I have 450 cc injectors and I'm trying to get my fuel system running right before I throw the turbo in. The problem I'm having is that I'm having to set my static pressure to around 20 psi (which causes my car to run so rich at WOT, that it has like half the power it did before the new fuel system) so that my idle pressure doesn't go below 12-13 psi. I'm trying to bring my idle pressure up to where my static is but that damn vacuum screw doesn't seem to do anything. I've tried bringing it all the way out and in. Someone please help!

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

the vac screw allows for you to bleed off pressure while in boost. It does not allow you to raise/lower your static fuel pressure. To adjust your idle pressure use the big screw on the top of your sfmu. That moves your pressure up or down.

Kevin
The old:


The new:

I thought that's what my bleed valve in the bleed port is for.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

The vac screw is for allowing you to run a more "steady" fuel pressure when in vac. If you notice, the FP will go up and down while in vac, with the throttle. You can use this screw to keep the fuel pressure from coming down too much away from the static(0 psi) pressure. We dont really need to use this, so keep the vac screw all the way in and tight. That vac screw has never really done much on our setups, as I have tried using it before also, without much luck. You may want to open up the bleed valve, or use a smaller disk/ring combo.

The top allen bolt is what sets your idle fuel pressure. The bleed valve will "leak" air pressure from the main SFMU chamber to lower the boosted fuel curve. The more air that is bled out, the lower the boosted fuel pressure, and vice versa. There is not much you can do with 450's and the SFMU only, to get a clean idle A/F..You really should not run lower than 20 psi of fuel pressure at full idle vac. A SAFC may help in this situation though.

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ya like xtreme said, i had to get a safc, and i have my 440's with idle pressure at 20psi and i still was runnign dirty rich so i got an afc and im right at .93 right now at idle

-MIKE-

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Hey they are blue tops from a 1st gen, I have a SAFC hooked up, but I don't like them so I would only like to use it if I have to. My car idles perfect even at 12 psi, the ecu can adjust correct from 20 psi or so and under (I have a pocket logger). The problem I'm having is that when I go WOT to static (0 psi) pressure driving I'm running insanely rich (over 1.00 and I can smell fuel in the air) and it's bogging the car down almost to the point of dieing (I have a '95, no fcd or missing link needed). The 8 psi change in pressure from idle to static is waaay more than my car needs. I'm trying to get it to idle at static pressure.

Edit: My o2 sensor is pretty retarded by now, I have a new one going in w/ my downpipe. This shouldn't make a difference though at WOT.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

yeah I'm having the same problem as you it runs great when its not WOT but as soon as I get on the throttle its rich as hell. I'm NA right now also. Perhaps it'll be leaner when I put the turbo in though. But I'm running with 30lb injectors I just use my SAFC to lean it down the high throttle but like a lot like almost -20% my low is 0%

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I'm thinking in order for the vacuum screw to work you must have that restrictor in line.

Think about it, w/o the restrictor the vacuum screw is just like a manifold leak which the ECU will compensate for by closing the IAC. With the restrictor inline there will be a pressure difference w/ a large leak in the sfmu and a small source of vacuum going to it.

I'll be able to get this thing to stop rising fuel pressure under 0 boost yet!

I'm tossing the SAFC in the garbage. Actually my roomate is going to buy it from me

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

I haven't been here forever! with that said, put a check valve inline on the vacuum source so the sfmu doesn't see any difference between static and vacuum. Open up the vac bleed port alittle to allow air in.

Sorry to revive a dead post but what the hell!!

I had tried one of those flapper type check valves on the vacuum source. The problem I was having with that is that I would get a extremely lean spot for the first 200 rpm or so that I would go WOT.

Ideally you want the vacuum screw working so that you can make it start rising the fuel pressure at around -2 in.hg. vac. I'm going to try one of those crappy ball fish tank check valves. The disc type take about 1 psi to crack open, which might be what was causing the lean spot.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

I'm using a cheapo from advanced auto and it works perfectly. I set my static pressure, put the check valve in, and now hold the same pressure all the way to 0psi. After that it climbs just as it should.

The flap disc type I was using came from advanced auto.

When I was using it I could slam the pedal to WOT and would misfire. I don't know if this was a too rich misfire or preignition from running lean. It was loud if that illiminates preignition? I didn't try running it w/ the restrictor inline, are you? I figured the 1/8" outlet on that check valve would be plenty, but now that I really think about it, that's not a huge flow restriction considering the size of the restrictor.

Any comments?

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

Well I changed it back to the following setup:

- Vac line from manifold to disc type check valve (same one as mentioned above) to 3/16" vacuum restrictor (found near the vacuum fittings at popular auto parts stores, sounds like it matches the one Hahn sends w/ their kits, works way better in what it's suppose to do than any welding tip I've tried), to SFMU
- Vacuum Screw Tightened All the Way In
- Nothing coming off the Bleed Valve
- <450cc dsm injectors> 18 psi idle & static fuel pressure
- <450cc dsm injectors> 46 psi fuel pressure @ 9 psi of boost on 93 octane

Seems to pull the best via my and a friends butt dyno at 46 psi max fuel pressure, EGT's stay under 1400* even on super long highway boosting (turbo's watercooled so maybe that's why they're so low). Leaner and I don't get detonation or high EGT's, it simply feels like it looses torque, same in the other direction.

Wideband is next on the expense list.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician