GMC Repair: 90 Bonneville stalling/no restart, purge valve, gm vehicle

Question
The last repair on the vehicle was replacement of the cold-start fuel injector, as the engine was frequently stalling shortly after cold starts.  That seemed to correct it and the car ran well for about six months.  Now cold starts are no issue.  The last start was cold and the engine ran and idled normally, including after being put into gear with brakes applied.  The shop that has tried to diagnose this problem checked the ignition circuit carefully and ruled out anything hugh voltage (we had suspected a coil pack).  They believe it to be a 12V problem, perhaps with something such as the purge valve solenoid relay.  They at one point ruled out fuel pump, but are now uncertain about that.  I did find a website related to GM vehicle engines where fuel pump electrical connector corrosion was cited as a known problem related to stalling.  Would this be able to make the engine shut down for one second and then run normally?  The dash lights (check engine, etc.) come on momentarilly when this happens and go off again when the engine resumes running.  The behavior generally has the appearance of an intermittant electrical contact failure, although that's hard to explain in terms of restoration of contact over time.  Perhaps an initial surge current at start-up helps re-establish the connection?  Would anything else in the electrical circuit be able to cause this problem?  We're resisting on principle just replacing suspect components, but it sounds to me as though replacing the fuel pump and in-tank wiring makes sense in this vehicle at this point with or without a problem... especially if it fits the behavior.-------------------------
Followup To
Question -
Low-mileage (65k) 90 bonneville runs great when running, but has intermittant engine hesitations of one to a few seconds at speed, sometimes stalling and unable to restart.  After the vehicle sits for some length of time (sometimes after many attempts to start), it will start normally on the first try and run great for some time (minutes to days) and then hesitate and or simply quit and again not restart for some time (also minutes to days).  Hesitations do not always mean stalling.  Much shop time checking all systems with no luck.  No useful codes available.  First occured when fuel was low after freeway driving in hot weather.  does not now seem related to fuel level or engine temperature.  No correlations yet found.  It will happen when engine cold or after driving for hours.
Answer -
What was the LAST repair on the vehicle ?. ANY repair of any nature ?. In most cases problems that arise days, weeks or even months later can usually be traced back to the previous repair.


OK, Since you have not yet determined if it is FUEL or IGNITION related makes a diagnosis very very difficult.

However, My first suspicion and the most common fault is with the electric fuel pump in the gas tank. These are well known for intermittent failures at 60,000 to 80,000 miles.

Again, with no conclusive evidenec to support a diagnosis, This would be my first diagnostic process to start with.

You can, Although NOT recommended is to give it a SMALL SHOT of starting fluid when you encounter this intermittent fault just to see if the engine starts and runs for a few seconds.

Do NOT over-indulge with the starting fluid as the sensors and the engine can be damaged as a result of EXCESSIVE use of starting fluid.

let me know.


autohelp

Answer
If it was my vehicle I would tie in a volt meter into the fuel pump circuit and install a fuel pressure gage both of which I made up with long extensions so I could but both units in the seat right next to me so I could monito these 2 areas for a few days to either rule OUT or rule IN these 2 areas.

The other problem area is the CRANKSHAFT SENSOR, If applicable to your engine design, As this to is a known high failure and intermittent failure component and again using my extra long leads tie into the sensor with an analog meter to see if a failure occured from the sensor.

The most common faults with GM are:

1. fuel pump.

2. Crank sensor.

3. Ignition module.

4. Coil pack(s).


Let me know.


autohelp