Engine cuts off at slow speed after 1HR of HWY driving

[shr3ddymurphy]

Hello, dealing with a real head scratcher..
2009 Tahoe LTZ 4X4
After driving smooth for 1 hour on the freeway, truck's engine cuts off at low RPM. Usually when I come to a stop sign after just taking an exit, or worse: when I hit some stop-and-go traffic during a long drive on the freeway. Took to mechanic, no check engine light no codes related to engine. ~170k miles on truck and I think I am the first to replace worn out parts.

Done the following so far
- 2 bottles of fuel injector cleaner: no change
- New fuel pump: no change
- New spark plugs + wires: no change
- New ignition coils: fixed issue for six months, then it came back

I'm thinking of doing fuel injector replacement next but I'm wondering if anyone else had this issue and can share what was the cause

 

[Sir_Hiro]

Would be better to maybe Datalog from the OBD port besides parts cannoning it. It could be a number of different things. Sensors, Fuel Issues. PCM BCM dying?

 

[Fless]

Throttle body dirty? Any possibility of a vacuum leak showing up after the warmup?

At idle do the short-term fuel trims change much from cold start to when the issue happens?

Maybe monitor and graph the STFTs while driving to see if you can get the graphs to show the stall.

 

[shr3ddymurphy]

Me and my mechanic scanned for codes and there was no significant errors that would relate to this problem (just airbag code, and tpms sensor, etc). Personally, I think the injectors are so old they're failing when hot, but not bad enough to throw code.

 

[Fless]

The only codes the injectors would throw are circuit codes. But the fuel trims show to some extent how they're working. There are other variables, of course.

Sounds to me like the IAC isn't working correctly or a vacuum leak that is intermittent.

EDIT: I would suggest an injector balance test, cold and hot.

 

[shr3ddymurphy]

Throttle body dirty? Any possibility of a vacuum leak showing up after the warmup?

At idle do the short-term fuel trims change much from cold start to when the issue happens?

Maybe monitor and graph the STFTs while driving to see if you can get the graphs to show the stall.

Hmm, have not checked throttle body. What's crazy is I keep having to remind myself that spark and fuel are working well enough on this vehicle for it to turn on and take me to another city with no apparent issues. Its not until I've been driving for over an hour and components get hot, that it decides to stall at 10> MPH.

As far as vacuum, my heater hose broke off once and I had to get it replaced replaced. Now that I think of it, I never had any issues until after that repair. Maybe it wasn't done right and vacuum/air ratio got messed up.. Not sure