Airflow sensor adjustment, L-jet troubleshooting Options

[Anton]

My 1.8 engine was running badly at idle and sounded harsh on acceleration. CO screw and dwell/ignition tune-up did not solve the problem. I thought it was time for another valve job until a 914 buddy of mine, Richard, adviced me to check on the airflow sensor. (IMG:style_emoticons/default/ohmy.gif)

After removing mucho messy glue on the cover (thanks, PO) and opening of the sensor, I found that the mixture was way too lean. There was a marking of the old position that was richer, but only after adjusting beyond this point, at a total of 8 (!) teeth on the wheel, idle became regular. What it did to acceleration and low rev. driving was even more remarkable... Is this what a 914 can do...? (IMG:style_emoticons/default/laugh.gif)

It all became evident after a period of driving with backfire due to wrong dwell/timing. Some of you will now probably say "evidently". Also I have heard of this problem before, "just readjust a couple of teeth on the wheel", but a total of 8 teeth! (IMG:style_emoticons/default/blink.gif)

Anybody care to comment on this? Is this usual for an L-jet?

BTW, I have not yet checked the current CO reading.

[Mueller]

Anton,

are you sure that you are not compensating for a vacumm leak? that would cause the car to run lean as well.


The O-ring on the oil fill tube can be a source of trouble.

[Anton]

Mike,

I checked all vacuum hoses and connections today; they are fine. O-ring for oil filler tube was renewed only last year. However, turning off the oil filler cap almost made the engine stall, so "the system works". (IMG:style_emoticons/default/laugh.gif)

Maybe there is something wrong with the thermo sensors or wiring. Humm...

[MartyYeoman]

I have a '75 1.8 with 2.0 pistons. I have had to adjust my air box by 6 teeth. You also have to adjust the small arm on the rotation plate to properly restore idle after spring softening (tooth repositioning). I keep two air boxes around. One for everyday use and one for biannual smog check. 8 teeth really doesn't sound to out of the ordinary.
Marty

[Qarl]

There is an adjustment screw on top (accessible without opening the cover). It's in that deep little hole.

There is also a way to change the characteristics of the AFM by messing with the cog and the spring inside. This essentially allows the flap inside to open more freely, tricking your FI computer to think that there is more air flowing in and this richening the mixture... (or something like that).

You really just need to mess with the outside screw first and use a CO meter to get your A/F ratio correct. This can cure some backfiring problems on deceleration.

Also.... DEFINITELY check for cracks in your tubes... I think you can spray some fluid (someone help me out) and "check for leaks". Have an extinguisher handy.

[Anton]

There is an adjustment screw on top (accessible without opening the cover).  It's in that deep little hole.

I know; previously it was turned all the way in to enrich the mixture. Now the engine runs best with the screw 2/3 out. I do not posess a CO meter; will check on that later (or sooner when the smog test comes (IMG:style_emoticons/default/wink.gif) ).

You also have to adjust the small arm on the rotation plate to properly restore idle after spring softening (tooth repositioning).

Arm for the fuel pump contact? Or the ridge in the right forward corner touching a small spring? The only other "arm" I see is sealed and adjustment would undo the previous actions. Please explain.