crosstraining

iTrader: (1)

Is the stock fuel pressure for an LQ9 the same as an LS1? Which I think is 58 psi?
Thanks

Old Geezer

iTrader: (3)

Yep...

sirhk100

For a newbie that doesn't know jack about the LS platform I fricken LOVE this forum!!! Rarely need to post!!! I've made a couple threads for info I couldn't find but simple threads like this have been a savior for answering questions I've had!!!

Beyer

I have a LQ9 (with a cam if that matters), and it has been running a little rough right off of idle. It seems to clear out fine at WOT.
The motor is in a jeep, and nothing has been changed in a few years and it just started doing it last weekend. No codes thrown. Fuel pressure is 60 psi with just ignition on, then it drops to 52 when at idle, then it drops to 50 when I rev it a little.
I am still using stock fuel pressure regulator, and am using a Airtax E8248 pump, and new fuel filter.
I did pull the vacuum line to the regulator, and it jumps back up to 60 psi.
Also, when I kill the ignition, it holds the pressure on the gauge.

Any ideas? Pump? Regulator?

JoeNova

Sounds like the regulator is working exactly as it should.
I would say fuel filter but you say its new.

Has it been tuned for the cam? Have you tried changing plugs?

vwdave

iTrader: (3)

Correct me if Im wrong, but arent most stock LS engines vacuumless regulators? I dont think I remember my Formula having a vacuum fitting on it.

JoeNova

The return style truck rails run a rail mounted vacuum regulator.

Beyer

It was tuned for the cam a few years ago, and has been running great until last weekend.
Changing plugs this weekend, to see if that helps.

Beyer

So is it normal to drop from 60 psi with ignition only to 52 psi at idle (I have read mixed reviews on this)? Trying to figure out if my fuel pump is weak and needs replaced.

JoeNova

Yes. That's what the vacuum line hooked to the regulator does. Vacuum pulls down the fuel pressure at idle.