Hey guys, I’m having some issues with my fc and after weeks of doing nothing but scrounging these forums and everything on the internet I haven’t really found the information I need. So I have a 1989 na fc rx7 with 100k miles on it, about 800 miles ago an unopened 60k mile s4 engine was put into it. All of the electronics were swapped to an s5 aswell as the intake and all the necessary stuff. This is where the problems come in, so everytime I drive about 5 minutes in I can only give it about 10% throttle or else it’ll bog and misfire and won’t make power, this however can be remedied by turning the key off and then back on. I believe that my omp is fried and that in turn fried my ecu. The reasoning is because my ecu will NOT throw codes. I’ve tried grounding the diagnostics sensor I’ve tried making a led sensor, the ecu itself will not push 12v to the diagnostics port. The omp is removed from the block and zip tied to my passenger side shock tower. I also happen to have a 1986 s4 fc with everything in it except the motor needs coolant jackets. So my thought process is that I could pull my intake manifold and all the s4 sensors and swap all my electronics including ecu and harness to the s5. Would this work? I’m dailying my s5 blue fc and am a broke college student who in no way can afford a link ecu. I was thinking of also just going the microsquirt route but am very scared to try to tune my own car and risk breaking my only daily as of right now. Any help would be much appreciated. Would it be worth the effort to swap everything over or should I just take the risk and get a megasquirt/microsquirt and run a wideband and gm coolant sensor.

 

Looks like you can get a S5 n/a ecu for under $100. Just need to sort out if your OMP is the problem or not so if you were to pick up a S5 ecu so you don't risk damaging it.
S5 RX-7 Ecu for sale | eBay

 

I already got one and it ran the car even worse than my current one lol, and even if I find a good ecu my omp is still cooked and an expensive issue. I could buy a microsquirt with harness and sensors for the price of a decent omp and yet another ecu

 

If your OMP is bad I don't know that any stock ECU is going to run right until you have a good OMP plugged into it. How much is a microsquirt? Looks like a used S5 OMP is around $250 but I guess there is no guarantee it works.
1989 1990 1991 MAZDA RX-7 FC3S S5 Electronic Oil Metering Pump OMP | eBay
If an FD pump could be made to work with the FC ECU they are way cheaper. $79 to $179.
Mazda RX7 FD3S 13B-REW OEM Oil Metering Pump OMP | eBay

 

an s4 ecu won’t throw my car into limp mode because a s4 omp is mechanical. I can look into converting a fd omp to work with my car but I haven’t found much about that on here or elsewhere. Microsquirts are about 320$ to 400$ for a kit with a wiring harness.

 

As you know from your original post some of the sensors are different between the S4 and S5 but there is also wiring under the dash that is different from what I understand, So the S4 ECU wouldn't be plug and play even after swapping the sensors that's under the hood. Your best bet if using a stock ECU is to get a S5 ECU working in your S5 car. The S4 ECU not throwing the car into limp mode over the OMP is a moot point if you can't get the S4 ECU to run the car at all. Lots of people have gone down this path of trying to use a different series ECU and their car never ran again.

 

thats understandable, I was just curious as to what was different body harness wise. I really want to go standalone but worried about everything it entails and money especially. I’ll try my best to source a working omp I assume in the meantime. It’s very annoying barely being able to get up to 60

 

Swapping the S4 electronics could help, especially since you have the parts. If the ECU isn't throwing codes, that's concerning. Microsquirt is a good option, but it requires some tuning knowledge.

 

I’m definitely considering going the microsquirt route, one my friends tuners is about to make a website with a pretty in depth guide to the tuning process and plug and play kits for the ms3

 

Unfortunately, not true. It depends on which S4 you have. The 1986 & 1987 OMPs ARE mechanical. The 1988 is electronic like the S5s. The ECU has to read an electronic OMP to keep it out of limp mode. I'm sure someone has found a work around for this, but I don't know what it is.

 

If the ECU isn’t throwing any codes, it could definitely be the OMP messing with things. Swapping over the S4 sensors and harness might help, especially if the S5 setup is giving you so much trouble. But honestly, if you’re considering Microsquirt, it could give you a lot more control and flexibility in the long run. Just make sure to take it slow with tuning; there are plenty of resources out there to help you out. Whatever you choose, I’d try to fix that OMP first before going all in on a new setup.