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E28 (1982 - 1988)

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Old 04-18-2011, 12:33 PM
Marrkk Marrkk is offline
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Location: San Diego
Join Date: Apr 2011
Posts: 4
Mein Auto: '86 636CSi, '01 330Ci
Smog Test Failure

Hi guys, I'm new to this forum. I posted this to the E24 forum with no responses yet, but since the E28 drivetrain is the same, perhaps an E28 owner can help.

I'm having trouble getting my '86 635CSi (manual) to pass smog here in California. I bought it at 100k miles, now has 202k. Been off the road for 5 years. Starting with my initial smog check, I have had trouble passing the low speed test, but have squeezed past before. This is the first time on the rollers, and it passed all but the low speed CO (15% high), but most of the other numbers were middling, just barely passed high speed CO.

Here's what I did before the test: New engine position and rpm sensors (bellhousing). New Silber plugs, Bremi/ rotor, Bosch coil; changed oil and filters (oil and air). Spark plug wires look in good shape, I believe I changed them before the last smog test. Checked vacuum lines. Ran the car on the freeway for 10 minutes @ 75 mph.

Since the failed test, I have done the following: adjusted the valves, removed my Dinan chipped DME and replaced it with a stock unit, changed the temperature sensor (the one for the DME), removed and checked the thermostat (80 degree, working - starts to open @75, fully open @90). Filled the tank with Chevron regular, added some injector cleaner. I had a different guy run a retest, he said it still failed, he than sprayed carb cleaner around, said it had an injector seal leak (I didn't detect any RPM increase), then offered to get it to pass for $200.

I'm not interested in a fudged test, and because of his offer, I also doubt his diagnosis. I obviously am trying to avoid buying a CAT, especially since the situation has not gotten worse in 100k+ miles. I also know the O2 sensor should be checked or replaced. Probably should have run out the gas with the injector cleaner. Probably should have run the car on the freeway for over 30 minutes. Perhaps should have added a can of "guaranteed to pass" I understand there is a dial inside the DME that allows adjustment of the mixture - can this be tweaked? What's the probability of injector problems? It runs and idles smooth as silk, great power, 800 RPM idle with the Dinan, 700 RPM with the stock.

Any suggested next step(s), focusing on the O2 issue?

(PS, is there any advantage of the OEM Bosch O2 sensor (OEM plug) over the Bosch universal at half the price?) Thanks for any help, guys!
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Old 04-18-2011, 02:29 PM
catso's Avatar
catso catso is offline
Location: Chicago
Join Date: Dec 2009
Posts: 3,115
Mein Auto: 2000 323i, 1988 528e
The OEM O2 sensor is probably the same except for the convienient plug. Check for both, the cost shouldn't be much different. Injector seals are not that difficult. If there's a vacuum leak it could be a very minor one from the valve cover or hose connection or porous old dried up hoses. Have you cleaned the IAC valve and carefully inspected the rubber hoses connected to it?
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Old 04-18-2011, 11:03 PM
Marrkk Marrkk is offline
Registered User
Location: San Diego
Join Date: Apr 2011
Posts: 4
Mein Auto: '86 636CSi, '01 330Ci
smog check fail

Thanks, Catso.
I bought a silicone vacuum hose kit and replaced all the vacuum lines. i adjusted the valves, so the cover gasket is new. The OEM O2 is more than double the price of the universal (best price online $120 vs. about $50 for universal) but the local shops who work on older BMWs all have told me they have had bad experiences with the universal - one refuses to install it. If you look closely at the pictures, you will notice different construction - the tips differ, for instance.

I'll clean the IAC valve, but with the valve adjustment and new plugs, the car is idling better than it ever has!

If I do install a new O2 sensor, and I pass smog, I'll probably pull it out and put in on the shelf until the next smog check.
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