Looking for some help trouble shooting an intermittant no spark condition on my 93 5.0l with speed density EEC IV. Thanks in advance for any suggestions........So far, I have good batt voltage, engine turns over, power to the coil, and only sometimes spark. I have a spark tester connected between the coil output and an engine ground. When I have spark, the motor runs well. It will die on occasion, but usually runs fine until I shut if off, then it will only fire some of the time. I have checked cap, rotor, wires, plugs, and swapped in a used TFI. Same thing..... Removed the computer, cleaned connections, looked at ground wires etc... When it has no spark, it will sometimes fire once as the the key returns to the run position????? I have another distributor to try, was thinking it may be the stator? Or ignition coil? Just seems as though coils usually work or not. (Plus its never the easy part to change is it...haha)

 

Yes , coils can and do give those type problems. If you have voltage to the coil and can determine that the negative side of the coil is being pulsed and you have no spark, guess what , IT'S THE COIL.

 

back to the drawing board. Installed a new coil.......same intermittant spark. Any other suggestions?

 

OK Since we couldn't be positive re the coil, Can you verify that the pulsing that triggers the coil via the ign module is constant .
I tried to do some homework on this system and this is the way it is supposed to work.
There is a hall effect switch in the distributor. This signals what is referred to as a PIP (profile ign pickup) signal to the TFI module which in turn sends that signal to the PCM. The PCM computes a Spark output signal and sends it to the TFI module which triggers the coil. The spark output signal contains the timing of the spark.
If you know how it is supposed to work now you can check each stage of the pieces involved.
Sorry for the confusing info previously sent. There is a shutter wheel in the distributor that works with the Hall Effect switch to generate the PIP signal.

 

Ok. I'll check those things. Thanks.

 

Installed a distributor out of a 5.0l H.O. that I had kicking around. Also put in a new ignition switch. Visually inspected wiring, cleaned up some grounds. Same problem. When testing for a pulse to the coil I get nothing. Still have batt voltage on one side though. I'm going to perform the TFI diagnostic tests, then look at the 60 pins going to the computer for proper power, and ground. I'm determined to solve this.......starting to p*ss me off!

 

Is it a good idea to remote mount the TFI? Do they fail regularly if mounted on the dizzy?

 

At one time had a whole fleet of them and never experienced any heat related problems. Ford did move them onto a remote heat sink due to heat problems. From my experience with them if you put the heat sink compound behind them when mounting, they never gave me any trouble. Different "maintenance persons" broke the tab that held the plug in place otherwise they gave little trouble.

 

Something additional that may be of help, if the SPOUT circuit is open the TFI Module will fire the coil without the timed spark from the PCM. That is how you set base timing anyway- Spout disconnected. If you were to leave the spout disconnected and still had the cutting off problem it would seem to be confined to the TFI module , the hall effect switch in the dist. or the connections. You already replaced the coil. If I come across any addl info , will post it.

 

Problem solved! It wasn't a component, but rather a connection. There is a relay that is powering up the EEC. It had a corroded connection. Cleaned up the terminals and it now consistantly fires up. I think I'll replace the relay as well. Good to have gone thru the whole system anyways. Gives me a better idea for next time. Thanks for the help.