I have a miss In #8 hole. I have replaced icm esc distributor cap and rotor. New plugs and wires. New injector. 135 pounds of compression. New ECM. What am I missing. Oh and no codes. What am I missing? Any ideas?

 

To state "135 pounds of compression" does not help at all with the diagnosis , and here's why ;

If all the other cylinders had compression readings of + or - 10 % of that 135 figure well then great , that would indicate a healthy cylinder . But what if all the other cylinders were 170 to 190 in THEIR readings , wouldn't that indicate a badly failed cylinder ? The readings have to be all taken together and raw pressure numbers aren't as indicative as the difference between cylinder's pressures are .

In short , what do the other cylinders read ?

Also , how did you determine that it's #8 causing the trouble ?

 

The highest compression is 140 and lowest 125. That was with me checking it myself. As in screw in tester, get out from under car, crank engine over several times then get back under car to see result. Not the best way,true but what I had to work with at the time. Possibility that some readings could have dropped a little before I got back under car to look at gauge.

The way I know it's number 8 is by pulling number 8's wire off distributer.

 

Hi trkdrvr ,

Ok , so if that cylinder's compression is a close match for the others , and you have replaced all of the ignition components (with your mention of having done plugs , wires , cap , rotor , and other etc in post one) then the next thing I'd look to would be fuel . Now I know you said you replaced that cylinder's injector and even the ECM itself , but have you actually verified that the ECM's signal is getting to the injector ? Unless you use a "Noid light" to visually verify the pulsed 12 Volt signal is getting to the injector you can't be certain that your new injector is actually being energized to spray . The strong possibility exists that an "open" wire or connector terminal could be keeping that injector from seeing it's signal . As an aside here , my 89 firebird was having all kinds of crazy come and go electrical problems till I discovered the wiring harness being cooked by the passenger's side exhaust manifold . Our cars seem to have a few places where the wiring harness can get into trouble , and the passenger's side engine harness (the one that loops around near the starter and such) would be something I'd give a good look at in your case if the noid light shows no activity .

Now , if your noid light test does indicate a spray command is being sent to the injector then I'd be strongly suspicious of a possible vacuum leak at that cylinder's intake manifold port . A vacuum leak on the intake side would not hinder the compression test (indeed the compression test is properly carried out with the throttle plates propped fully OPEN) and very likely could lean out that one cylinder enough to miss .

PS , is this an all the time "miss" , as in the cylinder never fires , or is this a miss whereupon the cylinder only occasionally misses and sometimes fires properly ?

 

How do you know number 8 is missing? Reading plugs?

 

When engine is idling, I can pull the #8 wire off distributor and cannot detect any Change. If I pull any other plug wire off the distributor, I can notice a difference.