Misfires and knock/tap sound. Need help!
Misfires and knock/tap sound. Need help! The car is a 98 Z28 with about 35k miles on it with the following mods:
MAC headers and ORP.
FTRA
MAFT
MTI pulley
MTI lid
Vig 3200
Transgo shiftkit
De-screened and ported MAF
The mild knock/tapping sound coming from the upper part of the engine on the passengers side started about 3 months ago and has become louder. At times it is louder and other times it is not very loud. When you first start the car after it has cooled down over night there is no knocking or tapping until the motor has been running for about 2 min and then it will gradually get louder. I have pulled the valve cover and pulled the push rods, inspected the rockers and the springs and it all looks fine. There are no exhaust leaks. What is strange is that the noise is louder after I switched to Mobile 1 this last oil change. There has been no loss of power. The car just ran an 11.96. I feel like I have a lifter problem. Is there a way to confirm this without pulling the heads? Opinions?
Misfire totals are from 4500 AutpTap lines from log files that consisted of 70% idling 30% driving.
CLY Misfires
1 1280
2 188
3 260
4 1786
5 286
6 1602
7 192
8 747
I have pulled all the plugs and they all look equally good. There does not seem to be any loss of power. I have swapped the coils and plug wires between cly 1 and 3 and between cly 2 and 4 with no relevant change in the number of misfires. The plug wires Ohm out at 300 - 400 ohms. The car uses no oil or water and there is no mixture of the two. My real concern is the knocking/tapping on the same side as cylinders 4, 6, and 8, which have the most misfires. Any suggestions as to what the problem might be? Any trouble shooting advice?
Thanks
John
MAC headers and ORP.
FTRA
MAFT
MTI pulley
MTI lid
Vig 3200
Transgo shiftkit
De-screened and ported MAF
The mild knock/tapping sound coming from the upper part of the engine on the passengers side started about 3 months ago and has become louder. At times it is louder and other times it is not very loud. When you first start the car after it has cooled down over night there is no knocking or tapping until the motor has been running for about 2 min and then it will gradually get louder. I have pulled the valve cover and pulled the push rods, inspected the rockers and the springs and it all looks fine. There are no exhaust leaks. What is strange is that the noise is louder after I switched to Mobile 1 this last oil change. There has been no loss of power. The car just ran an 11.96. I feel like I have a lifter problem. Is there a way to confirm this without pulling the heads? Opinions?
Misfire totals are from 4500 AutpTap lines from log files that consisted of 70% idling 30% driving.
CLY Misfires
1 1280
2 188
3 260
4 1786
5 286
6 1602
7 192
8 747
I have pulled all the plugs and they all look equally good. There does not seem to be any loss of power. I have swapped the coils and plug wires between cly 1 and 3 and between cly 2 and 4 with no relevant change in the number of misfires. The plug wires Ohm out at 300 - 400 ohms. The car uses no oil or water and there is no mixture of the two. My real concern is the knocking/tapping on the same side as cylinders 4, 6, and 8, which have the most misfires. Any suggestions as to what the problem might be? Any trouble shooting advice?
Thanks
John
Teching In
Joined: Feb 2002
Posts: 37
Likes: 0
From: Mesquite, TX
Re: Misfires and knock/tap sound. Need help! Common problem with LS1s is the valve springs. They don't necessarily break, just collapse. I had this same problem. Upgrade to the Comp 915s might fix your problem. Just a suggestion. I had this problem and that cleared it up. I line up my valve springs out of the head and the difference was up to 1/2"!
