Stalls - will not run with MAF plugged in.. Solved

[schekan]

First, Admin feel free to move to proper area, I wasn't sure where to post this. But wanted to give back to the forum I have used so often. My story may help others. I have attached photos as well.

My story is , 4.0 94 Ranger XLT. Most reliable truck I have ever had all of a sudden stalled, then had a hard time starting. Acted like it starving for gas.
So i did the obvious and replaced the fuel filter and pump. No change.

I ran the diagnostics with my code reader. And it had MAF codes 157 and 158.
I hit the junk yard, found a MAF sensor. Did nothing to change the stalling issue, truck was not drivable. It would stall seconds after starting. So for the hell of it I unplugged the MAF and it ran. Not the best but it ran. And from the forums I found out that is because it runs in a closed loop when there is a complete failure of a major sensor.

So I bought a new MAF and still no change. It was really pointing to the PCM, I removed the PCM and did a visual. I am an IT professional and have been working on PC's for 20 years, I can spot a bad MB by looking at the Capacitors pretty quickly. Well I saw no swollen tops, or leaking tops. So I put it back in and checked every ground and even ran wires directly to the MAF sensor. And still nothing.

So I decided to have a closer look at the PCM. I pulled both covers, got a really bright LED work light and a magnifier. And was amazed at what I saw. There was one Cap that blew out the bottom, and a diode that was crusty green. Not good. So I ordered a reman on Rockauto and it solved all issues. It runs like a bear again.

I wanted to share photos of what a bad PCM can look like with a visual inspection. Hope this helps someone, even if it's not the same symptoms if you suspect the PCM and see something like this then it is definitely bad.

 

[Denisefwd93]

I've read so many discussions on replacing PCMS and seems like you're one of the first to get the correct replacement on the first shot! congratulations!

 

[schekan]

Well thanks, As for "first shot" It took a bit to get to this conclusion... lol
But I wanted to show what to look for in a bad board. And boy it must have been failing for a while. I had some minor issues for months with a stutter here and there. Now it is like a new truck...

 

[Bird76Mojo]

I see a resistor and a capacitor...




GB

 

[Effieman]

How do you open the computer, just screws?
Haven't looked at mine YET, but all the odd running issues I've had for the last few years seem to point to the ECM. And I think a new one from rockauto is cheaper than taking the truck in for someone to troubleshoot.

 

[Vincenthdfan]

Excellent catch and even better...thanks so much for coming back and reporting your find/fix!

It helps others (such as myself!) when caught in the same frustrating situation.

I seem to remember RonD mentioning several times that he's found capacitors leaking in the computers before...all good stuff to remember.

 

[schekan]

Yes, just two screws i believe. And the top and bottom cover come off.

 

[schekan]

Also I had some issues with this truck for a while. It would be difficult to pull out on a hill sometimes, hesitated, almost like a dead spot in the throttle. Random rough idle, little things. The highway i drive to work each day has couple pretty big hills a few miles long, I could never make it up in 5th gear without having to drop to 4th. Now with the new PCM, all those issues are gone and I can actually maintain speed and accelerate a bit on that same highway. The truck runs better than ever. It must have been failing for a while and finally crapped out. I got mine at Rockauto as well. IT was cheaper that anywhere else.