[clint79]

So, I think I burnt the pcm in my bronco due to sending power down the signal return wire from the diagnostic port. Truck ran real rough not able to hold an idle afterwards and then after sitting overnight it won't restart. I checked the obvious like fuses and stuff and found no issues there. It is getting fuel pressure and spark (although unsure if the timing is right). Truck had no real drivability issues prior to the power to the ground issue. After some research I have dug up the following test for the pcm.

you need to check for B+ at Powertrain Control Module pins 1, 37 and 57. If no voltage, trace and repair circuits as needed. Check for good grounds on pins 40, 46, 49 and 60, repairing circuits as needed. NOTE: pin 46 is a sensor ground that connects internally in PCM to pins 40 and 60. If 40 and 60 are OK and 46 shows voltage,the PCM will need replacing. Check for constant5Vreferencevoltage at pin 26. If voltageis low, disconnect Manifold Absolute Pressure sensor, EGR valve position sensor and Throttle Position Sensor replacing any sensor thatallowsreferencevoltage to return. If voltage remains low with sensors unplugged, cut the Brown/White wire of pin 26 near the PCM connector. Check voltage on the PCM side of wire and if 5V now present, trace the wire to locate and repair short to ground If voltage remains low out of PCM and all powers and grounds check OK, replace PCM.

So, after I get my dmm from work tomorrow I will be testing the pcm and will update this post with my findings. Hopefully at the least this post will help others in need of testing their pcm.

 

[miesk5]

yo,
Quick review of pin-outs look good. Open EEC and look for leaky/burnt capacitors.
Capacitor Repair in a 90 5.8
Source: by dolittle (seedpress) at http://fullsizebronco.com/forum/showthread.php?t=180518
"... finally pulled the computer and, sure enough, two of the electrolytic capacitors had leaked. Not only were they shot, but the leaked electrolyte had begun corroding some pins on one of the semiconductors. The computer board is covered with a conformal coating to protect it against moisture and contamination, but the electrolyte had also seeped under or through that coating and discolored the board in places.

First I cut out all three of the electrolytic capacitors, although only two of the three had leaked. Then I tried to clean the spilled electrolyte. To remove the corrosive electrolyte I had to strip off the conformal coating where I saw board discoloration. I tried to clean the affected areas with rubbing alcohol, dilute acetone (used for finger nail polish remover), and WD-40. Also, one logic IC (integrated circuit) had three pins that were corroded by the electrolyte. I tried as best as I could to clean them mechanically.

The two leaking capacitors were 47uF 16V, and the third a 10uF 63 volt. I didn't have these values on hand, but coincidentally I had just bought a hundred 22uFs with a 63V working voltage. So by paralleling two of the 22s I was able to get 44uFs, and in series I got an 11 uf. Electrolytic caps have a wide tolerance range anyway, so I hoped that would be good enough. The one problem was all the original caps were 105 C temperature, whereas my replacements are only 85 C. But my computer is behind the driver's kick panel, instead of in the engine compartment. So, I am hoping it will work, at least for a while.

It was a pain to replace the caps! First, I found it difficult to solder the new, "paralleled" capacitors to the printed circuit board. Then, I wasn't sure how many layers the board had -- it's easy to overheat and ruin underlying layers. Finally, some of the copper pads to which the new caps were being soldered were also very close to fine-pitched copper traces. My finished "repair" is a real mess! But it seems to be working.

http://i873.photobucket.com/albums/ab293/dolittleproject/Bronco/IMG_4531-mod4.jpg

 

[Seattle FSB]

Follow-up to dolittle's issue, I sent him a good E0D PCM and it cured all of his issues. I think he spent way too much time trying to fix his old E0D PCM. :thumbup

 

[miesk5]

Follow-up to dolittle's issue, I sent him a good E0D PCM and it cured all of his issues. I think he spent way too much time trying to fix his old E0D PCM. :thumbup

yo SB,
That is VERY good of you!:thumbup

 

[clint79]

update

So worked on it some tonight. After checking the circuits I found that the pcm was indeed bad. After I removed it I found a lot of external corrosion with quite a bit inside also. Other than that i couldn't find much else except it smelt of electrical burning inside. Once replaced I will update. It's amazing to me that this truck didn't have driveability issues with all the corrosion.

 

[miesk5]

yo Clint,
Some get soaked due to leaks around weatherstrips that are damaged or worn.

 

[clint79]

yo Clint,
Some get soaked due to leaks around weatherstrips that are damaged or worn.

Was planning on sealing with silicone when reassembling. Just got to find an pcm now...

 

[clint79]

Pcm is replaced and truck is running great. Fuel pump used to run constantly and only cycles now like its supposed to. It seems a little smoother and responsive too. Definitely needs a tune up, but glad the issues resolved.