Ducman82

But you don't have spark still I take it. That's going to be the fun one in this situation.

dragonrob

I can go back to original harness and computers as I have all the parts .I know that they worked with the other engine.

Ducman82

That's what I would do. That way you know it all works

SeanR

Oil pressure sensor, engine temp sensor and the IMS are the only real differences engine side of the firewall. He must have the early LH/EZK (87/88) computers if he wants it to be plug and play.

SeanR

That would be the best bet.

soontobered84

+1

ramcram

Yes, I also think that's the way to go. 86 does not have knock sensor system, and the carbon canister venting is vacuum/thermo where as 87 on used electric triggered from the computer.
Your new fuel pressure regulator needs to be 30psi for the 86 computers, unless you use Porken's chipset. The 87 on computers/engines used 55psi fuel pressure.
Oh but of course the injectors on the S4 were lower capacity than the 86?
This calls for greater minds than mine.
S4 injectors, 55psi and 86 computer?
86 injectors, 86 computer and 30psi regulator?

ramcram

Thinking about this some more, I can see 2 possibilities.
My least favourite first.
Use the 86 computers, 86 injectors, 86 fpr and the 86 fuel rails. They all fit, I've tried them. This means of course using an 86 30psi fuel pressure regulator [FPR].
You said you have a new FPR, I'm assuming it fits the 89 fuel rails? So it's 55psi? Porsche changed the FPR fittings in 88, so 86 is a different fit.

Better, cheaper course to go would be to stick with the 55psi FPR, 86 injectors in the 89 rails, the 86 computers and fit the S300 chip set. This would work very well and would be much cheaper than buying a new FPR.
The 86 EZ unit uses a vacuum line to read engine load, this just Ts inti the same vacuum pipe as the regulator, so tat'easy.

dragonrob

I have found a 89 harness would that be the best way to go?

Ducman82

Did you get the IMS relays and board? Figure out what wiring needs to be changed? If not, then No

docmirror

We can jumper around the IMS board. If he puts the 89 harness in, the jumpers around the IMS are easy.

dragonrob

Yes I have the Ims relay and board I also have a 89 harness on the way I hope that this will work out. Rob

dragonrob

I should have the harness next week.

Hilton

Also needs to have the coding plug which matches the 87/88 harness. 89 coding plug in an 87/88 harness will fry the ground wire all the way through the firewall up to the ground point by the throttle wheel.

James Bailey

OUCH !! the voice of experience....