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

 

[Warriorpluto]

I remember reading a couple of threads on here with this same problem. Usually it's as easy as changing your oil. Has something to do with the vvt getting clogged when not doing frequent oil changes. Also could be the cam sensor or the tcc solenoid. All three of these will make your truck do what its doing and not throw any codes.

 

[Marky Dissod]

Before throwing parts at it, clean the throttle body (which is also the IAC), MAF sensor, and valve covers thoroughly.

 

[rdezs]

I keep thinking..... You mentioned you change the ignition coils and it solved the problem for 6 months. Then it came back.

I think the first order of business is, "What brand of ignition coils did you use?"

The reason I ask is because you can buy a set of eight coils all day long for $50 made in China, that might last you one hour or one year. The truth is.... If you're on a super tight budget and you absolutely need ignition coils, rather than buy the cut rate ones from China you're actually better grabbing eight OEM coils out of a wrecking yard from the lowest mileage wreck you can find. Otherwise stick to OEM, I'm not sure about the aftermarket. Someone here will be knowledgeable on which aftermarket ones are really good.

GM coils are actually pretty bulletproof. (We have a 2003 Hummer H2 with the 6.0, and a 2014 Escalade with the 6.2, both still using original coils. Escalade has 176,000 miles.) definitely check the plugs to the coils, as well as the large plug off the harness to the coil pack. Maybe by switching coils you temporarily fixed a corroded connection?

Lots of good ideas posted above. Just remember to do them one at a time, not three or four things all at once, so when you do fix it you'll know what the cause was. Then come back here and let us know, it will be useful to someone in the future that experiences the same thing.

 

[petethepug]

There is the fueling side too…

* Tired fuel pump.
* Evap can leaking carbon pellets.

Neither will throw a code but definitely will make you want to throw a match in the tank.