Ducman82

So today i hooked up my LM-2 with a wide band, and here is what i got.

at idle (1050 RPM per dash tach) 30 psi fuel pressure to injectors
Lambda reading 1.10
AFR 16.4
reading are a average, it jumps a little

at 2500 rpm
Lambda 1.06-1.12
AFR 15.6 ish

30 PSi is about as low as i can go on my Aeromotive Regulator

i can up the PSI and it gets richer for sure. i know when i was this low on fuel PSI, i failed emissions, and when i upped the pressure to about 45 ish, i passed just fine. but i want the car to run smooth and efficient.

thoughts?

76FJ55

I think you typically tune pressure for ideal AFR at WOT. you then tune idle and then tune the idle using the air bypass. I believe you are L-Jet? you sig line doesn't list year. The O2 then should help maintain 1.0 at cruise.

Ducman82

changed sig for year. using air by pass? you mean the AC air valve?

hacker-pschorr

Big screw on the front of the throttle body - turn in (clockwise) to lower idle speed.

Per the WSM - disconnect both vacuum lines going to the distributor and plug them. Turn down screw until desired idle is reached. Go slow, and blip the throttle a few times so it "settles".
Make sure the engine is nice and warm.

Like 76FJ55 said - you should really be setting A/F for WOT. Easiest way to do this is jumper the fuel pump with the engine off & set your pressure.

Ducman82

what should i set the idle too? about 750? i can see how adjusting the fuel pressure would help at WOT, so do i do a test run, see how it reads then, adjust from there?

76FJ55

on L-jet there is a bypass around the "barn door" which is used to adjust the idle mixture. the screw on the throttle body is used for idle speed control the one on the AFM is used for idle mixture.

The screw is visible in the AFM pic below, with a rough sketch of how it works.

76FJ55

Yes. To set the WOT AFR, you will need to log several runs at WOT. Adjust accordingly, and repeat, until you get the mixture you are looking for.

After you have the fuel pressure adjusted for WOT then set the Idle speed and mixture. This may take several iterations as well as idle mixture and speed are codependent.

Ducman82

roger that! thanks for the help. from what i read, a lambda of ..85- to 1.0 or a "little rich" is good for gas cars. or should i stick with 14.7 AFR at WOT?

dprantl

You should definitely NOT be at 14.7:1 at WOT. I would shoot for 13.0 - 13.5 on an NA stock-ish 928.

Dan
'91 928GT S/C 475hp/460lb.ft

Ducman82

so lean on the high end then?

IcemanG17

NO NO NO.....stoich at WOT is a bad idea...sure its ideal for cruising and good fuel mileage...but leads to detonation at high load in WOT conditions

Technically the best power is made around 13.0...but most tuners like the margin of safety that 12-12.5 gives (even richer boosted)

In general a stock 928 or close to stock 928 is pretty well tuned as is...my 84 Estate L jet racer is stock with a cat bypass & it makes great power at good AFR's and I haven't done ANYTHING to it....ZERO tuning...just run it...I am a bit lean in the midrange, but the AFR drops with rpm until about 12.6 at redline...hard to argue with 203whp-241 torque through an automatic when it was rated at 234hp-263 torque...

toofast928

Traditionally L Jet runs on the rich side. Yes bump fuel psi to 38. Make sure the WOT throttle switch is making contact at 70% throttle.
Be on the hunt for air leaks. The higher the manifold vacuum, the more responsive the AFM is to react.

Ducman82

hummm. ok. ill have to check that the WOT switch is adjusted right. i might have it set funky. any good tricks to figuring out the 70%?

hacker-pschorr

+1
Unless the car is modified, set the fuel pressure for WOT to the stock level.

From the WSM

Fuel Pressure (engine stopped fuel pump birdged) = 2.5 bar +/- .2 bar (36.26 psi +/- 2.9 psi)

Check value for idle = approx 2 bar (29 psi)

Maybe I missed something, what are you trying to fix and why did you install the adjustable regulator?

Assuming your car is stock or close to it and lean at WOT, check the WOT switch.
Another sensor to check is the temp II which directly controls the fuel injector pulse width. You can make an L-Jet so rich the engine dies simply by putting a resistor on the Temp II.

Ducman82

i installed the Reg along with 928MS injectors and rails. my old dampener and regs were shot. after my first dyno run a few months ago, and my disappointment, i am not working on getting the FP set in happy spot. And first thing tomorrow is to check the placement of the WOT and Idle switches. i have a feeling i set the WOT swith at, well, WOT.