I have an 85 GT (5.0, 5-speed, carb) that is misfiring. The suspect cylinders are 1, 2, and 6 as those exhaust pipes are warm while the others are hot, and those plugs will foul if I run it long enough.
What can cause 3 cylinders to be sub-par?
A little background. The car has been in storage for around 30 years, having been my daily driver before that. I am the original owner and the car is in very nice, original condition, with 79,000 miles. The car ran fine when I first started to resurrect it in 2019 (new vacuum lines, cooling hoses, etc.) and was okay after all that. This missing seems to be recent, though I am unable to pinpoint the exact day since I only 3 two weeks ago got a license plate for it and was not started all winter.
What is new: cap, rotor, plug wires, spark plugs (ACDelco CR43TS), and ignition coil. I replaced all the underhood vacuum lines (those that I could find, anyway), and as far as I know I did that right.
The carburetor gives a good clean squirt from the accelerator pump.
I swapped the # 5 & 6 plugs to see if the problem moved to the #5 cylinder. The #6 cylinder remains warm, so the plugs don’t seem to be the problem. I can smell unburnt fuel, presumably from the three warm cylinders.
A timing light shows activity on all 8 wires, so spark would seem to be okay. The distributor rotor is in about the right place in the rotation when cylinder no. 1 is TDC.
Firing order, as per the manual, is 1-5-4-2-6-3-7-8. This differs from the underhood decal which states the order should be 1-3-7-2-6-5-4-8. I tried that and the car wouldn’t even start. Can someone tell me what they use on their 5.0?
Compression is good on all 8 cylinders, ranging from 145 to 160 psig.
I'm stumped. Any ideas?
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