Here it is. I recently bought an 89 GTU. I paid $500 for the car in non-running condition. The seller said that it had fuel problems and had taken the upper half off. The car has immaculate interior and the body is straight, but the paint is terrible. Well, going on what the seller said, I replaced the fuel pump (which was bad) with one out of my parts car. I then replaced the injectors with ones out of another S5 engine. I couldn't get the car to start, and when it did it ran very rough and would not idle. It did seem to run smooth at 5k though. I tested sensors and found a bad TPS. Wow Mazda was sure proud of that thing. $399 if I remember correctly. I haven't replaced it yet. I also found that bits of catalytic converter came out of the exhaust. I tested the compression the other day and here's what I found. 115 psi on the rear rotor (90 per face) and absolutely zero on the front rotor. I tried to use some ATF and that didn't help at all. Here's the question. I have a good running S4 motor. Should I use this engine with the S4 electronics and harness or should I jus use the shortblock? Has anyone done this swap, and if so can you tell me about it? Please.

 

i say use the shortblock, and rebuild the thing. the s5s are heavier than s4s, so an s4 engine won't help performance at all. do the swap until you get the s5 engine running again, imo

 

Thanks for the info. I was weondering on how much the s4 engine would throw the s5 ecu out of whack though. Does anyone have any other suggestions for this. I am leaning toward swapping wiring too. Does anyone know if all the s5 stuff will bolt up to the s4 shortblock?

 

I did this exact swap. i took everything off of my s4 block and replaced it with everything on the s5. You have to block of the egr on the s4 block which is located on the middle iron. It was pretty simple nothing to hard about it.

 

also if you swap out the wiring you have to swap all wiring even under the dash. And it is no fun. your best bet is to just swap over all the s5 parts to the s4 engine

 

Your best bet is to stay within your series. Swapping the electronics over is a major pain in the ***.. However there are some writeups that Kevin Landers has made up to help guide you if you want to swap your S4 motor into your S5 car.

www.rotaryresurrection.com

 

Many thank you's to everyone that has posted. The only other problem is that I need the car to pass emissons after the swap. I also need to replace the TPS then. One other question. Are the front and rear housings on the S5 engine interchangable with each other?

 

bump