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E34 (1989 - 1995)

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  #1  
Old 02-10-2013, 08:37 PM
germx germx is offline
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Location: Richmond, CA
 
Join Date: Jun 2010
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Mein Auto: 94 530i Man, 01 740iL
1994 530i failed CA smog - bad gas?

Hi All,

I have an 03/1994 530i Sedan M60 Manual with 159k mi. Registration was due last month and along with it a smog inspection. I live in CA.

One fine Saturday morning after Christmas break I decided to get her smog tested. I didn't do anything to her, just warmed her up (about 25 min of street and highway driving) before pulling into a test place where the technician was just finishing up with another car.

About 6 years ago she failed smog around 120k mi. The Bentley says to replace the O2 sensors every 60k; so I bought two and replaced them. Took her back in and the technician (different guy of course) told me that as long as your check engine light (CEL) is not on these cars should never fail smog; all you have to do is get them nice and hot and they will pass. So I always wondered if I replaced the O2 sensors unnecessarily.

So back to my recent story. She failed all across the board at 15 mph. See the numbers attached. Excellent!!! A reason to work on her.

Stomp test revealed code 1444 (no more faults). Since I had no faults I suspected that one of my sensors was borderline. Faulty enough to fail emissions but not enough to throw a code. Maybe it was just my wishful thinking that it was a faulty sensor and not a cat.

First I checked the mass air flow (MAF) sensor, long suspected of being faulty. Even though I could not find numbers online to compare, it seemed like it was OK. Attached are the numbers (thought this might be useful to someone checking their MAF sensor).

Next I checked my O2 sensors. They are technically not due till 180k... and they also checked out fine (I think). Here is a video of the 0.2 to 0.8 V fluctuating signal between pins 1 and 2. You can see mine does drop below 0.1 V and does not quite reach 0.8 V but I thought this was close enough. Between pins 3 and 4 there was 13.7 V (for the heater).



I replaced my oil, oil filter and air filter. On my list of things to check next were the intake air temperature (IAT) sensor and engine coolant temperature (ECT) sensor, but I never got around to it.

I took her back in for a free re-test the day before she was due. This time I drove around for an hour before the test. The technician asked me what I did to fix the car and I told him about the filters, oil and driving around for an hour to make SURE she was hot. He said the car will not pass; he pointed at the high numbers from the previous test and told me there is something wrong with the car and changing filters and oil will not fix it. I told him that I had a free re-test and that I would rather take the chance than spending the next 4 hours at the DMV getting a registration extension. He said he will be very surprised if it passes as he put her up on the dyno and started the test. And very surprised he was.

As soon as he got out of the car he asked me if I put in different fuel. That question triggered something in my Swiss cheesy memory banks. A week after failing the first test I drove up to Sacramento and noticed that the MPG indicator was reading about 19 to 20 which I thought was a little low. I noticed a slight increase in MPG numbers (the usual 23 to 24) and performance after filling up along the way (always premium). I explained this and the next paragraph to the technician and we concluded the gas in my tank was old and that is why she failed the first time. I was also very surprised the technician remembered the feel of my car and also noticed an improvement in performance from the previous time. But he also said the dyno does put an extreme load on the cars which might mean his "sense" or "feel" is multiplied.

I ride a motorcycle to work most days. My car doesn't see the road that often any more. The last time I filled her up with gas was mid December. I went on Christmas vacation for about a week and a half. Took her to get smog tested about a week after I got back. Not a good idea. But I had no idea that gas gets lousy so quickly. Or does it?

After writing all this I've read that gas is pretty stable if stored properly. I imagine a car gas tank is proper storage. Maybe the gas went bad after four weeks... Maybe the gas was bad to begin with... Maybe there is something else wrong with my car... The numbers are still not strong (meaning it barely passed).

Sincerely,

Erik
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  #2  
Old 02-11-2013, 05:15 AM
BMWFatherFigure's Avatar
BMWFatherFigure BMWFatherFigure is online now
Old School
Location: Perth, Western Australia
 
Join Date: Aug 2012
Posts: 2,167
Mein Auto: E23;E30;E38;E32;E34 +
Fuel goes off in lass than a month. Not wildly off but bad enough. Fuel tanks are not the ideal storage situation.
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  #3  
Old 02-11-2013, 11:13 PM
germx germx is offline
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Location: Richmond, CA
 
Join Date: Jun 2010
Posts: 31
Mein Auto: 94 530i Man, 01 740iL
Good to know for next smog check... always get fresh gas.
I think my thermostat is stuck open and is causing my car to run rich... hence the high HC numbers
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  #4  
Old 02-11-2013, 11:58 PM
BMWFatherFigure's Avatar
BMWFatherFigure BMWFatherFigure is online now
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Location: Perth, Western Australia
 
Join Date: Aug 2012
Posts: 2,167
Mein Auto: E23;E30;E38;E32;E34 +
The ECM should compensate for any temp (otherwise it would not run cold, or hot). Change the 'stat though. Never does any harm. Then bleed, bleed, bleed to get the air out. Good luck with your repairs..
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Current:
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
Previous:
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i
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  #5  
Old 02-12-2013, 05:07 AM
snowsled7 snowsled7 is offline
The Ornery Old Man
Location: SW Mountains
 
Join Date: Mar 2012
Posts: 980
Mein Auto: GTI
A few weeks ago we started a Toyota PU that has gas from 10 years ago, no exaggeration. Starts, runs, drives, can't seem to tell any difference.

Thank goodness I don't have testing like that where I live, I would move
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  #6  
Old 02-13-2013, 12:17 AM
BMWFatherFigure's Avatar
BMWFatherFigure BMWFatherFigure is online now
Old School
Location: Perth, Western Australia
 
Join Date: Aug 2012
Posts: 2,167
Mein Auto: E23;E30;E38;E32;E34 +
or buy fresh fuel, hee hee
__________________
Good - Fast - Cheap: Pick any two.
Current:
E23 735i; E32 735iL (X 2 - 1 Alpine White and 1 Glacier Blue); E34 535i; E38 735iL; R50 Cooper; R55 Cooper Clubman.
Previous:
E21 318i; E30 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i
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