03 Yukon 5.3L Engine Stalls While Idling

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revans

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I have a 2003 GMC Yukon that stalls when idling. The vehicle is a 5.3L Yukon SLT with 189,000 miles. Stalling happens when the vehicle is at rest or while driving with my foot off the accelerator.

1) About 2 years ago, started stalling while coasting to a stop, but restarted easily and ran okay until the next time it stalled
2) Fuel pump and filter replaced by mechanic
3) Problem persisted
4) Replaced fuel pressure regulator and gas cap
5) Problem persisted
6) Car died and ran very roughly when restarted
7) Dealership mechanic could not find problem, but did reprogram the PMC. It ran okay when I drove it home.
8) Problem resumed
9) Determined that the car died when fuel gauge registered one quarter full
10)Wrong fuel pump and gas filter replaced by mechanic
11)Car died because ran out of gas because fuel gauge not registering level properly
12)Mechanic repaired wiring connector to fuel pump.
13)Car died on freeway and would not restart
14)Mechanic replaced cam and crank sensors (code # p0335, p0706, p1571, p1689)
15)Car ran okay for a short while and then started dying more frequently
16)I replaced throttle body with OEM part, replaced PCV valve, cleaned K&N filter and cleaned MAF.
17)Problem persisted
18)Took car to GMC dealership where technician “checked all circuits, checked maf data, ignition data, checked all ground straps and grounds at the back of the block, found the ecm internally failing”. I declined to have the technician do repairs at that time.
19)I purchased refurbished pcm programmed with my VIN and self-installed
20)Problem persists exactly the way it did before the pcm replacement. Car is undriveable. Appears to run lean. When I press the accelerator, car tach goes up and then immediately goes down.
 

swathdiver

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Rob this very much sounds like a bad Mass Airflow Sensor but could also be the throttle body and or a vacuum leak. Has the intake manifold gaskets been checked for leaks?

You need a good scan tool to work on these things. One that can data log, run graphs, see all codes in engine and elsewhere so you're not guessing and throwing money at it blind. The Tech2 is the answer. With all the issues you're having, it will pay for itself in short order.
 
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revans

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Rob this very much sounds like a bad Mass Airflow Sensor but could also be the throttle body and or a vacuum leak. Has the intake manifold gaskets been checked for leaks?

You need a good scan tool to work on these things. One that can data log, run graphs, see all codes in engine and elsewhere so you're not guessing and throwing money at it blind. The Tech2 is the answer. With all the issues you're having, it will pay for itself in short order.

Thanks for the reply. I do not believe that the intake manifold gaskets have been checked for leaks. How would I go about doing that myself?

What would a Tech2 tell me that the dealership technician's scan tool didn't tell him?
 
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revans

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Check fuel pressure WHEN ISSUE OCCURS. When my pump ****** up, it would run perfect until it began to **** up. Then and only then would I note a drop in fuel pressure. Also pull live data from MAF, TPS, IAC, spark advance and knock retard.

Any codes?
Nope. No codes except when the cam and crank sensors had to be replaced.
 

swathdiver

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Thanks for the reply. I do not believe that the intake manifold gaskets have been checked for leaks. How would I go about doing that myself?

What would a Tech2 tell me that the dealership technician's scan tool didn't tell him?

You can see various methods on youtube. I remember one where a fella poured water sparingly on the intake where it meets the head and watched for the idle to change. Others use smoke or propane or map gas. I would use propane from those little blue bottles.

It's quite possible that the Tech2 used one to diagnose your vehicle or its successor. What we don't know is how well was he trained and how much time he spent. Did he run tests with the Tech2 on the motor, graph the O2 sensors while looking for intake leaks, shut down the injectors or coils, compare the MAF readings to a published graph in coordination with the current air temp and so on. One of the most important are the fuel trims. If they are high at idle and go away once revved up, that's usually a sign of a vacuum leak and the intake gaskets being the culprit.

You can also monitor and test the fuel pump and see if its trims are within spec, see how hard it is working and if it or the injectors are bleeding down when the motor is off.
 

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