Tony

Ill look into it when i get back and perhaps, unless the answer is known 100% sure already , ill tell you the MAF voltage at
<best rain man voice>....8.....8.4....8.48psi.
Tap a wire and a few minutes in Logworks to set it up and i should be able to record it easily. I dont have the manuals in front of me, im a few odd 1000 miles from home, but which pin on the MAF...IIRC there are 5? Gaawd knows ive tested continutiy on all of them!

all for the cause.
all for one...the 928

John Speake

Hello Klaus,
The MAF voltage has been logged on several s/c cars, and we know it is still rising at 8psi and above. (over 6v output)

Also, I have measured the LH ECU with a variable MAF input voltage on my test jig, and I know where it tops out. (much lower than the MAF)

Hello Tony,
MAF output voltage is at pin 7 of the LH.

klatinn

Hi John,

That could be the problem. Most ECUs have an input range of 0..5V for their A/D's. Anything above that just pegs to the max value. It should be easy to rig a little potentiometer (10 turn) to experiment with that. I would start with a 50k pot. Connect one end to the MAF output, the slider to the ECU MAF input and the other end with a boost-switch or WOT switch (and possibly a relay) to ground. If the car has a WOT switch already that switches to ground, just connect a diode between the end of the pot (not the MAF end) and the switch. Kathode of the diode to switch. This way the scaling affects the MAF signal only during boost and with the pot you can adjust the amount of scaling. I assume this is a flapper style MAF?

Regards,
Klaus

John Speake

QUOTE:That could be the problem. Most ECUs have an input range of 0..5V for their A/D's. Anything above that just pegs to the max value."

Hi Klaus,
Yes that's the problem. I agree that you can attenuate the MAF signal to reduce its ouput to be in the right range (it is a hot wire MAF by the way). But one issue of concern is that MAF life will be reduced with prolonged use at these high output voltages.

However it is relatively simple to recalibrate the MAF to keep boosted voltages within the range of the ECU (no problem with the lower values at light load) and also prolong MAF life.

B951S

Just buy a split second box and you will be able to scale the voltage at a specific range from the MAF. You can have no change to idle and part throttle but at WOT, scale it back (if i understand what you are trying to do correctly)....

bd0nalds0n

What does the idle switch do when the throttle body is closed? Does the computer default to a stock "map" at idle, too, like WOT? I recently changed to a lower FPR, and the idle fuel pressure dropped from 50 to ~38. The car idles more smoothly now, but according to the AFM it still idles a litle rich. I'm not in the red areas, but in the yellow (it's a nordskog digital AFM). I don't have the WB02 hooked up, so I can't give a numeric value. But I'm curious as to whether the rich idle is due to bigger injectors in conjunction with a preset map/fixed pulse-width at idle which isn't entirely compensated by the lower fuel pressure...

Unless my problem is an old 02 sensor, or a MAF that is mis calibrated...

However, the feedback loop seems to work properly when driving around under normal, stable driving conditions (i.e., the AFM hunts between a little lean and stoich).

John Speake

Hi Brian,
When the throttle switch closes, the ISV loop is enabled. It blees in air in the corect quantity to try and set the idle speed to 675rpm (auto) or 775 (GT).

But at the same time you have the O2 loop also trying to get to stoich. I think the problem is that the ISV stsem is setting the airflow to try and get the rpm to the correct value, and at this setting the O2 loop can't keep control as it is out of its range.

You need to remap the LH ECU at idle rpm. Idle does not have a seperate map of its own.

What size injectors are you using ?

GoRideSno

Brian,
Can you provide the values of the lights for the Nordskog? I think that's the first thing you need to know.
If you drop the FP from 55psi at to 30psi at idle you effectively made the 30# injectors 22# injectors.
38psi is high for idle with the 85-86 FPR. Did you get a new FPR this time? Check your vacuum lines to be sure they are airtight make sure all of the vacuum ports on the TB are sealed off except the one that the main vac line is connected too. Make sure the 7mm nut on top of the TB is screwed all the way in.
HTH,
Andy

Tony

Make sure your manifold is sealed tight. I mean tight. I thought mine was the first time around but i would get a faint whistle now and then. It would even idle with the idle stab unplugged. After my recent going through of things, i did a much better job of sealing it up.
The car now quits when i unplug the idle stab. Since its so easy to get at on your car try un plugging it and see if the car still runs.

bd0nalds0n

Well hell.

My car will idle with the idle stabilizer unplugged. In fact, it idles great--and steady--with the stabilizer unplugged. With the idle stabilizer plugged in, I can hear it allowing air to go past, and the car idles around 1k RPM. With it disconnected, the car idles around 800. I recognize that this seems to imply fast air or a vacuum leak somewhere.

The fuel pressure regulator is new and came from 928 int'l. It looks like the used one I got from them, and says 2.5 bar on it. The invoice says it's for an 80-86. By my calculations, 2.5 bar is 36.27psi. Is the 2.5 bar the static pressure or the pressure under vacuum?

This is my AFM:



M7009 Air/Fuel Ratio, bar graph display

2 1/16" diameter.
Will work with your stock oxygen sensor or purchase sensor S8942 separately.
Displays 0-1volt oxygen sensor output.
10 LED bars, each displaying .1 volt.
Accuracy displays 14.7 : 1 Stoichiometric Air : Fuel Ratio.
5 bars = .5 volt = 14.7 : 1
Full LED lighting for optimum visibility.
"Blacks Out" completely when powered off.

I idle at the 8th bar, which should be .8 volt.

I really put the manifold on tight this time. I've checked for vacuum leaks in the system. Maybe I need to do an LH reset. The only manifold bolt that isn't screwed down really really tight is the rear one on the passenger side, which is an allen head that I was worried I would start to round. But it was pretty tight, just not as tight as the 13mm bolts that I could really get some torque on with the SC off.

As o2 sensors die, do they output higher or lower? I would guess lower. I do have a new sensor, but haven't installed yet.

The car doesn't smell rich at idle as it did @ 50psi. It idles very, very smoothly. It was rougher before.

In another post re: Steve Pappin's smogging problems, there was conjecture that as MAFs die they read too much air, resulting in an over rich condition. Perhaps this is creating a problem: MAF reads too much air, LH delivers too much fuel, o2 sensor reads too rich...unsure why the idle stabilizer would be letting in extra air causing 1k idle, unless it's trying to lean things out again.

This is really more of an annoyance than anything at this point--the car starts great, runs strong, and idles fine. I just want it to be perfect, y'know?

John Speake

QUOTE
In another post re: Steve Pappin's smogging problems, there was conjecture that as MAFs die they read too much air, resulting in an over rich condition.
END QUOTE

Hi Brian,
This is an incorrect theory. As the MAF wire erodes with repeated burn off cycles, it gets thinner, its resistance increases and then the output voltage is lower than it should be for a specific airflow.

Generally the O2 loop will compensate for this (up to a limit) under stoich working conditions.

Regards

bd0nalds0n

John,

I'm using 30# injectors which was the motivation behind switching to a lower FPR, along with the piggyback boost sensitive FPR.

John Speake

Hi Brian,
I'm sure Andy has a recomended set up for your configuration...

However I think the optimum solution may sometimes require some re-mapping, or maybe a piggy back system.

Regards

GoRideSno

Yep......because that's the best, and most cost effective way to do it. It is as much as anyone else that sells an SC kit does. And for whatever reason it yeilds a better fuel curve. Untill we are able to re-map then it's what I am using.

The car will actualy cruise with the proper mixture with the 87+ regulator (~57psi) and 30# injectors, but it wouldn't pass smog. With the 30# injectors and (~30psi) The 222kmi '87 S4 passed smog with flying colors this way. It actually did much better than my "87S4 that had a completely stock fuel system.
With the 30# injectors, the 85-86 regulator and the piggy-back 2025 regulator, the only reason to re-map is to not max out the injectors, which happens maybe about 2% of the time while driving on the street.

Idealy the 2025 would be replaced with re-maping of the LH. But there is no way to re-map the LH, until John is done with his work.


Andy K

John Speake

How the *** do I insert a picture file in a reply ?