ok.. I'm at wits end. After reading endless posts and replies about this problem, I will add my frustration.

I bought an '87 325i 2 weeks ago. It came complete with the check engine light burning. Code showed faulty o2. Previous owner had 02 changed 6 months ago with less then 10k km, but seeing as the scan said change 02, I did. Along with 02 I changed plugs, which were all shot. So, codes cleared, I drove along my merry way praying to the gods that all is well, but as I expected, the CE light came back on after 5 mins. Whats wrong ? I might add that the car failed the emissions test before I changed the 02, but i can't see the 02 being the culprit.

Ideas please.

Thanks
Jari
Toronto Canada

im thinkin maybe your cat converters are bad and causeing you to burn sensors. the bad cats will also cause u to fail emissions.

hmm.. car has 180,000 km (113000 miles?) cats might be gone, but the E-test report shows cats passed. How do they test the cats in an emissions test? Just a visual perhaps ?
Tonight I will test my o2 as soon as I figure out what the volt out puts are suppose to be and which leads to test.

they check the cat w/ a "sniffer" (not sure of the exact name) but it sniffs for hydrocarbons at the exhaust if there are too many hydrocarbons it usually means you are running rich, your o2 is bad causing you to run rich or your cat's are going. you really can't do a "visual" on the cat's. You will have to have an exhaust shop or an independant shop take the pipe off and look inside. sometimes the cat will make noise when revved and letting the gas go.

I agree, it's probably the cats or some reason why your car is running rich.

agreed.. car is running rich but why. I did volt test on o2 and reading are out to lunch, but I still don't think the o2 is bad. Volts are suppose to go up as engine gains rpms and vice versa as rpm declines. For some reason, my o2 was outputting higher volts at idle, then it was at around 3000 rpms. Is it then running too rich at idle ? or too rich at higher rpms? and as such its going beyond o2 specs tripping an o2 code?
I also just finished testing the TPS. According to book, tps should have continuity just a hair above idle, and again about 8-12 degrees from full throttle. I found continuity off idle, but not just off full throttle. So I assume tps is bad, or need adjusting but I can come up with no theories why this would make the car run rich. Ideas are welcome. I'll keep posting as I trouble shoot just in case someone cares :)

hmmm... dunno sorry. IIf I read your post correctly, it seems at higher revs near wot you are running rich, other than that it is fine.

Some things I'd look at: faulty injector(s), air intake leak somewhere, and maybe the ICV, or something w/ the timing.

Also, something to look into but I don't think it would be it, check the fuel pressure, usually if it's too high you will run rich but most times I have seen the regulators causing probs are when the regulators are running low pressure causing the car to run lean. so I dunno.

Usually , I'd say running rich wouldn't bother me so much as running lean.:b_blue:

Originally posted by jesd325is
im thinkin maybe your cat converters are bad and causeing you to burn sensors. the bad cats will also cause u to fail emissions.

The O2 sensor would come before the cats wouldn't it? How would a bad cat behind the sensor ruin the sensor? (This is an honest question, not just me being a smartass)

Phaedrus:
Not sure, but I suppose a plugged cat would cause exhaust system to heat up to abnormal temperatures causing the o2 to burn. I don't dismiss this theory, but after changing the o2 sensor, the CE light came on within 5 to 7 km of driving. I doubt if the exhaust has time to heat up enough to burn out the o2.

Update on throttle position sensor. I removed the sensor, and before spending $100cad on a new one, I carefully opened the old one and discovered the reason why no continuity at full throttle. One of the contacts inside was the slightest bit dirty. I cleaned it up, and all the contacts work. I'm just finished gluing the sensor halfs together with a bit of epoxy and waiting for it to dry. I'm sure the tps will work now because its such a simple device. Basically on and off switches at both near idle, and full throttle, with no function in between.
I hardly doubt this will solve my check engine light woes, but if we all pray together.......

the reason the light comes on after 5-7km after reseting the system is that the O2 sensor doesn't begin to transmit a signal until the engine temp reaches (I think) 85 deg., or to where the gauge comes just outside the blue area. Your problem sounds very similar to the one I've had for months now. I've tried everything imaginable. The idea that the cats could be the culprit is new to me, but I'm interested.

The bad cat theory as I see it would be that the cat isn't functioning and is blocking the exhaust. Because the O2 sensor is right before the cat, the blockage is present when the O2 sensor begins transmitting. Thus, the O2 sensor transmit an out of range signal and the car operates in an open loop mode. This is, of course, based on absolutely nothing. The one curious thing that makes me think this could actually be my problem is that if I remove my O2 sensor all together, I can drive until the engine reaches full operating temp before the CE light comes on. Before I get the fault code, my mpg skyrockets, but then plummets the moment the light comes on. If I start from scratch w/ the sensor in, I can only make it to just out of the blue as I described above.

(If one of the mechanical gurus happen to see this, I'd love to hear some informed comments)

My ce light comes on at normal operation temperature. If I clear the codes while the motor is warm, the light seems to appear a bit sooner. (time wise). Basically I think the car is running rich.
Any ideas how to lean it a bit ?

OK.. new update just in case anyone is following this thread.
I just finished testing idle air control valve, and the purge valve. I also tested resistance in the coolant temp sensor, and at cold, the ohms are higher then my manual says it should be, but its also a cool night outside. The car is warming up as I write this so I can test the sensor at warm. I'm still convinced something is causing the motor to run rich, and thus throwing the o2 sensor out of range. Perhaps fuel regulator ? sticky injector ? Once I've tested every possible sensor I can, I'll bring the car in to be scanned and have the fuel pressure tested.
As a side note, Does anyone know where the O2 Heater relay is located ?

Jari

new news!
I found the problem. I changed the computer and check engine light went away, and car passed emissions test yesterday.

I so happy!!!

Just a note to add here, I had a failed CAT (the "straws" collapsed internally) this caused backpressure that fouled the O2 sensor, replaced it but car still ran like a POS. All readings were "rich".

Basically was the old "potato in the tailpipe" problem.
I could have saved myself a bunch of diagnosis if I had simply tested the exhaust flow at the tailpipe.