1985 MAF and burn off module

[Nazgul]

Hello to all,

My maf sensor is altering voltage as shown on my scanner......however, after much closer inspection upon shut down...I am positive the burn off feature of this unit is NOT working. My question is what symptoms would this cause in engine operation.......I am sure something is not right with the way my engine is both running and idling.....but without me going into further detail....could someone suggest how the lack of a post run burn off would effect the day to day operation of the engine?......Would it effect timing?..fuel mileage?...idle?....spark advance? I think I have read enough here to find out it is located somewhere behind the dash and is fairly expensive, even used......I am installing a Pioneer AVIC-N2 navigation system and will have the dash off to run both the antenna for that unit and a hard wire for my radar detector so it would seem to be a good time for this also. The car runs.....ok I guess.....there just seems to be something missing...I just would like to know how important this function is.....Thanks in advance for anyones insight into this....My car is an 85 automatic and I know I dont have any relays near my batery xcept the fuel pump I think....Thanks again

Geoff

 

[mdsbch]

I also have an 85 automatic and had this problem about a year ago. What I found out, is the 85 doesn't have a burn off module relay like the other years of the C4. When you shutdown the car, the wires in the MAF should glow red for about 2 seconds, so you have to look real quick or you'll miss it. As to what it does to engine performance, I would think it would cause a deterioration in efficiency and performance, since the reason for it is to burn off any foriegn matter that gets on the sensor wires, which feeds the ECM information on the air flow so it can adjust fuel flow to for the proper A/F mixture. If these wires continue to acumulate foreign matter on the wires it will be feeding the ECM eronious information. Hope this helps.

Mike

 

[Nazgul]

Mike....Thanks for the quick answer.......I am SURE the wire is not glowing at all....last night I had my son kill the engine many times while I looked in the sensor and there is no glowing of any sort....we did it after the sun went down and with my underhood lights covered......My car gets lousy gas mileage....hunts for idle....which has dropped to the 600-590-580 range....stumbles on accelleration....will somewhat smooth out at constant highway speeds.....I have replaced ignition module....wires,plugs,cap etc,etc in search for this malady.....am I correct in my conclusion it is a small silver metal biox behind the dashboard somewhere on the passengers side?...and if you can....what was your car doing which led you to suspect yours? Thanks again for the fast reply to my problem....

Geoff Howitt

 

[mdsbch]

The small silver box that you are refering to behind the dash, I think is the ECM. It is a silver box about 5" wide by 7" deep and 2" thick and is located under the dash on the passenger side. Mine was giving me an SES code that pointed to the MAF (can't remember what the number was). The car wasn't running bad though. I ended up replacing the MAF with a refurbished one from Auto Zone (I think it was about $150) and haven't got the SES code since.

Mike

 

[AdvancedAutoCC]

85 MAF = PITA

Check the "gauges" fuse... the burnoff module gets its power from there. If the module isn't getting power, obviously it won't work. The gauges fuse doesn't affect the cluster (go figure), and usually a short to ground can be found in some of the other components that get power from it, including the EGR solenoid, and AIR system. The module itself is a bit hard to find, and horrifically expensive in comparison to other L98's (typically about $400-$500 when you can find one - reman). The module is about half the size of the ECM, and both are located behind the RH dash. The ECM comes right out the bottom, but you have to pull the breadbox to get to the MAF burnoff module. The 1985 system is unique to 1985, as for 1986 they went to a MAF relay, found out under the hood. The 85 system can be problematic...I know because I'm still finding gremlins in mine...

 

[Nazgul]

Great information.....thanks....just checked the "guages" fuse....10a , and its ok...But I am sure the wire in the MAF is 1, still there and intact{it is xtremly thin.....and 2, it does not glow in any way shape or form.....just tested it again in the dark and with my underhood lights covered.....I have a 180 degree thermostat and I let the car go over to 185 or so until it opens....and it drops down to 173 and begins to climb again....then I shut the car off while looking into the sensor.....that should be good enough conditions to see this function right? I de-screened the back but left the front screen in and cant see anything from either end... can see some of these on ebay right now for 75.00 and am thinking maybe I should look into one. I am reading a voltage change on my auto xray scanner so I think I can assume It is getting power.....just the burn off is not working.....I am no electrical wizard so im not sure just wires for that function could or would short out and leave the rest of the unit working somewhat......or a bad or weak ground would effect only the burn off....just wish I knew what symptoms I could expect from no burn off......Thanks again for the help and any new ideas...please throw them out here.....
Geoff

 

[OSU-VETTE]

Hey Geoff,

Did you replace your burn off module? I have to replace mine and while I don't like the cost, the performance is too low and the mileage stinks, so it is time to bite the bullet. Thanks for your help.

Jeff