Working on a 1994 Ford Ranger, 4.0L, automatic, 4x2, standard cab. Truck will start, then stumble and eventually die – takes about 5-8 seconds from start to stop.

When running cold, like when you just leave in the morning, the truck will stumble and occasionally blow puff of black smoke out the tailpipe, making me think its over-fueling. Once it gets warmed up, it will idle fine and drive, which makes me think ECT or the like, something temp related.

Installed vacuum gauge on intake and fuel pressure gauge on rail. Vacuum is good when starting (25mmHg+) and drops while stumbling/dying.

On initial key on, fuel pump runs, rail pressure rises to 40 psi, then drops to less than 5 psi over about 20 seconds if you don’t start the truck. Disconnected the pressure regulator return line and plugged, key on produced 60 psi at the rail, and it held, no drop at all while observed for a minute or two This made me think pressure regulator until the next step. Reconnected the pressure regulator, started the truck, 40 psi at key on, 35 psi while truck ran and died, steady. After truck died, gauge showed 35 psi and held for several minutes (had to leave, but it was at 35 when I left).

I have not replaced any of the sensors, as I am just getting started into he troubleshooting (just got the truck a month ago).

I’ve searched the forums and found similar issues with a swapped FPR or ECT or even MAF meter solved it, so leaning towards the ECT and FPR right now.

Would appreciate any thoughts, experience, or suggestions that might help accelerate the repair process.

 

Welcome to the forum

I also have 1994 4.0l but manual and 4x4

First thing I would do is to pull out the computer
I chased my tail on odd running issues a few years back, turns out 2 of the 3 capacitors had failed, replaced all 3, under $5 fix
The 3 Blue capacitors in this picture: Ford EEC-IV
They fail after 20+ years so need to be replaced regardless, so not a waste of time, used the higher temp black ones as replacements
It never set a code, I even force set codes(i.e. unplugged sensors) and it did report/set codes for those, caps were still the issue for poor running

Computer is in the engine bay driver's side "in the firewall" down low right in the corner sitting up and down not sideways
Has a larger 60 pin connector held on by a bolt
Then a cover holder with a nut at the top and bottom
PITA to get at, but worth it to take this off the table or find out it is the issue

You can replace hundreds of dollars in sensors and parts, and still be back at square one, lol

Clean the MAF sensor, once a year
Run a can of Seafoam in gas tank, once a year
Failing ECT sensor will usually set a code but not always, so can be replaced, its the 2 wire one, single wire sender is for dash temp gauge

As said above you can unplug and sensor and see if computer sets a code for that, this will usually indicate sensor is OK if no code is set when it was plugged in, not always but still an easy test

 

Thank you very much Sir, will start there and report back what I find.

 

Found a picture of mine




Just touched the Cap at the bottom and it fell over, lol
Top right was corroded on the underside and one leg disconnected
Top left was still OK but replaced it anyway

The white speckles are in the Clear Coat they spray on both sides of the circuit board to seal it, just FYI
You need solder wick to clear the holes for the new Caps, a solder sucker just won't do it

Take pictures so you know which one goes where, and the GROUND side
You have to match the uF value exactly
But you can use a Higher Voltage
So a 16uF 16v can be replaced with a 16uF 50v, but never use a lower voltage

 

Got the computer out, all three of those caps had bulged out the bottom, leaking on the leads, and two of the three had one lead corroded through - just leaned over like the one in your picture when I put even a slight amount of pressure on them. Found replacements on Newark, should be here this week, fingers crossed, I'll get them in and see what she does!

I'll post an update after I get it all together and turn the key.

 

Got the parts in and swapped the caps, reinstalled ECU and she fired right up and idled. There is a little bit of surging at idle, but before replacing the caps, it wouldn't idle for more than about 2 seconds.

Thanks again for the help RonD, your recommendation was exactly right!