Changed FPR, engine acting weird.


Registered User
I recently changed my stock fuel pressure reg. To the billet adjustable unit from super coupe performance. Set the pressure according to the instructions and the engine runs but I have noticed a couple things once I fired it up.

1. The fuel pressure doesn't decrease with engine vacuum but will increase when you snap the throttle. Engine has 15in of vacuum at idle.

2. Now there is a very weird popping noise coming from the exhaust some what randomly as the engine idles. Above 2k rpm the noise stops. Will post a video of the engine idling ~900-1k rpm. So you can hear the noise.

When this popping occurs the idle is unaffected. It doesn't cause the engine to stumble or act like it wants to stall. Thought it may be unburnt fuel igniting in the exhaust or something from a misfiring cylinder. Even though the engine idle wasn't rough or didn't seem like it was missing.

I started pulling plug wires one by one to see if the idle changed. When I got to the #1 cylinder wire and pulled it, the noise stopped and idle did not change at all. Soon as I plugged the wire back in the noise started, again idle did not change. After checking all cylinders this way, I found that pulling both the #1 and #2 plug wires off had no affect on engine idle, where as pulling the others the engine died out almost immediately. This issue with the cylinders I'm almost certain was present before changing the FPR. I'm just baffled that the engine can seemingly idle smoothly with 2 dead cylinders.

Next I pulled the plugs out and left them attached to the plug wires and grounded them, cranked the engine and the plugs were sparking. Should be noted that both 1&2 plugs were very blackened.

Did a compression test got 140 psi.
I am at a loss.
Update: never ever assume anything. I was poking around here in the garage and happened to notice that the two cylinders in question where flipped at the coil. #1 was plugged into #2 at the coil etc. I don't know why I didn't think to verify firing order. It's what I get for assuming previous owner put it together right.
WOW!! This is the same car that you drove 6 hours to get it home when you bought it? No wonder it had what you described as a "stumble" & no throttle response below 2,000 rpm.