Fellas,

I offered to replace a door latch assembly for a fellow 82 owner. I noticed it was missing on one cylinder when he arrived and I offered to fix that as well, thinking spark plugs, distributor cap and rotor, etc. His car has header pipes on it so it was easy to isolate the miss to one side of the engine. I cleaned the plugs and reinstalled them. N.G. I replaced the cap and rotor. Also N.G. Instead of missing it was firing late out of cylinder 7 at or above 2000 rpm. I replaced all the spark plugs but then--- whenever it is cranking the injectors spray solidly as if the computer thinks we're driving 80 mph. I changed the plugs back and it ran normally. A couple days later and this bug is back even with the original plugs.

I plugged in my laptop and read the diagnostics. The computer recognizes all the inputs and they look good. My only suspicion is that the signal from the distributor (engine speed) is occasionally wrong.

Any informed ideas would be greatly appreciated.

Thanks,

Steve Wolfe

 

You pinpointed a problem with #7. Did you check the plug wire with an ohm meter compared to any other cylinder with the same length wire?

 

You could also have a "bad" distributor cap. Depending on the manufacturer/source, there is some real JUNK out there being sold in the auto parts stores. I've seen caps with the inside contacts machined off center so some would almost hit the rotor and others would not be close enough to fire!

 

So, from what I'm reading, it appears that you think there are two issues, spark and fuel. I'm just wondering which app you are using to read the ALDL with? Are you using WINALDL from Joby, ALDL to serial data cable? If so, you can read CTS sensor, it's called CT in WINALDL. You should be setting a CEL for a cylinder not firing. If only on one cylinder it should be easy to figure out, it's not the ECM or the dizzy, it's from the dizzy to plug. Not a whole in that path really. As far as the fuel goes, it does or should spray a lot of fuel at crank or at appear that way. How is the idle other than the miss? If the fuel is excessive, the first suspect especially at cold start would be the CTS sensor since that is the main input to the ECM at crank, it needs to know the temp so it knows what table to use if cold.

If you can read the CTS sensor see if it is within range for a cold and warm start. You may want to install the newer type (two wire) with a weather package type connector if it's bad. Worse case on this issue would be...If the sensor reads bad, but pulling the sensor and in ambient temp, see if it reads correctly. You have an issue with the coolant and there is electrolysis going on and you will need to find where the radiator is grounding and correct that and drain fluid completely and refill. You can actually read the coolant with a meter, anything under .2 is ok. Another worse case is that the ECM is really bad for a driver and doesn't set a CEL, it does happen. Hope this helps.