ECU replacement/repair advice - 1989 COLT

Ah yes the ECU, In my day the only electronics you had to worry bout was the radio and the 8 track. But seriously, My sons 91 laser blew the ECU about four months ago, replaced it with one from the auto wrecker, it lasted 4 months. Last week we replaced it again. Being an electronics tech by training, a computer nerd by profession, and a back yard mechanic by circumstance, I decided to try and figure out what was wrong with the ECU's. The end result, is that I now have three perfectly working ECU's.

Yes it is worth changing the caps on spec, if your ECU is not working now, it could only get better. Just unsolder the old ones and install new ones (watch the polarity). Digikey sells caps over the net.

Of the three ECU's in my sons car, one had bad caps and the other two had failed, factory modes.

For your vintage, if the ECU is outputting codes, then the processor is running, and in all likely hood its some minor component that has failed. Perhaps a relay driver or solenoid control. For this age, they where usually just large transistors driving the outputs, very easy to test with an ohm meter.

By the way. Did your mechanic tell you what the codes are.

Oh yea, usually you can erase the codes by disconnecting the negative terminal of the battery, and leave it off for about ten minutes. If you truly have a problem, the codes will be regenerated by the ECU.

Computers around this age usually didn't do much more than monitor the O2 sensor and vary the fuel mixture accordingly (did you check the O2 sensor (a long shot)) If you can get the car running, check to see if the ECU is in fact varying the air / fuel mixture, perhaps the mixture solenoid is stuck in the rich position.

All you really need to service this year of vehicle is a digital volt meter and the service manual. You could even read the codes with the DVM.

Ray

Possibly caps, but it may also be bad contacts on several engine sensors. One of the most common is the set of sensors (through one 6 pin? connector) in the air cleaner (Mass Air Sensor, MAS) that will indicate about 4 codes. Sometime all thats needed is to R/R the contacts a few times with a squirt of WD40. Likewise the three big connectors on the ECU.

The 93-96 Colt / Lancer / Eagle Summit has essentially the same engine (4G15), and these ECUs may be compatible with your 89. Anyone know for sure?

Stewart DIBBS

Thanks for the reply. My mechanic did not know the codes off hand (the guy who worked on it was out when I called) but I plan on getting them from him. You stated: "Oh yea, usually you can erase the codes by disconnecting the negative terminal of the battery, and leave it off for about ten minutes. If you truly have a problem, the codes will be regenerated by the ECU."

Do you mean truly a problem with the ECU or with the components/systems flagged by the codes? I believe the mechanic told me he knew that the ECU was bad because he "cleared the codes" then ran the car for a spell and checked the codes again and then same codes came up again (with the exception of the coolant temp sensor, which he replaced). To me that means the components and not the ECU is bad. If the ECU were bad wouldn't you get different codes on the restart? Does that make sense? Thanks again.

I'm not a mechanic, but I am very familiar with embedded computer systems. Your conclusion that it's the components and not the ECU that are at fault makes sense to me. Unless the codes were from a self test of the ECU, in which case they could be reporting that the ECU hardware is failing. Can you find out what the codes were for?

What I meant was, if the errors are caused by failing sensors, and not the ECU, then resetting the ECU will clear the codes. Running the engine will regenerate the error codes. If after clearing the codes you check the ECU, without starting the engine, and there are no codes, then in all likelihood the ECU is not at fault. If you can run the car for a "spell" before the codes are generated, my guess is that your ECU is OK. You seem to be on the right track here, It makes sense, in thinking it's not the ECU. The ECU is always powered (even when you turn the ignition off and take the key out), that's why you have to disconnect the battery to clear the memory. As another poster said, check those connection points (the O2 sensor operates at less than 1 volt, doesn't take much to diminish this voltage at the connector). I think the very next thing you need to do is get the error codes, On my sons 91 laser, the ECU output a code, that when we looked it up in the manual, said "Replace ECU"

"The car ended up with him when, upon hearing some clicking under the dash, it just died. " here's the big clue guys.... the ecu was clicking and then the car died. the ecu clicks because it is cycling on and off. pull out the ecu and remove it's cover. look at the board in the area where the electrolytics are and check for residue and corrosion from the leaking electrolyte. on my '91 there was clear evidence of leakage before there were any symptoms. jim this is just the same deal as you see in vintage tube amplifiers, the electrolytics in the power supplies crap out and have to be replaced. on an eclipse, there are only 3 caps. you just need to get the polarity correct (positive and negative leads on the cap) i would at least try if i were you. the pricing you are getting on a replacement is off the hook! eclipse/talon ecu's from the early 90's are $100 the prized '95 eprom ecu sell for $250 most of the time. check out the parts traders.

The lowest price I saw online for a reconditioned ECU was $175. What is the "parts traders"? Where do I find these part traders? The car is a 1989 Mirage/Colt by the way. Thanks again for the help!

You are right.... I am an electronic engineer and 90% of all components problems, are the capacitors.... be careful when soldering ,use tools that can't have static problems , else the chips get destroyed and don't take the card in both hands while not have the normal static precautions.... The only not solid state (chips) components are most of the time the problem makers after 7-12 years .

have fun repairing...

simplet> "The car ended up with him when, upon hearing some clicking under the