Extremely High Fuel pressure after motor build

[christiane]

I just got my car back on the road after my build up and once I started it I noticed I had extremely high fuel pressure during idle. Prior to the engine build up my idle fuel pressure was ~34 psi now my idle FP is generally running around 66 psi. I am running the stock FPR. COuld this be caused by increased pressure causing an increased vacum at idle? If so is it possible to 'tune' this out or will I need to purchase an adjustable fuel pressure regulator? The car is not running terrible (but I am only turning 5000 rpms during engine break in) and the A/F ratio is comparable to what it was prior to the install. Anyone have any ideas/ suggestions?

 

[Old Mitsu Tech]

High vacuum will cause a lowering of the fuel pressure. You may have lost vacuum to the regulator. High vacuum is sensed as idle as idle and deceleration are your highest vacuum times. Low vacuum is sensed as acceleration and should raise the fuel pressure.

Good Luck

 

[92awddsm]

Replace the fuel pressure gauge. If it got bumped aroun during the build, it might have been damaged. If your a/f ratio is close to the same as before, it is kind of hard to believe that you are running 32psi fp increase. You would be running extremely rich and probably couldnt keep it running at idle.

 

[christiane]

I will double check that the FPR is getting vacum. It does struggle to idle, but like I said previously the O2 readings are not way off of norm it is richer than before (then again the readings are still cycling at idle). I did replace my fuel filter so I am wondering if the old filter was just so clogged that it was only allowing the 34 psi to reach the gauge sending unit.

I will look at the gauge but as it is an electronic gauge and the sending unit was removed from the car during the install I find that unlikely.

 

[oldman]

I didn't see a fuel pump upgrade in your profile, which pump do you have? Was the 34psi with the stock pump and 66psi with an upgraded pump? Did you remove vacuum lines? Follow the vacuum line from the fpr and tell us where it leads to.

 

[christiane]

I apologize about not having the fuel pump in my pro. Ayway, it is a walbro 190. When I got in last night from work I checked that the vacum line was hooked up to the FP. As for the plumming of that particular vacum circuit: it comes off the rear barbed fitting on the intake manifold, goes to a T junction where it is split to my boost gauge, and then to my FPR. After letting the car run the fuel pressure seems to stay between 40 and 50 psi. This would be acceptable if the car wasn't still stumbling around.
One additional issue I noticed was it does not appear to add additional fuel pressure as I reach boost (granted it is only 5 PSI at this point. I would assume vacum leak at this point, but my boost gauge is showingpsi and holding. Thanks for the help everyone.

 

[oldman]

As for the plumming of that particular vacum circuit: it comes off the rear barbed fitting on the intake manifold, goes to a T junction where it is split to my boost gauge, and then to my FPR.

The rear barb fitting is suppose to be hooked up to the brake booster, did you remove the brake booster hose with build in check valve?

After letting the car run the fuel pressure seems to stay between 40 and 50 psi.

At idle? It should stay constant cold vs. warm, the only change that should occure is slightly less reading on the gauge due to heat. Since you have the gauge in the car, this should not apply to you so something is definitely wrong. 40-50 psi is a huge change, are you saying it's bouncing around between 40-50 psi as you let it idle?

One additional issue I noticed was it does not appear to add additional fuel pressure as I reach boost (granted it is only 5 PSI at this point. I would assume vacum leak at this point, but my boost gauge is showingpsi and holding.

What is the vacuum reading at idle?

This what I suspect is happening.

1. Bad reading on the fuel gauge, I'm not familiar with an electronic unit with sending unit so you will have to make that determination on your own.

2. Defective fpr not keeping up with 1:1 ratio with intake pressure. My brand new Aromotoive AFPR was leaking pressure out of the adjustment screw giving me all kinds of trouble until I fixed it, BTW everyone with the Aromotive unit should check this as I'm pretty sure every new unit will leak unless you thread sealant it because the threading on the adjustment screw is not NPT.

3. Rare but not impossible, the 190 could be overrunning the fpr.

4. Improper installation of the pump resulted in damaged o-ring causing inconsistent fuel pressure.

5. Boost/vacuum leak.

Good luck.

 

[oldman]

BTW How are you able to run only 5psi? You must have massive boost/vacuum leaks.

 

[christiane]

I got up early this morning to take the dirt car out of the garage and put the DSM back in. Went through bled and adjusted the clutch some more. Then I started to inspect the vacum lines related to the FPR. I never really found anything, however when I started the car back up to take it out of the garage he fuel pressure was reading 34 PSI.

As best I can tell there must be some sort of small leak in that circuit. I will replace all of the vacum lines and get a new compression fitting for the end of the boost gauge.

I installed te 5 PSI spring in my external wastegate for engine break in and bypassed my boost controller in order to reach 5 psi.

Thanks for all your help.