FC3J

Hey well let me start by saying im new to rotary engines. I have both a ecu/pcm/ecm/cpu whatever you want to call it from a 87 and a 90. I have a 87 motor in my car. so first would i be able to run the 87 off the 90 computer?, and are there any main differences between the two wiring harness's? and lastly did both of the motors the 87 and 90 have a Maf sensor because so far ive only found 1 Maf sensor harness connector?

RotaryRocket88

iTrader: (7)

No, you can't use an S5 ('89-'91) ECU in an S4 ('86-'88) car without major rewiring. The plugs are not even the same shape, the wire order is different, and the S5 ECU will require S5 sensors.

All FCs have what is called an Air Flow Meter (AFM), which measures in-coming air volume. They are not interchangeable either.

Browse through the S4 and S5 FSMs, which are available free on the web. There are links in the 2nd gen FAQ if you need them.

FC3J

Well I have the wiring harness for both the 87 and 90. The body is a 90 but the motor is a 87. So I have all the sensors from the S5 minus the AFM and the whole S4. So i would be using the S5 ECU in a S5 car with A S4 motor is that still not possible?

RotaryRocket88

iTrader: (7)

The general rule is not to mix and match wiring, ECUs and sensors from different series. They are very different. You would have a much easier time using only the S4 block, swapping an S5 front cover and MOP/OMP on, then using the rest of the S5 electronics, wiring and ECU. There are some complications such as adapting S5 manifolds to an S4 block, but there are guides for that too. Check the links below.

http://www.rotaryresurrection.com/2n...o_s5_swap.html
http://homepage.mac.com/carldavis/intake.html

FC3J

Oh Ok great. Ill be sure to check those put thanks. One more thing though would it just be easier to swap the dash out for a 87 dash and use the wiring harness and computer from the 87 would you sill need to change other things over?

Or does that still fall in the mixing electronics between series which i think it does. so it would be s4 cpu, s4 harness, s4 motor s5 car.

RotaryRocket88

iTrader: (7)

You would either need an S4 front harness, engine harness and instrument cluster harness (in addition to the S4 emissions harness), or you would have to adapt the existing S5 wiring. When you say you have an S4 harness, I'm assuming you mean the emissions harness, which is the one connected to most of the engine sensors and ECU. Again, more complicated rewiring that can be avoided by keeping everything electrical S5.

FC3J

ahh ok im starting to get it but still need some clarification. Sorry lol but this is something im not real familiar with but, when you say keep everything electrical s5 do you mean all the electrical portions connected to the block like the link says (ie TPS, AFM, MOP, CAS ect.) and what is the front harness?

and if im not mistaken the Instrument cluster harness is also connected to the ecu right?. Again sorry for being a bit annoying and a noob lol

RotaryRocket88

iTrader: (7)

If you don't already have both series' wiring diagrams, you can get them here: http://foxed.ca/foxed/index.php?page...nual#secondgen.

When I say "everything electrical", I mean the sensors, wiring and ECU.

Page Z-7 of the S5 wiring diagrams shows harness names and locations. The front (F) harness is basically the main harness on the car. It connects to the emissions (EM) harness and ECU on the passenger-side of the interior, then wraps around behind the dash and connects to the instrument cluster (IC) harness and instrument panel (IC) harness (warning lights). After that it goes down to the fuse box, through the firewall, to a bunch of relays, up to the main fuse box and then to some more relays around the headlights and radiator. Along the way, it also connects to the engine (E) harness, which connects to some things like the CAS, transmission switches and starter solenoid.

This is why it's not as simple as just changing the ECU, emissions harness and engine sensors. In terms of wiring, S5s are practically a different car from S4s.

FC3J

Alright I get it now yea they are two different cars completely I may be getting a deal on a 90 13b so I may just swap the motors out to the one that should be there. Thanks for your patience and help.