93limited

Hi folks,

93 GC 4.0L. 300K+ miles. Was running great, no symptoms, just passed emissions, then a week laterwouldn't start. Cranks over fine and tries to start (gets a few combustions-- like you get when flooded). OK compression, 38 psi at rail, confirmed hot spark, new and tested CPS, tested both ASD and fuel pump relay, tested cam position sensor (so know rotor is moving), coil, plugs, inspected rotor and cap, no wobble on distributor shaft (aftermarket distributor installed 50K miles ago). TPS and NSS switch test OK and security system seems OK. PCM is alive and seems fine. Only error codes are usual 12 and 55 (but I disconnected the battery as part of the testing early on). I've let it sit overnight as thought was flooded, but no help and the plugs look dry. If I pump the pedal while trying to start I can smell gas so it's getting gas. The only suspicious thing is when checking spark, it seems that I get a spark only every second or so, which seems way too slow. The starter is kicking it over at normal rpm. I even sprayed some starter fluid in the throttle body with no effect. I'm out of ideas other than just start replacing things. Any thoughts? Thanks!

dave1123

The only thing that comes to mind is the timing chain. At 300K, it's probably stretched or may have jumped a tooth or more. Bring it to TDC #1 compression and see if the rotor is pointing directly at the #1 spark plug tower in the cap.

This may not be the problem at all, but it's something to check before you go nuts.

93limited

Yes, I'm afraid you are right. At TDC the rotor is off #1 plug about a half of a plug post. Strange thing thought when I installed the distributor way back when I made a mark there-- seems like that's where it has always been. Any way, will you get a no start being off by about a tooth on the distributor or will it just run badly? The fact that it was running fine and then just no start at all is puzzling to me.

93limited

Wanted to post what I found- may help some poor amateur. I finally got the timing cover off and found as Dave suggested above the timing chain had slipped badly. Cam gear dot was pointing 180 degrees away from crank gear dot. Really strange that rotor ended up just about right where you'd expect at TDC. Tricky. Also, the chain didn't have more than 1/2 deflection so I can only guess the gear teeth wore enough to jump. I did two stupid things I can warn others about. One, I ran a tap through to clean up the crank dampener holes since I had trouble getting the puller bolts as far as I'd like and I was worried about pulling out the threads. But I went too far and dug into the timing cover-- it's raised towards the dampener at that point. Two, I forgot to remove the big washer when I removed the crank bolt. It's so wide it overlaps the dampener so there's no way to pull the dampener with it on. I was using a 4 foot cheater bar before it hit me. Dampener came off after 21 years with a regular socket wrench on the puller, so if you are cranking away, you might want to stop a bit. Thanks for the help Dave.