91 n/a spitting after running a bit

[Pete_89T2]

Originally Posted by project86

i think what you can do with the omp on the s5s is actually take all the guts out so it doesnt work anymore and leave it plugged in. and then just premix. youre right about it not running if its not plugged in.

Nope, that won't work.... The stock ECU is looking for (a) electrical continuity with the OMP stepper motors, and (b) a correct feedback signal (variable resistance) returning from the position sensors that are part of the OMP - these position sensor(s) monitor the OMP position, so the ECU can have closed-loop control over it. Anything that mucks up these conditions forces the ECU into a limp-home mode. So your problem lies in three possible areas, not necessarily in order of likelyhood: (1) Bad OMP, (2) Bad wiring, (3) Bad ECU.

I would recommend getting the FSM, and following the troubleshooting procedures to the letter. There's a nice flow chart that starts with the CEL error code, and walks you thru all the steps to troubleshoot the OMP. It's not too hard to do, but you'll need to know how to use a volt/ohm meter. Given the age of our FC's, it's not uncommon to have wiring harness problems that cause these sorts of issues, sometimes at random and intermittently, so following the FSM troubleshooting procedures before just blindly swapping OMPs & ECUs will save you some grief.