I need some help diagnosing a fuel pressure problem. I have a Vortech boosted 383 LT-1 (12 pounds boost) with additional injectors at the throttle body. I also have pod-mounted boost and fuel pressure guages and a mityvac for testing. The problem is that fuel pressure does not rise with boost - although it tracks ok with vacuum.

Specific diagnostic readings:

FP at idle (18 inches Hg) 39 psi

FP at '0' vacuum 47 psi

FP at 5lbs boost 47 psi (should be 47 plus 5 = 52).
FP at 10lbs bost 47psi (s/b 47 plus 10 = 57 psi)

If I disconnect the vacuum line from the FP regulator I get 47psi

I have tested the FP regulator at idle - applying 10lbs pressure with mityvac gives 57psi at the pod guage.

I have tested and fixed all vacuum leaks (I had a couple of slow leaks due to old connectors) - all vac lines from intake hold pressure without leaking down.

I cleaned all harness connections and earth connections plus the positive wire 'cluster' behind the battery. Voltage at the fuel pump connector at idle is 13.6V.

I replaced the fuel pump with a new Walbro (thanks Greg)

I replaced the fuel filter as a maintenance item 2,000 miles ago. I am going to replace it again.

Now I am at a loss what the problem could be. I suspect maybe a fuel line blockage, but I am very suspicious that the FP does not track with boost at all.

Any suggestions appreciated!

Oh - and for those concerned about detonation I am running alcohol injection and also have the spark backed out 2 degrees per pound of boost, so I am not getting any detonation.

 

If you are runing the stock regulator they don't work very well as a boost referenced regulator. By boost reference I mean the regulator would raise the fuel pressure at a ratio of 1:1 so in saying that for every pound of boost pressure it sees, there will be a equal pressure rise in fuel pressure.

It may work at idle with your mity-vac, but under WOT conditions there is a considerable amount more fuel flow through the injectors. Did you connect a gauge to the regulator vacuum line to make sure that boost is sensed there?

Did you use the Vortech FMU that was supplied with the kit? That device will raise the fuel pressure at a ratio of I beleive 10:1 so for every pound of boost pressure it would raise the fuel pressure 10 pounds. You definitely need some sort of enrichment either through programming or with a FMU or with a alky injection system or a combination of the above.

 

The stock regulator should work just fine with boost.

FP at idle (18 inches Hg) should be 47 minus (18/2) = 38 psi
FP at '0' vacuum 47 psi
FP at 5lbs boost should be 47 plus 5 = 52 psi
FP at 10lbs boost should be 47 plus 10 = 57 psi

It seems to work as intended when the fuel consumtion is low, but not during wot.

I would look at the pump one more time.

You could disconnect the fuel return line from the regulator and run a hose to a bucket. Then you force the fuel pump to run using a wire in the ALDL connector.
Measure the fuel flow to the bucket.
Rise the fuel pressure using your mityvac and measure the flow again.

Do you get enough flow for your injector size?

 

I think I will do the fuel pump test as you suggest. One quick question - would you recommend re-using the fuel from th bucket or 'recycling' at a local recycling facility?

 

If the bucket and hose are clean when you start, then you can re-use the fuel.