High load detonation...
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Joined: Jul 1999
Posts: 150
From: Norman, OK
High load detonation...
This problem started about two years ago, after installing 1 3/4" RK Sport headers. I tried and tried to figure it out back then, but didn't get anywhere, so I just drive the car and avoid the conditions that cause it.
Since then, I have installed new MAC 1 1/2" headers, plugs, wires, coil, and the opti. The car now has 231,000 miles. Now the problem:
Under high load conditions, I get a bad detonation. Bad enough that I can hear it (ting, ting, ting from the engine) and the PCM pulls out the max amount of timing. Going up hills at highway speeds in 6th gear, and heavy throttle starts below 2,000 RPM are where the problem is extremely obvious. Wet or hot weather both tend to make the problem worse. Lower octane fuel definately makes it worse, although it will still happen with 93. 87 octane makes it substantially worse. All of this confirms that it is true detonation.
What might be causing this? The last thing I can think of is carbon build up on the pistons, to the point that they retain heat and that the CR has increased. I REALLY don't want to pull the heads unless that is really the problem though. I did have an intake leak, I fixed that at probably 100,000 miles. Now at 230,000, it is back with a vengance, after looking at my tranny a few days ago. Oil all over the bellhousing. When I pulled the intake (long ago), there was oil residue in the intake ports. I'm wondering if that caused substantial buildup on the pistons, and if the same thing is happening today. If I can get away with pulling just the intake, I'd prefer to do that. But I don't want to pull the intake and not the heads if that is really what I need to do.
SO, any tips from the experts? What could be causing the detonation? It is a stock LT1 file, I haven't messed with the timing. Has anyone ever cleaned the cylinders to cure a high-load detonation problem? Could it be something else? Seafoam does nothing for me.
Additionally, I have a problem above 5,000 RPM. This I believe might be the opti. This problem has developed since the detonation problem however, and I'm not convinced they are related. Maybe 60% of the time, above 5,000 RPM, the car will just stutter & cough.
Since then, I have installed new MAC 1 1/2" headers, plugs, wires, coil, and the opti. The car now has 231,000 miles. Now the problem:
Under high load conditions, I get a bad detonation. Bad enough that I can hear it (ting, ting, ting from the engine) and the PCM pulls out the max amount of timing. Going up hills at highway speeds in 6th gear, and heavy throttle starts below 2,000 RPM are where the problem is extremely obvious. Wet or hot weather both tend to make the problem worse. Lower octane fuel definately makes it worse, although it will still happen with 93. 87 octane makes it substantially worse. All of this confirms that it is true detonation.
What might be causing this? The last thing I can think of is carbon build up on the pistons, to the point that they retain heat and that the CR has increased. I REALLY don't want to pull the heads unless that is really the problem though. I did have an intake leak, I fixed that at probably 100,000 miles. Now at 230,000, it is back with a vengance, after looking at my tranny a few days ago. Oil all over the bellhousing. When I pulled the intake (long ago), there was oil residue in the intake ports. I'm wondering if that caused substantial buildup on the pistons, and if the same thing is happening today. If I can get away with pulling just the intake, I'd prefer to do that. But I don't want to pull the intake and not the heads if that is really what I need to do.
SO, any tips from the experts? What could be causing the detonation? It is a stock LT1 file, I haven't messed with the timing. Has anyone ever cleaned the cylinders to cure a high-load detonation problem? Could it be something else? Seafoam does nothing for me.
Additionally, I have a problem above 5,000 RPM. This I believe might be the opti. This problem has developed since the detonation problem however, and I'm not convinced they are related. Maybe 60% of the time, above 5,000 RPM, the car will just stutter & cough.
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