Fan relay

[1Gab Laser]

I've sorted out most of the bugs in my car by now but there's one left...

When I go on a "long" trip (30 minutes or more usually) my car starts running/idling funky. I've traced the problem to be something with the cooling fans. When I pull up to a stop, idle drops down to around 500 RPMs and it sounds like it's barely staying running. If I'm driving kind of slow, keeping it around 1000-1500 RPM, it acts like it stops running for a second then fires. I can't really explain it, I'd have to take a video or something.

So trying to figure it out I've let the car just idle for a while until it acts up. I've noticed that only the passenger's fan comes on. After a while, it'll start running crappy, then the drivers fan will kick on for a second, both of them will shut off immediately, and it'll run great.

I've tried replacing the little aluminum box on the fan and the mini harness, and tried a whole new fan, it hasn't changed anything.

Hooking power up to them DIRECTLY from the battery, both fans run fine, no problems.

So I'm thinking it might be some sort of relay that's gone bad or something? Does anybody know where I can find this or maybe know if that's not the problem at all?

Oh, and the temperature never gets past dead center.

 

[steve]

I'm not sure that the problem is with the fans. When they run they draw a lot of current and which causes the alternator to load the engine and forces the ECU to try and open the ISC bypass to keep the idle speed up.

That's where I'd start checking since the ISC motors on our cars are a known problem and when they go bad they can damage the ECU. Capacitor leakage is also a common problem and can independently damage the ISC drive circuits and disable the ECU from controlling the idle speed.

If this isn't working you could see the problems your reporting.

 

[1Gab Laser]

I'm not sure that the problem is with the fans. When they run they draw a lot of current and which causes the alternator to load the engine and forces the ECU to try and open the ISC bypass to keep the idle speed up.

That's where I'd start checking since the ISC motors on our cars are a known problem and when they go bad they can damage the ECU. Capacitor leakage is also a common problem and can independently damage the ISC drive circuits and disable the ECU from controlling the idle speed.

If this isn't working you could see the problems your reporting.

That's what I was originally thinking (not that in-depth, but that it was drawing too much current and overloading the alternator, basically). My brother (who's been a mechanic longer than I've been alive) said there's a relay somewhere that's probably gone bad.

How do I check the ISC and where is it?

Lucky for me, my favorite yard just got a 93 Eclipse 4G63 in last week. I was the first one to take parts off it

 

[steve]

How do I check the ISC and where is it?

Please download the factory manuals and read them. http://www.dsmtuners.com/forums/fre...tions/344490-download-1g-service-manuals.html The 1G Technical manual is a must read for all DSM owners.

www.dsmisc.com has some good information in their FAQ as does the DSM VFAQ

 

[1Gab Laser]

Please download the factory manuals and read them. http://www.dsmtuners.com/forums/fre...tions/344490-download-1g-service-manuals.html The 1G Technical manual is a must read for all DSM owners.

www.dsmisc.com has some good information in their FAQ as does the DSM VFAQ

I already have the manuals. I was just hoping for a quick answer but I can search.

 

[steve]

I already have the manuals. I was just hoping for a quick answer but I can search.

Then read the DSMISC FAQ it says how to measure the coils. They have gone through my past posts and condensed the information. I'm trying to cut back on repetitive posting of common subjects.

 

[1Gab Laser]

Then read the DSMISC FAQ it says how to measure the coils. They have gone through my past posts and condensed the information. I'm trying to cut back on repetitive posting of common subjects.

Thanks. I just tested them, there are 2 pin combinations that are reading way too low. One was ~3ohms, another ~6ohms. The other two were just over 28.

Hopefully the junkyard is open tomorrow.

 

[steve]

That means there is a good chance the ECU is also damaged so look for one of those too.

 

[1Gab Laser]

That means there is a good chance the ECU is also damaged so look for one of those too.

I've put around 3000 miles on the car, so its possible

But is there anyway to check it out first?

 

[steve]

In the worst cases you can see the blow drivers and usually smell them but since it wasn't a dead short the driver can be dead without actually burning up.

http://www.dsmtuners.com/forums/art...585-troubleshooting-fried-ecu-components.html
http://www.dsmlink.com/wiki/driver01

Without special tools you can't check case where it's bad but not burned up except by oberservation that the ISC isn't working like it should.

With that ISC the driver for those coils would have failed in a couple of milliseconds of you turning the ignition on.

 

[1Gab Laser]

In the worst cases you can see the blow drivers and usually smell them but since it wasn't a dead short the driver can be dead without actually burning up.

http://www.dsmtuners.com/forums/art...585-troubleshooting-fried-ecu-components.html
driver01 [ECMTuning - wiki]

Without special tools you can't check case where it's bad but not burned up except by oberservation that the ISC isn't working like it should.

With that ISC the driver for those coils would have failed in a couple of milliseconds of you turning the ignition on.

So you think the ECU is definitely bad?

Looking at that pic, it looks like the drivers just plug in to the main board of the ECU? Is that correct?

Also, my check engine light is on. When I disconnect the negative terminal for a while to reset it, it comes back on after about a day's driving. But when I hook up a test light or volt meter to the prongs (can't remember which ones it is now), it doesn't give me a "code". Could it be related to this?

 

[steve]

I'm betting it's been damaged and that it still has original capacitors which would need replacing. If it's not burned then it's pretty easy to unsolder the chip and replace it.

When you dig around looking for an ISC try to get one of the newer black plastic ones. They don't seem to go bad as consistently. The original metal ones all seem to fail over time of natural causes.

Rock auto has the best price I've seen for new ones at < $100.

 

[1Gab Laser]

I'm betting it's been damaged and that it still has original capacitors which would need replacing. If it's not burned then it's pretty easy to unsolder the chip and replace it.

When you dig around looking for an ISC try to get one of the newer black plastic ones. They don't seem to go bad as consistently. The original metal ones all seem to fail over time of natural causes.

Rock auto has the best price I've seen for new ones at < $100.

Good luck with that. This yard is the only one I know of with a 1g 2.0. There's another one like 15 minutes further that has a Sonata with a 4G63, would that one work?

Anyways I edited the post, must've been after you read it. Would the ISC/ECU have anything to do with that situation?

 

[steve]

Anyways I edited the post, must've been after you read it. Would the ISC/ECU have anything to do with that situation?

Do you mean that you have now connected the fans directly and they work but that the car still has the same problem independent of the fans?

You have already proved that you have a bad ISC. I wasn't convinced that the fan issue was anything but secondary to the problem and you have confirmed it.

 

[1Gab Laser]

Do you mean that you have now connected the fans directly and they work but that the car still has the same problem independent of the fans?

You have already proved that you have a bad ISC. I wasn't convinced that the fan issue was anything but secondary to the problem and you have confirmed it.

No, I hooked them back up the way it came from the factory. Direct from the battery was just a test.

I was talking about the check engine light, the last reply.

I just got an ISC and ECU out of the junkyard. Hoping the ECU will work, it's out of a 1993. If it wont work then I'm sure I can sell it for more than I paid for it, but I'll be SOL on getting one for my car.

 

[steve]

I was talking about the check engine light, the last reply.

The CEL on without a actual code (just getting the heartbeat) may be a ECU failure distinct from the problem your chasing or related. Not enough data.

 

[1Gab Laser]

The CEL on without a actual code (just getting the heartbeat) may be a ECU failure distinct from the problem your chasing or related. Not enough data.

Well tomorrow I plan on replacing the ISC and ECU. We'll see how it goes, I'll keep you updated.

Thanks for all the help.

 

[1Gab Laser]

I just replaced them, now it's idling up and down, and higher than normal. It never used to do this until it got warm.

The ISC tested out fine. The lowest reading was 28.5 ohms.

ECUs both had the same Mitsu part number on them but I think someone swapped the one that was in my car out before. There was a bolt missing that holds it in, and I didn't figure the numbers would be the same from a 1991 Laser to 1993 Eclipse but maybe I'm wrong on that.

Here's a video of what it's doing. It idles 1500-1700 RPM now, the backfire/drop is when it gets to 1700.
When it got warm, it used to do this but 1300-1100 RPM.
http://www.youtube.com/watch?v=W-iujIHifXo

 

[steve]

That's called idle surge. The first step is to clean the ISC and throttle body then following the instructions in the manual adjust the BISS and the base timing.

You shouldn't be having all that clatter under the hood. It sounds like more than just the lash adjusters. Did you change the timing belt and replace the tensioner or not preload the belt?

If after adjusting the BISS and timing you can't get the idle speed down to 750 rpm you'll have to start looking for vacuum leaks.

 

[1Gab Laser]

I just took it out for a test drive. Figured maybe the ECU needed some time to learn all the data coming in. Only drove about 3 miles.

It's acting like there's a rev limiter at 3800 RPMs. Also I went to make a 3 point turn and when I put it back in drive it stalled out crossways of the road. Wasn't fun.

I'm thinking the ECU I picked up is bad?

 

[1Gab Laser]

That's called idle surge. The first step is to clean the ISC and throttle body then following the instructions in the manual adjust the BISS and the base timing.

You shouldn't be having all that clatter under the hood. It sounds like more than just the lash adjusters. Did you change the timing belt and replace the tensioner or not preload the belt?

If after adjusting the BISS and timing you can't get the idle speed down to 750 rpm you'll have to start looking for vacuum leaks.

My camera makes sound seem a lot worse than it is. But I'll look into it.

No, I haven't done anything with the timing belt.

 

[steve]

The correct ECU for your car is MD166255. It was used on all 91-93 Federal non-turbo cars with either manual or automatic transmissions. It's the most common of all DSM ECU's because of the number of cars build with it.

 

[1Gab Laser]

The correct ECU for your car is MD166255. It was used on all 91-93 Federal non-turbo cars with either manual or automatic transmissions. It's the most common of all DSM ECU's because of the number of cars build with it.

Yeah that's the one that was in it and the one I picked up.

The one I got was definitely bad. Installed my old one again with the new ISC and now it doesn't hit rev limiter at 3800 like it did with the "new" one. (it did it going down the road)

It's still idle surging though. So you think its something to do with the timing? Inside the TB looked clean from whta I could see just pulling the air intake pipe off.

 

[1Gab Laser]

Yeah that's the one that was in it and the one I picked up.

The one I got was definitely bad. Installed my old one again with the new ISC and now it doesn't hit rev limiter at 3800 like it did with the "new" one. (it did it going down the road)

It's still idle surging though. So you think its something to do with the timing? Inside the TB looked clean from whta I could see just pulling the air intake pipe off.

Bumping....

 

[steve]

Please refer to http://www.dsmtuners.com/forums/newbie-forum/351669-fan-relay.html#post152011546 rather than bumping the thread (which is against the rules here). You still have a lot to do before there is any thing else to look at.

The BISS and CAS need to be set correctly for a good idle. That's a basic step.