rusnak

Edited: 1-4-09 This thread was started by me because my 911 did not pass smog. I found out that the idle mixture was too rich, and I needed to find out how to adjust the CO mixture, as well as set the idle speed. Thanks to JBrinkley, I found out that I need to disable the O2 Sensor when adjusting the CO mixture, and re-set the idle speed as well.

------------------------------------------------------------------------------------------
Original Post starts here:

I have a cat bypass and noticed that the exhaust really smells bad, as in lots of hydrocarbon exhaust smell. It smells like a Weber carb 911 that has unbalanced fuel jets. I suspect it's running rich, but don't know for sure. My tech did a test with an exhaust gas analyzer, and nothing unusual turned up, but I can't see what the fuel air ratio is in the test results.

I should add that all 6 fuel injectors are brand new, new dme, new fuel pressure regulator, new fuel pump, new intake elbow, and no vacuum leaks that I can tell with a can of starting fluid.

I'm thinking about buying an Innovate LM-1, but with the rpm transducer and data logger, it looks like I'd be spending about $400. Is it worth it? I'd be using it to check the fuel air mixture what, maybe once every 5 years or so, or whenever the car fails to pass smog. Plus I have to weld in a bung after the stock O2 sensor to check if it's doing it's job right? I can't adjust anything other than the little **** dial on the dme and the baseline CO adjustment. Everything else is controlled by the O2 sensor, which is also new and checks out, entering fuel control mode. What do you guys do?

old man neri

Without a cat it is going to smell a little. Any other symptoms? e.g. bouncing idle, burning excess gas....etc?

rusnak

ahh...forgot to add that I finally grew a pair and turned the CO adjustment screw on the air flow sensor box. I turned the screw righty-tighty (not lefty loosy) and the bad smell went away. I turned it about an eighth of an inch, and find it difficult to believe that was all that was wrong. I'd rather not be flyin blind when messing around with the fuel air mixture, which is why I'm contemplating shelling out dollars that I'd rather spend on things like brake upgrades.

rusnak

no bouncing idle, and the gas mileage is a little bit worse than 32-33 mpg average. I thought it might be the oxygenated gas robbing power though. It is not running hot, and power is good.

theiceman

you should be able to borrow one no ?

I did from a local lister after changing my airbox and it worked great, got a little advice from Pete on what to set the CO to and it was great after that ..

Brads911sc

I took the Cat off mine as well.. Backdated SSI's, Dansk Sport... it is the same.. Actually smokes a rich fuel filled exhaust until it warms up... seems ok once its warm... I took it to EurocarWerk and they set it cold, and full operating temp over a period of three days and says its fine. Think they set it so Id pass the SMOG when at full operating, which makes it run like **** when cold. Now that Im 25 yrs old, I convert to safety only... so Ill take it back and get it smoothed out or Ill borrow the tool... I might have to try the 1/8 a turn myself... does yours change when cold vs full operating?

rusnak

I was too afraid of burning a valve or something until I couldn't take the fumes anymore.

So, I only have about an hour or so of run time on the car since I turned the 1/8 inch (not 1/8th turn) "adjustment". I hate to call shooting from the hip an adjustment since it is just guesswork, like trying to guess which way the stock market is headed.

Mine was so rich I couldn't really tell if it smelled worse when warm. Now, it probably only smells as bad as my Ford F150 half ton pickup, which has no cat and runs a 2 barrel Holly carb.

I can live with the amount of fumes it produces now. I also noticed on the discussion board for the turbo guys that they run a huge amount of variance on their fuel mixture, from the mid-9s to 14s, wow!!

I'd love to borrow someone's LM-1 and get some free tutoring. Heck, for the tutoring alone I'd suck it up and buy one on evilBay. Anyone? Anyone?

Do you guys run your LM-1 or LM-2 with wideband O2 sensor after your DME O2 sensor? You don't disable the O2 sensor when you adjust fuel/ air, do you?

J. Brinkley

yes you do disable the oem sensor, otherwise you you'll read corrected afr's.
it's easy to fill a page about motronic's. I suggest the bosch manual. http://www.amazon.com/Bosch-Fuel-Inj.../dp/0837603005

You wont hurt anything adjusting the idle mix screw on the afm. It will only affect idle conditions for the most part, and drivability issues off throttle.
Borrowing a lm1 or 2 would be better than buying one for your intended use. There are cheaper WB set ups that can accomplish your goals.

rusnak

Hi Brinkley,

Thanks! I bought that book when it first came out at B Dalton booksellers.

so, if I disable the O2 sensor then I can basically remove the factory O2 sensor, unplug it, and screw the wideband LM1 O2 sensor in there? Sounds fairly easy. I aim for the Lambda ratio at around 2-3K rpm and under load? Do I drive around with the cords hanging out the engine compartment taped to the rear glass and coming in thru the sunroof? Seems like a 10ft cord might be a tad short.

theiceman

I did it and the device I borrowed came with a jig you fastened to your tip that suspended the O2 sensor in the tail pipe for idle adjustment. I adjusted it at idle, then set it and forget it .
The only real adjustment is at idle anyway. Not sure how much you can see but this is what the LM1 will show you . you can see where i bliped the throttle.

I was amazed how stable the read out was. I used an online table to convert AFM to CO .

http://www.perfectpower.com/Technical_info/afr.asp
Hopefully you can see where I trimmed it a little and now the readings are higher ( originally I was at about 13.4:1 and ended up at about 13.8:1 ) which isabout 2%CO and my78C runs great at that .

rusnak

iceman, your '78 has no O2 sensor, but it has a cat. You tested it after the cat right?

I wonder if I should test mine with a cat installed, after the cat?

Also, I thought the LM1 had an rpm input sensor. I guess I don't need one if I'm adjusting only idle, which is around 800 rpm or so.

theiceman

right on all acounts, my cat is gone, there is a test port in front of the cat i think normally. No matter. for me i put the bracket on the tail pipe and hung the O2 sensor in their.
it does have rpm input. don't need it though . it may be helpfull if doing high speed runs but i just did it at idle so didn't need it . took all of like 5 minutes to do . i think you check it at between 900 and 1000 on mine if i remember correctly. As you adust mixture idle changes so you have to readjust.

J. Brinkley

you test before the cat, at idle of 880. no need to drive around because everything else is in the chip.
what you are adjusting is idle mix.
with everything working right, no intake/exhaust leaks, dme, afm chip, injectors, FPR damper, etc. it's very easy to get a perfect idle and a smooth afr at warm idle. o2 sensor will make the idle fliutter -+ 50 rpm.

the lm1 has no rpm function by itself. but you don't need it to set idle mix. it's a cool tool but unless your adding a turbo and switching to carbs, it's expensive for what you can/could do with it.

the lm1 is the old unit, the new version is the lm2, it might have rpm function built in, I'm not sure.

and, you're right, the cords supplied with the lm1 are too short, depending on a few things.
I'd buy the cheapest WB you could get and set the idle mix at whatever people say is the norm for a NA car and forget it.
*a bad cht, or going bad cht sensor will mess this process up.

rusnak

Brinkley, got it, thanks! What does "WB" stand for though?

J. Brinkley

wide band, wb, narrow band, nb = o2 sensors