well this really isnt a question, more of valuable information to anyone who has a running s4 motor and wants/needs to put it in the car. and heres the story..

my buddy (rotorybullit) has a black on black GTU with 80,000 original miles, really a gorgeous car. the motor blew an oil seal a year and a half back. It sat in his garage waiting for a motor and he daily drove his 87 sport which wasnt a "looker" (sorry kevin ) and he got a wild hair up his *** and decided to swap the s4 motor into the gtu and use the s5 harness/injectors/and ecu. Everything on the motor was s4 with the exception of the s5 tb modified to run the mechanical omp. We got to the glorious day of initial start up, and it ran like ****. Over 1/2 throotle it would choke and backfire out the intake and all kinds of garbage. We trouble shot this for a month straight with no results.

Well i searched this forum far and wide with no results of anyone having problems with the swap (or anyone really actually doing the swap). Last weekend we decided to plug in the electronic omp (not install it, just plug it in, we zip tied it to the firewall for now ) and it fixed everything. Car runs great.

i know this was long but it was kinda a big deal for me and him figuring this out. The conclusion is with the s5 ecu/harness, the car will not run right AT ALL. If anyone could offer insight on why the omp not being plugged in makes the cars run like **** let me know.

 

I swapped s4 into my s5 and it runs fine. You have to swap everything from the s5 onto the s4. Rotary ressurection has a great website it helped me tremendously.

 

well not really "everything". All the sensors hooked up, besides the afm, we just didnt swap over the electoric omp becuase we didnt have a front cover off an s5. We had all kinda of **** not plugged in due to emissions removal, i just figured the omp wasnt a big deal. aparently it is.

 

Yeah, pretty common. If you are using a S5 ECU it needs to "see" the MOP or the ECU goes into limp mode.

And this has been covered quite a few times... maybe you searched wrong???

 

ok, i have the opposite setup s5 engine in s4 car.
all the sensors and injectors and wiring need to stay with the ecu/harness. the omp must be swapped, prolly best to run premix though...
and do yourself a favor and get a safc in that thing, the stock s4 fuel curve was miles too rich for my s5 engine, so id assume the opposite is true that car should be running lean.

just my $.02

 

its not my car, although i got alot of hours into labor workin on it. But ill definitely forward the information, We didnt search for omp cause we didnt think the ecu needed to see it . guess i was wrong, just a good reference for future noobs like me.

 

I hooked my elecronic up and just zip tied it to the frame out of the way. I run pre-mix now.

 

are we gonna have to run premix even if were running the mechanical omp??

 

Not sure, Pre-mix is better all around omp arent that reliable. It WILL GO INTO LIMP MODE without the electronic omp hooked up!
That is what ARI Yallon of rotary perf told me.

 

limp mode
swap front cover over

my t2 has a temporary s4 t2 motor on it right now

 

swapping the cover doesn't solve the limp mode of the S5 ECU not seeing a electrical MOP

 

^^^^He is right.... it will not. My trick worked it was the only option i had to work with.

 

it does,
seeing as how he would have a place to put a s5 mop on now
i guess i need to be really specific nowadays?