I have a 99 boneville with a 3.8L V-6. The other day drove to friends house and shut off. when I went to leave car would start and die right away. It ran prefectly on the way there. If I held it to floor it would start but when you let off gas it would die right away. When held to floor to keep it running smells really rich like its flooding.

Had it towed home and the next day it started and ran perfect. Fuel pressure is 48 psi. Vacuum line at regulator is dry. Today problems is back. There are no codes. fuel pressure is 48psi. Fuel rail holds pressure after it shut off so I ruled out leaky injector. Tested ECT sensor. Its was 1.6 volts on yellow wire at ECT sensor. Still no codes. Ran it approx 10 seconds with pedal floored, RPM jumping between 4800 and 4000, exhaust makes your eyes run its so bad. Still no codes.

What else will cause this? Is there a good scan tool to buy that will allow me to see all the parameters to find problem. I have heard of protocol converters that will link a lap top for this. Any suggestions out there.

first of all, do your car a favor and don't peg the rev limiter for 10 seconds, your engine doesn't like that.

second, we need to know what trim level you are, SE, SSE, SSEi to further diagnose the problem. you should put your year and trim level in your signature, accessible from the Profile menu up top.

Thanks harofreak00, I added to my signature and edited my post to reflect trim level. 99 Bonneville SE 3.8L. I have replaced the upper plunemum 3 years ago to new renforced one around egr coolant passage. at that time I had all injectors rebuilt and did extensive tune up. Car has maybe 10,000 miles since then and has run flawless since I bought it in 2002 other than the coolant leak in upper plunemum and of coarse the famous recall fuel pressue regulator

I had started the engine multiple times by WOT and letting it back to idle were it struggle for a few seconds and dies testing fuel pressure and checking spark at coil packs so engine was not cold when I did keep it running and would only hold it there long enough to clear it out. I was tring to keep it running long enough to set code. No harm to engine I have raced cars for years and know limitations to motors.

When you hit around 4k RPM in neutral or park, you are hitting the rev limiter so the engine will run terrible - by design - to protect it. As soon as the car starts, have someone disconnect the connection to the MAF, and see if that helps.

If you've got that terrible exhaust stink, it'* possible your catalytic converter has melted down and clogged. A plugged exhaust will cause the symptoms you describe. Again, this is just one possibility.

If it'* really rich, there could be a fuel/air measurement issue. A bad mass airflow sensor will cause this start-and-stall problem too. You could try unplugging the sensor and attempting to start the car 3 times to make it ignore the MAF. On the 4th attempt it should start if the MAF is the issue.

id say its your MAF sensor. had the same thing happened to me...as soon as you get the problem again, unplug your cable from your maf and try again. This should let you start your car, drive it normally, only the engine light will come on and do not drive it for long because it is bad for it since the sensor is there for a reason.

If it is, go buy a new MAF from Napa or whatever (around 120) and you give them your core (get about 20-30 back) and have your light shut off at a auto-zone or where-ever and your done....it took me about 3 weeks to find this problem which sucked...

Thanks everyboby,

Turned out to be the MAF just like you predicted. It started acting up again and I unplugged it and it ran fine.

I'm glad I Took the old one with there was a $70 core charge.

thats what we are here for...best wishes for you and you bonne..

-Mark