2000 pontiac Grand prix misfires when engine is cold

[koolbike]

Hi all,
This is my first posting. I am i need of help. My 2000 Pontiac Grand Prix saw the dealer several times for a misfire when the engine is cold. They installed new injectors cleaned the throttle body etc. I am about to give up and slowly running out of money from all the repairs. Is there anybody out there that has this problem?? Again this only happens when my car engine is cold. The misfire diappears once the engine been running for a couple minutes. The engine light comes on etc. After the last time the dealer cleaned out all the injectors and the throttle body it was OK for 6 months and now it is misfiring. They also told me to use 89 octane gas verses the 87 octane, i did. PLEASE HELP.
Al

[GTP Dad]

There are a couple of other items you need to look at. First, coils, plug wires and plugs. You didn't say anything about changing any of these. Also clean the mass airflow sensor, cleaning the throttle body only will not clean the mass airflow sensor. I expect you are getting two codes one P0171 and a misfire code P301-P306 not knowing which ones it is hard to say where to look. Try changing the plugs and wires first and see if the misfire goes away.

[koolbike]

Thanks for the reply. The dealer said the plugs and wires looked OK. Can the plugs or wires cause a misfire only during the intial startup> As mentioned the misfire only occurs for the first few moments when the engine sits overnight. I will try and locate the info on the codes. The dealer seems alittle besides themsleves on this one. I did notice that when i put injector cleaner through it when the problem first happened 2 years ago it went away. The injectors then had to be replace due to leakage and debri in the gas from the injectors cleaner. I had all the injectors replaced and tested along with cleaning the throttle body. My car was fine for 6 months. The only longshot i have is when i clean my car at the local spray off car wash i open the gas tank door. Can water be getting into the gas???? I said a long shot but it started to misfire shortly after i opened the door and shot water to clean out the dirt in the gas opening tray. Is the gas cap lwak proof?? I am baffled. I truelly do not want to take my car back to the deler for the 5 time because it will cost me a couple hundred bucks and who knows if it will be fixed again.
Thanks in advance for the info.
Al

Originally Posted by GTP Dad

There are a couple of other items you need to look at. First, coils, plug wires and plugs. You didn't say anything about changing any of these. Also clean the mass airflow sensor, cleaning the throttle body only will not clean the mass airflow sensor. I expect you are getting two codes one P0171 and a misfire code P301-P306 not knowing which ones it is hard to say where to look. Try changing the plugs and wires first and see if the misfire goes away.

[BNaylor]

The following information may be helpful for further assistance:

What model GP do you have?

How many miles on it?



Thrasher CAI, DHP v1.0 ECU, Granatelli CAI Tuneable MAF,
3.4 SC pulley, Hi-Flow CAT, u-bend delete, 180 TS,
TB spacer, MSD 8.5mm wires, AC Delco 41-932 spark plugs,
Goodyear Gatorback Serp. & SC Belt
ET: 14.3 @ 96 mph

[kustomkid54]

Originally Posted by koolbike

Thanks for the reply. The dealer said the plugs and wires looked OK. Can the plugs or wires cause a misfire only during the intial startup> As mentioned the misfire only occurs for the first few moments when the engine sits overnight. I will try and locate the info on the codes. The dealer seems alittle besides themsleves on this one. I did notice that when i put injector cleaner through it when the problem first happened 2 years ago it went away. The injectors then had to be replace due to leakage and debri in the gas from the injectors cleaner. I had all the injectors replaced and tested along with cleaning the throttle body. My car was fine for 6 months. The only longshot i have is when i clean my car at the local spray off car wash i open the gas tank door. Can water be getting into the gas???? I said a long shot but it started to misfire shortly after i opened the door and shot water to clean out the dirt in the gas opening tray. Is the gas cap lwak proof?? I am baffled. I truelly do not want to take my car back to the deler for the 5 time because it will cost me a couple hundred bucks and who knows if it will be fixed again.
Thanks in advance for the info.
Al

I'm sorry, everyone knows I LOVE dealers. But how can a group of people that should be drawing food stamps, say they looked at your wires (and plugs) and say they "LOOKED GOOD"? I mean they can't find half the stuff wrong with a car when they have it hooked up to every paice of eq. that the world has made.
To start out with, if GTPDAD tells you to paint your plugs green and it will run better. Buy the paint. If Bob tells you that if you put your finger in your ear and think happy thoughts and your car will be fixed, just do it. These guys put in about 8 hours a day on this site. The other part they read up on things to help everyone out here with their cars.
Next time, come out here, ask. Then you can pay the dealer to replace the things that they tell you you need. These guys are that good.

Boy, that felt good to vent.

[koolbike]

Hi,
I have a 2000 Grand Prix that i purchased new. I currently have 60000 miles on it and the injectors were all replaced 10000 miles ago. Can the plugs and wires cause a misfire only when the engine is cold???

Originally Posted by bnaylor3400

The following information may be helpful for further assistance:

What model GP do you have?

How many miles on it?



Thrasher CAI, DHP v1.0 ECU, Granatelli CAI Tuneable MAF,
3.4 SC pulley, Hi-Flow CAT, u-bend delete, 180 TS,
TB spacer, MSD 8.5mm wires, AC Delco 41-932 spark plugs,
Goodyear Gatorback Serp. & SC Belt
ET: 14.3 @ 96 mph

[BNaylor]

Originally Posted by koolbike

Hi,
I have a 2000 Grand Prix that i purchased new. I currently have 60000 miles on it and the injectors were all replaced 10000 miles ago. Can the plugs and wires cause a misfire only when the engine is cold???

You have to start someplace and I agree with GTP Dad on the plugs and wires. If nothing else its the cheapest place to start and part of the process of illimination. Do you have the original AC Delco platinum spark plugs and GM Packard 7mm plug wires? BTW - What engine do you have?

IMO - plugs and wires can cause the misfire whether the engine is cold or hot. As the engine warms up resistance values change especially in the plug wires, etc.

Do you have a digital multimeter and know how to use one? If you want to save money and before you start shotgun replacing parts I'll be happy to provide you with info on how to check resistance of the wires and an easy troubleshooting procedure.

With over 50K miles, I'd change out the spark plugs, regardless. The new AC Delco iridiums work well over the OEM AC Delco platinums.



Thrasher CAI, DHP v1.0 ECU, Granatelli CAI Tuneable MAF,
3.4 SC pulley, Hi-Flow CAT, u-bend delete, 180 TS,
TB spacer, MSD 8.5mm wires, AC Delco 41-932 spark plugs,
Goodyear Gatorback Serp. & SC Belt
ET: 14.3 @ 96 mph

[GTP Dad]

Wires deteriorate both internally and externally. If they are showing signs of wear externally you can see the wear and that is a good indication to change them. However, you cannot tell when the wires have gone bad internally just by looking at them. You have to test them with a multimeter to insure that they are still within specifications for resistance. And YES wires or plugs can cause a misfire when the engine is cold. A bad plug will not ignite the fuel properly and cause the misfire code.

Like I said before change the plugs and wires first, if that doesn't cure the probelm then move to the next step like a fuel filter, fuel pump relay, coils, ignition module and so on. If you had all 6 injectors replaced 10000 miles ago then the injectors are not the problem. I have a GTP with 143K miles and it has the original injectors and runs just fine.

Water can cause misfires but for $2.00 you can put a bottle of fuel line antifreeze in the tank and eliminate that as a source of the problem. Other misfire causes can be due to a lean condition caused by a dirty mass airflow sensor, that is why knowing the codes the dealer found is so important. I hope this helps clear up your confusion.