Hey all,

A friend of mine has an '81 vette with 70,000 original miles. Good shape--not beat up, but hasn't been very well maintained. Its too original, and some parts are failing on it, but nothing a little maintenance can't fix.

Anyways, the last time it was started was back in December and it fired right up and ran fine in the garage. Now, we attempt to start, and it will fire like crazy as long as the ignition switch is held in the START position. It'll run forever as long as you keep the starter enguaged, but the instant you let the key go back to RUN, it dies. It doesn't sputter and die, but just falls flat on its face. I had it running 2000 tachometer-indicated RPM with the starter enguaged (yea, I know it can't be good for it!).

I think we have an ignition module gone bad, but I want a second opinion before I just throw parts at this thing hoping it will run. For all I know the ignition switch isn't working right. I know little about the GM HEI ignition or even Corvettes for that matter. Cap and rotor seem to be original, spark plugs look original. We plan on replacing these items.

The plugs look very difficult to get to--what does it take to change these out? Just creative maneuvering of the tools? Does anyone have some FSM exerpts they'd mind sharing with me?

 

if the module takes a crap on you it will not work at all.it sounds like it is in the ignition switch to me sound like when the switch is on it is getting juice then when you let go it is not getting juice,check your switch and grounds,i really dont think it is the distributor,check all the wires to ignition, could be coil but i dought it.i would take a test light or volt meater,turn the switch on and check for power going to the cap,should be two wires green tack and red hot wire.if you have no juice coming from hot wire when switch is on then you have a ignition problem.you should have constant voltage to wire when switch is on,

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I guess the search continues. I've had a bunch of fords in years past that would do this exact same thing and the cause was the ignition module, but that is a different animal.

I'm sure the distributor, pickup coil, and ignition coil are not the cause of the no-run, but it sure wouldn't hurt to change them out after 25 years and 70,000 miles.

I'll have to take a closer look at it, but I remember there being a pigtail of about 5 wires coming out the back of the distributor, and without a good wiring diagram, I am pretty lost. I will check the coil for power. If it has power, there must be a ground missing which is controlled by the ignition module I'm guessing. I always thought there were two seperate parts to the module; start mode and run mode.

Where is the ignition switch at? Is it traditional GM design where the lock cylinder pulls a linkage to a switch under the dash somewhere? Depending on the wiring system, this could definitely be the problem. Either way, in theory, I could run a + wire to the ignition coil and it would run as a *very* temporary fix.

While messing around with stuff, I somehow caused the car to lose its entire electrical system; NOTHING worked. It turned out to be something loose + bare wires in the starter wiring harness. Jiggled it around and the whole car came back to life. Still won't run though, but I think that is an un-related issue. Again, it depends on the electrical system. We ordered a new harness through Ecklers, but I would still like a wiring diagram!!!

 

the switch is a traditional GM part from back in the 80's.yes you could run another wire to the cap.that would work.just make shure it has power when the switch is on and go out when switch is off and make shure the wire has 12 volts,

 

Ignition switch has 2 circuits in it, a start circuit and a run circuit. I believe CK is right, you probably need a ignition switch. [8D]

 

Well, I had power to the coil in both START and RUN key positions, so the coil was powered up just fine. Through studying wiring diagrams, I determined that I was able to unplug the engine computer from the distributor, and it would run on its own like normal. If I re-connected it while the engine was running, the engine would die right away.

So, I replaced the ignition module inside the distributor, and VROOM it started and ran just like it should even with the ESC connected.

So, its running, but it idles a bit rough now and has some kind of misfire during low-speed driving. I am hoping its not being caused by this cheap ignition module I installed. Plus, the CHECK ENGINE light is on now, and it seems to flicker. Does anyone know where the datalink connector on this car is? Any ideas on what is causing the rough running? Its not really bad, but it should definitely be smoother than it is. It didn't have this misfire last year. Cap and rotor are new. I have not yet done any diagnosis for bad ignition wires yet.

 

I hope you used a Delco module instead of a cheap Autozone one. [8D]

 

Yea I think that may be the case. Sometimes I just never learn. It wasn't an autozone one, but what is the greatest flaw of the "autozone" one?

I think I have a weak spark condition BECAUSE when I had my timing light on the car, about half the time it would flash. I never had that problem before. It has always given me crisp, clear flashing on everything i've worked on. Unless my timing light is getting old (already is).

So, if this module isn't getting the appropriate dwell time or something, that will result in a weak spark.

 

Well, the module only grounds based on signals from your stator or pickup coil. If you have an a/c volt meter, you can check the output of your stator. Should be generating about at least .500 to .800 volts a/c. Also, use a 12v test light clipped to the 12v + side of your battery and touch the - wire going to distributor and turn engine over to see if it flashes consistantly. That will tell you if your stator and module are working. If they are, suspect a coil. [8D]

 

Ignition switch is bolted to the top of the steering column with a rod that goes to key switch.


Very cheaply made, as with most of their products.

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