LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Misfire help needed and data interpretation

Old 12-13-2018, 05:10 PM
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Join Date: Mar 2003
Location: Louisville, KY
Posts: 341
Misfire help needed and data interpretation

See sig for car info.

Problem: cruising down the interstate smooth as butter all of a sudden the engine starts missing. like a switch was thrown.

What I've done:
New NGK TR55GP plugs, all eight
New fuel injectors (Accel 24#, all eight)
New fuel regulator (check vacuum tube for gas and smell - none detected)
Found bad O2 sensor left bank - replaced
Replaced Optispark with one barely used one on hand

Checked for spark using inductive timing light, all show good light
Checked wires for proper routing after plug change, multiple times
Checked for spark leakage at night; dry and misting with water, no visible leakage

Using a laser thermometer read the follow readings:
1 395F 2 506F
3 360F 4 740F
5 355F 6 900F
7 645F 8 920F
Temperature was read on the header tube just after the mounting flange. Engine idling with coolant temperature at operating temp. 55 degrees outside

Compression (didn't get to right bank)
1 150
3 180
5 180
7 180

Mainly need to solve the miss but also curious about the varying exhaust temperatures. Have datalog (Scan9495 and audio recording of exhaust and engine)
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Old 12-14-2018, 11:26 AM
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Join Date: Aug 2005
Location: Las Vegas
Posts: 245
Re: Misfire help needed and data interpretation

Lower compression on #1 and low temps on 1, 2, 3 makes it difficult to say it's to rich on the right bank or #1 cylinder is not sealing. I would start by pulling and reading all the plugs then a leak down test on each cylinder.
Testing and diagnosing is much cheaper than buying parts you may not need. But it does take effort.
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