic because of tach. And it almost always happens when raining or snowing
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Old 10-18-2011, 09:27 PM   #8 (permalink)
jhs123
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Here is an update...
Ordered new ECM from a vendor found on here. Installed it. It started up, but took several key cycles to run. After that initial start-up it seemed to run fine. Several trys later, it wouldn't fire unless the key was cycled 2 or 3 times. It felt like it needed more timing advance if it was a gas engine. It started very lazily.
Drove around for a few weeks with only a handful of no-starts, but the truck never stalled. I think this may be the fix. Just to make sure it was the ECM creating my new starting problem, I installed my original ECM and noticed it fired up immediatley and felt stronger through all gears. (but stalled randomly while driving a week later)
I contacted vendor and told him his ECM seems to work except for the starting problem, he sent me a replacement. This replacement one was terrible, I had to do a re-learn on it to get it to work. But when it did fire up my truck, The engine sounded like it had gravel in the cylinders and it threw out a bunch of codes I've never seen before. took it out immediately and sent it back.
So now I'm sitting here with a truck that doesn't start up reliably, but doesn't stall randomly. I keep my original ECM with me incase it won't start. Tonight it took 6 key cycles to start.
Could it be something else?
Shouldn't both ECM's sent from vendor be programed the same? Or am I just getting other peoples junk core ECMs?

Last edited by jhs123; 10-18-2011 at 09:32 PM.
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Old 10-18-2011, 09:57 PM   #9 (permalink)
ericw13
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in theory both should be programmed the same. I would look at the connector at the ECM and see if you have any bent prongs or corrosion. These connectors are supposed to be water tight but you know how that goes. I would clean the connector really well and make sure the prongs are straight.

I was under the impression that the ECM was vin locked- maybe i'm wrong. I would call a local scrap yard and see what you can find here.

I would be willing to bet that the vendor is selling core computers that people send in when they buy tuned units. They may have sent you an ECM for the wrong year model.
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Old 10-19-2011, 04:45 PM   #10 (permalink)
jhs123
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I've switched ECM's back and forth repeatedly and they have their own personalities. The OEM unit starts immediately and is strong but likes to throw a 0090 code every few tank fulls and stall. Driving home in limp mode gets old. The new one hasn't stalled or thrown any codes, it just feels soft and doesn't want to start every few days.
Vendor did ask me specifics about year/make/ model/ bed size...

How can I check to see if I have a good ECM? I don't think vendor will take return on electrical part.
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