bd0nalds0n

Since the car is back together, at idle I have about 50psi of fuel pressure which rises to 55-ish under full boost (8psi). Since I replaced the throttle position switch, I get 12.5:1 at WOT, the AFM hunts under modest acceleration like it always did, and the car runs just a litle rich when maintaining highway speed.

However, at idle, I'm getting around 9.9 - 10.4:1, which is undesirable for many reasons not the least of which is the odor, it's hard on the cats, and Carl mentioned that somewhere below 10.5 or thereabouts that the fuel actually scrubs the oil film off the cylinder walls. The idle stabilizer also has some trouble in this range, and the idle oscillates a little bit in neutral between ~500-~750, but is pretty stable under the modest load of being stopped in gear.

My question is: Is there anything I can do to lean out the mixture at idle, or is this just an artifact of running the 30# injectors?

I should have dyno #s to post sometime in the next week or so...

BC

I'd like to come out for the dyno run if possible Brian.

I'm just happy you have brought down the ratio in the WOT area. Whew.

BrianG

Brian, what's the leanest A/F ratio that you see? I'm curious about the total range that you are getting. Can you lean the idle mixture to a reasonable value by adjusting the FP-reg? If you can, is WOT still rich enough?

shaaark89

fuel pressure needs to be lower at idle which means the rate of rise with boost has to be changed. if you're only getting 5 psi increase in fuel pressure with 8 psi boost, your rate of rise is less than 1:1. if 55 psi is good at full throttle, then you knonw the endpoint you want to get to. need to find out what fuel pressure works at idle (eg 30 psi) and change the rate of rise so that with 8 psi boost you get to 55psi (in the example, 55-30=25/8= 3:1.) depending on the fuel management unit you're using that may or may not be an easy adjustment.

bd0nalds0n

Even with the boost-adjustable RRFPR screw backed almost all the way out, with the rise-in needle backed all the way out, the lowest I show is around 46 PSI and the same rich idle mixture. What *does* seem a bit weird is that the fuel pressure on my gauge doesn't seem to change at idle, even with the vacuum disconnected (for atmospheric), regardless of how far backed out (or screwed in) the RRFPR screw is set. The instructions on the BEGI website suggest that, given the above referenced procedure about disconnecting (and plugging) the vacuum/boost line, I could adjust the fuel pressure at atmospheric to establish the correct baseline fuel pressure. Yet screwed out or in, the fuel pressure doesn't change at idle (or when the vacuum/boost line reattached), but it does rise under boost.

BrianG

So that's a 7 lb pressure change....... that sounds pretty meagre! Do you know what it's supposed to be?

GoRideSno

Brian D,
Check out the reply to the PM you sent me earlier today. I'll post the results when I'm done.
Oh and Brian G, it's on it's way.....again

Andy K

Blown Beast

Your idle should be around 30psi w/30lb injectors and you need about 8:1 rise for your 8psi set up. Thats 8lbs of fuel pressure rise for every 1lb of boost....JFYI. Sounds like your Corky Bell FPR is not working rite.....however it is designed to only go down to 45 psi. Try using a ARFPR or buy the new BEIG (MR2035 it is supposed to have an adjustable fuel rate for idle) in conjunction with your FPR.
Just my .02

GoRideSno

Brian,

The ratios you mention seem way too high.

I must stress this....Please make certian that you have the correct Bosch part # of 0 280 120 308. I know you mentioned you just bought a new one. The reason I stress this is that I ordered a new one for an 85-86 once and I got........an 87+ part instead. The parts supplier thought they were the same part but the 85-86 part is the exact opposite of the 87+.
Next make sure you have the 85-86 throttle switch adjusted so that when the throttle closes all the way you hear a slight click from the switch.

.....There is no adjustment that you can do to the BEGI 2025 that will effect fuel pressure at idle (if it does there is something wrong or the vacuum line is off the regulator). Your stock regulator controls fuel pressure at idle and cruise. It is in no way adjustable. The "BEGI 2025 Piggy Backs" the stock regulator as boost comes on.
The BEGI 2025 has 2 functions:
1: When the BEGI sees atmospheric (0 on the boost gauge AKA when the vac line is off), it will automatically jump to the pressure that you establish at idle with the vacuum line off the 2025 and plugged. The purpose of this function is to prevent tip-in leaness. It does this very well and is one the main reasons I chose the 2025. You should adjust this so that during a full throttle run the mixture immediately goes between 13.5:1 to 11.5:1. Generally around 55-60psi at idle with the vac line off the 2025.

2: When the 2025 sees boost, it raises the fuel pressure by X psi per psi of boost. X psi is adjustable from 1psi to 12 psi by turning the **** on the needle valve. Generally with 1.5 to 2 turns clockwise from fully backed out is the correct setting for the needelvalve to get to around 11.5:1 throughout the RPMrange under full throttle. If this is not the case remove the very small restrictor in the end of the vac line that goes to the 2025.

.....Given thhe above, lowering your fuel pressure at idle needs to be acomplished in a different manner. For example one may order a $25 used fuel pressure regulator from and 85-86 and that will lower your fuel pressure at idle to around 30psi ****I think**** I'll know for sure by tomorrow.

HTH,
Andy K

GoRideSno

Rob,
FWIW I have had the pressure as low as 20psi at idle with the 2025.
I have used the BEGI MultiRole 2035 and prefer the piggyback 2025.

Andy K

worf928

Occam's Razor (the simplest explanation is usually operative) (and Andy K) suggests that you may have one or more vacuum lines not connected. I've seen more than one S4 with the manifold vacuum line connected to the flappy and the flappy vacuum line connected to the front damper. Check all the vacuum lines to the dampers/regulator and may sure they suck (vacuum) at idle. Of course with the twin screw you've got no flappy (right?) but what happened to the old line?

Carl Fausett

The problem may be the Begi/Cartech 2025 FMU itself.

That FMU has 1/8" NPT fittings - you cannot pass enough fuel thru them to NOT be restrictive even when all the way backed out.

I just experienced this on a L-Jet that I supercharged for a customer. Even with the screws backed out all the way, the 2025 was still restrictive enough just being there that it raised my fuel pressure at idle too high.

These years of Bosch FI engineering were unique in its engineering that it passes max fuel volume to the front of the car, only to return all the unused fuel back to the tank.... now-a-days, more modern FI systems pass only a little more than needed to the engine, and consequently, the return to the tank is much lower in volume.

The Begi 2025 is designed for these modern cars, and with the 1/8" NPT fittings, not intended for systems like ours.

The solution: use the Begi 2027 FMU instead - 1/4" NPT nipples, you can convert to -6 AN Aeroquip and use braided SS hose too. It flows correctly for these Bosch FI systems.

Dialed my customers car in with it and sent him home.

GoRideSno

As I said I have had the fuel pressure down to 20psi at idle with the 2025 so there is not a restriction. Maybe with the 16v car but not with the 32V.

The fittings of the 2025 accept -6 hose perfectly.

Andy K

bd0nalds0n

The new throttle position switch is the correct one (308). When I installed it, I oriented it so that the closed throttle switch "clicked" with the throttle against the stop, and tightened it down in that position. I also checked for continuity at WOT.

Is "tip in leanness" the phenomenon that acceleration less than what it takes to trip the WOT switch results in a momentary lean condition until the o2 sensor communicates to the EZK and the feedback loop can catch up? I have noticed that with the allen screw out, the car goes from stoich to somewhat lean under modest throttle, and as I twist the allen screw tighter, the car runs doesn't go lean but gets richerfrom stoich. I gather that this 2nd dynamic is desirable and gives me another goal to work towards.

It sounds like the answer, probably, will be a lower FPR, once Andy confirms this is workable. I thought about the other BEGI unit, but I hate to shell out another $350 if I can just lower the idle pressure using an earlier model part. It also sounds like with a lower FPR, I can adjust the static pressure HIGHER on the BEGI, if necessary, but not lower than the FPR's minimum, which should still make it customizable from somewhere-lower-than-50psi to 50 or higher. Which in turn should help the lean condition.

Sigh. Sounds like the supercharger is going to have to come off again--the stock FPR is behind the manifold, right? I better be careful, or I'm going to get good at this...or at least very practiced.

The line to the flappy was removed and capped at the actuator. I can double check that everything holds vacuum this weekend.

GoRideSno

Brian,
It sounds like you have the gist of the tip in avoidance aka center screw adjustment aka atmospheric setting of the BEGI 2025.

Besides the fact that the MR2035 is $350.00, the adjustments of the baseline fuel pressure and atmospheric fuel pressure are not exactly seperate making it kind of hard to adjust.

Andy K