1993 Pontiac Bonneville very difficult to start in the AM.

[Hemi Dude]

A lady in church has the hardest time starting the engine when it has sat overnight. Today it took her 30 minutes of trying. Anybody have an answer? 
It starts and runs fine when warmed up, though it ‘sounds’ a little lean when listening to the exhaust at idle even when thoroughly warmed up.

[E_Johnson]

Might need a new fuel pump.

If she lets you start the car, turn the ignition key to the on position and listen for the fuel pump and then wait until is stops so the fuel rail is fully pressurized and then turn the key to engage the starter.

[Hemi Dude]

11 hours ago, E_Johnson said:

Might need a new fuel pump.

If she lets you start the car, turn the ignition key to the on position and listen for the fuel pump and then wait until is stops so the fuel rail is fully pressurized and then turn the key to engage the starter.

Thanks for your reply: Early morning fuel pressure test with pressure gauge attached to pressure test fitting on fuel pressure regulator;

Initially, turned on ignition to run, gauge went to 22 lb on initial 'key on' test, then fell to 0. I repeated the 'key on' test, the same results each time.

While constantly cranking engine, pressure goes to 40#, engine tries to run but will not!  As soon as I release key from crank position, the pressure falls to 0 again.

This would seem to me as a possible BAD fuel pressure regulator, as on our MOPAR products, the pressure is supposed to hold at least overnight and longer.

What is the running fuel pressure supposed to be?

Thanks again for your help. 

[Hemi Dude]

After removing the pressure regulator and "sort of testing it" I feel it is OK. While attempting to start the engine again, I find it seems to be kicking back as I crank the starter. After several tries, it started and seemed to run on only one cylinder, then 2, then a few more until it was hitting on all 6. It still idles poorly, BUT when goosing the throttle, by hand at the throttle body, it responds without a single hesitation and revs up ever so smoothly. Holding at higher RPM, it purrs like a kitten.  Turning it off produced difficult restarting again.  [One of the 3 coil-packs has been replaced at some time in the past, any possibilities there?]

This is an OBD2 system, but I don't seem to find the connector under the dash on the left side as on newer cars. ???

[Bloo]

Does it have a cam sensor? There were some GM transverse V6s about that time that would run fine without the cam sensor signal but would not start without it. I do not recall which ones. It can't really be OBD-2 in 1993. If it is OBD-2, the year must be wrong. For 1993 you are looking for the old GM ALDL connector to connect a scan tool to, and I think it will need to be a fairly old scan tool to support something that is not OBD-2. The connector was usually under the dash on most of them, but the location was much less standardized. Look all under the dash on both sides, If it has a center console, look in and all around that too if you don't find it under the dash. Also the glovebox.

 

Lacking an appropriate scan tool, there was a way to short these out with a paper clip to get codes blinked out on the check engine light. A code 12 (no ignition signal) is normal, it just means the engine is not started. There is live sensor data in these systems too, but you need a scan tool for that.

 

 

EDIT: look here: https://www.obd-codes.com/faq/read-gm-2-digit-obd-codes-free.php

 

Note the positions of the "wings" on the bottom and the key on the top when locating terminals "a" and "b". If I remember correctly these were not always mounted right side up. Also there might be a cap over the plug.

 

Edited November 25, 2023 by Bloo (see edit history)

[E_Johnson]

I'm not an expert and don't know what the spec is for the car in question, but I would think that if you turn the key to the run position without actually starting the car, fuel pressure should be around 45 PSI and, once it's running, it would be slightly lower.   As you are aware, with the vacuum line is connected to the fuel pressure regulator, the fuel pressure should remain relatively constant, regardless engine speed/rate of fuel consumption.  If you disconnect the vacuum line from the fuel pressure regulator, pressure should vary with engine speed/fuel rate of fuel consumption.

The fuel pump might be bad or it may be a case of low voltage or a bad connection or ground.

Fast leakdown could be a bad check valve in the fuel pump, a leak anywhere along the fuel line (although I think you would smell that), a leak at the fuel rail or one ore more leaky injectors.

[Hemi Dude]

Thank you Bloo & E–Johnson for your responses, of course you are right about the car not being OBD2, my wife drives a '94 that is not. I keep thinking it is a 2003 for some reason.

I will look for the diagnostic connector, I have a Snap-On 2500 which I have used for years, that would work, IF I can find the correct adaptor.  

Thanks again, I'll let you know the outcome, it could be helpful to someone else as well.

[EmTee]

OBD-2 started with the 1996 model year.  I have done the 'workaround' diagnostic by shorting the two pins (A & B ) on the ALDL connector and counting the Check Engine flashes.  It's not fancy, but does the job at zero cost.

 

 

 

Edited November 25, 2023 by EmTee (see edit history)

[Hemi Dude]

Just an update; the car would not start Sunday or Monday, so it will be taken to the shop where I can analyze the problem and let you all know the outcome.