2001 Suburban 2500 8.1L Stalling at freeway speeds Roadside 911

SButler83 · July 21, 2019

I will be searching the forums here shortly, but I am semi-stranded on a 1,750 mile road trip with 5 kids under 10, over 500 miles from both my origin and destination.

I have a 2001 Suburban I bought with 260,000 miles on it. I'm now pushing 270,000 I made it to a hotel nearby a Chevrolet Dealer, but they don't open for service until Monday.

I was cruising at freeway speeds and suddenly the truck engine died and began coasting to a stop. I put the truck in neutral, restarted it, and it fired up and popped back into drive. About 150-200 miles it started happening more frequently.

When the engine loses power, the tachometer shows the engine speed dying out, so it is not a total loss of signal from whatever provides the signal to the tachometer. After dying out, the engine will fire back up and idle with minimal extra cranking. The engine starts up and idles well at these times, and I have had to idle it with the family in it and it runs the AC no problem at idle. I have not had the condition pop up at idle. Sometimes, the engine will recover itself and resume accellerating as we are coasting if I feather the pedal.

I have an AutoEnginuity scanner and a decent array of tools that I travel with.

MIL is not on. I have some history codes for:

P0461: Fuel Level Sensor Circuit Range/Performance (I believe this code was never cleared from before I replaced the sending unit previously)

P1172: Fuel Transfer pump Flow Insufficient - This one kind of makes me wonder. On the trip, due to having the kids in the car, I have refueled at various levels with the engine running for A/C. Alldata says this code will not set if P0461 is present.

P1431: Fuel Level Sensor 2 Circuit performance.

The only way I could see the secondary fuel pump effecting drivability, aside form usable fuel, is if the secondary pump failure has caused it to become an excessive current draw.

When I bought the truck, the fuel gage was not working, which I traced back to the primary sending unit in the tank. At around 265K miles. I replaced the fuel pump and sending unit assembly at this time with a new AC Delco OEM replacement part. Since that replacement, I have made the same 3,500 round trip road trip without issue about 1 month ago.

One difference this time is that the ambient temperature this time is considerably warmer outside, however the coolant and trans temp gages have been riding right at where they normally do.

Prior to that last trip as well, I put AC Delco Irridium spark plugs gapped at .045", and a 180F thermostat in the truck.

The only other issue that I had was that at one point the EGR became stuck open by a small piece of stray carbon that would cause the truck to not idle.

When the stalling symptoms first surfaced on this trip, I put a new AC Delco fuel filter in the truck and replaced the primary fuel pump relay just to rule them out, I would find it odd that a fuel pump would fail at that juncture at 5K miles old, however I am planning to get down to AutoZone and purchase a fuel pressure gage just to check that out during the moments when the problems are being experienced. The old fuel filter didn't seem restricted with a blow-through test.

I do know this truck has both a camshaft and crankshaft position sensor, and I have seen a lot of similar symptoms that relate to the failure of one or both of these. I think that's where I'm looking next if the fuel pressure checks out.

Am I correct in assuming that the engine would throw a DTC if an ignition coil or coil group was intermittently failing?

Any help greatly appreciated!

Thanks!

Steve

2001 Suburban 2500 8.1L 4x4, 270K Miles

JoJoJim · July 21, 2019

My 2001 Silverado had same situation. It turned out to be cam sensor. Not expensive auto parts store had one I installed in about 15 minutes. It is at front of engine up high.

Colossus · July 21, 2019

I'm betting it is one or all of the following:
Bad gas

Fuel Filter plugged

Fuel pressure regulator

Bad fuel sending unit (I know you said you replaced it recently, but stranger things have happened)

Edited July 21, 2019 by Colossus

Formulabruce · July 21, 2019

I had those symptoms with a dirty throttle body. Remove the huge hose clamp and clean the whole area well with Throttle body cleaner, NOT carb cleaner. Clean the throttle plate as well, both sides. This will sometimes throw a code, but not always. A bottle of Throttle body cleaner and 15 min with a clean lint free RAG JUST MIGHT HELP. Good luck !

Ps I run 160 T-stats in my LS engines in the summer and they all work in closed loop and run about 15 degrees cooler.

riverbanks · July 21, 2019

Any luck? fuel pressure ok?

SButler83 · July 22, 2019

So I checked fuel pressure, and it was dead on correct, (but this was when the problem was not currently present) Was not able to test during symptom display. I drove the 11 miles home with a fuel gage visible on the window and behaved nothing short of what I would expect. I was able to manipulate the truck to CA. The problem is most common at speeds around 50-62. If I get it going above 75 MPH, it would nearly never happen.

Certainly could've been some bad gas coming through.

The problem seemed to get less frequent as time went on.

I have a spare Cam & Crank AC Delco position sensors headed my way for the ride home. Probably will go ahead and throw the cam in. I have noticed the tach is a little bouncy. May be due for the coils to be changed, but I don't think an entire bank would crap out at once unless someone knows otherwise?

At 270K Miles, what are the odds that the crankshaft position sensor in that pig is original? Don't want to risk breaking off an original anywhere but the driveway at home unless necessary.

Thanks all!

riverbanks · July 22, 2019

Could be original,I felt bad for you, reading post, you mentioned, dealer,you know they wouldn't be able to duplicate the symptoms,money wasted,I would look into the egr again, keep us posted,good luck

HawkScot · July 23, 2019

I think it is a mistake to put a 180 thermostat in it (perhaps things have changed, but it certainly caused problems when it did it in the 90s). My understanding is that the computer thinks the vehicle is not warmed up properly and runs a bit rich, which eventually causes O2 sensor and catalytic converter issues. In my case, I had to replace both (after putting the proper thermostat in).

You indicate the temps are running normal, so perhaps the 2001 rigs don't have that issue. I have a OBDLINK MX bluetooth and the software to connect to on my phone that I run sometimes to watch things like temps and such. One of my daughters had issue with her truck and the oil pressure sending unit. The engine died in freeway traffic a number of times before she replaced it in the parking lot of OReilly's auto parts.

SButler83 · July 23, 2019

Before I had made that switch to the 180F & Irridiums, I saw many people having good results doing it. I do think it smoothed out my idle a little bit.

I have some throttle body cleaner and will attack that today. Cam and Crank sensors on the way too.

I did verify the EGR position sensor on the scantool to be properly closing.