Thread: Warm Start Stall - Stumped

Hey Guys,

Having an issue with my 01 GP GT with 205k. Have searched this forum and all over the web and am stumped.

Issue is the car starts fine when cold, but stalls when starting once warmed up. Once started (which will start with some throttle for few second), the car runs and idles great. Very similar symptoms as others on forum, but haven't had same results fixing issue. Have tried the following things:

- Clean Throttle Body Twice
- New MAF
- New IAC valve
- New Throttle Position sensor
- New Fuel Pressure Regulator. (Hose from Throttle body to Fuel Regulator looks fine)
- Swapped PCV valves from my Bonneville
- Plugs and wires about 20k ago. (Recently swapped coil packs and ICM blocks from Bonneville - no change)
- Fuel Filter 5k ago

Could this be a vacuum leak of some sort? Planning to get some brake cleaner in near future and spray all around to see if engine behavior changes.

Finally got frustrated and had the car scanned for codes. Two codes appeared, one for the rear O2 sensor (car has straight pipe) and other is U1304 - Loss of Universal Asynchronous Receiver Transmitter Communications. (Loss of UART Communications).

What does this code mean? Sounds like some hardware is malfunctioning from what I'm gathering online. (Very limited information) Anyone experienced this? Think the PCM is malfunctioning? Car also has real bad hesitation under hard accelerations in 3rd and 4th gears which I believe is TCC solenoid acting up.

I'm stumped. Any suggestion is greatly appreciated.

Thanks,
Eric

Have you checked to verify the ECT (engine coolant temperature) sensor is sending the correct information to the ECM/PCM?

No I haven't. Good Point! Think I may go try that now. The beauties of having Bonneville and GP with same drivetrain! ha

Only way I can check is by swapping sensor. Is there better way to check/verify?

Will have to try ECT tomorrow. Don't have much coolant left in garage. The temperature gauge seems to be reading like it always has. Simple enough to swap to see.

The MAF was replaced before the starting problem occurred. Replaced the MAF seeing if it would affect the trans issue I mentioned above.

Thanks for suggestions guys! Should get time tomorrow to work on it. I'm feeling optimistic again!

Hey Guys,

Haven't gotten around to trying the temp sensor yet. We got hit with some pretty cold weather and have been waiting for fairly warm day.

The rear O2 sensor is installed. I have replaced the front one on manifold about 20K ago.

Providing an update on this..

Replaced the Coolant Temp Sensor and car still seems to have the warm start stall. I have an additional question about the temp sensor though.

The car always ran about the first mark on the temp gage. Guessing about 180 Degrees. After adding the new temp sensor (BMB Brand), the car now runs up around 210 and little over. The car seemed to warm up rather quick this morning (30 degree morning) like the temp gage isn't calibrated to the sensor. I have released air from the system and seems to be at proper levels. I have the battery unplugged and letting it sit to see if it resets anything.

Is this common? Maybe my old one was reading incorrectly? Seems weird to me.

Thanks guy!

I mean the first line as in the first line over the 160 mark. The 1/4 gauge line I guess is better explanation.

I'm assuming this car has factory thermostat. I have never replaced it.

Thanks for the response! Figured it was probably normal but this car has always ran at the 1/4 mark until the sensor was changed. Thinking I may be changing MAF and trying to figure out this Warm Start deal.

I replaced the block which the coils mount to. Never changed the actual ICM wire harness. I did this to try solving the Torque Convertor issue while accelerating. Don't recall the time frame when the warm start issue arouse. Easy enough to swap around again (with harness) to see what happens.

Thanks for the help guys!

02NavyBlue - That's where my car always used to operate. I just took the car for a 5 minute ride,a bout 30 degrees out and this is where the temp gage is at now after replacing the coolant temp sensor.

Been working on this a bit more this morning.

Re-bled the system and was having same issue. Checked everything and didn't notice anything wrong and the car continued to read hot on the temp gage. Got frustrated so I head over to my Bonneville where it's being stored and grabbed my scangage. This is what I found:



So apparently the sensor I replaced (one in the LIM) is reading incorrectly and this is why my gage is reading high. But, is there a second temp sensor somewhere that the PCM is reading and showing the 186 degree temp? If so, are they the same sensor? I bought another LIM Temp sensor to swap it out hoping I got a malfunctioning one yesterday.

Any thoughts on this?