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Discussion Starter #1
specs:
2001 eclipse rs, 4 cyl, manual.

So recently my eclipse hasn't been able to keep a steady idle. It goes flutters up and down within 500-1000. I have changed all o2 sensors, replace the entire throttle body assembly (with Iac and tps), check for any possible vacuum leaks and found absolutely nothing. Then I get a p1500 code and it is either the alternator or ecu. Went out bought a brand new alternator and the code randomly comes and goes without any need to restart the ecu.

I have bought another ecu that is from the exact same model and year however local dealerships are saying I need to have the immobilizer from the same car the ecu came with, others say its all fine but I need a new ecu because the vin won't transfer, and another dealership said all I need is the ecu and it will transfer everything. So I need someone who actually knows what they are talking about and is experienced with swapping ECUs if you are not sure don't waste everyones time by posting.

Also, randomly the alternator will read 14.4 volts (like normal) and other times while the car is running it will read 12 volts and decrease all the way to 10 and won't charge, I replaced the cable from the battery to the alternator and it still happens.

If anyone could help me out I would deeply appreciate it I have been working on this damn thing for months and it's always something else. Thanks a lot guys.
 

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It sounds like you're throwing good money at parts you don't need. Rather than simply guess what might be wrong and buying replacement parts, spend your money on some halfway decent diagnostic tools like a Power Probe III and track down the bad ground you're getting. The tool will pay for itself the first time you use it. You probably just need to clean or replace your Big 3 wires.

Also, did you buy a remanufactured alternator or a new one? Sometimes, remanufactured alternators have worn out or bad voltage regulators that don't get replaced. This could explain the inconsistency in voltage readings. Did you check and compare the outputs of the old and remanufactured alternators at the store when you swapped it out? I'm betting your old alternator was fine and they sold you a part you didn't need.

Sometimes, the cheapest way to fix a car is to find a decent mechanic who knows what he's doing and pay him to do a diagnostic. Stay away from the dealerships if you want to save $$$.

Always remember, without very specialized and expensive equipment, generic codes can only point you in a direction. They rarely tell you the whole story (it's either A or B). Anything up or down the pipeline can cause a code to get thrown, so it's not always a simple fix.

How did you check for vacuum leaks?

Did you replace your O2 sensors with factory sensors or aftermarket? A lot of times, aftermarket sensors aren't worth the metal they're made out of.

Eclipses are finicky cars and in my experience, they often have issues with non-OEM parts.

Anyway, good luck with this. Sounds like you need to do some reverse engineering before you can go forward again.
 

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Discussion Starter #3 (Edited)
I am using a actron autoscanner plus and that is how I found the p1500 there was no service engine light. I ran all the diagnostics and monitored everything and everything was perfect, the ecu was saying it was running like it should be while the rpms are fluttering. After it gets warmed up it stays at about 800 and will act up randomly then straighten itself out.

The alternator was manufactured but I had a local shop open it up to check for the open fr terminal and he said it was perfect put it back together, tested it and it was 100% working. Threw it in the ecplise start it up still fluttering with rmps and then when you turn off the car and turn it back on now it won't charge.

And as for a decent mechanic around here there is no such thing lol the last guy I had look at it he stuffed rags in the iac slot and threw an iac valve on top of it and told me it was fixed....

02 sensors were factory. When I got the car they were missing and when I put them in it started acting up doing all this which leads me (among other things) to believe the issue is with the ecu it can't be anything else.

I had a shop do a smoke test and there was no vacuum leaks.

So when doing an ecu swap do I need the immobilizer from the same car I got the ecu from? Or can they do it with this ecu and just transfer everything over? Orrrr do I need to buy a brand new ecu because for some reason the vin numbers can't be transferred?
 

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And as for a decent mechanic around here there is no such thing lol the last guy I had look at it he stuffed rags in the iac slot and threw an iac valve on top of it and told me it was fixed....
lol... I think I used to work for that guy.

My understanding is that on some earlier models of the Eclipse, the immobilizer ecu needs to be replaced when you're swapping out the ecm. I believe that this applies for the 2001 model year for cars built through July 2000. Here's the Mitsubishi memo on it:



EDIT: Actually, it only looks like you're SOL if you own a Spyder. If you have a RS Coupe, you should be okay.
 

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Discussion Starter #5
Thank you very very much. So I should be all set with the ecu and have them do a simple swap. Only thing now is find a dealership mechanic who knows what they are talking about lol

I appreciate it again btw where did you get that?
 
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