: PO0300 Random Misfire Detected while at the track

04-20-2008, 04:15 PM
Hey, took the car to the track today. During my 4th run I felt the car starting to break up up top. It went slower and slower, until my 7th run was a 13.1 @105. The first two runs were 12.9 @ 115 (2.3 60ft) then 12.6 @ 114 (2.0 60ft). The third run was a 13.0 @ 100 because I hit 6th instead of 4th (yea, I sucked, but it was my first time with the car at the track lol). The next run I hit all the gears good but there was noticeable hesitation in 4th gear. After that the car just went slower and slower.

As soon as I left the track I realized under even moderate throttle the car was hesitating/bogging/misfiring real bad. Pulled the code and it was the PO0300. Me and my friends guess so far is a melted plug or something along those lines. I'm running the stuck plugs and I'll probably be pulling them to take a look tomorrow and replace with TR6, most likely. Any other ideas?

Here's a link to the timeslips: http://www.eastcoastgtos.com/forum/viewtopic.php?f=7&t=24&sid=83576988b1b90e99eed07cce9b27e959

04-20-2008, 04:54 PM
I had the same come today show up for the first time. I also have a Magnacharger, which has nothing to do with it. I ran this car with Brisks LGR plugs for three years now without a problem. Changed to TR6 and inmediaely started detecting misfires on cylinder 5 and 6, especially 6. I changed coils, wires and plugs from position and still had the problem ever so slight I thought it was normal. It was not. Today I got the P0300 code for the first time. Hooked my Autotap and 5 and 6 were misfiring again.

I have no idea what it is. For a while I been suspecting it is the wires which may tend to become loose, but I check them and they are OK. I have a set of Brisk Silver racing plugs sitting there which I tested with different results. They gave me some misfires here and there but not as the TR6. I only used them for a ride and put the TR6's back. At the track the car was very consistent the other night but it bogged down at my first competition pass and got eliminated. I thought then that it was the car running cold, which it was. Sounds confusing? Sure does. There is a ton of GTO's running TR6 without problems.

I have to look deeper into this problem for as of now I have no clues other than the car may not like regular plugs with the raised electrode. I am going to order a new set of Brisk LGR 15 to see if the problem goes away after I test again with the Silver racing ones. Question is why 5 and 6 consistently? Problem with the valves? God forbid.. a piston? I don't know. There is no sign of detonation. Tonight I cleaned the MAF just in case.

Different from you is that I see the misfires at low RPM's. If I nail the gas pedal the misfires go away. In your case I would think it is time for new plugs and to check the wires to see if they are plugged firm.

BTW, your Et's should be lower.

04-20-2008, 05:31 PM
I was pretty content with breaking 13.0 on my first pass at the strip with the car. 2nd pass was a good improvement at 12.6. I was expecting to continue improving but whatever the problem is I'm having, it had different plans for me. My original goal was to get as close to 12.0 as possible. Maybe next weekend at Englishtown if I can get this issue resolved. I still need to check their schedule though and make sure it'll be available

04-20-2008, 05:46 PM
I am going to swap the injectors from position to see if there is a bad injector. Could be so many things. It could be anything from a loose rocker, a bad head gasket, a lifter... I just hope it is something simple.

04-22-2008, 06:26 PM
I too am having a similiar problem, I might post my own thread about it as well... but here it goes.

On Sunday I changed my plugs as I do at the beginning of every season. I run NGK BR7EF, which is what would be a "TR7" without the protruded electrode. I run them at .025". I've done this for 3 years now with no issues whatsoever. So I take the car for a ride, all is normal. No hiccups, no power loss, no noticeable problems. About 40 miles later I get the misfire code. I figured I didn't seat a wire properly or something stupid. I checked over everything and opened up HPTuners. I was getting a much higher misfire count on #8 than all the others. I swapped wires with 6 and 8 and the problem stayed with 8. I then swapped wires, and coils, and it's still on #8.

Like I said there's no noticeable problem other than the Check Engine Light and misfire count in HPTuners. I might try swapping injectors and see if it follows. I really doubt it's an internal engine problem, as everything was fine before the plug change. I'm tempted to keep driving it and see if it goes away for some reason but it makes me nervous. I'm only showing the misfire at idle it seems as well. Like I said, running 15psi and it's smooth as silk under boost.

Any thoughts? And also just to triple check, #8 in HPTuners is the same as what GM calls #8 correct? Passanger side furthest back?


04-22-2008, 08:14 PM
Yes, #8 is the rearmost cylinder on the passenger's side. #1 is the frontmost cylinder on the driver's side, #2 is the frontmost on the passenger side and keeps on going from side to side till #8.

I am also going to repostion the injectors to see if the problem follws. First, I am going to run an injector cleaning treatment to see if the misfires goe away.

04-23-2008, 11:45 AM
I dont' see what else it could be but an injector or the ignition module itself

04-23-2008, 12:01 PM
The car just came back from the shop where the injectors were being flushed. I will hook it up to AutoTap later on after work to see if it made any difference. One thing that may be different between your car and mine is that I have a cam.

04-23-2008, 01:20 PM
everything was fine before the plug change

Moving/inspecting the plug would be lots simpler (and the more likely cause) than moving the injector.

regards, billb....

04-23-2008, 05:45 PM
Flushing the injectors did not help. Going to have to go through the trouble of moving them injectors around, Geez.

04-23-2008, 05:58 PM
I swapped plugs, wires and coils with no change.