choinga

Been working through a few recent 'issues'...one thing I'm figuring out is that my car has abnormally high fuel pressure at idle. I hadn't run my car in a couple days (fuel pressure gauge showed less than 5PSI) and fired it up. I got the idle to come up fine (no more surging, see my previous thread...) but the wideband AFR bombs into the 11's. It used to stay in the 13's at cold idle until it warmed it and it would move into the 14.7 range. It actually got down as low as 11.1, which is more rich than the Vitesse map is set for WOT.

Anyway, so I pop the hood and look at the fuel pressure gauge - it's at about 54PSI? When I stopped the car, that's where it hung on the gauge.

I've never really noticed what my pressure was at idle before - but that can't be right?

The strange thing is after driving around (and the car seems to be running on average more rich than usual, but when warm will eventually return to 14.7 at idle) the fuel pressure ends up at ~44PSI, which is more normal.

Any ideas? I've got a 10 month old 3BAR FPR and a brand new damper with the steel braid line replacing the stock hose.

Rogue_Ant

With a 3bar FPR, your fuel pressure should be ~43.5psi, without the vacuum line attached.
With the vacuum line attached, at idle your fuel pressure should drop some (about half of your vacuum in inches). Typically around ~35psi.


-Rogue

choinga

hmmm...then what the heck is going on. When I pull the hose off the FPR it goest up of course, which from 50ish PSI, is not good. I've just replaced my fuel pump (with stock OEM). I've got the big 83#'s injectors as a part of the Vitesse kit.

Rogue_Ant

You might have a restriction in your return line. Else, your FPR is bad.

choinga

Yeah, my FPR is new...like less than a year old...might change it out and see what's going on. I also replaced my damper with a brand new unit last month. Can't figure this one out...

Of course, I have to get my car inspected this month and this pops up.

fast951

The cold start AFR will be richer the colder it is. The cold start cycle lasts a short period.

How accurate is your gauge?

The problem is one of the followings. All tests should be performed outside of the garage, have a fuel extinguisher handy.

- Incorrect gauge - If trying a different FPR gives you the correct pressure, and no restriction in the return line, gauge is fine. Or if you have a second gauge to test with...

- Bad FPR.
Test with a different well known FPR. It does not have to be 3bar, this is for pressure testing only.

- Restriction in the fuel return line.
Write down fuel pressure at idle with vacuum line off. Disconnect the fuel return line from the FPR. Connect a fuel line to the regulator and let it dump into a fuel jug. Start the engine, notice any change in fuel pressure.
Note: you can perform this test by jumpering the DME relay to activate the pump instead of running the engine.
WARNING - no sparks near fuel jug... Best to have a long hose to place jug away from car.