I have a 78 with a 351m that just recently started giving me issues, was running perfectly fine when I drove it to work, and then I left work and it just quit, started idling really really low rpms. I could barely keep it running, for the next two or three days I went out and started it and it would run but again, at really low rpms, and just sounded like ****. And then a couple days later it wouldn't run at all, no fire on any cylinders, not a single explosion, just cranks and cranks and cranks, I've done plugs wires cap and rotor, coil, ignition module, pulled the carb and cleaned it, check all the wiring, and I have no clue what the hell is wrong. Any help would be greatly appreciated, I miss my baby girl

 

Welcome to FTE

Just so everybody is clear on this, you checked for spark at the plugs, and there is none?

 

No I checked the plugs, it's getting spark, looks maybe a little weak, but spark nonetheless.

 

Strong Bluish-white spark that snaps in the air, or a weak yellow or red spark? A weak spark in the open air will be nonexistent under compression. This may be the problem, at least by your description.

 

It's still a blue spark, I can tell it's enough to cause ignition.

 

Hm. Sounds a little bit like it may have "jumped time", when motors get to high mileage the timing chain starts to stretch excessively and can skip the cam or crank gear teeth etc. Put a breaker on the crank bolt and watch how much rotation is necessary for the distributor rotor to start moving. Place #1 piston at TDC on compression observe where rotor points to.

 

^^^^ good to check this....but if it jumped time, would he not get at least a fart from the 'ol girl? Then again, maybe not if it jumped a lot.


You say you bought a new brain box (ignition module)? Did you have the old one checked? And, did you buy a Motorcraft box? Should be a blue grommet(ed) one.

Bad brain boxes would show the same symptoms you describe.

 

Would a bad brain box still provide a good spark? Or they spark erratic? I assumed a good spark meant we could look elsewhere. Yeah it's easy enough to check the timing chain, and where it's (rotor) pointing. I agree it should probably light off, or backfire etc though.

 

A bad box is a downward slide... it'll fire up like nothing's wrong and run ok for a spell, then croak. Wait a few minutes and she'll fire right back up, but die in a little bit.

Next time, she'll fire up and die within a half hour (or so). Might or might not fire up again after waiting a while.

Next time, she won't fire at all...one can crank her over 'till the battery dies but, no cigar. Wait a while....same thing. It finally died for good.

Heat is a killer for these puppies, too - and the cheap one will croak faster or not fire at all. Where they're put - for the most part - on the inner top left fenderwell let's 'em get hot faster. Some people put washers under the box for air flow.....

This intermittent start/run/finally croak problem with old modules has been well documented by Number Dummy, Mike0o0o0o, etc. All said, and done, the Motorcraft is the only one recommended.....$40.00 or so?

 

That's what I was thinking, my first plan of action is to check the chain, and see where I'm at with timing, and then go from there, I'm really hoping to stay away from the brain, as you're all aware, they're a bit of a money pit.

 

Good plan of attack, especially when the dollars are tight.

Keep us informed and good luck.

 

Will do, I appreciate it guys