1992 G-Limited, Orange Engine lite on, no codes.

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MR2madlad
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1992 G-Limited, Orange Engine lite on, no codes.

Post by MR2madlad »

Hi guys

As title says, got orange engine symbol light is on constantly.

The car starts and engine runs fine now.

If i short E1 - TE1 in diag port then switch ignition to second position, the light is still constant on, no flashing.

I've unplugged the ECU completely to see is maybe the CEL wire from ECU had shorted to chassis (as i beleive the lamp in dash has a common 12v supply and ECU grounds one side of lamp to illuminate) and the light goes out so eliminated any shorts in wiring.

I've continuity checked all the engine loom plugs back to ecu like TPS, MAP, Dizzy, IACV the 2 vacuume solenoid valves under inlet manifold, all good.

I'm lost as to what ells it could be.

I bought car as a project non running, stripped and rebuilt the engine and it now runs nice, double and tripple checked everything is plugged back on / in.

The engine is the 3S-GE one with the spring cambelt tensioner not hydraulic if its of use.

Anyone have an idea on what might be the issue?

This morning I've changed the electrolytic caps in ECU as 2 were really bad, one leaked so much the copper track was eaten away, ive linked it back up (electronics repair engineer by trade) same thing, I'm puzzled now.

Cheers.



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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by jimi »

The CEL is fed from the the 7.5A gauge fuse and as you say grounded through the ECU to illuminate it, if unplugging the ECU puts the light out then logically it can only be an ECU fault that is putting it on.
Perhaps the side effects of the faulty caps has damaged (electrically) another component (chip or transistor etc) and that is keeping the light on.
Can't see what you can do other than replace the ECU. Might be worth another look at the PCB in case there's a bit of damaged track that you missed ? is the PCB double sided with plated through holes ? Possibly try trace the circuit back from the incoming pin, IIRC the PCB is marked with the pin designations, W I think is the CEL coming into the ECU
If the car is starting and running OK then the only real immediate concern would be MOT and I'm sure an man in your trade could overcome that fairly easily. Not suggesting you leave it like that, just a temporary measure if needed.
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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by benckj »

I agree with jimi as fault points to a faulty ECU. Replacement of caps is actually more difficult than most people realise due to the PCB configuration. Easy to either get a cold joint damaged part of circuit that can be near impossible to find. I’d try another ECU to eliminate fault then look at either replacement or better upgrade to aftermarket EMS as these electrical components are all past their use by date.

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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by abovetherim »

Where are you as I have a rev 1 n/a import ECU you can try to see.
Part number 89661-17280
1991 rev 1 T Bar n/a 3sge import. A work in progress!!!


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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by MR2madlad »

Hi all

Thanks for replys.

Ive traced the W back to a transistor which is used to switch lamp on, the transistor is fine, traced the base of this back to a chip, the chip sits below one of the capacitors that leaked so i took the chip out of pcb.

Under chip it was a bit green and furry and also around the chip legs under the laquer its all coated in, gave the whole lot a, clean up and checked all the pads and through hole plates on pcb were ok around the chip, all good.

Anyway after cleaning i stuck it back together and it worked fine for a few days even linking the diag port the light just flashed indicating no errors.

Now its gone back to orange light on so I'm thinking the chip with all green furry stuff underneath has died as the electrolyte must of penetrated the chip via the legs and now its dead and heating it up at soldering in made it work firva while

Anyway ive bought a new ECU off ebay REV 1 UK speck cheap so after a quick look I'm gonna try it and see, if its not right for the model MR2 i have I'm gonna rob the chip that runs the CEL light and swap to my original ECU and see what happens.

I put the faulty ECU on my rev 3 Turbo and it started ok but idles like poo but it proves the fault is with ECU as orange light was constantly on and again linking E1 / TE1 no orange light flashing just on, so it was worth swapping and i can now say that it is possible for a N/A ECU to run at idle on a rev 3 turbo. Obviously not ideal but as a quick test, perfect would of swapped my turbo one to the n/a just to prove but didn't have 10mm handy

The ECU i have has P/N 89661-17350

The one I've bought cheap off ebay has P/N 89661-17310

Ao if all ells fails i'm hopeful I can make 1 from 2.

Also when orange light is constantly on, even shorting the diag port the rpm / idle doesn't change like it does on my turbo so I think the same chip is used to enter diagnostic mode which it appears not to enter when in duff mode.

I urge everyone to check / replace the electrolytic caps in your ECU so you don't end up like me with a duff one and finding the correct part number puts me at £160+ for a used one that might be on verge of failing.

The one ive bought was £35 with shipping so defo worth a shot.

If anyone has a ECU with the 17350 part number local to Burgess Hill it would be brilliant if I could try on car it to proves my ecu is bricked for certain

Thanks

John

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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by jimi »

Just shows the damage the electrolyte can do, at least you have managed to narrow down the problem. As you say you may be able to make one from two if the other ECU has the same chip/ transistor setup. As you have found the ECU's are not interchangeable. There's quite a variation in pinouts, it's possible to repin the plugs, but still no gaurantee it would work. Does the chip you suspect have any marking/info that could identify it ?
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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by jimi »

You can download a list of the ECU numbers from here https://www.mr2oc.co.uk/know-your2/mk2/ ... mbers.html
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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by MR2madlad »

Update

I've finally fixed it, yay.

The leaking capacitors were duff but a red herring in my case, new ones fitted anyway as they are 28 years old and have a limited life, the chip was also a red herring but again worth my time removing and cleaning as it was green and fury underneath which is not good.

After a lot of in boot action attaching a lamp to the W pin on ECU and other end to +12v supply so I could see the light was on constant or flashing without bending neck over boot lid to look through rear window to dash, I finally figured it out.

The smaller top board was very sensitive to heat around IC501 and also gently pressing board when cold around the ribbon connector area next to IC501 it would work ok (CEL light would flash, left link in E1-TE1 permeant and ignition on switch 2 engine NOT running) release board light would stop flashing and be solid on.

Got my high resolution PCB inspection camera scope out and under microscope I could not see any dry joints to IC legs or ribbon connectors BUT I did see very very very tiny hair like wires between the legs of the IC on BOTH SIDES of PCB some looked like they were in the lacquer clear PCB coat too.

I think the ECU is of the age its suffering from TIN WISKERS - Google it!

What I have done is simply resolder the IC501 legs entire length both sides, the 5 SMD resistors between ribbon pins and chip pins and the ribbon connector up IC501 end then cleaned PCB with Deflux cleaner with stiff paintbrush poking it between the legs on the IC501 chip side of PCB and its cured the fault.

Possibly the heat is expanding the PCB enough the tin whisker breaks contact (same as pressing it) but when board cools it contracts (I let pressure off PCB) the whisker makes contact.

Mine is now fully working I stuck it in freezer for 20 mins to cool it down and its not gone into faulty mode like it did predictably, taken for a drive, working normal no CEL, link E1-TE1 CEL flashes constant to indicate no errors.

Can't say it will cure yours but just cleaning with IPA or PCB cleaner might be enough to sever the tin whiskers and cure yours, failing that resolder what I did above, noting to lose but potentially save a lot of cash!

hope this may help, wish I could of got a picture of the tin whiskers but I can't, still I'm happy now.

John

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Re: 1992 G-Limited, Orange Engine lite on, no codes.

Post by benckj »

Bugger me, what a find. Good job as I never would have guessed that issue. Makes me wonder what other gremlins are lurking out there.

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