Misfire Codes... help please

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01-25-2008, 10:53 AM

wasabigrinch

Thread Starter

Join Date: Jan 2008

Posts: 5

Misfire Codes... help please

I have an '03 GT, and I've been getting some misfire codes lately. I have a cold-air intake in the fender, a throttle body spacer, intake spacer, offroad x-pipes, short throw shifter, underdrive pulley kit, and some accel coil packs. I just changed all my spark plugs and coils recently, and I've double checked them to make sure that they are set in right. Previously, I had some misfire codes, andI changed the coil packs. When my car misfired before, I could feel it without any problem - it ran really rough. Lately, it has yet to misfire as far as I can tell, but it throws up random misfire codes. I talked to a shop the other day, and he said that it could be a number of things. My engine light is already on any way because I don't have any O2 eliminators on yet, so I scan the computer pretty frequently to make sure that there is nothing wrong. As far as I have heard, it could be my combination of intake/exhaust that is just causing it to run a bit lean and making a very minor misfire (I haven't gotten a lean or rich code yet). It could also be my coils sending some sort of interference - Ive heard of a lot of problems coming from aftermarket coils. Anyway, I just don't want to damage anything, and I would really like to get my engine light off for good (after I take care of the O2 sensor problem as well). If you have any input or advice as to why my car might be doing random minor misfires, please give me a heads up. It has about 86K miles on it. Thanks a lot!

01-25-2008, 03:37 PM

cliffyk

TECH SAVANT

Join Date: Dec 2006

Location: Saint Augustine, FL

Posts: 10,938

RE: Misfire Codes... help please

Quote:

ORIGINAL: wasabigrinch

I have an '03 GT, and I've been getting some misfire codes lately. I have a cold-air intake in the fender, a throttle body spacer, intake spacer, offroad x-pipes, short throw shifter, underdrive pulley kit, and some accel coil packs. I just changed all my spark plugs and coils recently, and I've double checked them to make sure that they are set in right. Previously, I had some misfire codes, andI changed the coil packs. When my car misfired before, I could feel it without any problem - it ran really rough. Lately, it has yet to misfire as far as I can tell, but it throws up random misfire codes. I talked to a shop the other day, and he said that it could be a number of things. My engine light is already on any way because I don't have any O2 eliminators on yet, so I scan the computer pretty frequently to make sure that there is nothing wrong. As far as I have heard, it could be my combination of intake/exhaust that is just causing it to run a bit lean and making a very minor misfire (I haven't gotten a lean or rich code yet). It could also be my coils sending some sort of interference - Ive heard of a lot of problems coming from aftermarket coils. Anyway, I just don't want to damage anything, and I would really like to get my engine light off for good (after I take care of the O2 sensor problem as well). If you have any input or advice as to why my car might be doing random minor misfires, please give me a heads up. It has about 86K miles on it. Thanks a lot!

[/align][/align]A lot more people would read your posting, if it were more easily readable--Ijust nowopened it and immediately closed it, but then I thought I'd see if I could help (I don't mean to offend, however I just finished reviewing some student papers, many of which suffered from the same problem)...[/align][/align]You need to use paragraphs, no one is going to wade through one humongous block of text--try it like this:[/align][/align]------------------------[/align]I have an '03 GT, and I've been getting some misfire codes lately. [/align][/align]I have a cold-air intake in the fender, a throttle body spacer, intake spacer, offroad x-pipes, short throw shifter, underdrive pulley kit, and some accel coil packs. I just changed all my spark plugs and coils recently, and I've double checked them to make sure that they are set in right. Previously, I had some misfire codes, andI changed the coil packs. [/align][/align]When my car misfired before, I could feel it without any problem - it ran really rough. Lately, it has yet to misfire as far as I can tell, but it throws up random misfire codes. I talked to a shop the other day, and he said that it could be a number of things. [/align][/align]My engine light is already on any way because I don't have any O2 eliminators on yet, so I scan the computer pretty frequently to make sure that there is nothing wrong. As far as I have heard, it could be my combination of intake/exhaust that is just causing it to run a bit lean and making a very minor misfire (I haven't gotten a lean or rich code yet). [/align][/align]It could also be my coils sending some sort of interference - Ive heard of a lot of problems coming from aftermarket coils. [/align][/align]Anyway, I just don't want to damage anything, and I would really like to get my engine light off for good (after I take care of the O2 sensor problem as well). If you have any input or advice as to why my car might be doing random minor misfires, please give me a heads up. [/align][/align]It has about 86K miles on it. Thanks a lot![/align][/align]------------------------
OK, so what codes are you getting? [/align][/align]I have Accel COPs and have not had any problems in 22k miles or so since I got them.[/align][/align]What plugs did you use, what gap?[/align][/align]The lack of MIL eliminators (make your own for $5) could make the PCM think you are misfiring because the rear O2 sensors are providing the same signal as the fronts. It won't affect the way the engine performance, however it can mess with the PCM's mind...[/align]

01-26-2008, 11:06 AM

ottos

2nd Gear Member

Join Date: Jan 2008

Location:

Posts: 213

RE: Misfire Codes... help please

Sounds like you ruled out a hardware issue. If you think all your hardware works fine, try driving it around some more, so the computer can learn the correct fuel trim needed. the PCM adjusts fueling a little rich or lean depending on a few factors, like misifiring.

The back O2 sensors are just to check the catalyst condition only.

01-26-2008, 11:16 AM

wasabigrinch

Thread Starter

Join Date: Jan 2008

Posts: 5

RE: Misfire Codes... help please

I've just gota set of pre-adjusted autolite plugs in there. I've never had any problem with them before. The misfires I have gotten in the last few weeks are on Cylinders 4, 7, and 1. Sometimes I'll just get one misfire. Other times I'll have 2 - but the car doesn't bog or feel like it's missing.

Yesterday, I made a set of MIL eliminators with radioshack parts, and they worked for a little bit, but the light still came back on. I'm going to double-check my work. No misfire yet though! I also have yet to get a code telling me I'm running too lean or too rich.

This sympathetic misfire thing has been going on for a while. I have driven it around quitea bit, andI have given it plenty of time to adjust as far as I can understand.

Last but not least, I have occasionaly gotten a code telling me that one of my 1st O2 sensors was slow to respond. From what I have been told, the few exhaust and intake mods that I have may have affected that.

Sorry about the huge block of info! I was in a hurry whenI tossed it out there! Thanks for theedit tho!