Hey Crew,

Need some help diagnosing a surging engine. It's not specifically at idle so I'm not sure if the surging idle threads apply. Details:

- Fresh Rebuild S5 engine (new hard seals, used housings and irons)
- installed in 1st gen racecar - emissions stripped, and all of the non needed harness has been de-pinned
- dual fuel pump and surge tank (LP pump to surge tank, HP denso pump to engine)
- no findable vacuum leaks
- OMP removed (premixing), tucked away and plugged in

On startup it seemed to idle fine. When we flipped the electric fan on, the surging seemed to start. Flip the fan off, and it seemed to be less.

Surges now at idle. Surges at constant 1/4 throttle. Surges at constant 1/2 throttle. Haven't tried to drive it yet. Best way I can describe the surge is its stable for 3-4s then surges up fast for 1 second and then settles back down. We don't have the tach working yet but will have one in on Sunday.

See videos for sounds (youtube links below).

Any help you can provide (or other applicable threads) would be very helpful.

Jesse

 

Sounds like it's running on one rotor. I would check compression, fuel injector operation, spark, and double check the wiring.

 

Adjusted the little idle set screw out and runs much better/smoother.

Now need to troubleshoot running lean on WOT

 

That's good, but odd that the set screw effected all RPM.