vicki711

I have a 95 z28 with the 4 cam kit just replaced all my injectors plugs wires fuel pump and filter no matter if it's running or key on it reads 37 psi.the car fires rite up but driving it starts to buck.any ideas

Injuneer

Are you measuring the pressure at idle, with or without the vacuum compensation line connected to the fuel pressure regulator? Have you measured the pressure out on the road with the engine under max load - WOT at over 5,000 RPM?

By "4 cam kit" do you mean the LT4 cam, or the LT4 HOT cam? Who tuned it for the cam? What size injectors did you install?

vicki711

Measured it with just the key on at an idle an wide open never seems to change..I installed the lt4 hot cam with stock injectors.gm tuners out of Minnesota retuned the ECM. Do I need to check the pressure with the vac line off the regulator?

Injuneer

At idle, vacuum line off the regulator (and plugged to prevent a vacuum leak) pressure should be 43.5 PSI. GM accepts anything from 41-47 PSI as within range. Reattach the vacuum line to the regulator. Pressure should drop proportional to intake manifold vacuum. About an 8-10 PSI DROP from the ne vacuum pressure with a stock cam. Maybe a 5-6 PSI DROP with the HOT cam. In other words if you have 43.5 PSI without the vacuum line, 37 or 38 PSI with the vacuum line is OK.

But at max engine load, WOT there is very little vacuum, so you need at least 40 PSI. A plugged air filter will increase manifold vacuum at WOT, and could reduce fuel pressure.

vicki711

I dbl checked the pressure all seems good there.this thing is really trying my patience

Injuneer

Did it ever run right after the tune? Have you ever scanned it for codes? Have you had the ICM tested? What plugs are you running and what gap?

Might be time for a data log using Scan9495.

https://www.camaroz28.com/forums/com...95-lt1-874306/