Fuel pressure issue

turtle64b

The voltage seems normal. As my car warms up, I notice manifold pressure drop (greater vacuum), which would drive fuel pressure down with it. I have the same pump and wiring kit but with larger injectors (1050x). Set reference (@ atmospheric pressure) to ~52 psi and then reconnected the manifold air line to the regulator. Hven't touched it since, no issues.

Jinxx

With my other nismo I had a supercharger on I never noticed any pressure drop and it was set around 52 as well ... I’m wondering if maybe it’s a regulator issue

turtle64b

The pressure should be set with the reference line (air line from the manifold to the regulator) disconnected. Manifold pressure with the car warm should be about 22in vacuum (-22 on my pressure meter). I notice that when I start my car in the mornings, vacuum starts out around 12-14in vacuum. This leads to pressure being lower than the set 52psi with the line open to atmosphere.

Not trying to be facetious or anything, setting of the reference at atmospheric pressure and the reason for the manifold tap are to ensure that fuel pressure is always the same relative to manifold pressure. Again, I'm not saying that you don't know this, just for anyone who might read this and not know why that line is there.

With your Nismo, the reference could have been set up incorrectly or differently at the recommendation of a different tuner. Seb told me 52psi at idle with the line disconnected. Then reconnect the line and all was good. Perhaps someone either wanted a higher pressure or set the reference at idle with the line connected to the manifold.

I hope this helps, I will look at my regulator pressure when I get home to see what it reads.

Jinxx

I know how to set the pressure ...but once the pressure is set ,shouldn’t it remain consistent ..the manifold does have a brief period when starting that the vacuum is less but once it idles down the vacuum should be at it max ( mine is around 18) and at this time fuel pressure should be stable ....which mine is ,what I’m seeing is if I go for a drive after this and come back and check it the pressure is about 5 lbs lower even with the same vacuum (18) ....I assume the voltage was the issue because at the time I was still on the stock wiring...and I noticed that fuel pressure was higher when my voltage gauge was over 14 and lower when voltage was under 14 ...thinking that was the issue added the voltage wiring kit ..but still same thing ....to be fair with my other car the fuel pump was the 255 walbro and it held pressure consistent at 52 ....when this car was tuned it was around 45 it drops to 40 ....not sure what could be changing to cause the drop fuel filter is new ...I guese it leaves the regulator or pump

Also the vacuum reference would be for increase fuel pressure as boost increases in a idle state the pressure shouldn’t change ..yes it is different with the vacuum line off and it is open atmosphere but set point should remain the same after setting