2001 Suburban stalling issue

[kbuskill]

First off, not my truck, just trying to help a buddy.

My buddy just got a 2001 Suburban and it will randomly stall for no apparent reason.

It has 275k miles on it but "supposedly" had a "new" engine put in it with "only" 100k miles on it by the previous owner.

I noticed right away that someone had cut 2 of the small ground wires that break out of the main harness, toward the back of the intake manifold and normally go the back of the passenger head/block, and added wire to them using the cheapest butt connectors available and ran them to the ground stud on the firewall where the braided ground strap bolts.

First thing I had him do was remove the butt connectors and solder and heat shrink those 2 wires. The next thing we did was wiggle and move every harness under the hood to see if we could get it to act up... nothing obvious.

I checked under the under hood fuse box and found nothing obvious wrong.

I next had him remove and clean the ground wires on the drivers frame rail. He drove the truck for 2-3 days without any issues but it has now started stalling again.

When it stalls, sometimes it will crank right back up, other times it will not. It cranks fine but acts like its not getting fuel or spark.

The one thing I noticed the other night is that when it won't start the fuel gauge reads empty. When the fuel gauge reads proper the truck will start and run.

I am leaning towards bad grounds or negative battery cable.

When I first checked the codes it was throwing codes for everything. There must have been 50+ codes showing but after cleaning the ground on the frame and clearing the codes the CEL stayed off.

Any help would be appreciated. I have never owned a GMT800 so I am not familiar with possible common problems.

 

[Doubeleive]

check and clean the harness for the fpcm, next time the fuel tank shows empty check the fuel pressure

 

[kbuskill]

check and clean the harness for the fpcm, next time the fuel tank shows empty check the fuel pressure

If it were in my possession it would be easier to diagnose. It cuts off on him randomly while driving and I'm not there to check anything... lol

Unfortunately he is not very mechanically inclined so it makes it difficult.

I didn't have a fuel pressure gauge the other night but it did shoot fuel out of the rail when I depressed the schrader valve.

 

[Doubeleive]

do you have a tech2?

 

[exp500]

Following the clues- are fuep pump relay and gas guage seperate power leads? probably but I'd have to check diagram.
It does sound like attack of the electridal gremlins! I would also look at underhood power distribution box/fuse panel for corrosion, Verify battery connections both ends.

 

[George B]

No start and fuel gauge showing empty would lead me to look at the fuel pump module. I seem to recall an issue with the harness at the fuel pump getting crispy.

 

[kbuskill]

do you have a tech2?

I wish.

 

[kbuskill]

Following the clues- are fuep pump relay and gas guage seperate power leads? probably but I'd have to check diagram.
It does sound like attack of the electridal gremlins! I would also look at underhood power distribution box/fuse panel for corrosion, Verify battery connections both ends.

We pulled the underhood fuse box up and everything looked good under it. I wiggled all the connectors under it to see if it would act up to no avail.

I think the next step will be to pull and clean the ground at the battery cable/engine block.
Maybe replace the cables as a precaution.

Do the GMT800's cables suffer from the internal corrosion as bad as the GMT900s do?

 

[kbuskill]

No start and fuel gauge showing empty would lead me to look at the fuel pump module. I seem to recall an issue with the harness at the fuel pump getting crispy.

I knew the GMT900s had a fuel pump module, wasn't sure about the 800s.

Is it mounted under the truck above the tank or ???

 

[George B]

I knew the GMT900s had a fuel pump module, wasn't sure about the 800s.

Is it mounted under the truck above the tank or ???

I meant to say the fuel pump and sender assembly. The early plugs were sketchy and were updated somewhere along the way. There is also a dedicated ground back there.

 

[Doubeleive]

Only notable ground issue's with the 800's is with the brake module and headlights that I can think of, I can't remember if it was the 800's or 900's having issue's with the fuel pump control module harness getting wet/corroded but it would be in the approx same location under the frame somewhere above the spare wheel. I was just thinking if you had a tech2 you could check everything when it shuts off and see if you can figure what gives the tech2 will tel you the commanded state of pretty much everything. there could be a dtc saved in there also that your off the shelf scanner won't read you need a tech2 or snap on, etc...

 

[kbuskill]

Only notable ground issue's with the 800's is with the brake module and headlights that I can think of, I can't remember if it was the 800's or 900's having issue's with the fuel pump control module harness getting wet/corroded but it would be in the approx same location under the frame somewhere above the spare wheel. I was just thinking if you had a tech2 you could check everything when it shuts off and see if you can figure what gives the tech2 will tel you the commanded state of pretty much everything. there could be a dtc saved in there also that your off the shelf scanner won't read you need a tech2 or snap on, etc...

Someone has pulled the big 60A fuse for the ABS. When we put a fuse in it the ABS module starts running constantly. My research tells me it is bad/cracked solder joints on the relay inside the module and reflowing the solder joints should fix it.

I did hook up my OBD2 adapter and use the Chevrosync app on my phone to look at the ABS codes and BCM codes and what not.

Like I said, it had like 50+ codes showing in the ECM which I believe was from it losing its ground causing it to freak out.

I will keep you guys posted. My buddy works a weird schedule so it may be a week or so before we get to check things out.

Thanks for all the input so far, keep it coming.

 

[Doubeleive]

and sometimes a broken ground on the injector harness which could probably be a cause of what is happening, that may be something to check

 

[kbuskill]

and sometimes a broken ground on the injector harness which could probably be a cause of what is happening, that may be something to check

Yeah, I was thinking injector harness or coil pack harness, that is why I wiggled and moved around all the harnesses to see if it would act up.

I was also thinking maybe the crank sensor or cam sensor. But with the fuel gauge not working when it acts up it leads me to believe it is some sort of grounding issue.

I also noticed the throttle body makes a high pitched noise when the key is in the run position with the engine off. I have read alot about guys having stalling issues with these trucks and cleaning the TB fixed their issue.

 

[sparkvark]

My 01 Yukon has a recall maybe 16 years ago for the fuel pump wire harness over heating. Maybe it wasn't done on this Suburban.

 

[kbuskill]

So my buddy dropped the fuel tank and replaced the fuel pump and pigtail harness.

The pump he pulled was a Delphi and the pump pigtail harness had already been replaced as evidenced by the heat shrink butt connectors that were on the harness.

I had him cut out the old butt connectors and harness and install the new ones on the chance that the old connectors weren't making good contact.

We also removed and cleaned the throttle body.

It ran good for 2-3 days and back to the same issue. Stalling or not starting with the fuel gauge reading zero.

When the fuel gauge reads properly it will start and run.

I am still leaning towards an intermittent ground issue or broken wire in the harness somewhere causing the random problem.

If the GMT800s are like the GMT900s then the gauges work off of the BCM which makes me suspect the BCM or it's wiring or the ECM or it's wiring.

I hate the idea of just throwing parts at it in hopes of fixing it..

I was really hoping that it would set a CEL so i could check the code and hopefully point us in the right direction but thus far that hasn't happened.

The ABS and BRAKE lights are still on. He removed the EBCM from the ABS unit and I opened it up and resoldered/reflowed the joints on the power leads, the relay, etc. But when we installed the 60A fuse for the ABS, the pump just continues to run constantly just as it did before so I guess the EBCM needs to be replaced. Although I am certain that is a separate issue from the stalling/no starting issue.

 

[exp500]

It sounds like a ground problem by the tank- It was better after wiggleing it for fuel pump swap.

 

[kbuskill]

It sounds like a ground problem by the tank- It was better after wiggleing it for fuel pump swap.

It was also better after cleaning the ground on the frame rail below the driver's door... it ran great for 2-3 days after that before acting up again.

I still believe it is a ground issue however. Next up will be getting him to clean the main grounds on the engine.

 

[Fless]

It was also better after cleaning the ground on the frame rail below the driver's door... it ran great for 2-3 days after that before acting up again.

I still believe it is a ground issue however. Next up will be getting him to clean the main grounds on the engine.

One of the grounds to check is the one in this video at 2:30. Supposedly it should connect to the engine block, but if the firewall to driver's side head ground is in good shape that should suffice.

 

[kbuskill]

One of the grounds to check is the one in this video at 2:30. Supposedly it should connect to the engine block, but if the firewall to driver's side head ground is in good shape that should suffice.

Thanks for the video, but that has already been remedied on his truck. I think I mentioned it earlier in this thread, but when he got the truck, the PO had spliced the two ground wires that go to the rear of the passenger head in the same manner as this video shows.

I don't like/trust butt connectors, especially the el cheapo ones like in this video, and the ones that the previous owner had used to make the repair so I had my buddy solder and heatshrink new wires onto them and ground them at the stud on the firewall.

I believe one of the two wires is the ground for the coil packs and the other is a ground for the oil pressure sensor but I'm not 100% sure.

I am skeptical that the braided ground strap is making good connection so that will probably be left in place but a new ground added to it between the firewall stud and the side of the alternator bracket, along with cleaning up the negative battery cable where it bolts to the engine.

Tech 2 should be delivered Tuesday so maybe we can get a better idea of what is actually going on next weekend. I will keep you all posted.