Engine turns over but wont start, ignition?

[SCtractorboy]

I figured this was a ignition issue as I would let the engine warm up and it shut off once it had warmed up. It didn't choke out or anything as it would when starving for fuel. Once I allowed it to cool, several hours later, it would start back up again and repeat this process (for for about 10 minutes til warm and then just stop without restarting). I've been on the way to work and it just shut off and leave me on the side of the road.

I started by replacing the plugs and wires. After this it ran perfectly for a few days without any issue. On the way home from work (maybe about 5 minutes after I left) it just shut off in the middle of traffic and I had to pull off. Again, it would not start back up. I went back the next day to try starting it and it run like there was no issue and I made it all the way home, which is about a 30 minute drive. Made it home, it idled soooo smooth and then I shut it off. Go out a couple days later and it won't start at all.

Researched anything and everything I could about ignition issues and decided to replace the ignition coil. Replaced it this morning and still nothing. Only other thing I could figure is the distributor itself or timing.
I recently replace the fuel pump as well (like within the last 6 months) so I wouldn't think it is an issue.

 

[Cuba]

Unfortunately the most accurate time to test it is when it doesn't start.

You need to verify if you have spark or not.
You can test for coil spark using an Incandescent Test light connected to ground to verify spark out of the coil. NEEDS an AIR GAP, as in don't touch the tip of the test light to the coil output (goes to center of dizzy), just let it hover and you'll see the spark.

You may want to disconnect the injectors at the TBI so no fuel is emitted. If this is your setup. There's no vehicle info.

I would start guessing ICM at this point (Ignition Control Module), at the base of the Dizzy. But we need to start somewhere by doing tests. Otherwise you'll be throwing endless supply of parts at it.

 

[Cuba]

Researched anything and everything I could about ignition issues and decided to replace the ignition coil. Replaced it this morning and still nothing. Only other thing I could figure is the distributor itself or timing.
I recently replace the fuel pump as well (like within the last 6 months) so I wouldn't think it is an issue.

I doubt it's your timing at all due to the fact that it runs normal intermittently. It's either timed or not, unless Dizzy base bolt is loose and you'd have other symptoms of farting and back firing, etc.

 

[1987 GMC Jimmy]

I agree with @Cuba. Is this the truck you posted about before - the '85 C10 w/ a 305? If so, it came with the ESC distributor and the ICM with all the little pins. Six, I wanna say. The spark test that I like to use is the little inline tester that's on the shelf at the parts store. It just goes between the plug and the wire. It's a good test for spark presence, but you actually need to pull the plug and do that test for spark quality. What I would do is pull the ICM and take it to Autozone where they can bench test it. Have them do it four times if they just want to do it once. That's important because it sounds like it hadn't quite failed yet when you were having intermittent issues and now it may or may not have failed completely. That's the quickest and easiest way to rule that out.

 

[HotRodPC]

What they said above, BUT.... Let's get this terminology fixed too.

Turning Over IS Cranking. So you mean, it's turning over, but won't start. Or It's cranking but won't start. Don't feel alone. Go operate a tow truck or Roadside Service vehicle and see how many times you hear this. TONS. Now you know.

 

[SCtractorboy]

So got an early start this morning to remove the ICM an have it tested and come to realize the connector wasn't even connected. I tried starting my truck before I plugged it in just for the heck of it and of course it wouldn't start, plugged in the connector and tried starting and it fired right up.

BUT, I moved the truck after I'd let it run just to see if it would stay running once it warmed up and it did fine. Shut it off, cut the grass and go to start it back up about 45 minutes later but it's still just turning over and won't start. Everything's still connected this time.

Does that still sound like the ICM should be replaced? I'm sure it wouldn't hurt for me to have it checked still.

 

[Honky Kong jr]

I would say so. If when it was running and the plug was loose the added resistance of a loose connection would play hell on electronics.

 

[1987 GMC Jimmy]

^^^Same

 

[SCtractorboy]

Just had my ICM tested and it passed, but I replaced it anyways. Still won't start though. Also tried shooting some starting fluid into the carb and still nothing.

Stumped as to what I should try next, any feedback?

-Josh

 

[Honky Kong jr]

Are you getting good 12v to the distributor? If not make a jumper to that terminal and try to start it. Wait this is HEI right?

 

[SCtractorboy]

It is HEI, what's an easy way to check the voltage on the distributor?

 

[HotRodPC]

Coil Pick up or coil. Are you familiar with using an ohms meter? It's not real common for a coil to go bad, but they sure can. Also USUALLY when a coil does go bad, many times, it'll start but as soon as the coil gets hot, it'll die. How you check for spark while cranking? Pull a plug wire off and hold just off a grounded source, and have someone turn the key to crank it and see if it's arcing.

 

[HotRodPC]

It is HEI, what's an easy way to check the voltage on the distributor?

Hook a Voltmeter to the 10gu wire that plugs into the coil via dizzy cap. One plug is marked TACH, one is marked IGN. Make sure the wire is going to IGN.