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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.
 

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You are on the right track about intake gaskets. Regardless of the lean issue, you definitely should replace the intake gaskets with the aluminum framed intake gaskets if they were not done. (may be the source of lean condition to a particular cylinder)
Check your fuel pressure regulator. Remove the vacuum hose and check for gas dripping out a strong gas smell,if yes, a bad regulator. It would be a really good idea to check for proper fuel pressure at the rail. I am running around 53 with vacuum off. You should definitely change the fuel filter if you have no previous record of being done recently. Hopefully, you do not have a failing fuel pump at this time. You may have to do a fuel volume test if you continue to have fuel indicated trouble.
It would probably be well worth the money for a scan gauge. I use the earlier aeroforce model, and it has been very helpful. You will find out if the PCM is trying to add fuel or not.
These suggestions are a good place to start. A lean condition can lead to detonation and death of an engine very quickly.....Congrats on your new GTP!!
 

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Discussion Starter #3
I am curious about the lean condition. If a vacuum leak were always there, would it not trip all time?

I was thinking about the possible fuel delivery issues and how that would be related to engine temperature. I had a 92 Buick years ago and when it was warmed up, it would stall. A failing fuel pump was causing vapor lock. I will have to pick up a pressure gauge and continue on.
 

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after the maintenance and fuel system checks, check the resistance of the coils, a missed spark will read lean to the o2 sensor and a vicious cycle begins where it's adding fuel it doesn't need
 

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OK. didn't have a chance to check out everything today because I was at work. I did check the fuel pressure regulator and it appears ok. There was no fuel leaking and no strong smell of fuel.

I hooked up my cheap scan tool to my computer so I could read the freeze frame data. Here's what I got:

DTC for which freeze frame was stored P0171
Fuel system one status: closed loop
Fuel system two status: Not supported
Calculated LOAD value: 6.27%
Engine Coolant Temp: 143.6 F
Short term fuel trim bank one: 14.84%
Long term fuel trim bank one: 16.41%
Intake Manifold Absolute Pressure: 13.03 inHg
Engine RPM: 1,388.00 rpm
Vehicle Speed Sensor: 24.23 mph
Air Flow Rate Mass Air Flow Sensor: 2.04 lb/min
Absolute Throttle Position: 5.49 %

The engine temp will need to be addressed because I think the previous owners either took it out or the one in there was a where it fails in the open position. Engine temp never approaches 180 degrees F. Unless the stock gauge is extremely off.

Tomorrow I hope to pick up a few more tools, like the fuel pressure gauge and a vacuum gauge. Probably take off the EGR and make sure it is clean as well. I hate throwing good money after bad to fix this, but I would rather spend $30 to $50 on a new sensor or a new tool than have to pay a shop for hours of work to have them find nothing.

When I first started driving, we had a 1990 Dodge Caravan. One day it started to have intermittent starting problems. The engine would crank and crank, but didn't appear to be firing. Over 8 months, the van was into the shop every few weeks (under warranty thank god). After replacing a bunch of sensors, modules, and the PCM, it turned out to be a loose wire in the plug for one of the modules. Had it not been for blind luck, we probably never would have found what actually caused the problem.

The story behind finding that loose wire is pretty funny. My dad and some buddies were out hunting birds in November about 40 miles out of town in the middle of nowhere. After about an hour of the van not starting, my dad got frustrated and threw a bunch of snow on the engine and it started. Over the next few months, any time it would not start, we would pop the hood and throw snow on it. I wasn't til after the van was fixed that we realized the snow was probably bumping the wire and completing the circuit so the van started.

I love all the advantages of fuel injection, but sometimes I would love to be able to pump the gas, hammer the petal, and wait for the car to start. My old 79 Camaro always started and always ran. Only got 10 MPG though and less than 200 HP.

I will let you know what I find tomorrow.
 

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While you are out running around looking for fuel gauges and stuff, you might want to pick up a fuel filter too. Might have been awhile since it was changed.
P0171 = System Too Lean (Bank 1)
 

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Clarification. Ignition module= the module used for the ignition key..not the ICM.
 

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Discussion Starter #9
Just a little update:
Picked up the fuel pressure gauge and the vacuum gauge.
Fuel pressure is low at 20 PSI. Vacuum is good and constant.

I checked the pressure regulator and it appears good. I pulled the vacuum line and let it run for about 5 minutes, and no fuel leaked out. I also checked it after the engine was shut off, no fuel and no smell of fuel. So the regulator is likely ok.

I am guessing the fuel filter hasn't been changed in years. So rusted, I couldn't get it off even with multiple treatments of good penetrating oil. Tomorrow I am going to pick up a fuel line and cut out the old filter. Really hope it is the filter and not the pump.
 

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Almost done. I replace the upstream O2 sensor and the lean condition and the O2 sensor code are now gone. I still have to test it in real world stop and go traffic when the miss normally develops.

I had to order a fuel line repair kit so I can change the fuel filter. I completely stripped the line trying to get it off. Used a good penetrating oil and everything. Oh well. Repair kitis in the mail.

We just bought a 2002 Impala with a 3800 for my wife. This experience will go a long way to work on her car.
 

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Finally fixed. It looks like the previous owner knew the fuel pump was failing, so they swapped out the sending unit for something from another car, definitely not a GTP. They also forgot to re-install the o-ring between it sending unit and the tank, which was not only causing 0440 codes, but had resulted in a significant fuel spill when I was filling the car one day.

I ordered a new pump, which took a few weeks to receive over the Christmas holidays. I was surprised to find out the pump didn't match what was in the sending unit. That's how I found out what the previous owner had done. I was searching online and happened across a guy locally who had a complete sending unit for $50. He had written off his GTP and still had this lying around. Dropped it in and it has been smooth sailing ever since.

I am excited to start slowly working on the performance side of this car to make it a little more peppy. Probably start with a smaller pulley and a cold air intake.
 

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Glad you resolved such an aggravation. It is difficult enough to trouble shoot a problem with KNOWN components, let alone botched fixed including eliminating the O ring seal. The fuel vapors in the car must have been brutal!
 

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If your car engine is misfiring then you must know that the engine is actually skipping over important processes of combustion cycle and this usually causes the engine to work very roughly. Just due to this problem your car engine would not be working properly and efficiently. A car owner must take it seriously and should make his car’s engine repair as soon as possible. He should consult any good car mechanic and make sure that the problem is resolved at the earliest for better performance of the car.
 

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I am excited to start slowly working on the performance side of this car to make it a little more peppy. Probably start with a smaller pulley and a cold air intake.
I really hope you didn't drop pulley sizes without a tune........:icon_eek:
 

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You are on the right track about intake gaskets. Regardless of the lean issue, you definitely should replace the intake gaskets with the aluminum framed intake gaskets if they were not done. (may be the source of lean condition to a particular cylinder)
Check your fuel pressure regulator. Remove the vacuum hose and check for gas dripping out a strong gas smell,if yes, a bad regulator. It would be a really good idea to check for proper fuel pressure at the rail. I am running around 53 with vacuum off. You should definitely change the fuel filter if you have no previous record of being done recently. Hopefully, you do not have a failing fuel pump at this time. You may have to do a fuel volume test if you continue to have fuel indicated trouble.
It would probably be well worth the money for a scan gauge. I use the earlier aeroforce model, and it has been very helpful. You will find out if the PCM is trying to add fuel or not.
These suggestions are a good place to start. A lean condition can lead to detonation and death of an engine very quickly.....Congrats on your new GTP!!
After reading this question I was having the same issue , I went out to my car waited for it to go almost warm I wiggled the top of the wire Intake Air Temperature Sensor Wiring Harness Connector Pigtail and it started warm Behavior throttle up , then down up then stall. I got the wires into a good position and glued it . did great for the hour I was cleaning the car. this issue arrived before lean mix , and cylinder 6 misfire. and most codes disappeared , o2 sensor is the only one left.. so far I haven't taken it out on the freeway yet . But I feel. hopeful... this was same issue I was having with MAS mas airflow sensor. it would die on the freeway , replaced many MAF then changed pig tail connector and was great again .. now I am slowly changing my connection wires.. I was going to start with the gaskets lol oh my 2001 grand prix GT minnesota lived car 135.000 miles, excited to my drive to walmart tomorrow , ll let you know what happens
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.
After reading this question I was having the same issue , I went out to my car waited for it to go almost warm I wiggled the top of the wire Intake Air Temperature Sensor Wiring Harness Connector Pigtail
 
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