85 Running Rich at Idle Only

[DRACO A5OG]

Gentlemen,

Sorry to bring this up again, but for those who had rich idle issues when warm. Did you find the fix?

I have checked everything twice, CHTS, ICV, Vacumm Leaks, DME, Relay, AFM, Fuel Pressure, New Refurbed Injectors, Plugs and still can't get her to lean out no matter what I do:

AFM adjustment screw has been turned out 9-10 counter clockwise and still reads top fluctuation of 0.81 volts on the O2 Sensor.

I've even taken the screw completely out and plug the hole with my finger and finally got a 0.63 top fluctuation.

I re-installed the Stock Chip and no change on volts.

Soon as I connect the O2 Sensor she would start to lean her out at idle lowering the RPMs 40+/-.

She has perfect runs in all gears with proper Mixture, Strong and Steady. She only acts up on occassional stops or stop and go traffic.

TIA

[DonMo]

You might want to look at your AFM flapper, sometimes the surface gets a little dirty or something keeps it from sealing completely. Result, you get more air past the flapper which works just like a vaccuum leak.

[DRACO A5OG]

Thanks DonMo. Will check that out.

[Bart_dood]

Also check the flapper stop, its a metal L piece with rubber coating. Its on the air filter side.

[DRACO A5OG]

Thanks Bart Dood.

[pozee]

Draco - I don't think it does, but, any chance this may have something to do with the injectors you used?

[DRACO A5OG]

Actually she got leaner with the alternate BMW injectors. The OEM injectors caused a 80+ RPM drop.

Thanks though, I appreciate it.

[Bart_dood]

Originally Posted by Bart_dood

Also check the flapper stop, its a metal L piece with rubber coating. Its on the air filter side.

Actually I take that back, at idle the flapper should be open, giving an output voltage of about 1-1.2 volts, so the stop is basically irrelevant at idle. Check the VFM output voltage at idle, you'll have to splice into the wiring somehow to read it.

[DRACO A5OG]

Great, Thanks Bart Dood!

BTW, where is the VFM (Variable Fuel Meter?) What should be the out put?

TIA so Much!

[don911]

I had a similar issue a few years ago. My issue was two of the pins for the AFM connector pushed back when I installed the connector. You might pull the rubber boot back and make sure all the pins are fully seated.

[DRACO A5OG]

Originally Posted by don911

I had a similar issue a few years ago. My issue was two of the pins for the AFM connector pushed back when I installed the connector. You might pull the rubber boot back and make sure all the pins are fully seated.

Thank you Don,

I will check the connector.

Jim

[slodave]

Jim, STOP fiddling with your car and drive it!!

[DRACO A5OG]

Originally Posted by slodave

Jim, STOP fiddling with your car and drive it!!

I know Brother, I know.

I hate being so freakin anal.

[DRACO A5OG]

Well it appears the culprit is my Air Flow Meter (AFM or MAF).

Check Connectors = Good
Checked OHMs = 1.89, Good

Voltage Check with a 9 Volt Battery reading 8.88 on DVM

Here are the results:

OHMs: 1.89K = Good

0.56: Barn Door Closed/or at rest
1.20: Slowly Opened to first mark on the potensioner
2.46: 2nd mark
3.67: almost 3rd mark then
6.07: for a split second then
4.17 - 5.34 until right before the last mark then
7.23: for a split second then
2.18: fully open Barn Door.

I think something is wrong with my AFM. Someone said I should use an analog meter but the 944 guy used a DVM too and he stated he got 0.50 volts at rest and gradual and steady rise in voltage until full throttle 8 volts.

I wanted to verify this so I was fooling around with the arm and got it to read 4.23 volts at rest and slowly moved the arm and it rose steady and gradually and managed to go 8.83 volts at full throttle/open barn door. I think the Sfernice 8404 Potensioner is bad.

I got nervous so I put it back. Test Drove and yeap same thing, rich at 0.82 volts at O2Sensor disconnected.

[DRACO A5OG]

Update:

SUCCESS!

It was my AFM.

In fact the new used 40K '88 production AFM (indicated on the Potentionmeter 8804, April 1988) was turned in all the way and I got 0.63-0.69 volts on the O2 Sensor.

I had to lower my base idle, very smooth and responsive.
I will use an LM1 to fine adjust the AFR

Thanks Kevin & Steve.

[dmcummins]

Ive seen where you check the voltage on your 02 meter to determine if your running rich or lean. I assume from the previous post that your shooting for around .65. As you know I'm still trying to sort my 3.2 out and if I understand it correctly a reading of .3 would indicate lean. My 02 sensor is on the drivers side and it reads .3, while the LM-2 sensor on the passenger side is reading 14.5. I welded a bung on the passenger side.

So is the drivers side of my motor running lean? If it is, what would cause it. I wonder if an injector was clogged, if this would cause it. Its about the only thing I havn't replaced. I may try and run some techron threw it and see if it helps.

[ischmitz]

FYI, the response function of a narrow-band O2 sensor is almost a step function. In normal operation the O2 sensor output bounces between 0.1 and 0.9 volts constantly as the Motronic adjusts the mixture. It is very hard to tell whether you are lean or rich by gauging the raw output. The bouncing signal requires an integrator with a very slow time constant to get a proper reading. A DVM is not suitable here.

That's why a wideband sensor is what you want here. It's output is much more linear over a wider A/F ratio range.

Ingo

[DRACO A5OG]

Originally Posted by ischmitz

FYI, the response function of a narrow-band O2 sensor is almost a step function. In normal operation the O2 sensor output bounces between 0.1 and 0.9 volts constantly as the Motronic adjusts the mixture. It is very hard to tell whether you are lean or rich by gauging the raw output. The bouncing signal requires an integrator with a very slow time constant to get a proper reading. A DVM is not suitable here.

That's why a wideband sensor is what you want here. It's output is much more linear over a wider A/F ratio range.

Ingo

I totally concur. I was only suggesting as if one is in a pinch to use the O2S+DVM to obtain a 0.20-0.60 readiing but one should always verify with a LM1.

Update:

Had my buddy hook up the LM1 and after some tweeking we got 14.7!!!

The new AFM and new refurbed BMW "364" Fuel Injectors was defintely leaner than my old ones and we had to loosen the tension spring on the AFM to get the proper reading on the LM1.

The reason for this, the AFM appeared to be too tight so it would not allow the WOT to read at 13.1. It was reading 14.2 at Full Throttle (WOT). Once loosened 4 clicks we got the desired readings.

The idle is so smooth now. I never knew how the idle was supposed to be but now I know. Can't get the stupid grin off of my face. The RPM idle down from speed is so smooth and settled right down to 880RPMs, dead on.

[slodave]

Now go drive your car and stop playing with it.

[DRACO A5OG]

Originally Posted by slodave

Now go drive your car and stop playing with it.

Roger That Captain Dave!