For some time now, I have been troubleshooting my old 3rd generation F-body trying to tie up loose ends and problems that have existed for a long time. Right now, I am stuck and cannot seem to find whats wrong with the engine. Cylinders 1 and 7 are quite a bit colder than all the others, cylinder 7 is the worst and is running 400 degrees down.
At this point, I have pretty much tested everything. I have swapped injectors, swapped the connectors to the injectors, swapped spark plugs, tried different wires and replaced the distributor. I have done a compression and leak down test, and have found nothing wrong. My Megasquirt ECU has diagnostic features that allows me to check the signal from the VR sensor, and it shows that the ECU is both receiving and sending clean signals to and from the ignition.
I am now thinking that my issue might be with the fitment of the intake manifold, and that there could be a leak between the bottom of the intake ports into the valley of the block. I have noticed some oil on the spark plugs of the offending cylinders, so I think that this oil is coming from this valley leak. It was suggested to me that I might have bad valve seals, but I checked them when I put on new valve springs and they looked like new and were tight.
I think I have trouble shot everything else within reason, so I’m hoping this is the issue. Even though engines are pretty simple creatures, we sometimes forget how many things can go wrong until something actually does. Troubleshooting this thing has been a pain, but it does make me appreciate a perfectly running engine.