intermitent no spark

[Fixit]

This one has been driving me nuts for awile....

This truck is a 1986 c10 half ton 2w drive with a 4.3 liter V-6 and a manual 3 speed on the tree transmission. It has a 4 barrel quadra-jet and electronic ignition.

Here we go... I'm driving around and it's running pretty good when all of a sudden the engine cuts out like someone flipped a switch. I coast off the road and wait a while then try starting it. It starts and runs like nothing was ever wrong with it. It tends to do this more when it is raining or the truck is wet.This problem continues to get worse. Now some times the truck will not start at all rain or shine (it always turns over fine) and it needs to sit a lot longer before it will start again.

I have had a mechanic that I trust look at this truck. He told me that it would not do this problem for him. I asked him if he got the truck wet. He told me that he actually put a hose on this truck for awhile and he also soaked the distributor and the truck just kept running even with all this water.
Like two days later the truck cuts out again at three in the morning in a commuter lot . Currently the truck is sitting in my driveway and I can't get this thing to start at all.

I have checked for spark and found none when this truck would not start. I do have 12 volts at the distributor with the ignition in start or run. I have replaced the entire distributor, rotor, cap, pickup coil, ignition coil in cap, spark module in the distributor and the plug wires. I have not changed the ECM yet. By the way this ECM has only 7 wires going to it and there is no ALDL connector under the dash and to the left of the column like on my 88 Suburban so I can not get any check codes.

If anyone out there knows what this is please give a yell. This has got to be one of the hardest problems I have come across and I'm getting sick of throughing parts at it.

When I was changing the above parts I also repaired a bad engine ground. Could this bad ground have messed up my ECM? Does anyone out there know how to test if this ECM is good? I'd like to know before I spend the 90 bucks that Napa is quoting me just to find out that I still have the same problem.

[screwballl]

sounds like a similar problem to what I'm having.
right now it wont start and for me ive already replaced the coil, dist cap and rotor and carb with all new parts...
as mine is a 76 theres fewer parts but it does sound like the same problem except mine doesn't cut out while driving *yet*... very random and intermittent, will work fine for a few weeks then die again... one idea i had was the fuel pump but even with starting fluid, it doesnt ignite as if theres no spark. It turns over fine so the starter, battery and related strating comonents are fine...
i am cinfused by a very similar problem...
we need help!!!

[Fixit]

Have you checked to see if you have 12 volts at the coil when the ignition is in the start or run position? Also I'd pull one of your spark plugs and hold it against the block while an assistant cranks the engine to see if you have spark. Use a pair of insullated pliers when you do this unless you want a new hairdo .

[8t5Silverado]

I don't know about the V6's, but the small blocks had no electronic controls aside from the ESC (electronic spark control). It's the metal box that looks like an ECM behind the glovebox. All it does is retard the timing when the engine knocks.

My truck wouldn't start. Then all of a sudden it would. And then back again.

I had to "jump" the wires on the 4-prong plug going to the distributor.

There is a way to bypass the ESC and eliminate the problem, you'll just have to set your timing right and leave it alone.

Check out Jeff's site www.73-87.com for instructions. Swervin Ervin helped me when I had my problem (it was his website before).

Good luck.

[Fixit]

Thanks!!!


I went to the site that you linked to and read up on that fix. I did not want to cut into the wire harness to splice the cables at the distributor yet so I unplugged the connector from the ESC and jumpered the Black and Green wires that go to the distributor with a short piece of 12 gauge solid copper wire. When I turned the key the truck started and ran great. Now I know the problem is with the ESC or it's wiring. I'll ring out all the wiring (7 wires total) and then decide to disable or repair this system. To be honest I'm a little leary of desabling it but if you have run yours for a year like this I'm definitely going to consider this. Have you noticed if your truck is running to rich or lean after this change?

[screwballl]

as i dont have the ESC in mine, someone suggested the ignition/spark module for mine which was probably for the most part replaced in later years by computer controlled components...

[8t5Silverado]

Well, to be honest, I got a new ESC. Somebody on another board had one they had bought ($130 or so) before deciding to just get a different distributor and so I got it really cheap.

I will eventually do the same.

A lot of people do this without problems, unless you run the timing too advanced and use cheap gas. This is how all of the late 70's trucks with HEI are, so don't sweat it.

Be prepared to have to jump the truck all of the time until you bypass it.