Another random stall out thread.

[littleblazer]

So, I've been chasing down this issue for well over a year and a half now, I have a random stall out, when it's hot out more so, that I can't catch with my scanner... (long story) The following is a list of items replaced or checked:
Throttle body cleaned
O2 sensor replaced, code for heater circuit and it was very lazy.
Cam sensor, It failed the tap test as per May03lt's video.
CPAS, had a ton of oil in the connector
Coil pack, because it died...
Tightened the bolts on the intake
Fuel pump, it also died
Fuel tank pressure sensor, it failed on the envoy so I was parts swapping until my check engine light came on.

So basically I am now looking more towards an intermittent connection, maybe a sensor. Now I had said earlier that I was thinking a throttle sensor, here is why. A friend of a friend had a trailblazer, this man was a gm tech, that was doing the same thing, what he did was he drove around with the tech 2 until he caught it, well it ended up being the tps. But this was an ss, so I'd imagine the whole thing is different, but it was a starting point so I have been data logging tac data. At idle voltage according to the dash is 14... torque says 12.8, meter on the battery says 13.7-13.9. Any input on things to check would be much appreciated.

 

[Mooseman]

If there is a discrepancy between the throttle and the pedal sensors (or with what the PCM is commanding during cruise control), it is supposed to throw a code and put the truck in REP. But thr glitch could be so minute, it just shuts down. I don't know. I'm just guessing here.

If you have a pick-a-part nearby, maybe try another throttle body (or borrow one from a friend). Same with the pedal. I realize this is throwing parts at it but don't know where else to go with this.

 

[littleblazer]

The only other issue I could come up with was a failing brake booster, but it does it in park so that rules that out. But a sudden quick drop in vacuum under load might have done it. I want to try to catch the tac module data, hopefully before I go to school. Being 80 miles from home with limited tools could be an issue should something go. But the feel is all the usual suspects have been ruled out I guess.... great.

 

[Mounce]

Does the envoy have the v8 or i6?

If it has the v8 you could still definitely swap the pedals between the two if there was enough downtime. Not the throttle body though, or at least I'd think not.

 

[littleblazer]

Does the envoy have the v8 or i6?

If it has the v8 you could still definitely swap the pedals between the two if there was enough downtime. Not the throttle body though, or at least I'd think not.

Both are I6... I might have found my donor car.... hope dad doesn't mind.

 

[Sparky]

"Gee dad I don't know why yours is acting like mine used to!"

If you do swap parts, do one at a time.

 

[littleblazer]

Yea I got the hell no... so yea

 

[Mounce]

I thought that was ridiculous for a second but then I remembered that your problem is internment and it might take a week for it to act up again and it'd be bad to have it happen to your mom if you swapped the issue part lol.

 

[littleblazer]

Tech 2 ride along continues I guess.

 

[littleblazer]

One thing I wanted to add was I get the check gauges light when it stalls. Not that that really matters. Didn't do it today on the ride along.

 

[Sparky]

That light turns on usually because when it stalls the oil PSI hits zero so it is alerting you something's wrong. Same has happened to me if I've stalled the Trailblazer or the Camaro.

 

[littleblazer]

I figured it would be unrelated. Thanks for the clarification. [emoji106]

 

[littleblazer]

Update: did it 3 times Monday since I didn't have on the tech 2. Hasn't so much as surged since...

 

[littleblazer]

Surged today, left the tech 2 off... no stall

 

[Mike w]

My problem was the throttle body.. I had same problem same symptoms and swapped the throttle body and its been fine since. What led me to the throttle body was 2 TPS codes that were stored, and they never set the Check engine light.

 

[littleblazer]

Hey guys. With warmer weather around the corner I know work isn't far away and I know I'll start having this issue again once I'm driving everyday again. I do have a possible lead/avenue to explore though. A friend of mine was having a similar issue with his boat, occasionally it would stall, loss of power etc. For him it ended up being a crank sensor. I don't know if we even have one and I don't recall seeing it in the Tech II data lines that's why I asked. But wouldn't something like that trigger a code or something?

 

[mrrsm]

In combination ...the CPAS and CPS will cooperate with the PCM to keep the engine running if the Crankshaft Position Sensor goes "T*ts Up".... But any performance discrepancies between the three as they "cover" for the failed Crank Sensor will cause the engine to stall... Anything small... like changes in oil pressure or a sketchy CPS can make the engine quit and not throw any codes to provide any clues. If the Crankshaft Position Sensor must be changed...you will very likely require a CASE RELEARN as well. This White Paper PDF mentions this issue, too:

http://vortec4200.com/index_htm_files/vortec4200.pdf

From Page 21...

"The PCM provides a limp-home mode for ignition timing in the event either the crank or cam sensor fails. It continues to control timing based on data from the functioning sensor and warns the driver with a warning light."

From Page 22...

This assumes that the "back-up sensor" is functioning correctly... at all times:

"The cam position sensor identifies the position of the exhaust camshaft. A trigger wheel on the cam phaser aligns with the sensor’s tip. As this target rotates, the cam position sensor reads the changing magnetic field and sends a digital signal to the controller. The sensor is installed in the front of the cylinder head. It has an o-ring to prevent oil leaks. The cam position sensor also provides a back-up to the crank sensor to allow engine operation in the event of a malfunction. A position sensor failure will not cause the engine to stop running."

 

[littleblazer]

I'm back. so the other day it almost happened but I caught it and attempted to throttle out of it per say. On a carburetor you could throttle and it would surge almost. Well pushing the pedal down some when it happened in drive it rolled forward as if I just let off the brake. The pedal position didn't really seem to make a difference which I guess is right since the tb is just for air flow. But I would think it would change the metering and adjust fueling as well. This leads new to believe that it may not be anything on the throttle control circuit. Thoughts?

 

[DAlastDON]

Degrease the engine bay then spray every nook and cranny with the spray pictured below. Spray the PCM twice.

 

[MAY03LT]

There's a ckp signal pid in one of the engine data thingys. But I've personally verified that the live plot won't catch a fast spike or drop out of cam/crank. You might get lucky and have it drop long enough to get some hard evidence.

 

[littleblazer]

It's a 5 volt square wave correct? I can borrow a scope to check it.

There's a ckp signal pid in one of the engine data thingys. But I've personally verified that the live plot won't catch a fast spike or drop out of cam/crank. You might get lucky and have it drop long enough to get some hard evidence.

 

[MAY03LT]

Nice. Yeah 5v I tap signal at the pcm.