Caps leaking on 1990 E250 ECU

Doubt whether you'll find too many people interested in the subject on this particular group. Electronic topics here tend to be limited to proper usage of a DVM to measure battery drain... Trying to troubleshoot a problem with a shorted sensor input I desperately searched for a schematic of the PCM in one of my vehicles, coming up with zilch. So it's great to know someone who deals with those for a living. As for your leaking caps, those cheap aluminum electrolytics don't last -- usually don't leak, but rather dry up and increase their series resistance a hundred fold within a few years. How badly that affects performance depends on what the cap is doing in the circuit. If it's in some sort of a switching power supply, that would be the worst. The one you showed seems to be pretty well marked. Why not simply replace?

Hey there. Thanks for the reply.

Yup, that's the plan for tomorrow when I'm back in the office. I will remove the caps, lift that one resistor, clean up underneath everything, check for shorts, clean up leakage, etc., etc., then replace the affected components with new units. I was just posting here to get some discussion going on the topic.

This also gave me a chance to read up on all the EEC-IV information out there. Wow. You guys have been busy! :) I love that little J3 test port thingie. DSM ECUs have absolutely nothing of the sort. Will have to hook up to it with the ol' logic analyzer to see what's going on. Or just hit Moates.com and buy their inexpensive adapters and stuff. Moates is on top of that pretty well.

Thomas Dorris

"twdorris" wrote

I guess 1990 was too early for the "stolen formula" escapade?

I was always "told" that there was something along those lines much earlier than the incident the Wikipedia article references. I'm pretty sure a similar thing was going on back in the late '80s/ealier '90s. The caps in question on this particular van ECU have a date code of about mid '89, FWIW.

Thomas Dorris

Oops, sorry. Moates.net.

Thomas Dorris

EEC-IV is very old news. Very primitive by today's standards and out of production for 12 years now. Its main advantage is reading diagnostics with nothing more than a paper clip and a test light. Incidentally, what in the world is DSM?

Rather than re-invent the ECU, did you scan it for codes?

Al

Who said anything about re-inventing the ECU? It just needs to be repaired.

That leakage residue is acidic and will eat everything around it. In fact, it's already doing a pretty good job of that on my ECU as you can see from the pictures. It can also become conductive and introduce shorts that can cause all KINDS of other problems, some of which are catastrophic to the ECU.

So it must be cleaned up or else it will cause problems. There's absolutely no ifs ands or buts about it. We've seen it for years on the DSMs. Although the caps on the DSMs are typically much worse that these it seems.

Anyway, to answer your question, yes I did try to scan it for codes. But the code reader (an AutoXray 6000) just kept saying "No communication". After that, I decided it was time to pull the ECU because I had no other way at the time to confirm whether the ECU was working at all or not.

Thomas Dorris

Thanks, but of course I'm aware of its age. There is one other advantage I can think of to the EEC-IV ECU platform...it's installed in my van. :) So that's the platform I'm going to focus on, old or not.

Turbocharged Eagle Talons, Mitsubishi Eclipses, and Plymouth Lasers produced between 1990-1999. Not exactly a "modern" platform either, of course. But that doesn't mean everyone is scrapping them either.

Thomas Dorris

I thought I'd follow up on this. I replaced the caps and did some slight rework on that one poor resistor. One lead was *just* about to fall off. The whole thing looks much better, but the van still refuses to start. I didn't expect this to cure the no start problem anyway. The leakage just didn't look severe enough yet to be causing it. But it was definitely severe enough to require attention.

I'll keep digging and I guess I'll update this thread with the findings.

Thomas Dorris

Your ECU may or may not be responsible for the no start. As usual, check for spark and fuel pressure first. If memory serves, there will be spark, at fixed timing, even if the ECU can't control ignition. If you have spark and correct fuel pressure, it's time to check whether the injectors are firing.

Incidentally, with EEC-IV you don't need any scanners to read stored codes or to perform on-demand diagnostics. You put the ECU in diag mode by grounding the single pin connector. You read the codes with a test light connected from B+ to the STO pin in the 6-pin diagnostic connector. Plenty of information about the details all over the web.

Thanks, Happy. But this all started as a standard diagnostic procedure. Checked for spark, got none so I started to track back to components that might be involved. It came down to the TFI module and the ECU. Since the ECU was easier to reach and I had an interest in it anyway, it came out first. The TFI modfule is next. I just gotta figure out how to get to that one bolt holding the distributor in place so I can rotate it out before I can even attempt to get the module off. I've never dealt with a distrubtor before, so this has been a bit of a learning curve for me.

But the whole point of this thread was simply to discuss the potential issue with the ECU. I was first curious whether others had seen this and then I interested in making people aware of this potential on these old, forgotten platforms.

Thomas Dorris

Just to finally update this thread. The problem was a malfunctioning MFI relay (powers the ECU). But the problem wasn't just that the relay stopped working. I wish it had because then the problem would have been more obvious.

But nooo. The relay was working *just* enough to keep stuff powered up, but then not actually function when you crank the engine. It had just enough voltage drop that it really confused the ECU and apparently just about everything else too, including me. :)

Oh well. Lesson learned. I enjoyed the exercise anyway. I wanted an excuse to dig into this van a little deeper and that's what I got.

Thomas Dorris