I have a 1987 ranger STX that I am having problems with. I replaced the coil, module on the distributor and the computer but I still have the miss. Ther is no pattern to it that I can see. Its not like a miss but it will be running good and just for a split second it sounds like it shuts off and it runs good again. It will do the same thing driving or setting at idle. I bought this truck new in Nov 1987. I have pulled most of my hair (what hair I have) out trying to figure this out Could anyone point me in the right direction, its driving me crazy.
Thanks for any help.

 

Welcome to FTE.

i had the same head scratching / hair problem trying to trouble shoot a similar no trouble code clue, random engine stop running problem, on my 94 Taurus 3.8 L. That puppy would just randomly, smoothly, stop running, like the ignition had been switched off.

Mine turned out to be spark going missing from a faulty ECM randomly losing control & turning the ICM off, so it was a Spark going missing problem. When you pulled over & cranked the engine, it would Always immediately smoothly restart & run like nothing had happened. It could be days, weeks or months before it would do it again. Happened when I was on a downhill run to get a State Inspection. Drifted 1/4 mile to the station pulled in & noticed the Fuel pump was still running, so that was Finally my clue it was Spark randomly going missing & after having the ICM bench tested ok with heat applied & looking at the ignition schematics, the ECM went to the top of the suspect list, because it controlled the ICM. So, I pulled & inspected the ECM for overheated components or wiring, cracked circuit board or race ways, connector pin / socket corrosion, bent pins - spread sockets, bad wire crimps. Found numerous internal suspect cold looking solder joints & reflowed the worst ones but no joy. Finally opted for a 40% off Advance Auto reman Ford ECM & that Finally put things right.

Not suggesting thats your problem but it is likely to be a spark or fuel problem, question is, how to trouble shoot it without tossing parts at a milli-second happening!!!
Did the problem come about suddenly, after some event???

Scan for pending, or set trouble code clues, or for any ECM snapshot clues it may have been able to grab & store.
A bunch of beginning thoughts for consideration, let us know what you find.

 

Mine will not shut off completely just for split second and it will jerk and continue on.

 

Mine will not shut off completely just for a split second with a jerk and continue on .

 

Right & because its of short duration, is why I'm suggesting its spark, rather than fuel, which would tend to give a longer lasting pause.

 

Seeing as how this puppy has a distributor, inspect the cap inside & out for moisture, cracks or carbon tracks. Same for the rotor especially inside where it fits over the distributor shaft. They like to crack, or electrically break down in there.

If no obvious things found, try a distributor cap, plug & coil wires wet-down test after dark, using a spray bottle of water, while watching for a arcs & sparks light show from weak or damaged secondary high voltage insulation, like internal & external spark plug ceramics, plug wire insulation, rotor, distributor cap & coil insulation & listening for a change in idle speed as you spray each individually.

 

Did the problem come about suddenly, after some event, like a spark plug, coil, ignition wire work, or Damp / Wet, weather change. Does it happen more often in wet / damp weather, or on hard pull when the engine is under load???

 

It will do it sitting at a high idle or just normal driving. No pattern to it at all. It just started doing it one day.

 

Ok good feedback, the "It just started doing it one day" jogged my memory some more on my then brand new Rangers suddenly occurring random miss, that began right after the Dealers best engine tech had replaced the spark plugs, chasing another problem. It would feel like the engine had shut off & right back on, even at a stoplight idle. One day I got caught in a Louisiana style frog choaking down pour, just as beginning a mild up hill grade @ 45 & this time it Really began to lay down & i began to wonder if Id get home, yup it got that bad But it had become Really warm, wet & damp / very high humidity out. Gave Roger the engine Tech that info & he promptly prescribed & performed a "wet down test" that found #6 spark plug external insulator had cracked.

SO, begin with that as suggested above After Dark, as with some luck it could help narrow down the above secondary ignition component close inspection suspect list, like it did for Roger 20+ years ago
As suggested above, do the wetdown test after dark, one item at a time, as its easier to see electrical break down in dim light & with this vintage vehicle, you may have more than one problem point. A bunch more thoughts for consideration, let us know what you find.