Slight Miss

[bru333]

My '87 Camaro has developed a slight miss. Most noticible at idle. This engine has 18000 miles on it (rebuilt long block, other info in sig). I've replaced cap, rotor, plugs and wires, cleaned the injectors and replaced the fuel filter. Next up is checking the valve adjustment (thinking maybe one or more nuts has backed off the rocker).

Take a look at the plugs and see what you thinks going on.

photos of plugs

[fastTa]

Hey Bruce, it's a little difficult to pinpoint a few indicators on all of your plugs because of the all the brown coating.

But all of your plugs show way too much timing on the ground strap and electrode insulator. Your #2 plug shows signs of relatively minor detonation and too low of an octane fuel. #3 shows a much more serious detonation problem.... again it looks like too low of an octane for how much timing this motor is seeing. The heat range on your threads on 1, 3, and 5 show a pretty good heat range, but they all show signs of way too much ignition timing. Ideal timing to avoid detonation will leave the color contrast on the ground astrap right around the apex of the curve. Your ground straps show the color contrast too far down towards the threads. This is an indicator of too much timing. 4 and 6 again show signs of way too much timing and likely octane+timing induced detonation.

All those deposits that you see on your plugs also will end up on your valve seats and can cause a number of problems including a miss.

[bru333]

way too much timing and likely octane+timing induced detonation.

Base timing is right where it should be, 10*. But when I reconnect the EST wire it jumps up, to 14* !

[fastTa]

Are you bypassing the EST by jumping terminal A and B first before setting the idle timing? It should be right around 10 with the EST bypassed. I don't think you can just unplug the EST from the distributor on the injected models.

Does the timing advance with increased engine speed?