I have a goofy problem that I can't seem to beat and am out of ideas. The engine 90% of the time will not start after it's been running for any length of time, including even a few seconds. After shut-off, It'll turn over fine, but won't fire. It appeared to have spark as tested by pulling out the #1 plug and grounding it (visual). If I connect it to a running vehicle (~14 V) with jumper cables, IT WILL ALWAYS START, if I disconnect the cables it won't.

The battery has 12.5 V, as does the distributor (12.3V). According to the wiring diagrams, that would imply the ignition switch is good. This was all tested while in the no-start condition. Distributor/coil/pick-up coil/ign module/cap/rotor/wires/plugs all new. Engine grounds verified in good condition.

The car starts fine when dead cold, and will also not start with a jump from a non-running vehicle (which helps verify my battery is good). I realize I could be getting a weak spark, but what could cause that based on all I have replaced? If anybody could suggest a way I can get this thing to fire reliably without a 14V battery , I would appreciate the input. I also had the battery load tested and it checked out ok, 700 CCA plus at all loads it was tested at.

 

My guess is ignition coil. As the voltage drops(i.e. 12 volts), a dying coil will need more and more time to charge up the same amount(about 6 amps) regardless of battery condition. Goes along with your reported weak spark. Weak spark could also include ignition module, so don't forget that.

 

I agree, it could also be vapor lock, pull # 1 wire next time and use a spare spark plug to see what kind of fire you are getting.

 

Thanks for the advice! My ignition coil is brand new, as is the module. I probably should mention I slightly modified this engine in that I have the primary fan run anytime the ignition is on and use a 160 degree stat. I noticed some carbon build up on a few of my plugs, though not bad. Running the engine this cold I could see it causing advanced spark plug fouling. I replaced them all today and so far has started every time. I don't yet know if I have solved this issue, but the success rate is better.

I am no pro mechanic here, so cooter, if you would please enlighten me on some causes of vapor lock, as it could very well be that. For a time, I thought this was a fuel delivery problem. It gets 47 psi at the rail in the no-start condition. The pressure bleeds off at an acceptable rate, according to the threads I've read on that matter here. I am hoping having that kind of pressure would tend to not have the fuel boil, but I just don't know. Thanks again for your input.

 

Well, good luck. If the vapor lock lead don't go nowhere, heres my thoughts.

I've had ignition modules bad out of the box. Especially the $20 ones.

Your advanced plug fouling could also be a weak ignition, which you mentioned earlier. Follow the symptoms. Replace the coil with a known good one(ohm test won't show borderline dead...trust me), and least get the module tested. Maybe even check the plug wires in the dark.

I'm only certain of this because this is the exact same story I went through a month ago. My plug fouling was also being helped by a leaking TBI unit, so I fouled 'em real quick.

 

Thanks, pizza guy. I will check that out. I happen to have an $80 Bosch ignition module on the ready, as when I went to replace the one on the original distributor, I had a bolt head snap off. Easier to replace the distributor than tap it out, for me. I bought one of those "loaded distributors" so I'm sure the module was probably straight outta the junkyard, LOL!

I have a pro mechanic friend tell be to check the battery cables, both positive and negative. In many instances the cables will ohm ok, but volts split apart under load.

So I'll do both and we'll see what happens. I am confident with the coil, because that is top of the line and brand new. At the absolute least I am replacing 20 year old parts, so it is not entirely a waste of money here.

True to your word, pizza guy, I also have a bad injector in my TPI unit, so that could be an additional cause of my fouled plugs. Your thoughts are highly appreciated and thanks for taking the time to lend me your knowledge!