Bernie

Hi All,

I realized today that the MAF on my car is a used replacement unit form 928 International. There is a very good chance that this unit was installed on the car without testing or adjusting the mixture.
Has anyone had good results with setting this? What procedure and equipment were needed to adjust the MAF.
I know what the readings are supposed to be but would appreciate any BTDT's.

Thanx

John Struthers

Bernie,
The Nichols site has trouble shooting info for K- Jetronic, L and LH, Jetronic. Pinouts, vacuum, tools,...

Mike Schmidt

The MAF sensors that were used on later cars are not adjustable. If the MAF sensor you have is adjustable, it can be done with a volt meter or one of the air/fuel ratio gauges.

With the engine running at normal operating temperature, disconnect the O2 sensor plug. Using an air/fuel ratio gauge, adjust the allen head screw on the MAF until you get a 14.7:1 reading on the gauge. If you're using one of the gauges with the 10 LEDs, adjust the MAF until the gauge indicates half of it's full range. A volt meter can also be used instead of the air/fuel gauge. Connect the ground lead of the volt meter to a good ground on the car, and the other lead to the signal wire of the O2 sensor. Adjust the MAF until the meter reads .5 volt. Using either method, the reading may not be completely steady. If that's the case, just try to get the adjustment so that the reading is about centered at where it's supposed to be. Reconnect the O2 sensor plug. It might be a good idea to disconnect the battery and reset the computer after the adjustment is made.

Bernie

Hey Mike,

I have so busy with the GTS thread that I forgot all about my own car!!! hehehehe
Thanx for the advice.
I don't have a mixture meter so I guess it will be a VOM. My car has a O2 preheat connection and then the sensor return itself. I guess that's the one I am to hook up to?
I'll give it a try and post back if I get anywhere.
See you back at the GTS thread.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Mike Schmidt

[quote]Originally posted by Bernie:
<strong>My car has a O2 preheat connection and then the sensor return itself. I guess that's the one I am to hook up to?</strong><hr></blockquote>

The heated O2 sensors will have three wires. I don't know if they are the same color on all O2 sensors (Bosch, Porsche, other), but on my car there are two wires of one color, and the third is a different color. The one wire that's the different color is the signal wire. It should show somewhere between 0 and 1 volt before you do any adjusting, and is the one that the positive lead of the VOM goes to while doing the adjusting.

MichaelR

On a related note, how many folks found that they had no "plug" over the MAF adj screw? Mine doesn't, and I was wondering how important this is since the manuals says that you should replace it.

Ted928

mine doesn't have one. i assumed the previous owner "got at it" although that would surprise me. perhaps they always don't come with one????

Mike Schmidt

The plug is to keep people from tampering with the adjustment and affecting emmissions. It's the same idea as the plugs that were put over the idle mixture screws on carburators. Without the plug anyone that knew how to turn a screw could start messing with it. With the plug, you had to know the screw was actually there, and how to remove the plug before you started messing with it. Basicly it's a cheap easy way for the auto manufacturers to comply with emissions laws requiring that the adjustments are "tamper proof", but still have them be able to be accessed by shops without too much trouble.

Just because your MAF has a screw there, do not assume it actually does anything, especially if there's no plug over it. There is no adjustment capability on at least some of the later MAF sensors, even though there may be a screw in there. You could turn it all day long and all you'd get would be a sore arm. That's why no plug was put over the screw to make it "tamper proof"