where is the 02 sensor on 1979 928

[bmwbeemer7]

Does anyone know the location of the 02 sensor on a 1979 928? I have a problem with the car running a little rich, black residue on the tailpipe, and bad gas milage. Thanks in advance!!

[Danglerb]

79 is CIS no o2, somebody else may know about adjusting the mixture, but they are known for having the worst mpg of all 928's.

[Pete R]

I think my 79 had an o2 sensor on the y-pipe.. I know the y-pipe I took off had one but it could have been replaced by a PO, maybe it shouldn't have been there. The mixture is changed with a long allen in front of the airbox to the fuel distributor. I had a shop set mine up with a tail pipe sensor. I don't know what the O2 sensor would do if it was there.. maybe open the air pump flow for emissions.? What do you consider bad? My tired 4.5 liter only got about 15mpg, my euro rebuilt 4.7 gets 16-17 (i know it would do 19 if I got on the highway and kept my foot out of it)

[bmwbeemer7]

Thanks Danglerb. I'll check with someone on the mixture. You are right about the gas milage. It is terrible on gas. Concidering the price of gas here in Col, SC is about $3.35 for reg.

[bmwbeemer7]

Thanks Pete. I'll take a look anyway on the y pip this morning and see if it's one there. Mine gets about 15mpg too or less. Have a nice week!!

[rjm65]

No 02 sensor on 79 as fuel injection is CIS-K.

You want to make sure the system fuel pressure is to spec, as are the cold and warm control pressures. You need a CIS fuel injection gauge set for that, great investment if you plan to have your CIS a long time, or do what I do and find a buddy that has one. Easy to follow test procedure in the WSM, begins page 25-5.

I like to think of control pressure being the primary mixture adjustment, and the allen screw through the airbox used to fine tune.

I get about 17-18 mpg on the highway, leans toward the 17 with the AC on.