Hello, everyone. I'm new here so if I have done anything wrong or am in the wrong place please let me know. I am having a hard time figuring out an issue on my Ranger. 1994 Ranger 4.0 V6. It was running fine, then one day it wouldn't start. Engine will not start when it's cold. I can force feed it some gas or starting fluid and it will start and run. Once started it idles very rough and once hot it can restart. If I try to drive it, I get black smoke when giving it gas(50% throttle or more). I have tried to pull the codes but cannot get anything. I tried doing the CEL flash count and the light just stays solid. I purchased a OBD1 scan tool and cannot get anything to pull. I got it started and hot and unplugged the MAF with no change to the running condition. So I decided to replace the MAF but that didn't help. I have checked fuel pressure, which is at 35psi at idle and goes up with the rpms. I have tested the TPS and it reads fine, .8V closed and 4.8 WOT with smooth increase throughout the throttle range. I have also noticed that it cuts out over 3/4 throttle. I checked for vacuum leaks by visually inspecting them and spraying all the lines and manifold gaskets with brake clean and there was no change in the idle. I'm assuming there is a sensor issue, but want to avoid just blindly changing things. Any suggestions are greatly appreciated. Thank you in advance!

 

Welcome to the forum

While its a pain to get at I would pull the computer and have a look inside it
Its in the engine bay down low on drivers side inside firewall, you will see the main wiring harness and the 60-wire connector at an up/down orientation
Google: Replace 1993-94 Ford Ranger ECU Computer and Location

Watch the video

Unhook battery!!!!
I got the lower nut off with a swivel and long extension
I also removed cruise control unit(well moved it over), and removed the large round connector on firewall, just 1 bolt

Here's why you should do this now
There are 3 barrel type(radial) capacitors that will fail after 20+ years, they leak and effect several systems in different ways so there is no "one thing", but no start cold and rich running are two symptoms of this leaking issue

I had to do my 1994 4.0l computer a few years back because of this, went thru several "non-fixes", lol
It you can solder or have a friend who can solder it's an under $5 fix to replace these 3 capacitors and not hard to do
Computer with covers off looks like this: Ford EEC-IV

You can see the 3 blue capacitors, they have different values so take pictures of what goes where, and capacitors have a + and - side that's important as well
Replacement Capacitor voltage can be higher but not lower, say you have a 16uF 25v old cap you can use a 16uF 50v to replace it, won't effect anything, but don't use a 16v
And capacitor can look OK but one wire is broken, corroded underneath, picture of mine, just wiggle cap and it feel over, lol:



My 1994 has been running great since the replacement, do all 3 regardless of condition when computer is out
Newer Black capacitors have a longer life that the blue ones, but either can be used
The white "speckles" on the circuit board is a clear spray on seal Ford puts on after boards are assembled

Once capacitors are out clean up the leaked fluid as best you can, it cause shorts