Stuff all turbo guys should know about the BEGI FMU

[Guest bastaad525]

Just got off the phone with one of the reps at BEGI, asking a ton of questions regarding their FMU's and found out some interesting stuff.

 

 

I know the guys here who have bought them have all bought the number 2022 FMU, the one recommended for factory, OEM turbo cars (most of our Z's). However, most guys here have also talked about or had problems with, this FMU running too rich under mid boost, partial throttle operation. The problem is that the FMU starts to up the fuel pressure the moment boost comes on, whereas the stock EFI already supplies enough fuel up to and a bit past stock boost levels by itself, so the FMU is adding too much fuel causing a rich spot. I've had and read many interesting discussions here about this fact, and for a while was convinced that the BEGI or ANY FMU was NOT the right way to go because of this.

 

I've pointed out many times before that BEGI also offers an FMU that has an ONSET OF GAIN adjustment, which is to say, you can actually set at what level you even want the FMU to start affecting anything. I had figured that you could use this to get rid of that flat spot, by setting the FMU to not do anything until 7-8psi was reached.

 

Well I was partially right, at least . The FMU model #2025, the one recommended for N/A cars that have had aftermarket turbos/superchargers installed, does have the onset of gain adjustment, just as I have described. Unfortunately, it may NOT be the end-all answer to the problem. This feature was actually set up to allow you to have the unit start upping fuel pressure BEFORE boost is reached in the manifold, but it can be adjusted the other way as well. The rep at BEGI informed me that with the onset adjustment backed all the way out, he believed the highest point of onset you could get the unit to go to would be maybe 3-5psi. Still, that IS something. That's 3-5psi that you wouldn't have a nice fat richspot from too much fuel. He also believes that they might be able to work out something, maybe make some kind of kit with a different diaphram or spring pressure, that would be low price and easy to install, that could change that and have the unit do nothing until higher boost levels are reached.

 

Additionally, for anyone who has already purchased the 2022 FMU, I was informed that there are VERY few differences between the 2022 and 2025, basically they are the same unit, the only difference is that the 2025 has an adjustable allen screw and locknut on top, and internally has a spring and washer that the 2022 does not. He told me they may also consider creating a low cost package including these parts so that anyone wishing to have the onset of gain adjustment could just purchase and install to change their unit to the 2025.

 

I couldn't get one today as planned, everyone is out of stock, but found a place that should be getting some more 2025's in by tommorow, so should have one installed by then. It will be a while before I can get back to the dyno... too much money spent this last two weeks on the Z, but I will sooner or later, and will let you guys know just how much adjustment I'm able to get out of this thing and what effect it has. Also, the rep I spoke with, Trey, said he would like to arrange some testing there at their factory, to find things out like just how high of an onset point the stock unit can be set. Trey is also a Z owner, btw and is now also a member of HybridZ. He's got a 240 that is on the backburner now but is just waiting for an L28ET swap, with a very interesting EFI setup. We agreed to stay in contact and he'll keep me informed on what they find or come up with, as well I'm sure he'll post here if something like a kit would be offered. He was very cool over the phone and it was a very informative discussion... hopefully this leads to good things for those of us too cheap/lazy to upgrade to larger injectors and just want to get the most out of what we have

[Guest bastaad525]

BTW, another idea that I read here, I think Cygnusx1 mentioned this one to me but I'm not 100%... a PERFECT, CHEAP way to keep ANY FMU from doing anything until a desired boost level that YOU decide on.

 

Install a grainger style adjustable ball and spring valve inline with the boost signal line going to the FMU. Or heck, even a bleed type boost controller could probably do the trick. Set the valve to stay shut until 7-8psi, and voila... no extra fuel until your boost level gets higher than the stock EFI was designed to handle. I will almost definately do this if I get any rich spots at low boost... I still have some of the parts left over to make another valve.

[cygnusx1]

An FMU is nothing more than a needle valve.

 

The needle gets pulled UP by vacuum and pushed DOWN by boost. You can add springs, screws or air bleeds to adjust how far or when the needle moves.

 

It is used to control fuel flow back to the tank after it goes through the fuel rail.