23Racer

Something hit me last night in bed while I was laying there and couldn't sleep.

As some of you guys may be aware, I have been having ongoing fuel mapping issues with my setup for a while. We got the car all set up and running great at Toronto Motorsport Park which is a track with fairly short straights, all 2nd and a bit of 3rd gear stuff and tight corners where you are on and off the throttle a lot. The car reacted very well to the changes. The A/F's stayed consistent all day and the car shut off and restarted very well.

We thought the car was nailed and then we went to Mosport. At Mosport, which is very high speed full throttle stuff with periods of 30 seconds plus with the car wide open, we ended up having to pull a ton of fueling out of the car to get it toi run clean all the way up the straights. And by a ton I am talking about 20% in the upper bins.

So as I was pondering all of the variables that could cause this and why it was happening, one thing hit me. In my setup I am running stock NA 440 primaries and TII 550 secondaries with a stock fuel pressure regulator from an S4 on the end of the rail without a vacuum line hooked to it. I am also running a 190 LPH Walbro in the tank to ensure that I am getting enough fuel and this Walbro runs wideopen all the time.

So, could the Walbro be overpowering the ability of the stock NA fuel pressure regulator to bleed off fuel pressure and during extended runs, build up fuel pressure to the point that it severely effects the Fuel Mapping so that the car runs rich on extended full throttle pulls?

Ideas, comments and no I have never put a fuel pressure gauge on the car as I thought with all stock stuff, it shouldn't be needed.

Eric

peejay

Fuel pressure regulator issues manifest at idle when it needs to bypass the most.

Walbros aren't particularly beefy pumps in the grand scheme of things. The Bosch pump I have in my car has more flow and no stock regulator ever had a problem with it.

j9fd3s

iTrader: (3)

so maybe that theory doesn't work, but that doesn't mean fuel pressure is consistent for some other reason.

Higgi showed me datalogs of his 20B where you can clearly see the fuel pressure regulator stop increasing fuel pressure as boost increased.

hIGGI

iTrader: (7)

Actually i have run into issues of FPR (SARD) not being able to reduce pressure properly, whenever its caused by too small diameter of return fuel line, having return line routed to fuel surge tank or the combination of more variables....

Problem shows up after everything getting warmed up, on cold start fuel pressure is 3 bar and it could get up to 3,5 bar after few hard runs, making mixture very rich...and ruining oil very fast....

I already bought Aeromotive FPR and plan on installing it, but waiting for another chassis to arrive before getting involved into building new fuel system....

bumpstart

where was you lot when i had to argue with the trolls that a bypass fuel system requires same sized return line to minimise pressure regulation issues at low demand and or at high fuel temps

to the OP.. yes it is well established already that the popular walbro and the 044 both can be problematic with creeping fuel pressure at low fuel demand with stock fuel reg ,, especially when the two speed pump circuit is not there or bypassed


PS
and also.. ( on a 1:1 reg ) if the fuel differential pressure ( compared to manifold pressure ) goes up ( gets a larger differential pressure ) ,, then simply,, the pump cant keep up or the reg cant shut fully
( or is missing its reference line .. or has a faulty PRCv solenoid or has a supply current or earthing issue )

peejay

A thought.

Are you using speed-density or alpha-N?

If speed-density, connect the fuel pressure regulator to the same port as the MAP sensor.

If alpha-N, convert to speed-density.

23Racer

I am using Alpha N as there is no way to measure speed density on a 4 ITB setup accurately. Also, the vacuum drop off from idle to just cracking the throttles is pretty severe, so the only way we could get things to run cleanly and consistently was with Alpha N.

My retun line is the same size as the inlet line, howver I think I am going to put a pressure sensor on the fuel rail to see whats happening. I think it is interesting that we had to pull fuel out the longer we had full throttle pulls.

Eric

peejay

I don't seem to have any problems with it. Run a 1/4" or larger hose to a junction block (not daisy-chained) and sample off of that.

23Racer

DUH........ now I feel really stupid. Thats how I pull the vacuum to get the power brakes to work.
Feeling monster stupid now. Forget everything that I have ever said about this previously.

Eric