Voltage Needed for MAF?

[sneed21]

Your help is appreciated:

Running through a test on the MAF sensor. I am only getting 4.9v on the clip when tested. When I open the flap to the MAF voltage only rises to 5v, and doesn't go back down to 4.9v once the flap is closed. I checked the V at the DME terminals and it also shows 4.9. The factory manual specs = 8v or higher and when the door is opened V is supposed to rise. The manual is great, but it doesn't tell me what to check next if I don't get 8v or higher. I've changed out the MAF w/ a known good one, and also changed the DME w/ a known good one. I don't have the wiring diagram for the car. Can anyone give me the routing for #6 and #9 wires off the MAF clip to the DME?

Thanks!

[nynor]

what year/model car?

[bigyagi]

i would say take a look at either FRWILKS page, or CLARKS garage, each one giving a test procedure for the afm.
i have an early car (84), and i used the FRW test set-up, consisting of a 9v battery, and vom.
with the flap door shut, i measured 184 mv. the range is 150--250 mv, i believe. and opening the flap to full open, produced a progressive voltage increase to about 7.8v.
either page will help you out. i think the later models have a 5v input, but each one is fully discussed.
good luck!
bob.

[sneed21]

It's a later model 85.5. It does read the 250mv also. Thanks, I'll check Frank's site.

Update: Checked Clark's and FRWilk's sites. My input V is correct, but my output is stagnant. What's odd is that I've tried another MAF, that I knew worked, and it made no change.

Thanks for the help,

[bigyagi]

hmm, i would take off the plastic cover on the afm, and check that the output wire has continuity, then take a look at the moving wiper contact. as the flap is moved, the wiper arm moves over the resistive board, and thats what changes the output voltage. maybe you have a deep groove, or really bad contact.
i'm not very good with the electrickery part of this car, but there are some real experts who i'm sure will help you out!
bob.

[fast924S]

ohh just a small correction its a AFM not a MAF

[sneed21]

Originally posted by fast924S
ohh just a small correction its a AFM not a MAF

Don't worry, at this point I have other names I'm calling it.

[fast924S]

HAHAHAHA

[DannoXYZ]

"My input V is correct, but my output is stagnant. What's odd is that I've tried another MAF, that I knew worked, and it made no change."

You might a have a short between your 5v supply wire and the AFM air-flow signal to the DME. Where are you checking for this signal? Best to have everything hooked up, then measure the AFM signal at pin#7 near the DME (small green/red-stripe wire). That way, you can verify that this is the signal that the DME itself is getting. Here's what the voltage should be at various operating modes:

car OFF, key ON, flapper-closed: 0.25v
idle: 0.79-0.85v
3000rpm 3rd-gear 45mph steady: 2.0-2.1v
fully-open (have assistant push door open fully): 4.6v