Well I finally bought my dream car, a 2000 Pontiac Grand Prix GTP. It has the supercharged 3800, all stock. When I first got the car, it was throwing codes in the 300 range for misses in bank one. Sometimes P0300 would come up as well. The O2 sensor would also read lean on the first bank as well. There were also codes showing MAF sensor issues as well. I don't remember what the MAP codes were, but they were MAF sensor codes.
When the engine is cold, it was a little difficult to start, but always started up after a few cranks on the starter. Once running, it would run fine, until the engine temperature started to climb over 80 degrees Celcius. At this point a serious misfire occurs, especially under throttle, and especially when boost kicks in. This would eventually trigger the P0300 codes, the lean condition codes.
Being a new to me car I decided to change the plugs. The first plug wire I pulled on pretty much fell apart when I pulled on it. I ended up replacing all 6 plugs and wires to be safe. I also put in a new MAF sensor and for good measure a new crank position sensor. This seemed to fix almost everything. Except for the occasional stutter, all appeared good. The check engine light stayed off and rescanning the DTC's only resulted in the O2 sensor issues.
Today, after driving around and running some errands, the misfire came right back. Again, when the engine is cold, no issues. It's not until the engine temperature starts to come up that the misfire appears. The check engine light came back and now codes P0300 and P0440 come up.
I know the P0440 is part of the EVAP system, but from what I have read so far, a P0440 shouldn't cause the severe hesitation and misfire.
I forgot to mention that I am getting extremely bad mileage, around 10 to 12 mpg. Having driven a gas guzzling 1997 Suburban I can be extremely light on the pedal.
A few questions:
1. What would cause this condition only when the engine is warm? In my "logical" thinking this would seem to point directly to a specific issue. Again my "logical" thinking is that most issues would occur regardless of the operating temperature.
2. Would a vacuum leak somewhere lead to P0440? My feeling which could be supported by the lean condition in bank one makes me think that a vacuum leak could be part of the problem.
3. Would a vacuum leak cause really bad mileage? My "logical" brain is split on this. If this were a carburated car, a lean condition probably wouldn't result in poor mileage, especially if it were a vacuum leak. But with a fuel injected electronically controlled engine, the PCM is probably continuously compensating for this by adding more and more fuel.
4. Can you have a leaking intake manifold gasket (upper or lower) that doesn't result in coolant leaking into the engine?
5. If there was a vacuum leak, wouldn't the supercharger "fix" the problem as soon as boost kicked in? My thinking is that if there is a vacuum leak that is causing a lean condition, as soon as boost kicks in, the leak is irrelevant as the atmospheric pressure inside the engine is greater than the atmospheric pressure outside the engine.
I do have a OBD2 code reader, but it only reads the codes, no live data. I am going to see if it stores a snapshot, but I am not sure.
When the engine is cold, it was a little difficult to start, but always started up after a few cranks on the starter. Once running, it would run fine, until the engine temperature started to climb over 80 degrees Celcius. At this point a serious misfire occurs, especially under throttle, and especially when boost kicks in. This would eventually trigger the P0300 codes, the lean condition codes.
Being a new to me car I decided to change the plugs. The first plug wire I pulled on pretty much fell apart when I pulled on it. I ended up replacing all 6 plugs and wires to be safe. I also put in a new MAF sensor and for good measure a new crank position sensor. This seemed to fix almost everything. Except for the occasional stutter, all appeared good. The check engine light stayed off and rescanning the DTC's only resulted in the O2 sensor issues.
Today, after driving around and running some errands, the misfire came right back. Again, when the engine is cold, no issues. It's not until the engine temperature starts to come up that the misfire appears. The check engine light came back and now codes P0300 and P0440 come up.
I know the P0440 is part of the EVAP system, but from what I have read so far, a P0440 shouldn't cause the severe hesitation and misfire.
I forgot to mention that I am getting extremely bad mileage, around 10 to 12 mpg. Having driven a gas guzzling 1997 Suburban I can be extremely light on the pedal.
A few questions:
1. What would cause this condition only when the engine is warm? In my "logical" thinking this would seem to point directly to a specific issue. Again my "logical" thinking is that most issues would occur regardless of the operating temperature.
2. Would a vacuum leak somewhere lead to P0440? My feeling which could be supported by the lean condition in bank one makes me think that a vacuum leak could be part of the problem.
3. Would a vacuum leak cause really bad mileage? My "logical" brain is split on this. If this were a carburated car, a lean condition probably wouldn't result in poor mileage, especially if it were a vacuum leak. But with a fuel injected electronically controlled engine, the PCM is probably continuously compensating for this by adding more and more fuel.
4. Can you have a leaking intake manifold gasket (upper or lower) that doesn't result in coolant leaking into the engine?
5. If there was a vacuum leak, wouldn't the supercharger "fix" the problem as soon as boost kicked in? My thinking is that if there is a vacuum leak that is causing a lean condition, as soon as boost kicks in, the leak is irrelevant as the atmospheric pressure inside the engine is greater than the atmospheric pressure outside the engine.
I do have a OBD2 code reader, but it only reads the codes, no live data. I am going to see if it stores a snapshot, but I am not sure.