Getting multiple cylinder mis fire code

[JayW1]

I have a 2000 GTS, essentially stock motor with 18000 miles on it. My check engine light came on and I took it to the dealer as I have an extended warranty. Code P0300 (multiple cylinder mis fire) came up and the tech said he found corroded 2,6, and 7 plugs and wire terminals. Replaced plugs and wires but also recommended a fuel injector cleaning for $200. None of this is covered under the warranty so I decided to see how the plugs and wires would do and declined the injector cleaning. My second trip with viper and the same code came up (had it checked at Autozone). I bought some fuel injector cleaner you put in the gas tank but don't how good it will work. The funny thing is the car seems to be running fine. Idle is perfect and I don't notice any loss of power.
My questions are should I go ahead and let them clean the injectors?

Can I damage the engine by driving it hard with a suspected mis fire?

Are there any other things I could easily check my self as I could have replaced the wires and plugs and saved $285 in labor costs (that were not the problem anyway)?

The good news is that I don't think there are too many things left that wouldn't be covered under the warranty to address the problem. If it is a coil, vacuum, or fuel issue other than injection cleaning I would think it would be covered.

Thanks for any advice.

 

[99 R/T 10]

If it had been over a year, you should have done the plugs/wires yourself first. Second, I don't know how much the dealer will charge for the injector cleaning service, but 1tony1 does an outstanding service and provides a graph of the service(before/after I think). PM him for the details though.

Third thing, it could be one of the two coil packs going bad. Another resource to check is Chuck Tator, 914-763-3136.

 

[99 R/T 10]

PM Tony here: 1TONY1

 

[ViperJohn]

When the check engine light is illuminated the car will not go into closed loop operation. Did you have the check engine light cleared? Regardless, I would go ahead and pull the PCM plugs off and reset the computer. The check engine light condition will be cleared. If the misfire still exists, the check engine light will come back on in about 75 miles or so.

The misfire detector only operates when you let off the gas, is the car backfiring or popping at all on decel?

 

[Jack B]

When the check engine light is illuminated the car will not go into closed loop operation. Did you have the check engine light cleared? Regardless, I would go ahead and pull the PCM plugs off and reset the computer. The check engine light condition will be cleared. If the misfire still exists, the check engine light will come back on in about 75 miles or so.

The misfire detector only operates when you let off the gas, is the car backfiring or popping at all on decel?

I think you have to rethink that one, doesn't the PCM only block closed loop for certain codes. That usually occurs when it sees a perceived lean condition, an engine misfire could be construed as such.

 

[prevnine11ownr]

I had the same problem on my 2000. Turned out to be the coil packs !!

 

[ViperJohn]

I think you have to rethink that one, doesn't the PCM only block closed loop for certain codes. That usually occurs when it sees a perceived lean condition, an engine misfire could be construed as such.

Well, when I typed my response late last night, I was worried I may mistake closed loop and open loop back wards. However, I can speak from experience that after my car would throw P0300, it ran like poop. The PCM is adjusting fuel trim and timing so drastically there car would buck a lot. I spoke to two different tuners and both surmised the car was not running in closed loop, hence the issues. Once i would clear the code, there was a night/day difference until the code returned.

The issue was rectified by West Coast Viper re flashing my PCM. But I thought I remembered reading in the service manual that misfire detection was one of the factors to not allow closed loop operation.

 

[JayW1]

If it had been over a year, you should have done the plugs/wires yourself first. Second, I don't know how much the dealer will charge for the injector cleaning service, but 1tony1 does an outstanding service and provides a graph of the service(before/after I think). PM him for the details though.

Third thing, it could be one of the two coil packs going bad. Another resource to check is Chuck Tator, 914-763-3136.

Thanks for the resources. The dealer wants $200 to clean the injectors.

 

[JayW1]

I had the same problem on my 2000. Turned out to be the coil packs !!

Thanks, I am thinking the same thing.

 

[JayW1]

Well, when I typed my response late last night, I was worried I may mistake closed loop and open loop back wards. However, I can speak from experience that after my car would throw P0300, it ran like poop. The PCM is adjusting fuel trim and timing so drastically there car would buck a lot. I spoke to two different tuners and both surmised the car was not running in closed loop, hence the issues. Once i would clear the code, there was a night/day difference until the code returned.

The issue was rectified by West Coast Viper re flashing my PCM. But I thought I remembered reading in the service manual that misfire detection was one of the factors to not allow closed loop operation.

I failed to mention that the dealer said he cleared the code and flashed the PCM after replacing the plugs and wires. Again, the car has never run badly but it does pop on decel (not a loud backfire) and has been doing that a long time. I actually thought that was normal. I may need to just take it back to the dealer but I wanted to try and avoid any costs that I could easily do myself. Thanks again for the help.

 

[JayW1]

Does anyone know if the number 2, 6, and 7 cylinders are all on the same coil pack?

 

[99 R/T 10]

I failed to mention that the dealer said he cleared the code and flashed the PCM after replacing the plugs and wires. Again, the car has never run badly but it does pop on decel (not a loud backfire) and has been doing that a long time. I actually thought that was normal. I may need to just take it back to the dealer but I wanted to try and avoid any costs that I could easily do myself. Thanks again for the help.

A mild "pop" is normal. Do you still have the cats installed? If not, the "popping" is more pronounced. I think Tony charges $10 per injector to clean, it can't hurt to do, that's for sure.

 

[bluesrt]

usually a multiple misfire code is due to injectors,maybe sludgy from sitting,injector cleaning of 200 dollars will do it,but just drive it and dump a can of seafoam in the tank and it will work the same..seems with only 18k on the clock,i wouldnt get to technic to quick.

 

[Steve-Indy]

"Does anyone know if the number 2, 6, and 7 cylinders are all on the same coil pack?"

Yes, same "pack" made up of three separate coils per 2000 service Manual

 

[JayW1]

"Does anyone know if the number 2, 6, and 7 cylinders are all on the same coil pack?"

Yes, same "pack" made up of three separate coils per 2000 service Manual

Thanks, since those were the plugs and wires that had issues, this seems like a probable cause to me.

 

[JayW1]

Sorry to dig up an old thread but I just wanted to follow up for anyone that may have the same issue as I had.

I got great help from Chuck Tator as usual and he provided me with some new coil packs. After I installed them and cleared the code the code has never come back (over 5 trips)

I appreciate all the help on this forum (incuding AB for the wires)

Thanks again.

 

[RedEnuf93]

I had similar issue, but no codes (OBD1). After talking to Chuck, he sent me 6-pack coil and it took care of it.

 

[Steve-Indy]

JayW1, thanks for the followup, as it helps all of us. Glad you are good to go!!