While accelerating I heard and felt a small "thump" (like a backfire) and my car quit running. The engine turns over with no problems, the injectors still squirt fuel, and the rotor turns. The engine almost fires up as soon as the key is turned, but won't start or even act like it might after that... although it continues to turn over and over and over...
There aren't any codes on the computer (it just flashes 12 - 12 - 12, etc etc) , and the check engine light never illuminated. Nothing leaking out of the engine anywhere.
Any ideas on what to look for next? What's a good way to see if spark is getting to the cylinders?
What else might cause a small "thump" and then keep the engine from starting?
HELP!
Thanks,
Rob

 

Sounds like an ignition problem to me.

Pull off a plug wire and stick an old spark plug in it. Lay it on the intake so it is touching metal.
Crank eng and see if there's a bright blue spark.

 

I'm thinking ignition, too. Is the distributor powered off the cam or crank? Anybody know? I'm also thinking timing chain or something in that area...
Rob

 

the distributor is driven by the camshaft, which is driven by the timing chain, which is driven by the crankshaft.

confused yet? lol

actually, the distributor is driven by a gear that is part of the camshaft. i'm not sure how the gear is made to be part fo the camshaft, but that's for a another discussion.

at the front of the camshaft, there is the timing gear, and chain. when they wear out, they can take up excess slack in the chain, which may possibly throw your timing off. i wonder if that may be.

also, not sure if they did this in the 80's, but didn't some sbc's come with nylon cam gears? if it does check out to be the timing chain, do yourself a favor and get a good double-roller setup, or go to a gear drive..... a little more noise, but no chain to stretch.

 

might also check the ignition module. It controls the spark output.
they have been known to stop working while driving.

 

OK, that's the way I thought it worked! Someone suggested to me that the timing chain might have busted, but I can watch the rotor rotate as the engine is cranked. I guess I'll try hooking up a timing light and see if anything happens with it while the car is cranked.
thanks for the replys guys!
Rob

 

Thanks! I'll look into that, too.
Rob

 

Sounds to me like a bad timing gear - phenolic teeth stripped off of the chinesium factory cam gear. I've been driving a couple of different cars when that happened; it's unmistakable once it's happened to you.

If that's what it is, the behavior would be: as you spin the motor, it just spins and spins; then it starts spitting back out the intake; then it acts like the timing is way advanced; then it almost starts, maybe it does a little, then it starts running terrible and dies; as you continue to crank it, it starts sounding like it has no compression; then it starts spitting back through the intake; etc.

If it's doing that, don't mess with the distributor (especially DON'T TOUCH THE TIMING); just get it towed somewhere that you can put a timing set on it. Don't run your battery down or burn up your starter trying to start it, it won't happen.

 

quick easy check, take your oil fill cap off and look down in there to see if the rocker arms move while someone else cranks it over that will tell you if there is a problem with the timing chain. but Id lean more towards the ignition system if I were you

 

What would we be looking for while were looking at the rocker arms? I mean, what would be out of place? Just wondering because this could help with my problem

Adam

 

just see if there is movement there, because the timing chain through the gear through the cam, through the lifters moves the rockers

so basically jsut look for movement

 

Good idea. Thanks!
Rob

 

You're looking for more than just "movement"... you're looking for them to be moving in synchronization with the crank position.

An easier way to spot that is to line up the timing mark, and look at the rotor position in the dist; then spin the motor over for a little while, maybe 3 or 4 revolutions worth; then line the timing mark back up; and see if the rotor is exactly where it was (or 180°) away; if it isn't, it's timing chain time.

 

Cool. When (if?) it quits raining and drys up a bit I'll give it a try.
Thanks,
Rob