I had an issue with my FMU and it was causing extremely high fuel pressures at idle. I fixed the FMU issue which was a chore! Now, my fuel pressure is 43.5 at idle and it increases through the rpm range with boost to 85psi as it should. Now, when I run through the gears, my car backfires @ 5k rpm. Anytime I get above 4500-5k, I"m getting a backfire and not just one. I have to pull my foot out of it, then it stops. I have changed multiple fmu settings from the lowest to the highest and no change. Still backfire's I tried increasing the fuel pressure from the afpr to 52, and nothing!

What gives?

 

I forgot to add, when I have my car in idle, vacume gauge is reading a steady 15. When I put my car in drive, it drops to 12-13 as it always has thanks to my cam. Now, here's an interesting thing that is going on. Every so often, the car will loose vacume and it seems the car is loading up, then it corrects its self? It does not do it very often, once every 5-8 minutes only when it's in drive. I HATE MY CAR

Thanks for your help!

 

valve float

how old are your springs

also stock hei will not handle the r's

 

Nope. My car was running fine until I put the smaller injectors in. I changed the injectors to the larger ones that I was running and it's still running like crap. I checked my valve lash and it's perfect. Your though process is on the same line of thinking as mine. Tomorrow, I'm going to check and replace plugs, wires, cap/rotor and check my coil.

Thanks for the comment and idea

 

Turns out, my MDS box was the problem. My revlimiter is not allowing my Z to go above 5k. My ignition box is over 10 yrs old...time for a new one