Computer Problems

[Billi]

I was having problems with my 93 4.0l, Idle surging, highway surging, no power when cold. Fuel filter/pump fine, no codes.
Long story short, It turned out to be bad capacitors on the computers circuit board. I know I saw something about this online somewhere else, so I pulled out the computer, pulled off the cover and sure enough, two of the three electrolytic caps were swollen and had fluid stains on the board. I purchased new ones at radio shack and replaced them. Total cost $3.60. Truck runs like new now. I'm going to try to get a better write up done with some pics.

 

[Big Jim M]

What a wonderful post..thanks.
Big Jim

 

[Earl43P]

Indeed.

I'm anxious to see the photos.

 

[MAKG]

You know, MOST failures on the PCM end up being power transistors. They get fried by shorts to ground or low resistance in actuator circuits. I wonder if anyone has tried to change one. Should be fairly straightforward.

As long as one uses a heat sink....

 

[Billi]

Hey I'm sorry I never got around to posting some pics, but my "non-ford" has been eating up my time. Haven't have any more problems since the repair. I'm not saying thsi si the fix-all for all computers but it worked on mine.
Electrolytic capacitors are round can shaped component with a plastic sleeve on them. Inspect them closely, the exposed metal top should be flat, and not have any sort of residue on it. Look around the base of them as well if they are leaking there will be discoloration or even an oily residue around the base. If you have any bad ones, I would replace them all.
Electrolytic are one of the few components that do degrade with age, and if they are left un-powered for a very long time they will fail also.
For replacement the info you need is on the side of the capacitor. Write down the voltage, and the capacitance value (uF). When you go to get replacements, the most important thing is that the uF number is the same, the voltage can be a little higher, but not lower. Capacitors do vary in shape and size some, but as long as they are about the same it should be ok. When replacing capacitors be aware electrolytics are polarity sensitive, make a note of how the come out, the polarity is on a stripe on the side of the plastic jacket.
I'm not going to teach soldering, but if you haven't done component replacement on printed circuit boards, then I would suggest practicing on some other old broken pc board first. If you have any doubt about your ability to do it without damaging the circuit board, find some one else to do it.
I hope maybe this will help someone else. I bought my capacitors at radio shack.

 

[HYPED_87]

well check it out i recently rebuilt my 2.9 it ran good before hand but i gotta see wut i can mess up i guess. I ported and polished the heads upper and lower intake manifolds put headers on it and a bigger tb also went with the msd coil and the accel module with accel plug wires and a # hotter on the spark plug but before i tore it apart i eliminated the egr system along with the mechanical fan and put the electric fan on it ran beautiful throttle response was so crisp and i didnt get any codes from that so after i put it all back together with the mods i had done it was runnin like shit missing under 4000rpms and i was pulling codes all kinds of codes [egr,closed loop mode,tps sensor] so could the capicitors be bad on in my computer would that do it or is it a ground issue....info on this would be highly appreciated and ill be glad to help anyway i can.....THANKS

 

[Bob Ayers]

A few years ago a friend of mine had a Porsche 924 that was giving him trouble. Intermittently, it would shut off on him. Luckily, one Saturday, it stayed "dead" long enough for me to diagnose the problem (using a DVM, and my scope). The problem was the DME (Porsche equivalent to PCM). I then
proceeded to take the DME apart, and do further diagnostics. The problem I found was in a 5V regulator circuit, which was used for the digital components. The 5V regulator circuit was made up of discrete components (transistors, resistors, capacitors, and a zener diode). I upgraded this circuit with a linear 5V regulator, which had much better characteristics.

Here is a photo, showing my "upgrade":

 

[Bob Ayers]

Hey I'm sorry I never got around to posting some pics, but my "non-ford" has been eating up my time. Haven't have any more problems since the repair. I'm not saying thsi si the fix-all for all computers but it worked on mine.
Electrolytic capacitors are round can shaped component with a plastic sleeve on them. Inspect them closely, the exposed metal top should be flat, and not have any sort of residue on it. Look around the base of them as well if they are leaking there will be discoloration or even an oily residue around the base. If you have any bad ones, I would replace them all.
Electrolytic are one of the few components that do degrade with age, and if they are left un-powered for a very long time they will fail also.
For replacement the info you need is on the side of the capacitor. Write down the voltage, and the capacitance value (uF). When you go to get replacements, the most important thing is that the uF number is the same, the voltage can be a little higher, but not lower. Capacitors do vary in shape and size some, but as long as they are about the same it should be ok. When replacing capacitors be aware electrolytics are polarity sensitive, make a note of how the come out, the polarity is on a stripe on the side of the plastic jacket.
I'm not going to teach soldering, but if you haven't done component replacement on printed circuit boards, then I would suggest practicing on some other old broken pc board first. If you have any doubt about your ability to do it without damaging the circuit board, find some one else to do it.
I hope maybe this will help someone else. I bought my capacitors at radio shack.

Electrolytic capacitors also have a temp. rating. The better grade electrolytic capacitors are rated at 105C, which should be used for automotive applications.

 

[jrkeef]

Hey Bob, I just found this site and registered today. I think my PCM problem is too terminal for a fix. I searched for weeks for the correct PCM - F37F-12A650-VB unsucessfully. One of my employees found a PCM in a junkyard out of a similar 4.0L Ranger and we stuck it in and the truck runs, just not well. I am wondering if anyone has resources to find the correct PCM. I understand the Standard Motor Co. part # is
EM4417 and Borgwarner #ECC 286. Alternatively I had installed a "CHIP" on the original PCM years ago. Assuming the CHIP didn't fry with the computer would it make sense to put it on the computer I got from the junk yard and see if it helps the fuel - air mixture. This is a 1993 Ford Ranger Spash 2wd Automatic 4.0L that I bought new in 93. I can't just let it fade away.

 

[MAKG]

You can buy rebuilt PCMs from an auto parts store. You have no idea if a junkyard PCM works; it's extremely difficult to test in the field.

They aren't THAT expensive for EEC-IV. Probably well under $200.

 

[Bob Ayers]

Hey Bob, I just found this site and registered today. I think my PCM problem is too terminal for a fix. I searched for weeks for the correct PCM - F37F-12A650-VB unsucessfully. One of my employees found a PCM in a junkyard out of a similar 4.0L Ranger and we stuck it in and the truck runs, just not well. I am wondering if anyone has resources to find the correct PCM. I understand the Standard Motor Co. part # is
EM4417 and Borgwarner #ECC 286. Alternatively I had installed a "CHIP" on the original PCM years ago. Assuming the CHIP didn't fry with the computer would it make sense to put it on the computer I got from the junk yard and see if it helps the fuel - air mixture. This is a 1993 Ford Ranger Spash 2wd Automatic 4.0L that I bought new in 93. I can't just let it fade away.

First thing I would do is scan for codes with the computer you have in your truck now.

 

[MAKG]

Yeah, that's probably very good advice.

Lots of people blame everything up to and including the weather on the PCM. Computers can only create decent output given correct input. If your chip lies about that, it could be a problem (some chips modify the settings tables, others mess with the inputs -- the latter should be used only as doorstops and mild parts heaters).

It's VERY hard to imagine the PROM itself as frying. Most PCM problems cook one actuator circuit (power transistor) or one voltage divider, or fail in voltage regulation. And ALL of these happen not because the parts wear or rot, but because faults elsewhere kill them. Shorts to ground kill power transistors. Shorting VREF to ground can burn out power regulation (perhaps the capacitors mentioned in this thread). And so on.

Think of this as running self-tests, not acquiring codes. No code confirms any fault. They must ALL be confirmed independently for successful troubleshooting.

And you simply cannot distinguish PCM faults from actuator or sensor faults, or from wiring between them, even WITH codes (alone), let alone without them.

 

[Bob Ayers]

Disconnecting the battery with the engine running is probably the best way to destroy a PCM!

 

[jrkeef]

Thanks for all the replys. The original PCM is definately fried. I had my local auto parts shop send it out to the shop they use to rebuild PCM's and they sent it back saying it was beyond help. I have been to Ford and all the auto parts outlets in Lafayette looking for a new or rebuilt PCM. I have search online dealers and I have been to eBay. When I found this site specific for Rangers I though I would give it a shot. The junkyard find PCM that is in it will allow it to run and I drive it daily. It has no power and no gas milage - about 10MPG. I don't have equipment to check codes or reset. I am still considering putting the old performance chip on the junkyard PCM to see it that helps. Unless the chip is what fried the old PCM it damn sure can't hurt. Meanwhile I posted a parts needed thread on the classifieds here.

 

[MAKG]

It won't help.

And I'm always amused when OBD-I owners claim they don't have the equipment to check codes. Is there a paper clip shortage in Louisiana?

See the tech section for instructions and diagrams.