rig is a 89' F-150.
Back in 2000, I pulled the blown efi 302, and replaced it with a carbed 351, then later a efi 302..

recently, I swapped in a efi 351, Motor ran when pulled, but I went through it anyways. The engine harness is from the bronco(as is the 351) the vehicale harness was the orriginal one from my truck. After getting te motor in it, wired, and putting all the high pressure fuel ines, and pump back in, it fired right up. Being that there was no cooling system in it, I only ran it for a few seconds, on about 3 or 4 different ocassions.

today, I finaly secured the correct waterneck, so I could plumb the cooling system, and it would not start, no spark, tach didn't move when cranking.

I determined it was obviously the TFI module, so I swapped on a buddies spare(with good thermal paste) It cranked over twice, fired once, and never fired again, no spark.. wtf? changed computer, nothing.. so Im postive its another dead tfi..

Now, what would cause them to die so fast, bad wiring? dead short? I've only got one more good tfi, and I'd rather not fry it in 5 seconds. Any ideas?

sounds somewhat like a dead short... id find a wiring diagram... and see if the 351 has a diffrent harness compaired to the 302 harness. i know you swapped the engine harness, but ive heard that the chassis harness (im assuming that you mean the headlight harness?) is diffrent from motor to motor...

anyway, to be safe, id check to make sure the harnesses match up wire for wire...

Did you slather some dielectric grease between the TFI and the distributor mounting surface?

Did you slather some dielectric grease between the TFI and the distributor mounting surface?

"I determined it was obviously the TFI module, so I swapped on a buddies spare(with good thermal paste)"

read much? :laughing:

"I determined it was obviously the TFI module, so I swapped on a buddies spare(with good thermal paste)"

read much? :laughing:

Thermal paste? Is that sort of like sore muscle heat treatment?

NAPA doesn't sell thermal paste...they do sell Dielectric grease.

Could also be the pickup in the Dizzy or the MAP sensor.

There are several things other than the TFI that can cause no spark. You need to do some testing not parts swapping.

If the pick-up in the dizzy is bad it will take out the TFI. It is a best prctive to replace both with your troubles. There is also a resister between the TFI and EECIV, if it goes, it can take out your TFI and/or computer. I think it is a 28,000 Ohm resistor. I had to replace mine once.

well, since I figured out a bunch of new stuff, and thought this thread was dead... I had madea new one here (http://www.pirate4x4.com/forum/showthread.php?t=601466)

Changed the pickup in the distributor, all the wires pin out great(and pass a wiggle and tug test)

The 22K ohm resistor from the coil signal wire to pin 4 on the ECM is good as well.

haven't checked into the MAP, I guess I'm not really sure how that would affect it, but I'll test it to be sure I guess..

Thermal paste? Is that sort of like sore muscle heat treatment?

NAPA doesn't sell thermal paste...they do sell Dielectric grease.

Why would you put dielectric grease on something you are trying to transfer heat off of?

When you buy a new TFI module it comes with thermal paste because using dielectric would make a problem even bigger.

I still think there's a wiring issue somewhere, either way good luck. Maybe source another harness or something. Always nice to have a spare parts truck