So I am new to the forum and have a strange issue I can't figure out. So I felt I would come here and see if someone could shed some light on the problem.

I have a 1978 Ford F100 302, recently rebuilt the engine and transmission, and added an AC. I went to start the truck, and to my surprise, it would not start. It turns over fine but won't start. So I checked for the spark from the coil; all looks good there. I replaced the following during the build, new coil, new distributor, new ICM, new plugs, and wires. I used my meter to check all wiring from Distributor to ICM all good no shorts, Coil to ICM all good no shorts. So here is where the craziness starts for me, at least.

I pull the wire that goes from my coil to the center pin on the distributor. And if I leave the cable loose over that pin, the truck starts up fine and run's like a champ. But the minute I seat the coil cable onto the distributor, the truck stall and quits running. So I figured I would replace the wire from the coil to the distributor. But again, had the same issue as before, the truck runs fine with the coil cable lose on distributor. And stalls out when seated back correctly. I check for voltage on the coil's positive side and read 12v and 12 v on the opposing side. I have looked at the wire schematics for this year's truck, and there is not much there, so it seems simple enough. But what I noticed is a 1.5 Ohm resistor inline from the ignition switch to the coil on the positive side. Which seems it would drop the voltage on the positive side to around 7v or 9v give or take. But I did not ready any resistance in that wire. Should I try to add a ballast resistor, or am I suppose to have 12v on the positive side. And why would it run with the coil cable not making full contact on the distributor center pin?

Thank you in advance for any ideas to try.

 

Hello Isaac....This is an interesting problem so I am going to take a shot at it to see if I can help.

First off, I am going to assume you have the stock duraspark 2 ignition system on this truck. If not, then describe your setup please.

Second, We know that you changed the distributor, coil, ICM (control box), plugs/wires.

Third, your running/dying problem occurs when you have the coil-to-distributor wire pushed down onto the distributor cap terminal. When the wire is pulled from the center terminal and is laying right above it, then the engine will run....good so far?

OK...it seems that you have found the culprit. It appears to be hiding in either the distributor, the cap and it's adapter below it, the rotor, or in the electronic pickup unit located in the distributor.

If you have had time to look at other similar problems on this forum, you will find that quite a few of the issues can be traced back to "new" parts being defective out of the box. Seems to be a recurring problem. Do you still have the old parts (Coil, Distributor, ICM)?

Back to your situation....since the engine will run with the coil wire just hanging over the cap terminal, that means the ICM is seeing the make/break signal from the pickup coil in the distributor and firing the coil as intended. But, when you push the coil wire back onto the terminal of the cap, the engine quits, indicating the ICM is probably no longer getting the trigger signal from the pickup coil. Seems then that you should be taking a closer look at what is changing around the entire distributor when you push the wire down onto the cap....

Couple things come to mind....One: When you push the wire down, the cap and it's adapter piece under it could be pinching the pickup coil leads (wires) that pass through it inside of a rubber grommet. Take a good look there and also look for broken/cracked wire insulation or crappy connections inside the distributor. As a further check, you can connect your multimeter to the purple and orange terminals of the pickup coil leading into the distributor. I don't have the specific continuity/resistance reading for the circuit at hand, but it can be found elsewhere on this site. If you are showing proper continuity, then try wiggling the wires at the grommet and pushing up and down on the distributor cap to see if you can replicate the electrical dropout. I suppose you can repeat the tests with either the purple or orange wires connected to the black (ground) wire and see if the pickup is grounding out.

The other thing is whether or not the distributor cap and/or rotor inside are cracked or just not very good quality. Check those real good too. See how much up/down play you have in the distributor shaft with the rotor removed. See any signs of metal-to-metal contact under the reluctor (the star shaped wheel that resides under the rotor)?

I haven't addressed any of the other items you mentioned, such as the resistor wire, as it seems that your distributor needs some more scrutiny first.

I hope this helps Isaac. Please keep us posted.

Regards,

Jim

 

Man things have got complicated . To what end is this beneficial. Stand alone ignitions produce plenty of performance without these wonder boxes.

 

Highorder77,

Thank you for the reply, Just wanted to answer a few of your questions and let you know how I think I will get out of this rabbit hole I chose to crawl into.

First off, I am going to assume you have the stock duraspark 2 ignition system on this truck. If not, then describe your setup please.

• Correct it is a DuraSpark ignition, I just replaced old components with new ones.

Second, We know that you changed the distributor, coil, ICM (control box), plugs/wires.

• Correct all changed out.

Third, your running/dying problem occurs when you have the coil-to-distributor wire pushed down onto the distributor cap terminal. When the wire is pulled from the center terminal and is laying right above it, then the engine will run....good so far?

• Correct as well

So not to go to long on this. I am suspecting a bad part somewhere seeing how I have had bad (new) parts in the past. But I also feel we are having a resistance issue somewhere casuing problems. I know that spark plug wires should have so much resistance per foot to keep a balanced system. But I have yet to check the plug wires I would need to see the specs for these before testing. I did test all wiring from distributor to ICM for continuity and shorts to grounds and all looks good there. I tested wires from ICM to Coil for continuity and short to ground and all good there. I also tested between purple and black and orange and black and I don't see any grounding out. I also Tested with and without Coil to Distributor wire connected to see if somehow that caused a short somewhere. All tests were done while the engine was not running.

So here is what I decided to do after a bit of research. I am going to change this entire system out and go to an HEI distributor with Coil onboard. This way it's a one-wire hookup that will take all the other components out of play. I think it will be best for the overall system, seeing how this is my daughter's truck and it will simplify things. Plus it keeps me from going to crazy chasing ghosts and wasting time. There are times in life when we have to cut our losses and move on and this is one of those times.

I should receive the new distributor on Friday and Ill keep you posted on the outcome of that. Again thank you for the response, much appreciated.

And Christmas, thanks for the comment, I am moving on and going the that exact route.

Isaac

 

Hi again Isaac - thanks for the update.

Good luck with your next step and please share any "Ah-Ha !" moments with the curious here if you discover any....

Regards,

Jim

 

Highorder77,

Just got done working on my truck. I installed the new HEI distributor got it all hooked up and pulled out all the new/old stuff. Coil, distributor, ICM, and removed plug wires and put in new HEI wires. I got all excited and went to start the truck and crank but no start. So after pitching a bit of a fit .

I didn't really know where to go from here. So a friend of mine suggested I replace the spark plugs, at this point why not. What I noticed was that the plugs I put in there were Motorcraft ASF32CA, and when I went to get new ones, the guy behind the counter suggested that I use Motorcraft ASF42CA plugs so said what the heck and took those. I think the only difference between the two is one is platinum and one is copper, one runs hotter and the other a bit colder.

Anyhow, I went ahead and took those plugs and got them installed on the truck. Turned the key over and it started right up and is running like a champ. I am at a total loss here, how would the plugs make the difference. Unless some were grounding out somehow, or if its still a resistance issue and one plug gives more resistance than the other. Who the heck knows, the truck is running now and its on to check for leaks and top things off to make sure the rebuild is all good. Then it's back on the road.

Thank you Highorder77 for taking the time to help me think of things to look for. Hope this helps someone in the future.

Isaac

 

Were the previous spark plugs (when it wouldn't start) platinum? Seems unlikely they would prevent it from running though. I hope you have at least some un-used swear words left over in reserve, if it happens again lol.

Pulling a spark plug wire slightly used to be real common technique to get a heavily fouled plug to fire in a lawnmower, say. A wide air gap anywhere in the secondary circuit greatly increases the ignition coil firing voltage. In this instance, enough increase to overcome all the sludge on the plug and get it firing through the crud again. I don't think that's what was happening here (plug fouling) but a data point to think about.