ECU Caps...

[skelly]

Hi - I found the following quote in a thread from a few years back and wanted to ask a follow-up question without reviving the old thread:

Most often the acid from the caps attacks the fuel pump circuit first.

The tell-tail for this is a rapid clicking sound from the dash area while the car is running , this is the fuel-pump relay cycling its butt off , trying to keep electricity to the pump constant.
Thats a good indicator that time is short.

My `90 exhibited this behavior (FP relay clicking rapidly) last night. It's the first time I've experienced it, but I've only ever started this car a few times as I just recently acquired it. The car has been otherwise sitting with a dead battery in the previous owner's driveway for more than a year.

My question(s) are: is it too late to save the ECU once this state has been reached? I already have a capacitor replacement set in my posession and can replace the caps as soon as this afternoon, however I won't be able to get the ECU out and open it up for inspection until that time. Is the circuitboard irrepairably damaged once the relay starts flipping out like that? Is the relay doing that because it relies on the cap to be functional and it is failing, or because the cap has caused damage to the surrounding PCB?

I'm just trying to decide whether I should begin shopping for a replacement ECU before I head home today. I am experienced in electronic tech work, but that'll only help me if the board is still salvageable at this point.

Your input would be appreciated!

- SK

 

[DSM90AWD]

Hi - I found the following quote in a thread from a few years back and wanted to ask a follow-up question without reviving the old thread:



My `90 exhibited this behavior (FP relay clicking rapidly) last night. It's the first time I've experienced it, but I've only ever started this car a few times as I just recently acquired it. The car has been otherwise sitting with a dead battery in the previous owner's driveway for more than a year.

My question(s) are: is it too late to save the ECU once this state has been reached? I already have a capacitor replacement set in my posession and can replace the caps as soon as this afternoon, however I won't be able to get the ECU out and open it up for inspection until that time. Is the circuitboard irrepairably damaged once the relay starts flipping out like that? Is the relay doing that because it relies on the cap to be functional and it is failing, or because the cap has caused damage to the surrounding PCB?

I'm just trying to decide whether I should begin shopping for a replacement ECU before I head home today. I am experienced in electronic tech work, but that'll only help me if the board is still salvageable at this point.

Your input would be appreciated!

- SK

The acid from the capacitors etch at the traces on the board. Depending on how bad the damage is (which you won't know until you open it up) it may just be a quick CAP replacement.

Mine went with the same tell tale and luckily the damage to the board was minimal. So was just a matter of cleaning it up, replacing the CAPS and recoating the traces (Jeff Oberholtzer did my work btw).

 

[oldman]

pm "steve", the ECU expert/wiseman. He has fixed two 90 ECUs for me already.

 

[skelly]

Okay, thanks fellas.

- SK

 

[skelly]

Sure enough, two of the three caps had just recently began to leak, possibly brought on by the rising temperatures during the day (I haven't been driving the car; it's just sitting parked while I do all the major maintenance stuff.)

The electrolyte had oozed its way down beneath one of the surface-mount noise-filter capacitors and started some sort of carbonization reaction beneath it. I actually let my dad remove that cap as he's much more skilled at working with SMT soldering since he's been doing it for 40-some-odd years. He can use two soldering irons and grab the part from either end with the iron tips and pop it off the board fast enough that the heat doesn't have a chance to damage the component. Forget that!

Afterward, I cleaned the board up with alcohol and scraped out all the carbonization under a microscope to make certain there is nothing conductive bridging the traces where the SMT cap was. After that was a quick re-install of the replacement caps. We left the SMT cap off because there are two others bridging the same two traces and we figured they could likely handle the filtration without the third one that we removed. That concluded last night.

This morning I reinstalled it and fired her up - back to normal operation (no flippity FP relay), and back to my original problem which inspired all the work I'm doing: a faltering idle.