This problem has me beyond stumped and I’ve been throwing things at it hoping something would stick. I apologize for formatting and any grammatical errors I’m on my phone and irritated to the high heavens.

I have a ‘94 Ford Ranger STX 4.0l 5speed manual with manual shifting 4x4

Sometime last year it started to randomly pop up with an engine light and when I tried to use an OBD1 reader but the damn thing won’t enter test mode. Yes, I’ve read the manual and followed it step by step but after the 000 it won’t react when I hit TEST/HOLD. The light would disappear at times but then eventually return until it ended up being constantly on. After a while it started having some intermittent problems: idling funny (pulsing), ran rich, fuel pump nonstop priming, delayed acceleration that turned into it seeming to die when I floored the accelerator, mpg dropping to nearly nothing (gas coming out of exhaust bad.)

I replaced the fuel pump assembly, just replaced the alternator, and manually re-soldered the capacitors in the ECU because I opened it up and saw they were corroded. Adjusting the idle to be higher seems to help the pulsing idle situation but it’s still has all the other problems. I’m having a feeling I might have to entirely replace the ECU but am desperate for other opinions before I throw another chunk of change at it, and who knows if that will fix it.

 

Welcome to the forum

Yes it was the 3 capacitors failing, my 1994 4.0l had similar issues when that happened
But its been fine now for a few years after replacing them

But never had a no communications issue, but I always used a paper clip to put the computer into test mode and counted CEL flashes to get codes

About the only thing that commonly fails on these engine computers was the 3 capacitors, so a used one is not a big gamble if............your are willing to replace the capacitors, because that's all a "rebuilt" 1994 computer will have had done

Do you have the Part Number of current computer, It will start with F47Z-12A650 << this just means 1994 Ranger computer, nothing else
The last 2 to 4 digits are what matter, they tell you engine size, emissions and manual or automatic trans

Go here: https://www.car-part.com/
1994
Ford Ranger
Computer Box, engine<<<part
USA?
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A new window will open, you want an ECM(Electronic Control Module)
Scroll down the list to find your Ranger model, 2WD or 4x4 doesn't matter but its listed
MT = manual
AT = automatic
The 12A650 is left out because ALL Fords use/have that number for ECMs even in 2024
So it will have 1994 Ranger(F47Z) then the suffix you want to match
Select what you need
Search