1990 stx no start, diagnostic help

[BuckinRanger]

Ladies and gents,

Long story short I got taken on a truck I was planning to user as a donor. Ive searched the forums and tried suggestions for a couple weeks; Need help to get it running, have a few questions...

The truck: 1990 stx 4.0l manual.

the problem:No spark, can't hear fuel pump, no CEL, won't start on starter fluid, code reader shows nothing.

Fuses all check good. I've checked grounds on ecm all good except pin 46 (signal ground) which I believe is correct unless the engine was running?

Am I missing a possible ignition power issue?

Will the engine fire with the ecm unplugged?

Any input greatly appreciated!

 

[BuckinRanger]

Side note, came with replacement ecm, results same with both ecms

 

[PetroleumJunkie412]

It sounds like the ecm is completely shorted, or not receiving power.

Removing ecm from ford engine is same as if you would remove your brain - you're not firing up without it.

 

[RonD]

1990-1994 4.0l Ranger has a separate spark module, EDIS-6, so would spark without engine computer, but no fuel

Should be 4 wires at the coil pack, one will be a Red wire, test if it has 12volts with key on, if not then ignition switch is not working
Or its fuse in engine bay fuse box is bad, usually Fuse #1 50 or 60amp fuse

If the CEL is not coming on with key on then computer is not powering up, which would also point to ignition switch or its fuse

 

[BuckinRanger]

Thankyou sir. I will report back findings

 

[BuckinRanger]

I've got power at the coil on the red wire, fuse to fuel relay is good and has power, ignition fuse is good and has power. Still no cel or codes on tester. Coil appears to have been replaced. Do you know which signal wire should light up on ecm if it's getting power from ignition? Or any other thoughts?

 

[BuckinRanger]

Any idea where this plug should go? To left of steering column very short

 

[BuckinRanger]

Possibly worth noting at well, battery light and abs do kick on with ignition

 

[RonD]

If you have 12volt at the coil pack with key on then engine should start by adding fuel manually, 50/50 test, computer is only used for fuel injection not spark in pre-1995 Rangers

Pins/wires 37 and 57 at the computer should have 12volts with key on, its from the EEC/PCM Relay at engine fuse box
You can also test for 12volt at IAC Valves red wire, it gets 12v as well from EEC Relay, and easier to get at

On the OBD connector the Self Test OUT is the Ground for the CEL in the dash, the CEL bulb gets 12v, like the Battery Light and ABS bulbs, with key on, and the computer then grounds the CEL to turn it on, that ground runs thru the OBD connector, i.e. the self test OUT slot
So you can test the CEL bulb with key on and then grounding that self test out slot
OBD connector lay out here: https://www.therangerstation.com/tech_library/OBD_I.shtml

Thats just to see if CEL bulb is burned out or working



No that connector doesn't look familiar, need to see the wire colors on the back to maybe find out what its for
Near drivers door could be "power group" option, i.e. power windows and door locks

 

[BuckinRanger]

Thanks for response. Based on this test, CEL bulb is burnt out. So could it be as simple as a crankshaft sensor and a bad fuel pump? I feel like obd should be throwing some code on tester? Truck is only 31 years old lol

Also, see attached pic of wires but this is all manual car so you're guess is probably correct.

 

[RonD]

You can put a test light, 12v bulb, between battery positive and the Self Test OUT slot, it should light up with key ON, if computer is powering up

Crank sensor would cause no spark and no fuel injectors, so do 50/50 test to see if it fires, if it fires then crank sensor is fine

Fuel pump issue would cause no start but not no spark

 

[BuckinRanger]

I dropped it off at spark chaser. Thanks for help I will report back with what I missed.