FMU Tweak
 

Well, my BEGi FMU is not wokring as well as I'd like it to:

When I drop the unit to 0 ~hg. of vacuum, the unit acts a little random. Sometimes it slowly rises to the set 55psi level, sometimes it sitcks a 35psi for a few seconds then shoots to 55psi, and sometimes it misses 55psi altogether.

What I'm noticing on my fuel pressure gauge under load is that it's failing to raise to pressure levels the first 1-4psi of boost transition. Since it's being slow to react most of the time the fuel pressure sits at around 40-45psi untill it finally catches up and starts to rise rapidly. On my datalogs this is showing a rich tip in (02 clamp) followed by a large lean hump, then a flat AFR as the unit catches up with the demands.

I was worried that it might have been the spring causing the reaction, as I notcied it started threading itself on the adjustment knob. So I added a washer between the two to prevent it from doing so. This did not help.

I also made sure to grease the piston up fairly well and verified it could move freely and without any bind or effort. Still no change.

The diaphram looks good and the unit technically functions properly (eventually gives the right amount of fuel pressure for the right amount of boost).

The only other thing I can thing of is a faulty shim, but I would have thought it would cause this problem. I threw my Vortech FMu back on in the time being and verified a quick reaction to around 50psi with the vacuum line is pulled.

(I emailed BEGi about it, guess this is why it was only $25)

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All in all I like how my Vortech FMU has been working and it's giving me a perfectly flat AFR but tends to richen up post 5.5K. What I was thinking about doing was installing a pressure regualtor of some sorts on the signal line of the unit. This way since the amount of rise is based on boost levels, I can regulate the signal thus keeping the fuel pressures to a peak spot. See anything wrong with this reasoning? This way I can crank the boost to 12psi as I want to, and keep the fuel pressure at 100psi, regardless of the disc ratio putting it at 100psi of fuel at 8-9psi of boost.

Doing this might have you running too lean at higher boost levels at midrange RPM. Just a thought.

guess I'll never know without doing it? I don't want to change how to unit works, I just want it to reach a point where it stops increasing the fuel pressures. If my BEGi just needs a shim replaced or overhaul, it might just be easier to use that, but if I can get the results I want with my vortech unit, might as well keep it.

Might be more work than it's worth. To get it to work correctly, you'd have to put a pressure regulator that bleeds off pressure after a set psi.

For example, for ease of math, let's say your base pressure is 40psi and you have a 10:1 disk in there and want a max of 100psi, then whatever regulator you have has to bleed off pressure in the signal line over 6psi of boost. That way you'd get a nice 10:1 rise in pressure that peaks at 100psi. Just putting a restrictor in would not do it, as this would be the equivalent of putting in a disk with a lower ratio.

You'd be kind of creating a BEGI afpr out of your vortech by adding one of those bleed valves.....hmmm....

Personally, I'm quite happy with my Vortech(blasphemy) and I see what you are talking about at the higher rpm's with mine. I just consol myself that the few times I hit high boost at high RPM that I am protecting the engine a little more by running richer.

I brought that up last month: https://www.miataturbo.net/forums/showthread.php?t=5009

I couldn't find a pressure regulator or pressure blow off that was sensitive enough. The theory is sound.

Ben

I remember that post. Were you able to test it at all? I know Ace Hardware sells needle vavles with all the brass fittings. I was thinking of giving that a shot.

BTW, running additional injectors is looking very appealing to me at this point because you can actually dial in boost fueling and not have to run high fuel pressures. Might have to jump on the deal of the day.

Ben

http://www.technicalspecialties.net/...M='CA'

I'm going to try the 850-AA. Can regulate from 0-15psi.

At 10psi I'm at 100psi of fuel. If I set the unit to control the flow to a max 10psi, I should be able to boost it up higher and still mantain 100psi of fuel. That should be good for 250BHP, maybe around 12-14psi of boost.

My AFPR has worked perfectly since the day I got it. But as with many other FMU's mine runs too rich all the time. Even if i set base pressure at 50psi it reaches about 100psi by 10psi of boost and just keeps going until it hits 120psi @ 12-13psi of boost. So my rate of rise is always a little higher than I would want, and I have not found a way to lean it out. When I get on it my car basically shoots black smoke out the back, has been doing it like that for years.

I decided it's going to work. I just placed the order for the regulator.

If you want to "cap" the max fuel pressure in the rail, then only allowing so much boost in the the unit will allow you to fine tune a max point. Great for running larger injectors and keeping the FP down.

15psi -> regulator -> 10psi -> FMU

If your looking to adjust the rate of rise like a BEGi, then a needle valve should work in the same exact way as the BEGi unit. I think I can pick up a non-relieving needle valve up from the local hardware store and try it. Since what you are doing in lessening the signal you are basically increasing or decreasing the fuel pressure curve. This "tweak" could basically take your static FMU and make it slightly adjustable. The theory is no different from the BEGi FMU.

3psi -> needle valve -> 2psi -> FMU

This may cause a lean tip-in as the unit will not react as fast, however if one is still using a 12:1 disc, it should provide useful.

got my regulator today, came quick! should have some results and plots up by the end of the weekend.

Sounds like it's time for an EMB :)

or MS, but yes it would be easier.

hahahahahahahahaha

Thanks for that

results stink! It performed as Bruce thought it would.

My low/mid AFR was effected but the upper rpms stayed about the same. The inital tip in is leaner and not a smooth. Both AFRs compared below:

https://www.miataturbo.net/forums/at...7&d=1162838194

looks like I see this project in the near future:

http://forum.miata.net/vb/showpost.p...3&postcount=33

boy do I need an EMS.

I decided not to give up so easily and try it again using a more aggresive 8:1 ratio disc. This might help give higher pressures faster and keeping the low/mid AFR in check. But we'll see, chances are it won't help but who knows. I could see on the fuel pressure gauge that the rise seemed a tad slower with the regulator in place so the added restriction might have adjusted the amount of rise.

is this valve your using dealing directly with fuel pressure or boost signal to your fmu?

it's alerting the boost signal into the FMU. I think it's adding a bit of a restriction to the unit as compared to before so the amout of gain may have been affected. I'm going to try a 8:1 and 10:1 disc to see if it behaves how I hope. It will take a few minutes and might as well try.