Author Topic: Help again... car running very rich. (Read 3153 times)

Kingsly · « **on:** January 02, 2009, 03:06:10 PM »

Okay, passing smog has become a bloody nightmare. First she failed across the board, high NOx in particular. I dove into the intake manifold and replaced all the vacuum lines, new intake manifold gasket, new DISA gasket, etc.

Also replaced the O2 sensor (she was throwing a code). CEL is being a persistent bugger and still insists that I need to change the O2 sensor, even after being cleared.

Since my temp plate had run out, I needed to try smog again so at very least I can fail and get an extension. Sure enough I failed.

NOx is way down, well within spec (yay for new vacuum lines!). However HC is way up, failing both tests and now I am a "gross polluter". Shove it, Al Gore! :cool:

I am assuming I've always been running rich, but vacuum and manifold leaks were helping everything out by leaning the mixture a bit.
To be specific, I'm now ~13.5:1 rich of stoichiometric (14.7:1), leaving lots of incomplete combustion and making Gore cry.

Here's where it gets interesting. I threw a diagnostic computer on and it told me there was a short between, I believe, pins 70 and 71 on the DME, which relates to the O2 sensor circuit. The PO had the DME replaced following the dreaded rain gutter short, and said he'd had a CEL ever since. I suppose it makes sense that the DME itself could be bad, causing a short, and thus getting false readings from the O2 sensor, making it richen the mixture erroneously.

Thoughts? I've got one month to fix this problem, and no more extensions after that.

roundel318 · « **Reply #1 on:** January 02, 2009, 10:09:16 PM »

You have a spare ECU to test with?
This is the stock chip?
Can you run a temporary test circuit for the O2 sensor?

Kingsly · « **Reply #2 on:** January 03, 2009, 03:42:26 AM »

No spare ECU. Turner chip (which actually helped a bit upon installation, oddly)...

How does one go about running a test circuit?

roundel318 · « **Reply #3 on:** January 03, 2009, 07:30:08 PM »

I am not sure how many wires, etc the O2 sensor uses, but running a wire that isnt in perm placing but safe enough it wont come loose and get cut up by a moving part.
This seperate wire would allow us to rule out your O2 wiring, unless you have an idea of which wire is bad / cut?

Nomadic · « **Reply #4 on:** January 04, 2009, 05:02:10 PM »

You might take a look at the ECU's board to check solder joints & see if anything is fry'd. I know that bad ICV (for example ) can damage some parts of a ECU. (search) ECU's seem cheap and widely available.

Does the motor come up to full temp? PO had a low temp thermostat in mine and replacing with stock thermostat helped me get through emissions.

How do your plugs and wires look? Coil packs on their way out can cause all sorts of havoc. PO said raw gas was coming out the exhaust before replacing the coil packs. And running seriously rich can damage the cat converter.

Emissions can be a pain but it really helps (forces ) tune our cars. I forget the exact numbers, but doing vac hoses, icv, and thermostat my 200k 318is went from gross failing to passing with like 60% of allowable NOx & HC. (load not idle). This was with a old O2 sensor and 200k Cat (probably damaged at that) These will get replaced soon on my quest for 30MPG

My stock 100k 96 Jetta 2.0 passed with 1/10th of the legal limit NOx and 1/4 HC limit! The jetta still has its orig O2 sensor and cat. If anything... the emission regs are too lenient here in Seattle. (but still a PITA)

Kingsly · « **Reply #5 on:** January 05, 2009, 03:55:05 AM »

The motor runs up to full temp. I took off the clutch driven fan the first time, and put it back on for the second run. Coil pack and wires look okay, but who knows what's really going on under the surface. I'm glad NOx is down... I was beginning to think I'd never get all the different vacuum leaks fixed.

I'm not running absurdly rich, no gas coming out of the tailpipe! Judging by what the diagnostic computer said, I am going to grudgingly assume it's my ECU. I highly doubt it's my wiring harness, and the O2 sensor is brand new.

What years/serial # range am I looking at for a new ECU?

roundel318 · « **Reply #6 on:** January 05, 2009, 10:04:07 AM »

I have a spare #175 ECU (E30 M42 318i/is) with a stock chip I can send as a loaner to test with if you like.
I am in Boise, Idaho.

Kingsly · « **Reply #7 on:** February 11, 2009, 02:13:36 PM »

Okay, thought I'd post a follow up. Pulled a known working DME and installed it in my car. Drive around for a few hundred miles and then went to get smog.

Most nerve racking 15 minutes of my life...

And she passed with flying colours! Everything was not only within allowable limits, but just a hair above average! The guys at the smog shop were very impressed after hearing the saga of the last six months attempting to pass, especially given the car and the miles she had, on the original cat nonetheless.

tjts1 · « **Reply #8 on:** February 11, 2009, 02:53:58 PM »

Note to self: swap stock chip back in before smog check.

Kingsly · « **Reply #9 on:** February 12, 2009, 12:32:07 PM »

Hah now I've got the opposite problem, I have to swap my turner chip into the working DME now that smog is over.