i just finished installing a complete procomp cdi ignition. mechanical advance, new coil, wire, plugs, distributor, everything. truck is a 75 f250 with a 390 and c6, 600 holley. driving along great, running smooth as ever and then boom, pow, bang!!! started backfiring like crazy and died. nows it sitting on the side of the road and i'm stuck! what could have happened now? i took the coil off and metered it, its fine, the magnetic pickup seems to be working (beeps when unplugged, like msd6a boxes), the ignition box fuse is good and i have fuel in the carb. now it wont even sputter when i try to crank it....

 

Sounds like the box failed. I would call ProComp.

 

Ohm out your plug wires; they shouldn't be more than 7Kohms per foot. Make sure the coil plug wire is seated properly.

Also - do you have oil pressure? (making sure you didn't sheer a roll pin on the distributor).

 

You did not happen to leave the dizzy loose did you?
I am sure that you did tighten it properly, but it sounds as though the timing went south. Many good mechanics have left a fastener loose.
This is the first thing that came to mind.

 

nope, its all tight. that was the first thing i checked. i also took the coil wire off and stuck a screwdriver in it and set it down so it would arc, and it would not arc. i meter the coil and the "ohmage" is all good. i'm beginning to think the brand new ignition box is fried...which doesnt really make any sense. i hate my luck

 

The screwdriver test is tough to be accurate with. You're not guaranteed a good ground on external engine metal especially if it's painted. But it does sound like your box could have gone south.

 

i am going to check the roll pin on the distributor drive gear. that would cause the timing to go way out quickly, hence backfiring, and if its not turning the rotor, the magnetic pickup would not be triggered, hence the coil not firing. i'll hope for the best...

 

Yep, that's what I was getting at when I asked if you had oil pressure the moments before it went. Best of luck.

 

i appreciate the info fmc400, i wish i had thought to look at the oil pressure guage. i'll keep you posted, thanks!

 

Good luck mabigredtruck !!! hope it's not too hard to fix & get runnin' again

 

I agree. being broke down is never fun.

 

roll pin on the distributor was in a bout 8 pieces. Popped a new one in and reset everything but now I'm worried its going to happen again. I could easily turn the oi pump by hand and still have great pressure, so what could cause the pin to break? Thanks for all the info!

 

I figured as much. That pin shears for only one reason - when the pump locks up. That pin actually serves to save your engine. If, for whatever reason, the pump locks up and the distributor shaft freezes, the roll pin will shear before the distributor gear and cam gear start grinding. It also cuts the ignition for you, since you'll have lost pressure.

I'd love to tell you you're out of the water, but pumps don't lock up without reason. It's the most well-lubricated part of the engine. It's possible you have something that got caught up in there. You can try to go ahead and keep running it, but it's very likely that it will happen again, and you could suffer bearing damage with whatever froze the oil pump circulating around in there. Once you start shearing roll pins, it's pretty common for it to happen again. You could hope for the best and just keep running it, hopefully that works out okay for you. Hopefully whatever froze the pump got through and the filter got it. The oil filter, of course, is fed after the pump. A small mesh screen on the pickup is the only thing protecting the pump itself. The proper thing to do would be to pull the oil pan and take a look at the pump and pickup because it's likely you'll find some bearing material or something similar making its way through there. But I'd hate to suggest for you to do all that labor only for me to end up wrong and you find nothing in there. You're going to have to make a judgement call. I can only list the facts.

 

I totally agree with fmc400, it may never happen again but it could happen right away also. It happened to me and I never found the cause but I did remove the pan and pump to check for damage or parts in the pan and nothing. It's better to be safe than sorry.

 

What type of roll pin are you using, a solid pin?

If so, that's not the correct one. It won't last a NY minute!

What you need is a split pin (1/8" x 13/16" long)...it's split along its entire length, so when its driven in, it tightens up.

If you are using a split pin, it's prolly the original and has lost its tensile strength...time for a new one.