ECU Problems??? (Long Post)

[Lil John]

I've been having some problems with my brother's 90 Plymouth Laser. Its also FWD and Turbo, and basically stock.

I'll you give you the rundown of the problem. It all started a couple of months ago. The car ran great. Once in awhile the temp gauge start acting up. The needle would be right in the middle where its suppose to be, and then out of no where it would peg the H (hot).
It only happened sometimes. The car wasn't actually hot either.

Then one day he came out to his car and it smelled like rotten eggs insided. So we new that the caps had leaked. So we took it out (it was EPROM too ) . We stuck another one from a 90 Turbo Laser. We weren't sure if it was good or not. We plugged it in and the car ran great for about a week. And then, it would die once in awhile. After it would die, it would usually start right back and be fine. We checked into it and thought we had found the problem. The negative battery cable was rubbing on the battery tray and there was some bare wire showing. We figured it was shorting itself out. We taped it up and thought we had fixed it. But no, a day later it was doing the same thing. It kept getting worse and worse. Some the days it would start and run great other times it would start and run like crap, and others it wouldn't even start at all.

We then tried a couple of different ECU's out two 92 Turbo DSM. One was actually fresh, it had just been rebuilt. I know there are some differences between the 90's and the 91-94's with the tach and etc. But we thought it should still run the newer ECU's. They didn't work at all. The car would barely start and when it did it ran like crap. We had to keep our foot on the gas to keep it running. It was the same with both ECU's, even the rebuilt one. You could hear the ECUs clicking on and off repeatedly.

So, I got an ECU from a 90 Turbo (AWD) and tried that. That one hasn't solved are problem either. The other day I jumped it (the battery was low) with my other car and it started right up. But the instant I disconnected one of the jumper cables, the car car died right away. And now, the car will start for about a second and then die. It does this every time. Its starts for a second and dies. The factory boost gauge also acts funny. When you turn the key to "On" the boost gauge reads 0lbs. like its suppose to. But as soon as you start to crank it over, the boost gauge jumps up to +7lbs. and then +14lbs. I know that isn't right. I can hear the ECU power up likes it suppose to. I'm going to try to see if there are any CEL's. I know it did awhile back when it was acting up the battery has been disconnected since then. We did change the Coolant Temp. Sensor but nothing changed. The ISC was also making some weird clicking noises when you turned the key so we unplugged it, but that didn't make a difference either.

Anyone have any ideas? Do you think its ECU related, something else, sensor? Like I said, it did run for a few minutes recently while the jumper cables where hooked up from my car to his. So its getting fuel and spark, which we have checked for also. Sorry for the long post, but we just need some help. My brother is getting tired of driving a rusted out 1993 Pontiac Sunbird while we try to fix his Laser. I appreciate eveyone taking the time for reading this and hopely giving us any suggestions to try.

-Thanks, Jason

 

[justin0469]

I would say stick with the 90 Laser ECU but sounds like the problem may be somewhere else. When you had the jumper wires connected it was fine. As soon as you took them off, it died. That seems to me that maybe its not getting spark without it. I am just suggesting things and not trying to take charge like I know whats happening but maybe change out the battery with a known good one from your other car?

 

[femmeDSM]

Well...First of all, an ECU from a 92 should technically at least try to start the car, but should not be used for any length of time unless the wiring to the tach, etc, has been performed.

I would try to scan the ECU for codes. If you don't have a datalogger, you can use an analog voltmeter (or a digital if it has the sound output).

It sounds to me like you have been putting more bad ECUs into the car -- have you tried putting one of *your* ECUs into a known running DSM to see if it fails to start the car, instead of the other way around?

Also, how are you checking for fuel and spark?

If you are truly having ECU problems, I would contact "steve" on this board -- he will be able to help you figure out what's wrong with your ECU(s).

Also, I've heard of a blown ISC motor frying ECUs - might want to check that out. You can hook it up to a 6v battery (not 12v, as this will ruin it) and see if you can get it to power on. There's a VFAQ about this if you need the link.

Was the car doing anything else out of the ordinary before this happened?

 

[steve]

I would contact "steve" on this board

I'm not a good resource right now unless you want to read through past posts and see what might apply. I'm stuck in the hospital for a few more days and will be moving a little slow once I get out.

Steve

 

[oldman]

I'm not a good resource right now unless you want to read through past posts and see what might apply. I'm stuck in the hospital for a few more days and will be moving a little slow once I get out.

You mean slower.

 

[femmeDSM]

I'm not a good resource right now unless you want to read through past posts and see what might apply. I'm stuck in the hospital for a few more days and will be moving a little slow once I get out.

Steve

Oh no Hope you are feeling better soon. We will be lost here without your DSM wisdom.

 

[Old Mitsu Tech]

You mean slower.

Ohhh, steve got busted.

 

[Lil John]

I'm thinking the ISC motor may be causing the trouble inside the ECU's. When I turn the key, the ISC motor clicks like crazy for about 5 seconds. I think this is causing the car not to stay running running. Last night, when I tried to start, I held it to the floor to try to keep it running. It revved up to 3000rpm and then died right away. As it was revving up, I could hear the ECU clicking. I did take apart the ECU last night, it also smelled kind of funny. The only thing I could find was on the bottom side of the board, there was a little bit of some kind of goo (kinda like what it looks like when the caps leak) by one of the ISC drivers. I'm not sure if this would keep this ECU from working. I also thought that the bad ISC motor may have cause this. I know when we tried the two different 92 ECU's the car would idle up and down like crazy which would also probably be caused my a bad ISC motor. I just hope we didn't mess them up either. I'm going to try both of them in a different car just to make sure. But anyway, what do you guys think?

-Thanks again, Jason

 

[femmeDSM]

Sounds like you are on the right track. I would check your ISC motor just in case -- my bet is that it's shot. Here is the link that shows how to test it: http://dmtalon.v8eaters.com/ISC.html

Note that the info on this page is for a 91+, but the testing procedure is still the same. On mine, the ohms were all within specs, but hooking the unit up to a 6v battery showed that it was bad, so that's the only "real" way to be sure. Also, you will have to replace yours with another '90 -- a 91+ ISC will not work on your car. Just a heads up. Pretty safe to say that most parts on our '90 cars are this way, unfortunately.

Also, just in case you were wondering, the ISC is a blind stepper motor that does not communicate with the ECU, so if it goes bad, you will not throw a CEL or a code. The ECU talks to it, but it doesn't say anything back.

A "new" ISC motor for our cars runs about $200-$250, but I got mine on Ebay for $40. They usually run used anywhere from $30 - $75.

Good luck.

 

[Lil John]

Also, I've heard of a blown ISC motor frying ECUs - might want to check that out. You can hook it up to a 6v battery (not 12v, as this will ruin it) and see if you can get it to power on. There's a VFAQ about this if you need the link.

I was reading another post, and from what I understood, Steve said that the ECU has ISC motor drivers (6 of them I think?) located on ECU board and that a bad ISC can damage them. I think this is right, but can Steve or anyone else confirm this?

I'm going to change the ISC motor and try another ECU and hope for the best.

-Thanks, Jason

 

[femmeDSM]

Yes, your ISC drivers are located near the top right side of the ECU. I believe there are 4 of them.
Found a pic for you via search - http://dsmtuners.com/forums/attachment.php?attachmentid=57627
They are circled in red at the top of the image.

Switch out your ISC and try a known good '90 Turbo ECU, and I bet you'll fix your problem

 

[Lil John]

Yes, your ISC drivers are located near the top right side of the ECU. I believe there are 4 of them.
Found a pic for you via search - http://dsmtuners.com/forums/attachment.php?attachmentid=57627
They are circled in red at the top of the image.

Switch out your ISC and try a known good '90 Turbo ECU, and I bet you'll fix your problem

Yeah, thats the picture that I saw too. Your right, there is only four of them. I'll let you know what happens.

-Thanks again, Jason

 

[Lil John]

Well, I changed the ISC motor and swapped out a different ECU. All that I had available was the pair of 92 ECU's that I had tried earlier. My 90's are going to be sent out to have the caps replaced. Anyway, it fired right up and idled pretty good, except for the idle surge (it always idle surged in cold temps after the car had warmed up). The only problem is when you step on the gas, the rpms won't rev up. They go up a little and then right back down which still makes the car undriveable. I'm hoping this is just because of the 92 ECU. Would the 92 ECU in a 90 cause these symptoms? Hopfully ihe ISC motor was the only problme. I guess I'll have to wait and see how it runs once I get the caps replaced in the 90 ECU.

-Thanks, Jason

 

[steve]

Did you swap pins 6 and 14 when you put the later ECUs in. You have to swap these pins when crossing the 90/91+ car/ECU interface.

Steve

 

[Lil John]

Did you swap pins 6 and 14 when you put the later ECUs in. You have to swap these pins when crossing the 90/91+ car/ECU interface.

Steve

No I didn't. I don't plan on keeping the 92 ECU, I'm going to be putting back in a 90 ECU. I just wanted see if it would run. Since I didn't swap pins, is that the reason for the car not wanting to rev up and the tach acting funny? The car starts up just fine and idles fine also. Just when you step on the gas, the rpms drop.
-Jason

 

[steve]

Swapping the pins takes 60 seconds. You need a small jewlers (or eyeglass) screwdriver to release the retainer and pop the connector out.

In my car, not swapping the pins causes it to run like crap with a '90 ECU. Those pins are for MAF reset and IPS. As soon as I swap them the car goes back to running great.

Steve

 

[AWDPetmitsu]

Did you ever test your old ISC? If the resistances were all in spec and close to each other and it passed the function check with the 6V battery test, then changing it out does nothing.

 

[Lil John]

Hey guys. I changed out the 92 Turbo ECU with a 90 Turbo ECU. Actually picked it up for $45 from a local junkyard! It has also been recently rebuilt which was a nice surprise. I did change the ISC motor which was bad, which probably messed up the ECU in the first place. So, I plugged in the ECU and it fired right up and ran great. Thanks for everyone's help.

-Jason