I'm diagnosing an issue I have w/ my motor cutting out at high load & RPM. When going WOT above 5k+ rpm it cuts out. The higher the load / higher the injector PW the more it cuts out.

Engine has a CC306 w/ 1.6:1 rocker rollers. And I just paid MadZ28 for a tune. It helped a LOT with the cutting out. However it still does it. I thought perhaps I'm not getting consistant fuel pressure? So I just hooked up my fuel pressure guage and started the car. the guage at idle read 41.5 psi. When I reved it up the guage bounced all over the place, going as high as 50 psi. Is this typical? I'm really not sure how to diagnose a fuel pump.

What other components could be causing this? I have a new opti.

 

Start the engine. Pull the vacuum compensation line off the regulator. Pressure should be between 41-47psi (unless you told MadZ28 you were using some other pressure). Put the vacuum line back on. Pressure should drop proportional to intake manifold vacuum, which with your CC306 is going to be less of a pressure drop than you would see with a stock cam. Maybe drop 3 to 5psi. Then tape the gauge to the outside of the windshield, and take it out on the road, full load/max rpm. The fuel pressure should hold within 1 to 2psi of the "no vacuum" pressure you got at idle.

Revving the engine under no load proves nothing. You need to see what the pump can do at max load.

 

eeek. I was getting a pressure drop of around 5 psi. I have an after market AFPR set to around 45 psi. When I would hammer on it it would go up to about 50 psi. Then it as I slowly let off it stayed went down pretty close to 45 psi. Then when I tried the same thing and closed the throttle completely right after reving up under load down the highway it would drop to about 38 psi.

~Matt

 

Did you set the AFPR at 45psi with the vacuum line on or off? You want to set it with the vacuum line off. Your pressure is actually a little on the high side the way you have it set.

If you told MadZ28 you were running 45psi, its likely he assumed that was when set correctly without the vacuum line connected. If you are actually running 50psi without the vaccum line, the injectors are supplying about 5.5% more fuel than he intended. Might be running a little on the rich side at WOT.

 

The drop after you let off the gas is from high vacuum. All of this assumes you have zero vacuum or really close to it otherwise your wot fuel pressure will be lower than you think and you may assume your pump is not keeping up. I think it would be prudent to watch a large scale vacuum gauge at WOT hooked to the same line or in close proximity to the manifold reference line going to the regulator to verify 1-2 inches of vacuum at WOT and rpm. If not your fuel pressure will be a bit lower than what it is during the hose off setting.