hello all,first time poster and new to the forum,I have a 91 ranger xl 3.0 v6 manual trans with over 300,000 that I bought a year ago,to make a long story as short as I can my pcm died so got another one out of an identical ranger and now I'm having a weird spark issue.

The coil will only spark one time when cranking the engine,with each succsesive try it only gives off the one spark,here's a list of things of checked already-

1.back probed the pip sensor with an led tool,I'm getting proper pip signal

2.coil and ccd tfi are new but tested old coil and new one,both coils are fine

3.to rule out a bad tfi I've sent it back for a replacement but somehow I don't think its the tfi but don't know I've had new parts be bad before

4.checked voltages at the coil+tfi+pcm,everything seems to be right

5.all relays and fuses good


Anybody having or had this problem before?

Many thanks

 

There is a separate power path to TFI module for key positions START and RUN.

With key on(RUN) you can see 12volts at the TFI or Coil +, if testing
But with key turned to START that power is cut and START power is activated thru the Clutch switch or Neutral switch(NSS, automatic), this is a safety feature.

The coil would already be charged with key on, so would give 1 spark when key was turned to START, but wouldn't spark again if there was no power on the START input of TFI module to recharge the coil.

Good look here at TFI wiring: Ford EEC-IV/TFI-IV Electronic Engine Control Troubleshooting

The "S" post on the Starter Relay(on fender), which is working since starter motor works, has the same power path as the TFI START wire, both are powered thru the safety switch and usually spliced together after the switch.

In diagram for System Test #7 in the above link you can see the N/D Switch(safety switch) on the START power wire, if this is the problem you can trace wire back to the break, or cut it and add a new Splice to the "S" wire on starter relay.

 

hi ron,thanks for the tip,I'll check it out in the morning and post my findings,I have/had rigged up a starter switch to crank the engine while working under the hood,I had the wire to the "s" switch removed and my manual switch from the B+ of the batt to the terminal where the s switch goes,I had the key turned to run as well and still I got the one spark,I tried bypassing the clutch saftey switch but with no results,I will do as you suggest and see if I'm getting power at the start input of the tfi when key start is engaged.

 

The "S" wire has voltage or key wouldn't activate starter motor.

But in your above description with Remote starter button, if key was in RUN(on) when you used the button then you should have gotten spark.

The ignition switch(key switch) is what controls the power pathway for RUN and START positions.
So if key is left in RUN(on) and you manually activate starter motor(remote push button) then TFI module and coil should both have power and you should have spark

 

yes thats what I thought as well,what I get is one pulse(spark) then steady voltage(12v at coil) until the key or remote stater is engaged again,I've got a new pcm and new tfi,as mentioned before I sent the tfi back for a replacement just to rule out it being bad from the get go,some how I'm doubting it tho,I wonder if it could be these aftermarket tfi modules,it's a generic one I bought from am auto parts,as I was just finishing this reply I recieved a message from the dealer that sold me my pcm,he says the pcm needs to be reprogrammed but it don't make sense to me,it came out of another early 90's ford ranger with a 3.0 v6 and manual trans the same thing as mine,I don't understand why it would need reprogramming,I am really pining for my old point and condenser auto's from years gone by right about now,this is such a pain

 

TFI system is self contained, it can make spark and run engine without PCM connection.
PCM is only used to advance and retard the spark, it doesn't create the base spark timing.

Coil will have 12volts when key is on, and hopefully when key is in START, it is never off until key is.
The Ground on the coil is cut to make the spark, that's what points did, and that's what distributor rotor sensor and TFI do, they cut the Ground(-) on the coil to make it spark, when lobe on distributor rotor is detected.

So only difference between points and TFI is that there are no worn out points to re-gap or replace.

I think the only reason people liked the points and carb days is because they had to work on them all the time so understood them better.

Electronic systems break down so rarely that people get frustrated because they don't know them that well, because they haven't had to working on them weekly, lol.

 

lol I think your right my friend,from what I've read about the grey versus black ford tfi modules is that the tfi-iv(grey one) will do like you just explained above,if for any reason the pcm signal is disrupted or not present the tfi will take over with base timing,the tfi-ccd(black one) however relies on the pcm and can't function without it since it controls the dwell time for the coil,but this is what I've read,often what we read is different from reality.but to be honest as extremley corroded and burnt out as my old pcm was it's a wonder it worked at all