help! what fried my ecu

[dsmgirl17]

hey. so i just got this 1991 gsx and the ecu is toasted. its at the 47uf at 50v capacitor, and im not sure if this was caused by the capacitor leaking or something else. the pics might help.
im trying to figure out why this thing blew, and i was messing with some wiring a day before this happened so maybe that has something to do with it..
i was installing a new head unit for it.
i found that the ground that was in the radio harness wasnt connected to any grounds. so i grounded the wire on a bolt and the next day my car died and the ecu was smoking...hmm..
conincidence? or was it the ground i made?

hopefully the burn marks can help tell you experts if it was the cap that burst or if it was something i did/wiring in the car.

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if anybody has any advice on how to track down what blew this ecu PLEASE help me!!!!!! thanks

 

[TrevorS]

Looking at the photos, it looks as though a capacitor may have shorted and taken out the diodes feeding it. When I see that black smoke appearance, there's usually one or more cracked axial lead components nearby -- resistors or diodes. I've a '90 GSX and one day in the rain it blew up similarly, except worse ! Since the board itself appears to be burned, it's unlikely it can be rebuilt, so you're probably stuck with getting a replacement.

This could have happened purely due to age, but I guess one always wonders about "coincidences". Where did you attach the radio ground? Is there any possibility any portion of the ECU harness could have been pinched during your radio install?

 

[bertrenolds]

Looks to me like your IACV or some people call it the ISC is bad, they short out the ecu when they fail. Those capacitors look like they've been replaced and there isint any acid damage so I'll be it was the ISC or if you have dsmlink you didn't use a buffer to connect up your wideband.

 

[dsmgirl17]

i attched the radio ground to one of the 2 bolts that are right below the radio assembly and kinda hard to access. im pretty positive i didn't pinch any ecuador wires with the radio. and i dont think its the isc ### in the pictures i saw of ecus that died due to isc issues it burnt up in a different place. although i did have a surging idle when the car was cold.

 

[TrevorS]

Well, whatever caused it, it's pretty clear the power supply burned up. If one of the ECU peripherals that interface with the board drivers/receivers caused it, I'd expect the lucky driver/receiver to be fried and even then, it probably wouldn't hurt the power supply. For it to sink enough current to overheat a power diode, there should be board damage elsewhere as well, and probably a cracked chip at the same location.

 

[bertrenolds]

It looks like that one specific capacitor failed so I would send it ecm link to have them fix it or try to find someone local and get the capacitors off ebay. It shouldn't matter as long as the radio was grounded but who knows. The grounding point for the ecu is on the same metal the you grounded to.

If your just looking for a unsocketed 1g ecu you can find one for under $100 on here in the clasifides.

 

[TrevorS]

If your just looking for a unsocketed 1g ecu you can find one for under $100 on here in the clasifides.

Just make sure it's a 1G GSX ECU -- may even need to be narrowed down to the first two production years. I think there may have been some changes for '93-'94, can't remember for sure though, it's been awhile since I had to replace mine.

Come to think of it, just get one that has the same number on the ECU cover and you'll be fine.

 

[And_44]

Those are original capacitors. Big and bulky. Newer capacitors are smaller. The ECU's ive had go bad on me in past where in exact same location from leaking capacitors. Probally just timing no relation to radio install. A hunting idle is a symptom of leaking capacitors aswell. It can be worth sending in to ECMtuners for a repair only if its an EPROM ECU. If not I would just find a replacement with new caps or cheap one in still good condition and send it in to get cleaned and recapped. You'll be 120% satisfied with ECMtuners work.

As for what year. Your GSX is a 90 so the ECU's are different then 91-94s. You can use a 89/90 ecu from any manual turbo talon, laser, or ecilpse be it a FWD or AWD. The fuel trims are slightly different between the 2 drivetrains but not noticable when driving. You cannot use an Auto ecu. They had different fuel injectors, turbo, and fuel pressure. Also an Auto turbo 89/90 are extremely rare or none exsistent. You can use a 91-94 ECU but you will have to modify some things to get it to work properly. Doing a search will yeild you those mods if you decide to go that route.

 

[dsmgirl17]

ok you are all so helpful . so you dont think any wiring shorted ot out it was ###### just the cap leaking? also what does that capacitor control?? so i can make sure the wiring is good and not fry my new ecu

 

[stuckwithgsx]

Possible dumb question, but with the ground on your radio not connected that means your radio was not working right? If so did it work after you hooked it up? And between that time and a day later did the car still run? Is it an aftermarket radio? I ask because possibly you found a black wire and assumed it was a ground wire, when it really had power going through it. And I do not know but taking information from earlier post saying the ecu shares the same piece of metal that you used as a ground, then I would disconnect that wire before installing the new ecu. Then add power to the radio independently and make sure the radio is good, and that black wire really is a ground.

I'm also pretty suprised a fuse didn't blow. If it's wiring I would imagine a fuse would blow, unless it had something to do with the common ground of the ecu previously mentioned, then the current would go direct to ecu and avoid all fusible links right?

 

[dsmgirl17]

i dont think this has to do with the radio. ### it ran while it was hooked up for a day, if it was gonna happen it would have happened right when i started the car, and the radio was still on after the ecu died.
i got 12v on pin 106 which is supposed to be a ground, and no power on the mpi control relay 107 pin, and no power on the power supply pin 102. but i have 12v on the back up power supply pin 103
so it looks like there is a short to power on pin 106, can anybody tell me where that ground wire runs to?

 

[TrevorS]

ok you are all so helpful . so you dont think any wiring shorted ot out it was ###### just the cap leaking? also what does that capacitor control?? so i can make sure the wiring is good and not fry my new ecu

That capacitor doesn't really "control" anything. It provides energy storage (a reservoir) and functions to stabilize the local "rail" voltage so the various chips and devices can function reliably. To DC, it should essentially be an open circuit, but for AC it's similar to a short. The problem is that they tend to dry out with age resulting in the internal electrolytic shorting and allowing DC currents that can damage both devices and board.

When mine went the car stunk terribly and you'd of sworn there was melted wiring and everything else. However, it was just due to the burned components and board caused by ECU capacitor shorting -- nothing at all else was wrong. Took months for that smell to dissipate though !

I'm also pretty suprised a fuse didn't blow. If it's wiring I would imagine a fuse would blow, unless it had something to do with the common ground of the ecu previously mentioned, then the current would go direct to ecu and avoid all fusible links right?

A fuse can't protect against this kind of failure. Semiconductor devices die extremely quickly whereas it takes much longer for a fuse to melt. In this and my case, I doubt the fuse blew at all, otherwise the board wouldn't have time to char -- but 10A is a big fuse compared to all that's needed for this kind of damage.

PS. Hmm -- looking at the schematics, it appears the main ECU power feed has a 20A fuse routed through the MPI relay (ECU/MPI pin 107). It's the "Battery Backup" feed that has the 10A fuse (ECU/MPI pin 103). Plenty of current available to do damage if something shorts.

 

[dsmgirl17]

sweet! thanks. ill do some more research and let yall know what/ if anything shorted out to cause this or if it was just the cap being leaky.
thanks for all the replies you guys helped tremendously