Gas, spark, compression; still won't start

[jms5580]

Been a while since I've posted but I'm desperate this time. Recently replaced my radiator. Had it running, seemed like it would miss when revved. Idled just fine though. Got it out on the road and couldn't get past 50% throttle without it stumbling. It would get hot at times when it first warmed up but then held at 180. The other day I took it out, it heated up to 240 for a few seconds but dropped right down to 180, all was good. A couple miles later it just about stalls on me, no power at all. I limped it another mile downhill with it backfiring through the carb to a parking lot and let it sit for a couple hours while I went hunting. Came back and she wouldn't start, not even a cough. I checked fuel, spark, etc. All the quick and easy stuff. All checked out, although when I pulled the plugs they were covered in a yellowish ash. Still nothing. Had it towed. Took a gamble on the timing chain and knocked that out yesterday. Had a lot of slack but it didn't look like it jumped time. Drained the oil this morning (looked fine, even that had been done in the past month), refilled fluids and cranked away. NOTHING!! I rechecked the basics. Getting fuel to plugs, getting spark to plugs, good compression. I'll be honest, I haven't checked ALL of the cylinders (no help at this point), but I'm baffled as to what could even possibly be the culprit here. I even gave it a few shots of starting fluid and nothing. Any ideas?

 

[Bronco Junkie]

Have you checked the timing?

 

[jms5580]

Haven't rechecked with a light but it's where I had it before everything went south which should be pretty damn close.

 

[ransil]

acts like distributor is 180 out

 

[BRONCROB]

What type of ignition are you running?Sounds like a firing issue to me.

 

[ugly74]

Have you popped the valve covers off and confirmed that everything is in good order...all valves doing what they should?

 

[08ag]

couldn't get past 50% throttle sounds like its running too lean, that would also cause it to run pretty hot. A bad thermostat or bassackwards will cause it to overheat as well. Lastly, as already mentioned, timing seems that it could be a good bit off, and that will also cause it to run hot. But the fact that it was running at all, i wouldn't think it was timing.

A yellowish plug is indicative of a lean condition as well.

Next step, Id replace the plugs.
Check compression on all cylinders to make sure you didn't melt through one.
Holley carbs have to have CLEAN CLEAN CLEAN fuel. the needle seats will be the first to stick, not allowing enough fuel in. or you could have a jet plugged up etc etc

 

[1973 Houston]

Timing chain?

 

[69red]

big vacuum leak?

 

[jms5580]

Replaced the timing chain. I'm running a q-jet with pertronix flamethrower II coil and duraspark box. Both are roughly two years old, not a lot of miles. I suspected a vacuum leak and checked all major areas, but I would expect at least a stumble if I have fuel and compression.

At this point I'm suspecting weak spark from the coil, causing it to not spark under compression.

 

[DirtDonk]

And it was running perfectly fine before the radiator swap? Or had you even had it running before that?
What prompted the replacement in the first place?

Did you use a flushing chemical when changing out the coolant? If so, was it the really nasty stuff that needs to be neutralized before you're done?
Reason I ask that is just wondering if you have some head gasket issues.

Is this an older engine, new one, or somewhere in-between?

Paul

 

[DirtDonk]

Forgot to ask. What else did you touch during the radiator swap? Could you have yanked on any power wires for the ignition?

Paul

 

[nvrstuk]

Plug in a new Duracrap box and you should be good. Try it and let us know...

 

[demesauce]

Not to point out the obvious, but is the battery fully charged?

 

[DuctTape]

Plug in a new Duracrap box and you should be good. Try it and let us know...

I had a strange running problem with same thing had gas and spark and had suddenly gone south.

Replaced my ignition module and that was it. About tore my hair out figuring it out. Didn't realize those things can go bad like that (still spark).

 

[broncobilly72]

where did you check for the spark to the plugs? I find an easy way to check is to pull a plug, ground it to the engine block, crank the starter and look for spark at the plug itself. Do this and f you get spark all components are working correctly.

 

[nvrstuk]

Not necessarily so with the Duracrap box. It can send out signals for the distributor but they might be random, etc. Same symptoms you are getting... borrow one from somebody and then buy a spare. ALWAYS get a Motorcraft replacement. Do not get anything else, stick with a Ford module.

 

[jms5580]

Last time I believe my symptoms were pretty close and it turned out to be the coil or ICM. One went and then took the other right behind it. The truck ran fine prior to all of this. Got a hole in the rad so I got a new one. Didn't run into anything electrical. Even disconnected the battery while I did it. Truck has unknown miles. Though the timing gear was aftermarket. I tested spark with the plug in the boot grounded. I know Advance Auto tests modules so maybe I can start with that since it is free and easy.

 

[jms5580]

Box was ok. Looks like it's the coil. Have compression on all cylinders and I'm getting gas. Coil spark is yellow and weak. Initial resistance reading was 15,000 ohms, but now I can't get anything. Will be replacing this week.

 

[DuctTape]

where did you check for the spark to the plugs? I find an easy way to check is to pull a plug, ground it to the engine block, crank the starter and look for spark at the plug itself. Do this and f you get spark all components are working correctly.

I got spark that exact method and I had a bad ignition module. Never occurred to me that the module could be delivering the spark wrong. I can say from personal experience that you can have spark with a faulty pertronix ignition module.