Rev3 94 ecu issue

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Rev3 94 ecu issue

Post by m122794 »

A couple of times over the summer my engine decided to die when pulling to a stop at a junction and I didn't think too much of it. I just restarted and all seemed fine but I've also been having various random lights coming on in the dash although the car has seemed to work OK.
As the car is off the road for the winter I thought I'd have a look at the Ecu and three of the electolytic capacitors were just beginning to leak so I ordered a full set of new ones and replaced them all. The car now starts and idles perfectly.

I'm aware the rev1 and 2 ecus are having issues but it looks like the later ones are beginning to go as well so it might be worth checking yours if you have the chance. Generally electrolytic caps have a lifetime measured in hours but should last 20-25 years before giving up.



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Re: Rev3 94 ecu issue

Post by Padraig 04 »

What would you be looking for exactly when the ecu is open? Do the capacitors swell or is it just leaking?
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Re: Rev3 94 ecu issue

Post by m122794 »

A couple of things really - the top of the can sometimes gets a bit domed but usually you can see some fluid leaking from the bottom seal where the wires stick out. If this sits on the PCB for any length of time it will etch the copper tracks away and then the repair is much more involved (and expensive if you can't do it yourself).

The ECU for my Rev3 is PNo 89661-17500 and it uses 8 electrolytic caps:

C809 10uF 50V
C512 10uF 50V
C820 15uf 35V
C004 33uF 35V
C002 47uF 63V
C101 100uF 10V
C510 100uF 10V
C105 220uF 10V

I got the whole lot delivered for a few pounds and 30 minutes with a soldering iron. Like I said previously, 3 were in a poor condition just beginning to weep and all of the rubber seals were hard so not much life left in any of them.

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Re: Rev3 94 ecu issue

Post by jimi »

It mainly seems to be an issue with 90's capacitors, it's very rare to see similar problems with MK1 ecu's which are 30+ years old.
I've come across similar problems with capacitors in consumer electronics from around 2000, mainly seems to be psu's affected from what I've seen/experienced.
Thanks for posting your ECU capacitor list, I'll put it to KY2 , would be very useful if anyone has a list of capacitors for the other Rev ECU's. :cool1:
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Re: Rev3 94 ecu issue

Post by m122794 »

Yes, and I think its possibly a cost-related issue as well: you can get caps rated for more service hours at higher temps and higher voltages but the ones in my ECU were pretty-much 'bog-standard' lower rated units. The ECU gets pretty warm where its mounted in the boot of the Mk2 just above the exhaust and is covered in carpet just to insulate it even more so the caps have a pretty hard life.

All my replacements were at least rated at a higher voltage or service life than the originals.

If it helps, here's the list of the Manufacturer's part numbers of the caps I bought.

C809 10uF 50V PANASONIC ECA1HAM100X
C512 10uF 50V PANASONIC ECA1HAM100X
C820 15uf 35V RUBYCON 200RX3015M8X
C004 33uF 35V PANASONIC EEUFR1V330B
C002 47uF 63V RUBYCON 100YXF47MEFC10X16
C101 100uF 10V PANASONIC EEUEB1H101S
C510 100uF 10V PANASONIC EEUEB1H101S
C105 220uF 10V PANASONIC EEUFS1H221LB

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Re: Rev3 94 ecu issue

Post by Padraig 04 »

Think I'll add this to the "Lets do all these things while the engine is out" list :laughing
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Re: Rev3 94 ecu issue

Post by rick_mr2 »

Hi all,

Hope resurrecting this thread isn't an issue. Just wanted to share my experience with bad capacitors on my 95 Rev 3 N/A.

Last summer I started having ignition issues, misfires, fuel cuts while driving (hard cuts.. basically had to jump the car back to life while poodling down the motorway!), poor/rough idle to the point that I would stall if idling for more than 30 seconds (holding the throttle on a bit at stops to stop it stalling became 'normal'), over fuelling, dangerously powerful pops and bangs.. the list just kept getting bigger and bigger.

I did the stupid thing of logically knowing all along I should test and inspect the ECU as it manages, you know, the drivability of the engine, I didn't. I instead replaced nearly every sensor that touches the cooling and ignition system, the MAP/MAF (can't remember which one the NA has), the coil, firing pack, coolant (burped it more times than I care to think about), TPS, vacuum lines.. the list is embarrassing.

Anyway, last week I have had enough and pulled the ECU to open it up. Guess what, I can see of the 8 capacitors 5 had visibly leaked, 2 bad enough to damage adjacent PCB tracks. One cap I'm pretty sure wasn't even connected to the board any more as a leg had completely corroded. How my car ran is really anyone's guess.

I replaced all 8 caps this week and re-routed the damaged PCB tracks with some surface wiring and it's quite simply transformed how my car runs. I'm sure I cant remember it ever running this well since I bought it 10 years ago. Revs freely and nicely, power feels to be back, no flat spots, no rich fuel smell, no rough idle! Only thing is its lost some idle "bark and burble" out of the loud pipes (which was just the over fuelling I bet) :laughing

Everyone, if you haven't already, check the capacitors in your stock ECU's, 30 years hasn't treated them well. Judging by how many of these threads I'm seeing all over the net we are just walking into a ticking time bomb here. Anecdotally Rev 1&2 mk2 ECU's less prone but could not see enough evidence to say for sure. I would argue 20-30+ year old caps of any mk/rev/grade are highly likely to be out of spec by now regardless, it's not just life hours or heat but age definitely kills them also, even if they don't leak they can dry out and go bad.

Job is easy enough to do for anyone competent with a soldering iron. You will need the replacement (quality) caps, solder (w flux ideally) de-soldering tool (I personally use de-solder braid but lots of people people like the suckers), some isopropyl alcohol and cotton buds to clean the mess the old caps leave. Also, don't panic if the board's CXXX label number etched on the board next to each cap doesn't match, just make sure the capacitor values match. My Rev 3 UK ECU differed from a few guides online, I'm led to believe Rev 4+ is also different. The good thing is they all use the same caps just in slightly different locations and CXXX board labels. The values of all 8 caps are as far as I can tell all the same (they were on mine, but always check your own!)

To avoid ordering capacitors at minimum order quantities there is a seller on eBay listing the ones you need with a handy visual guide here at the moment:https://www.ebay.co.uk/itm/115844810506 ... media=COPY (I used his kit out of of convenience, had everything I needed), alternatively order them off Farnell or something. I am not affiliated to either.

We all need to be checking these before wasting money on sensors and other tasks like I did I would say! One for a KY2 article I think!
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Re: Rev3 94 ecu issue

Post by jimi »

While not disagreeing that 30+year old electrolytic capacitors may be of of spec, I don't think that's the full story.
The funny thing is that capacitor failures are pretty much confined to MK2's, I can't recollect coming across a similar problem with MK1's. When I worked offshore I had a lot of dealings with old electronics lots of 30+ year old gear that still functioned perfectly well. It seems to be 90's gear that's affected the most. I seem to remember a big scandal a out fake capacitors around that time.
I visually checked the caps in my cars ECU (1988) and my spare ECU (roughly the same age) a year or so ago and both appear OK, car runs perfectly.
rick_mr2 wrote: 27/06/23 17:28 We all need to be checking these before wasting money on sensors and other tasks like I did I would say! One for a KY2 article I think!
I quite agree, if I had a MK2, I'd be checking the ECU even if the car runs OK, for all the time it takes
Are you volunteering to write one ? ;) Feel free :th:
Do in thread in MK2 Useful Info and I'll convert it to a KY2 article
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Re: Rev3 94 ecu issue

Post by _Al_ »

I pulled the ECU from my 1997 rev 4 JDM G-Ltd last week and all caps look absolutely fine. Could have been installed yesterday.

That being said if I wasn’t planning to drop a V6 in there I’d still be tempted to do it as preventative maintenance given how many others have failed.
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Re: Rev3 94 ecu issue

Post by jimi »

It was worth checking Al. at least now you know it looks OK :th:
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Re: Rev3 94 ecu issue

Post by rick_mr2 »

jimi wrote: 27/06/23 19:59
Are you volunteering to write one ? ;) Feel free :th:
Do in thread in MK2 Useful Info and I'll convert it to a KY2 article
Will get on this over the next couple of weekends while I am reparing the 2" hole I spotted in rear wheel arch while pulling the ECU out last time! :blink:
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Re: Rev3 94 ecu issue

Post by benckj »

The MR2 ECU’s seem to have a higher failure rate than other cars of similar vintage. The capacitors are the weak point with this PCB much like the gauge assembly for RPM/ speedo.

Given age of electronics and old programming technology I’d be more inclined to replace ECU with an aftermarket EMS especially if it’s a turbo with standard mods.
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Re: Rev3 94 ecu issue

Post by jimi »

benckj wrote: 07/07/23 22:55 The MR2 ECU’s seem to have a higher failure rate than other cars of similar vintage.
I'd qualify that by adding MK2 ;)
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Re: Rev3 94 ecu issue

Post by benckj »

Probably correct as the MK1 & 3’s don’t have those issues.
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