CK5 Network
Become a member of the largest online community for Chevy K5 Blazer, Suburban and C/K series truck owners!

Ls swap fuel issues

Cucv_M1008

Cthulhu Forever
Premium Member
Joined
Jun 24, 2010
Posts
1,686
Reaction score
422
Location
Carver, Oregon
Stock 5.3, stock tune vats EGR and other things removed from the PCM. new in-tank AEM 50-1000 fuel pump new fuel regulator on the fuel rail rebuilt injectors that came with the truck, the engine surges and won't idle, fuel pressure goes up and down between 40 and 50 psi and won't go past that. I'm so out of my league with this and I don't understand why it's doing this. I have about 5 grounds on the engine/trans combo (do I need more?) any help would be great.
 

Babaganoosh

1 ton status
Premium Member
GMOTM Winner
Joined
May 30, 2007
Posts
14,208
Reaction score
7,316
Location
Phoenix Arizona
What fuel regulator did you use? some of the cheaper corvette fuel filter/regulators don't work. If you have the one on the rail with the vacuum line it might be leaking.
 

Cucv_M1008

Cthulhu Forever
Premium Member
Joined
Jun 24, 2010
Posts
1,686
Reaction score
422
Location
Carver, Oregon
What fuel regulator did you use? some of the cheaper corvette fuel filter/regulators don't work. If you have the one on the rail with the vacuum line it might be leaking.
I used the one on the rail, I have a return line with my system so no corvette system. I used a new hose also that connects the regulator to the intake vacuum system. Picture is current, I pulled intake to change from cheap gaskets to FelPro and install GM knock sensors.

regulator.jpg
 

Cucv_M1008

Cthulhu Forever
Premium Member
Joined
Jun 24, 2010
Posts
1,686
Reaction score
422
Location
Carver, Oregon
No, its still dead and Im closing it up for the winter, I dont have a garage to put it in right now.
 

ZooMad75

#crawlabago
Premium Member
GMOTM Winner
Joined
Apr 5, 2003
Posts
6,948
Reaction score
14,143
Location
Pueblo, CO
Did you attempt to adjust the regulator? Should be a security torx screw dead center in the regulator. It might have a dab of paint over some or all of it to discourage adjustment. Pop the paint off and adjust the regulator while running with a gauge on.

It's pretty fine adjustments as a 1/4 will jump pressure by a bunch.

Typically low fuel pressure is one of three things. Low pump output, miss adjusted regulator or stuck open/leaky injectors.

So if the adjustment does not make a difference and since the pump is fresh I'd focus on the injectors. One thing to do is keep the fuel pressure gauge hooked up and run the engine. Shut the engine off and watch the gauge. If everything is ok, the gauge may only drop a few psi but hold for a long time. If an injector or multiple are leaking you see the pressure drop quickly after shut down. Keep in mind there is a check valve in the pump that will hold pressure on the line when not running. If that check valve leaks the same pressure drop will happen. To know for sure you can clamp off a rubber section on the return line to eliminate the check valve leak. If the pressure drop still happens, start looking at injectors.

I'd suspect the injectors if they are original. Ethanol fuel is not kind if they sat for any length of time. Might get away with pulling them and cleaning them. Worst case you pick up some injectors for it.
 

az_762_nato

Dysfunctional Veteran
Premium Member
Joined
Apr 8, 2007
Posts
516
Reaction score
117
Location
Colorado Springs
Do you have a CEL on or throwing any hard set codes or pending codes? The RPM surging can make the vacuum surge, which in turn can make the fuel pressure surge with a vacuum referenced regulator. The cam sensor and map sensor plugs are very close to one another and have the same plug so it's easy to get them crossed accidentally and that can definitely set codes and make it surge badly
 
Top Bottom