AFM Tuning and Cal

[aston@ultrasw.c]

I have been working on the AFM for days! making adjustments and taking data.

I have the very informative tech sheets from Sal Carceller.

Engine is an 88 3.2 with headers and a SW base line chip. Two objectives: pass emissions in AZ which is not hard and richen the mixture across the entire range as SW suggested based on my WOT data.

OK first things first.

Engine fully warmed up taking data with an LM1 at idle.
O2 sensor disconnected: AFM voltage 0.73V, AFR 14.19, 860rpm, engine purring nicely.
O2 connected: AFM .67V, AFR starts at 14.2 but gradually drops to 13.24 over 30 seconds, 860 rpm, engine seems happy.

First question: Is the idle AFR set with the O2 connected or disconnected? I have conflicting info.
If connected, does this drop off indicate a bad O2 or is it just warming up?

I have adjusted the spring tension, wiper angle and idle mixture. I just can not achieve an AFM voltage of 1.13 with the engine running well. If I manage to force it closer (1.05) the engine runs like a dog, super rich no matter what I do with the spring, or the wiper, or anything.

With the idle smooth at .7V, the WOT AFR is between 13 - 14

Second Question: Shall I ignore the AFM voltage? I just can not achieve the ideal numbers suggested by Sal.

BTW I have checked the track and it looks pretty good for 211K miles. I have moved the wiper north and south with no change. I checked the 5V supply, cleaned out the AFM body. Fuel pressure is right on.

Thanks for any insight.

[scarceller]

First,

The voltage of 1.1V at idle is from my 3.2L which is far from stock! I posted that number for reference only. The output voltage from the AFM is directly proportional to the amount of air being ingested at the given time. This means that in your 3.2L you simply seem to ingest less air at idle than my engine does.

Do not force the output voltage of the AFM to a given value. What you want to do is:
- get car at idle fully warm
- disconnect O2 sensor
- and set AFR=14.2 via the air screw on the AFM

This procedure will get set your mixture slightly rich, then when you plug in the O2 sensor the mixture will be pulled lean to 14.7AFR by the closed loop function of the DME.

But you said that when you plug in your O2 sensor your car goes very rich into 13.x AFR, this is most likely a bad (shorted) sensor. If the O2 sensor shorts out it will simply pull the O2 signal to ground and send a false lean condition to the DME. When DME sees this it thinks the engine is very lean and attempts to richen the mixture.

I have another very good doc on AFM basics and at the end of this doc I explain how the wiper arm adjustment and spring tension works. Bottom line is you really don't want to mess with spring tension unless you fully understand it's function! My doc explains this in detail, I'm sending you my doc via the PM you sent me. But since you do have a LM1 WB you could fine tune the spring tension by looking at the results from a recorded 2nd gear WOT run.

I also suggest you unplug your O2 during all tests, actually these cars run better with the O2 disconnected if they are setup properly. As for having emissions issues I'm sure it's because you have a bad O2 sensor and you had it plugged in during emissions testing. My car passes emissions with O2 disconnected.

One last thing is you did not mention if you adjusted Base Idle Speed? there is a procedure for this as well and is usually done along with base mixture.
I'm replying to your PM as well.

Originally Posted by aston@ultrasw.c

I have been working on the AFM for days! making adjustments and taking data.

I have the very informative tech sheets from Sal Carceller.

Engine is an 88 3.2 with headers and a SW base line chip. Two objectives: pass emissions in AZ which is not hard and richen the mixture across the entire range as SW suggested based on my WOT data.

OK first things first.

Engine fully warmed up taking data with an LM1 at idle.
O2 sensor disconnected: AFM voltage 0.73V, AFR 14.19, 860rpm, engine purring nicely.
O2 connected: AFM .67V, AFR starts at 14.2 but gradually drops to 13.24 over 30 seconds, 860 rpm, engine seems happy.

First question: Is the idle AFR set with the O2 connected or disconnected? I have conflicting info.
If connected, does this drop off indicate a bad O2 or is it just warming up?

I have adjusted the spring tension, wiper angle and idle mixture. I just can not achieve an AFM voltage of 1.13 with the engine running well. If I manage to force it closer (1.05) the engine runs like a dog, super rich no matter what I do with the spring, or the wiper, or anything.

With the idle smooth at .7V, the WOT AFR is between 13 - 14

Second Question: Shall I ignore the AFM voltage? I just can not achieve the ideal numbers suggested by Sal.

BTW I have checked the track and it looks pretty good for 211K miles. I have moved the wiper north and south with no change. I checked the 5V supply, cleaned out the AFM body. Fuel pressure is right on.

Thanks for any insight.

[scarceller]

Please PM me with your correct email address.

[aston@ultrasw.c]

The voltage of 1.1V at idle is from my 3.2L which is far from stock! I posted that number for reference only.

OK I will not sweat the actual voltage.

when you plug in your O2 sensor your car goes very rich into 13.x AFR,

correct, I will try a new O2 sensor, it looked suspicious to me.

you really don't want to mess with spring tension unless you fully understand it's function

or you have a good sense of humor....I think i have your AFM for dummies tuning guide, it is very helpful.

you did not mention if you adjusted Base Idle Speed

yup i am adjusting that with the jumper.

I moved the spring a couple of clicks, then tuned up idle/mixture etc, then did 2nd gear WOT runs and analyzed the data.

The results followed your guide but not exactly. Maybe the O2 sensor was messing things up. I will change it out and try again.

Thanks for your help.

[scarceller]

When doing your WOT runs do them with O2 disconnected. You want to setup the AFM spring tension and such with the O2 not connected.