smog issues

[bergmane30]

Hello all, i am new to the e30 crowd and i had a question about an issue i had when i brought my 87 325 e to the smog shop. So basically what is happening is that when the shop starts the part of the test where the car is accelerated to 50 mph the readings jump up and down up and down and they are to erratic for the test to be completed. When idling the car does vary in rpms a little up and down up and down' but i did not think that this would effect the smog test. any help or suggestion would be greatly appreciated.

[jlevie]

I think you are saying that while the car is on the roller and running at 50mph the exhaust gas mixture is jumping around. That would make me think of a bad AFM or a fuel delivery problem. Intake leaks could also be a factor.

[01330i]

I had this same problem today. The guy told me this "the computer revs are jumping up and down erratically and I can not get an accurate reading so the computer shuts me out and i can not test the car. I have never seen this before in my life." which is assuring.

My car drives perfect and im confused. any help would be appreciated.

[bergmane30]

Thank you jlevie that is exactly what i was trying to say. 01330i that is also what the smog tech told me. Now my next question, a new AFM is not cheap, is there any way to test my AFM to see if that is the problem before i purchase a new one. In addition, how would you recommend i go about testing the other issues you mentioned as possible culprits. Thank you for the help.

[jlevie]

Run the fuel system tests in the Bentley. And since intake leaks can aggravate an AFM fault, have a shop run a smoke test on the intake and crank case and fix the leaks it finds. There is a way of crudely testing the AFM, but it is simpler to swap in a know good used part.