Hi guys - My P1SC is showing ~7-8psi of boost, but I don't think it's generating enough fuel pressure at WOT.

At idle it's ~42-46, then goes up to mid 50's i think on the fuel pressure gauge when at WOT.

Shouldn't it be spiking well into the 60's-70's under boost?

I'll be doing more scanning later, but it definitely showed some lean spots last time I was out.

The FMU screw on top was all the way to the right (clockwise), have not changed it the other direction and gone out again yet, but I'm not sure what else to check.

 

You want yor fuel pressure to rise on a 1:1 ratio with boost so from a basline of 46lbs + 8 lbs boost = 54lbs fuel pressure at max boost. So mid 50'sis reasonable. If you're leaning out under boost you'll want to add more fuel not fuel pressure. Are you using a wideband to log the afr?

 

Thanks for the reply.

I knew the 1:1 ratio, and it does seem to be 46 -> 54, so that makes me feel better.
Thought I had read it was supposed to spike up even higher briefly before going back to that range.

I'll be using a wideband the next time I'm out tuning and will add more fuel at the required spots now that it seems my FMU is working properly.

 

You have a PM

 

If you have a FMU it should be raising faster then 1:1. The stock regulator raises 1:1, an FMU should be like 10:1.

 

KS91Z28 - Thanks for the tips. I do have a new fuel pump already and the filter was changed w/in the year too.

MattODoom - Are you sure about the 10:1?? If that is the case the FP should be well over 70-80psi, no?

Can I get a definitive answer here folks? Don't want to be chasing ghosts.

What else can I do to verify proper pressure is being received?

 

Depends on the rate of the FMU. There is different ones, 6:1, 8:1, 10:1, 12:1 some are adjustable, etc. But it should not be 1:1, if it is, somethings wrong.

 

TPInside, I have the 88-92 P1SC kit for my car. When I was running the FMU, inline pump and stock pump, under boost (around 4k rpms) I was in the upper 70's for fuel PSI. My is look for 70-80 PSI of fuel under boost.

 

Thread jack...

With stock size injectors?
I have recently encountered a problem with my 3.1 (bearing) and was going to keep moderate boost. But I'm getting a 3.4 soon, so I'm going all out on the 3.1 and seeing what happens . I have an 8:1 FMU and have adjusted my base FP down so the car would idle with 24# inj vs stock 15#. I'm reading about 27psi FP now and at 15psig of boost, I would see 147psi? I don't think the stock fuel delivery can handle that (or can it?), did you have any problems with that much pressure, or did you upgrade for the S/C?

 

Stock motor including injectors. There were either 19# or 22#'s I ditched them for 60#'s because I'm now into a bigger engine and more boost.

 

Using the spreadsheet I came up with based off of fuel flow change as pressure increases, you would need a FMU with a 6.1:1 rising rate which would make for a total pressure of 110.5 psi which is higher than I have seen anyone go to. Your probably better off tuning for it with the computer than using just an FMU. Fuel flow increases with the square root of the new pressure divided by the original pressure.

 

Keep in mind that some injectors won't spray properly above 90 PSI. An FMU is good, but the max. PSI must be inline with what the injectors can handle.

 

I've got some blue top Denso's.

 

Good stuff....