no spark

[torso25]

i have an 83 chevy pickup. i just recently got it so i don't know the history of it. but, i will drive it for a while and it will just stop running. every time it is the same reason, no spark. usually i can just unhook the battery and it will start right up. to me and everyone else i've talked to this makes no since at all. but this time it stoped running and it will not start at all. i have replaced the the distributor cap, coil, rotor, all the plugs, and wires, i also had the ignition switch checked and it is good. however i was told that there is a relay switch on the fuse box, this could be the problem. but there is a spark going to the distributor but nothing coming out. i only have had the truck for a month and it has done this to me about 4 or 5 times. if anyone has any suggestions or any ideas i would be more then happy to hear them.

[72 rs]

have the ICM (ignition control modual(sp?)) checked. its the small black peice in the distributer that some wires attach to (under the rotor).

[torso25]

i had that checked and it was good.

[old dawg]

If you've got a good spark going into the dist. cap and nothing coming out, it's gotta be a bad cap or rotor. If the rotor has a thin spot or crack near the shaft, it can ground out your spark.
If your spark is weak going in, then that's a different matter....I would think something in the electronics. I don't have a factory manual for that year, but they usually have a pretty good troubleshooting chart for problems like this.
I know that ignition module (how would they check one of those?) can cause lots of problems like this.

[jkinney]

I know is may not sound right, but I've had modules do that, check out fine ......and then do it again. They dont cost alot, but to double check yourself (I dont like to spend money unnecessarily either) have it checked again, and have them run the check three times. That will get it up to operating temperature (simulating underhood temperatures, they are sensitive to heat) and then if it checks out okay, start doing a process of elimination through your ignition system. Get a Digital Ohm Meter, and check the pick-up coil as well. Post if you need real numbers to compare to, and If I cant get to it in time, I'm sure someone else can. Good Luck!

[old dawg]

The last guy might have changed the module without using the thermal grease under it....that stuff is important. Also, if you do get a new module, get a name brand. There are some brand-x ones out there that just don't last. I learned my lesson with those!
My last problem with modules was a lot like yours....it would just quit like I'd turned the key off, then sometimes kick back in again before I got off the road. Sometimes not, but it would start back up again. I finally replaced the module and that fixed it.

[NitWit]

I have the same problem on my 85 305 PU. It started fine, I would be driving and would loose spark. Sometimes I wait 10-15 min and it would start and drive fine. sometimes an hour. No rhyme or reason to it, and it didnt happen every day. (spring and summer operation)

I swapped the module and it seemed ok for a few days then it started happening again. Then it just quit. No spark.

I first rebuilt the distributer, new Pick up coil, module and that little round capacitor, coil, cap and rotor, everything. No spark. I got Chiltons and metered it had all the correct voltages in and out, coil etc. I then borrowed a distributer from a friend and tried it and still no spark. I ran a new ground to the block, no spark.

I will check the ignition switch to make sure I am not loosing power to the distributer while starting but assuming that checks out ok, what else could it be?

[toivo]

sounds like your coil is heating up and shorting out. that will cause an intermitant spark. especially if it starts again after cooling down. tge pickup coil can also cause the same problem

[JWhite8055]

Yep, if your certain it's not in the distributor cap, rotor, pick-up coil our ICM, then the only other thing is the coil itself.

[amac209]

if you ground a test light and probe the (-) side of the coil it should blink when the engine is cranking. also make sure your have a constant 12v on the positive side of the coil. if theres 12V on the pos and the light doesn't blink(neg) theres a problem with the module, pickup etc. if you don't get 12V on the pos coil go after the ignition wiring, switch etc. if this test passes the problem is either with the coil, wires, cap, rotor, carbon button, plugs. you can check the coil resistance i think it should be somewhere around .6ohms primary and 40,000ohms secondary. also check the resistance of your wires usually they're around 1,200 ohms per foot.
good luck