Bad day for my 98 GTP P0300

[eippermx]

I drove my GTP to work. Just got it through Cali smog, she's running great. Until today when I made a right turn, started accelerating and POW! Sounded like the crack of a backfire. The car is mis-firing and has no power. I coasted the car about half mile with a couple of bare accelerations to get it to work. I start smelling rotten eggs. Not a good thing from my brand new cat. I looked underneath the car and see the cat is cherry red. I turned the engine off immediately thinking the car was being run super lean by the PCM. After a little investigating I found the embarrassing problem. The number 5 MSD plug wire had been cut in half by the radiator fan. I coded the car, it read one code, P0300, random mis-fire detected. I field fixed the plug wire with a butt splice and vulcanizing tape. No joy when I fired up the car it was still missing. I went to town, bought a wire set and a coil. I thought maybe the coil had gone south when it was unable to ground the voltage that would have normally gone through the plug & jumped to ground. I was able to gain a little power, but I have a very pronounced mis-fire, and even when I clear the codes, I still get the P0300 code.
I'm missing something that's under my nose.

I'm thinking could the cut wire have taken out all 3 coils?
Cat?(Cat-No cat efficiency codes)??
O2 sensor (no codes to indicate they are bad)??

I've seen quite a few threads concerning P0300 of which quite a few folks do not post with the results of their findings/successes.

One other thing, hardly no tools where the car is located at. I'll bring out my compression & fuel gauges next week to properly troubleshoot it. I'm hoping there might be an answer to my dilemma from what I've expressed so that I can take the right stuff with me when I go to my work location next week.

Any advice would be sorely appreciated.

[GTP Dad]

Try changing the plugs. It is possible that the plugs fouled or are burned beyond service. Second are you certain they gave you the correct plug wires. Third, I doubt you took out all three coils with the cut wire.

I wish you luck in trying to fix it. Let us know what you found.

[tblake]

What you can do to test and see if the coils are firing is to just unplug the plug wires at the coil side and crank the motor for a couple seconds. You should see a good blue spark between each of the coil terminals.

[eippermx]

Thanks for the info!

GTPDad: I went to the nearest town (a podunk kinda place..Napa, Kragens, and Autozone are the only parts places in town) and bought a set of wires from Autozone and put them on. I went from 8.5 mm wires to 7 mm. Thanks for the advice...I'll definitely take a spare set of plugs with me on Tuesday.

TBlake: Thanks for the tip! Plus, I'll take a DVM and check the resistance at the terminals.

I'll post Tuesday night with the latest on my saga with my ride.

[eippermx]

At lunch time today I swapped out the plugs with a new set. I started up the car and it was still experiencing a miss. The 3 MSD coils measured - Top: 6.6K ohms, middle 6.5K ohms, Bottom: 6.6K ohms. I remembered Tblakes tip. I removed each of the cables one at a time, fired up the engine momentarily and saw the spark coming off the studs of the coil. When I did this, the engine idled even more badly than before. When I removed the plug wire from the middle coil, I started the car, no spark at the coil, idle didn't change. I did same thing with the other plug wire, and got the same result.

I replaced the coil with a new one. I got the same result. Then to insure that the new part was good I swapped it with the top coil. The results are the same top new coil sparked and the middle coil did not. The bottom coil sparked so its good.

Looks like I have a bad ignition module.
Anybody agree or disagreed???

[tblake]

Agreed! Maybe the coil grounged itself out through the ignition module and fried it.

[GTP Dad]

That would be the next logical step in the elimination progression. If that doesn't fix it you will probably have to check the injectors to insure they are working properly. Good Luck!!!

[eippermx]

Problem with the miss SOLVED! Thanks once again, TBlake GTPDad - I replaced the ignition module and my GTP fired right up on all 6.

TBlake, I agree with you when the #3 wire was cut it, the voltage momentarily grounded to the block and "burned" out the portion of the ignition module that energized the cylinders #2 & 3 coil.

I've a funny feeling I'm not out of the woods yet. :

The P0300 codes were cleared in order to turn off the SES light. The reason I did that was to see if a CAT efficiency P0420 code is detected which would mean I fried either my CAT or possibly my rear O2 sensor. More to follow!

[tblake]

could the P0420 be the result of excessive unburnt fuel being dumped into the cat converter due to the 2 cylinder ignition miss?

[eippermx]

When I wrote the last post, I was thinking that the P0420 code would make its "debut" after I installed the ignition module and ran the car. So far so good it hasn't reared its ugly head.
When I fired up the GTP at work today to drive it 125 miles back to home, it spewed out black when I first started the car. After a couple easy going gooses on the throttle, the exhaust cleared up. I'm thinking maybe that was carbon/particulate matter that had accumulated in the CAT and the Magnaflows. Once I got past the airdales and got on to the main highway, my GP shot up to 105 mph before my cojones started...Any way, self de-balling myself - I ran the car 70 mph all the way back to the house. No SES light...So far. As of this writing, I didn't observe any blue or black smoke coming out the car after I fired up after it had sat for a couple of hours cooling off at the house.