Another P0306 Misfire Problem

96 5.7L 160K ran good until the fuel pump stopped 2 weeks ago. Replaced fuel pump with a Carter and the dreaded P0306 misfire showed up. Started reading up on this forum; checked fuel pressure, 60 psi with key "on" positioin, drops to 53 psi when motor is running. O.K., decided to put a Delphi pump in after reading about part store replacements. Same fuel pressure? Could the fuel pressure regulator be my problem?

Here is a list of parts I threw at it so far:

-Fuel filter
-MSD 8.5mm wires
-Delphi cap & rotor
-AC Delco platinum plugs
-#6 injector poppet.

Thanks,
CSR44

96 5.7L 160K ran good until the fuel pump stopped 2 weeks ago. Replaced fuel pump with a Carter and the dreaded P0306 misfire showed up. Started reading up on this forum; checked fuel pressure, 60 psi with key "on" positioin, drops to 53 psi when motor is running. O.K., decided to put a Delphi pump in after reading about part store replacements. Same fuel pressure? Could the fuel pressure regulator be my problem?

Here is a list of parts I threw at it so far:

-Fuel filter
-MSD 8.5mm wires
-Delphi cap & rotor
-AC Delco platinum plugs
-#6 injector poppet.

Thanks,
CSR44

YES
Could be pressure regulator.

Also check compression and switch plugs and wires on that cylinder.

What is the camshaft retartd setting?
Any other codes?


The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.