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I've got a stock '94 Civic LX (D15B7) at about 140k. About a year ago my ECM stopped grounding the main relay for the fuel pump when it is especially humid outside, solid MIL. So after my painstaking diag I picked up a matching ECM (37820-P06-A52) for 20 bucks at a junkyard and it works, except for the fact that it's stuck in limp in mode, so it's pretty much only good for getting to work on time when my other ECM is acting up.

When I tried to pull codes on the junkyard module the MIL stayed on solid, but my SRS light flashed steadily. I don't know if jumping the service connector for the MIL causes the SRS to flash, but a solid MIL while trying to pull codes would be an indication to me that the primary IC, which I believe is the OKI M66207, is toast so it's only running off the secondary, limp in, IC.

What my goal is, is to not spend several hundred dollars on a reman when I know that I have the parts and skill to cannibalize and make one fully functional, I am just lacking the diagram on the internals. I would think swapping the M66207 would probably work, but I prefer to not just start swapping IC's and caps randomly. If anyone can tell me either, what in the "good" (working except for in humidity) causes that issue, or what in the "bad" (junkyard/limp in) ECM is causing it to be stuck in limp in mode I would be greatly appreciate it.

I've been researching this for ages and the only thing I've really found about being locked in limp in mode like that is if you fudge while chipping them, which isn't the case.


Any and all help is well appreciated,
James

 
Rep Power: 518

Biggest issues I know of is bad caps on soooo many electronic products from ECMs to TVs to motherboards worldwide.
Electrolytic capacitors that leak acid can damage surrounding circuits and components. Been a problem for decades now.

Replacing all the caps is a starting point, along with cleaning up any residue they may have left. If you are lucky that may be all it needs.

 
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Yeah, that was my first thought, then I cracked it open, and it is immaculate. There is no residue, no corrosion, no discoloration, it looks like a brand spankin' new ECM. Ah screw it, what's 250 bucks, if I can get one through O'Reilly around here, just going to have to wait a while

 
Rep Power: 518

Send one of yours in for a rebuild? Check your local NAPA and other quality parts suppliers for this service.

 
Rep Power: 204

just a thought but caps don't have to be leaking to be unstable....



maybe when you have some time soak the entire board in 100% isopropenyl and scrub it with a qtip perhaps there's just some small bit of electrical conductive material causing a bridge somewhere on the board...focus on the IC legs.

Check the solder for broken connections too... like this

 
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I'll try that Zone, worse case I'll order a reman for the time being, then I can play around with these two without fear of toasting them.

I didn't notice any bulging or misshapen caps anywhere, but I'll give that a shot too Stock.

Thanks much

 
Rep Power: 204

Hey, I was reading through your original thread again and what exactly was the problem with the first ECU? Your MIL light was on all the time or the car wouldn't start? I was wondering that you couldn't just use another ground location for the PGMFI. Did you investigate the fuel relay for problems because they are a known problem. Also I watched a rather entertaining youtube video of a guy frankensteining a P06 ECU so he could 'chrome' tune with it and it seems like it was a popular thing to do with that ECU. Have you held both of them up next to each other (MoBo) to make sure they are actually the same?

 
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Stock, the issue with my original ECM is that when it is humid it fails to activate the main relay (for the f/p). When it isn't humid it works just fine. All the grounds I can find have been cleaned and replaced if need be. If I put a different ECM in it will work 100% of the time regardless of weather. Both my ECM's come out of their casings and are identical down to the last detail except for manufacturer. I can get another PCM but I'd prefer to just repair one of mine with parts from the other.