I'm hopefully about to purchase an rx7 FD rolling chassis, and i wanted to avoid an odometer discrepency. Can i use the USDM ECU thats included with the car on the JDM motor? I can't find anything that would make them incompatible, has anyone done this?

 

You're actually asking a few questions here.

First off, the odometer goes with the instrument cluster - it retains the odometer reading, the ECU has nothing to do with it. Remember, this is a car that was designed in the early '90s when things were much simpler .

Second, the US ECU will run a JDM engine just fine. Smart way to tackle the problem is to get the Japanese motor, go through everything to make sure it's 100%, then install. There are some minor differences with the JDM and US wiring for the ECU itself. That's moreso your question, and it depends on what harness you'll be using.

Dale

 

Thanks dale. I'll be using the JDM harness so i spose I'll use the JDM ecu also. How's your experiance with the ebay importers been? I'm REALLY leery about buying a motor from those guys.

 

well the USDM ecu will be looking for some emissions that simply dont belong. You can find the N3A7-Japanese ecu's pretty cheap.

while you're at it - might as well use the 16bit harness and ECU;

 

I think it would be pretty tricky to use the later 16-bit ECU and harness. The harness only goes to 2 of the plugs on the ECU, the other 2 plug into the dash harness. You'd have to do a LOT of wiring work to get that all to work together.

The Ebay JDM motor importers can be tricky. I've bought 2 JDM motors for parts in the past - one had a blown rotor, the other was good, but that's OK because I was buying them for parts.

I think more of us folks in the US need to buy JDM motors - it's a great, inexpensive source for many of the core parts we need, like turbos and engine parts. Both motors I've bought were very low mileage, the rubber vacuum hoses were still soft, the wiring harness was still soft and nice, etc. But, factor in that you might have to go through the engine. There's nothing more frustrating than putting a motor in your car then discovering that you have to pull it all out again.

Regardless, buying a JDM long block nets you a LOT of part that can be sold to help defray the costs - low mileage turbos, transmission, wiring harness, intake manifolds (which are the JDM versions with no emissions), fuel injectors, etc. etc. etc.

Also, it's always smart to take a motor like this, put it on an engine stand, and strip it to the short block, then clean all the parts and put them back on with new gaskets, sealed up and installed right. Not to mention the oil pan - that's normally trash, as the motors sit on the oil pan and are crushed by the time you get them. The oil pan has to come off and be re-done.

Dale

 

The other plug runs to the main - front harness.. it has stuff like diagnostics port, etc in it. i think the rpm output for the tachometer. I have a few of the 2000 / 2001 main / front harnesses here - I guess I could should look.

 

Thanks Dale, a wealth of information as usual. I was just gonna strip it to the shortblock and compression test it... I got less than 95 PSI i gotta rebuild. Any ideas what i should strap the motor to to test it? just put the shortblock in the car and test lol?