97 SL2 Cylinder 4 misfire

[yoyodyne]

Our SL2 was running fine, son drove it to the store. When he came out to drive home, the car ran rough,he barely made it home. Had SES light on,pulled the code, was a code p0304, cyl 4 misfire. Did the old trick of pulling the plug wires off one at a time, sure enough, pulling 4 off had no effect on the way the car ran. Put in new plugs and plug wires, cleaned the coil pack towers, and swapped the coil packs around. No change. Borrowed a spark tester, getting good spark to no 4. Swapped the nos 3 and 4 injectors, still no change. What's left? The wiring to the injector looked OK as far as I could trace it. Where does the injector fire signal come from, straight from the PCM? I assume one of the injector wires is a common to all 4, the other going to the PCM individually. Anyone know what pin of what connector the injector wiring goes to,so I can ring them out?

[ssicarman]

With good spark to the plugs through the plug wires then the secondary ignition is ok. Check the wires at the injectors for power when cranking. One side of the injector connector should have power when you crank. The other side is the ground wire. It should pulse when the engine is cranking. Easiest way to check for power and ground is to get a NOID light to plug into the inector connector. With it in crank the engine and if it flashes things are good there.

If all good there then check the compresion.

[BarnOwl]

Use a mechanics stethoscope or put a long screwdriver on the number 4 injector and put your ear up to it. You should be able to hear it clicking. If you can, you know the injector's getting a signal. You really need to do a compression test, I'm beginning to suspect a burnt valve.

[Greg1]

Originally Posted by BarnOwl

Use a mechanics stethoscope or put a long screwdriver on the number 4 injector and put your ear up to it. You should be able to hear it clicking. If you can, you know the injector's getting a signal. You really need to do a compression test, I'm beginning to suspect a burnt valve.

I was going to mention a possible burnt valve too. It does seem odd to have that happen in just a short drive though...