Air fuel ratio

[Porsche 935]

I have a 84 Carrera i purchased a few years ago and am trying to work out the bugs. Fixed air leaks and installed a wide band 02. Car ran extremely rich. Had after market chip, so swapped out for sw chip. Been running well and 02 gauge went bad. Just installed new gauge. Had issue at idle with surging. O2 said lean, 16 to 1 . Adjusted air fuel meter. Nice idle around 14.5 to 1. But never see more than 14 to 1 during hard accell or wot. By the way car has 218000 miles on it. Do you think there is a fuel supply issue or motor just worn out? Also hasn't been driven much lately. If I unplug factory o2 no more surging. Car burning some oil so I don't think o2 working properly anyway so i have left it unplugged.

[wreckah]

are you certain the AFR values are correct?

with WOT at 14, you should be noticeably down on power...you should easily feel that.

how does it accelerate?

[wreckah]

e.g. ii dont think my car would idle at all at 16 AFR...i'm sure it would misfire like crazy.

[Raceboy]

911 air cooled engines should run at lambda 0.85-0.88 (AFR 12.5-12.9 for gasoline only people) at full throttle.

[Techno Duck]

Check that the wide open throttle switch is adjusted correctly; this is the only way the DME knows to richen the mixture at full throttle.

See the section at the end of this PDF.

http://www.911chips.com/C1INSTR.pdf

[Porsche 935]

Well, installed another wideband sensor but no real change. Car runs and pulls great. The only change I made was putting a 45 degree extension in the sensor bung to get it away from the heat. At start up I see 13.8 or 13.9 and heads up to 14.4 as it warms up. But never see 13's no matter how you drive it. I checked the air fuel meter track and even repositioned but no change. Don't want to throw expensive parts at it but would like to see it run as it is suppose to. Maybe engine won't pull air flow meter open since it is so high mileage or maybe fuel pressure not changing with vacuum loss. But would appreciate any help from anyone who may have had these issues. Many never know their is an issue if they don't have a wideband.

[Techno Duck]

Did you check the wide open throttle switch??

[Porsche 935]

Are you saying the air fuel ratio never gets any richer than 14 to 1 unless you have your foot pegged to the floor?

[Techno Duck]

Read the section i indicated of the PDF.

The wide open throttle switch tells the computer to richen the mixture when at full throttle. If the switch is not adjusted correctly the computer will never go rich.

[Porsche 935]

I will check tomorrow and update. Thanks!

[dicklague]

Originally Posted by Porsche 935

Well, installed another wideband sensor but no real change. Car runs and pulls great. The only change I made was putting a 45 degree extension in the sensor bung to get it away from the heat. At start up I see 13.8 or 13.9 and heads up to 14.4 as it warms up. But never see 13's no matter how you drive it. I checked the air fuel meter track and even repositioned but no change. Don't want to throw expensive parts at it but would like to see it run as it is suppose to. Maybe engine won't pull air flow meter open since it is so high mileage or maybe fuel pressure not changing with vacuum loss. But would appreciate any help from anyone who may have had these issues. Many never know their is an issue if they don't have a wideband.

what brand AFR are you using? do you think it is working right??

[cabmandone]

When you say you're adjusting the AFM, you mean the idle mixture screw that you access at the bottom of the AFM right? You mention no surging once you unplug the o2 sensor which seem strange since my car never cared if the 02 was plugged in or not.
If you're adjusting the idle mixture screw, I was instructed to disconnect the o2 sensor then set base idle to around 14.2-14.4 at tip in you should see mid to high 13's and at WOT depending on the chip tune you could drop into the 12's
I'm not sure it has anything to do with your issue but I was told to verify the Fuel Qaulity Switch in the ECM was set to zero.
https://www.911chips.com/fuelsys.html

Also, where is your wideband o2 sensor mounted in the exhaust? I have a cat delete with a bung for the o2 sensor which puts my sensor just before the muffler.

On fuel pressure I was told to disconnect the vacuum line at the regulator and that the AFR "must drop significantly" if the regulator is working properly. I'd share the entire writeup I was given by an engine tuner but I never got permission to do so.

[Porsche 935]

Ok, checked the wot switch. Only shows continuity when I press gas pedal hard to floor. So going to check linkage first and if that is ok, going to try to adjust sensor on throttle. For the other gentlemen, yes I am adjusting the idle mixture at the air meter and it is 14.2 with the o2 unplugged. My o2 is mounted in the same place as yours and it is an AEM. Same as I use in my twin turbo and it is brand new.

[Porsche 935]

Ok, adjusted throttle linkage. Upon inspection, found hose clamp for throttle body boot blocking the throttle from opening completely. Fixed that. Pulled vacuum line off fuel pressure regulator and car ran slightly richer at idle. Took for a ride, no changes. Plugged o2 sensor back in , car idling at 13.4, cruize at 14, and wot 12.4. Good with that but how do i get idle back to 14.1 with o2 plugged in? Did notice computer setting at 2 on fuel qualty screw which is +6%. Try setting back to 0 which is no added fuel. What do you think?

[Porsche 935]

If I set fuel quality at 0 , idle back to 14.1 and does not richen up wot. No in between, stumped.

[Porsche 935]

Tried position 1, idle and all throttle positions at 14.1. Did notice when i ohmed the wot switch out. Readings were erratic. Think it is bad? But car runs great. Or problem in dme? Don't have one to swap out and check. Heard they deteriorate over time.

[trond]

mine will not idle at 14 or above. It seems to like 12,9/13,1
I run 12,7-13 at higher loads and just below 15 on cruise
Have not looked at plugs but tailpipe is darkish. Engine runs nice and 21-24 mpg

[Porsche 935]

Put switch back to position 2, still 14.1. So maybe factory o2 not functioning properly. High mileage, 35 year old car, not working like soppose to but you would never know if the wideband wasn't there.

[trond]

do a plug chop. Are they white then it runs too lean. If brown maybe it is OK ?

[spuggy]

Originally Posted by Porsche 935

High mileage, 35 year old car

The O2 sensor, for the narrowband 3-4 wire heated types used in the mid-80's, has a expected/rated lifetime of 30,000 - 60,000 miles - and will last much less than that if you poison the fuel cell by using leaded gas.

You could try testing it; pretty easy to do. 3-wire designs ground the sensor signal through the exhaust, BTW.

If you replace with a universal sensor, do NOT solder the wires, use a sealed connector (e.g. SuperSeal or Weatherpack) or heat-shrink them to make the join pretty.

All Zirconia dioxide cells require a source of reference "outside air" to perform their comparison; a peculiarity of the Bosch design is that this is intended to travel down the stranded wire core (presumably, they felt this was better than having a hole in the outside of the sensor to potentially get clogged with road crud).

So crimped connectors only, no heatshrink...