GregBBRD

I'm not sure I ever memorized this detail. I'm always too busy trying to keep it from unwinding, completely. Once you lift that retaining spring, it becomes very evident. The thing tries to unwind itself (this is the direction you want to go) and making it tighter requires effort.

I didn't want to get into the performance enhancing part of this adjustment....however, virtually every single one of these cars will run way better, with a richer mixture.

There was one "amazing" thing I found on the 944S engines. If I bolted on an airflow meter from a 3.2 Carrera engine, the additional power was incredible. They ran those engines very, very lean.....too lean to "correct" by loosening the spring. Apparently, the "chip" on the 3.2 liter version was "calibrated" differently and the change would add a much better fuel mixture. I did this to many of these engines....with very happy customers.

GregBBRD

Perhaps an interesting factoid for those who have interest in why these things need to door spring adjusted.

The 914 1.8 liter engines "ate" these air flow meters like they were candy. The door would distort (from a backfire) and then rub on the internal aluminum of the actual meter. Sometimes the door would actually stick at some position and never move again.

At any rate, the replacement Bosch air flow meters came so stinking tight that these engines would barely run....and if you sent a customer off with a new, unadjusted air flow meter, the engine would "lean sneeze" and ruin a brand new air flow meter very quickly.

We had to adjust each and every one.....had to find the correct "sweet spot" for individual vehicles.

I once had the opportunity to ask a Bosch engineer type why this was...."Why couldn't they supply an air flow meter which actually was rich enough to run the vehicles?"

Simple answer...."We have to ensure that we never deliver an emission related part that is too rich for any possible senario.....so they all get set to the "leanest" position."

granprixweiss928

Thank You Greg for your insight and comments on this thread. I will make the adjustments as we discussed and post some pics. Going to be a while till I can get to it however.

granprixweiss928

Some videos on youtube relating to the adjustment of the AFM spring position, so you can see whats inside the AFM.

sam281

Anyone know how to fix a electric seat? can't get to the bra cause the seat is all the way foward

Sent from my iPhone using Rennlist

The Fixer

^ Start a new thread^


On topic:

When i first took a look at this Bosche AFM i recognized it was the same unit that was in my 3.2L Carrera, they have the same part number.

It is also the same unit in the early '80s BMWs and many other Euro makes with smaller motors.

It's a parts bin solution for the US 928 imo. And worth careful machining to improve it as best you can. I promise I won't 'harp' on this again.

It was worth the time I spent smoothing out and increasing the air passage size as best i could to improve air flow. Done it with 911s and Beemers..it always makes a noticed improvement.

The 'barn door' stop sits in the air flow and can be reduced in size by a 1/2 a square cm easily. You could probably find a more elegant out of the way solution for a stop too. I may look at this.

There are crude castings edges in many places inside the air passage that can be filed and smoothed out considerably.. you can mill it out several mms inside to transition better from the AFM to intake manifiold then sanding the surface smooth or leave swirl marks or polish whatever your preference..

Similarly i noted the connection (transition) between the air box and the AFM has very sloppy tolerances from the factory for a performance car.. careful (match) filing took away about a 1/16" of material hanging into the air flow (in total) around the perimeter of the opening into the unit which further disrupt air flow. These little improvements can mean real gains.

Carefully connect the airbox to the AFM and be sure the mating surfaces are perfectly flush. I like connecting these two parts (box/AFM) prior to inserting the AFM into the intake manifold to be sure the passageway is perfectly alligned. (it's easier too)

This is a great way to spend an afternoon because you will note a power increase immediately. I may go back in and do more.

9two8

All well and good.., however the K-jet cars without an AFM also experience this bucking annoyance , anyone know what to adjust in this case ?


Ken
80 928 S
5 Speed

UK

antsmands

I fashinoned a 1/8 in thick fiberboard gasket to take up the space between the AFM and airbox. Nice fit, no slop after that.

Crumpler

So, as somebody still learning systems, when I adjust Ohms on the outside of the MAF to make it richer-- am I accomplishing anything tangible?
Are we talking micro adjustment from the outside versus a macro adjustment inside with the door spring?
Or am I missing it.

The Fixer

The OP should replace the large O ring on the end of his AFM to rule out a vacuum leak there.

Ken,

When my 5-speed Porsche 911 bucked, (and it seems this is a manual car problem from those posting) does this lead anyone else to believe it's also drive train related?

My butt and gut thought this bucking occurred (again in my case) due to slight wear in the diff and CV joints which could be magnified in situations due to fuel issues. It was also only bad in first gear at idle, which supported my hunch.


I think the OP has different symptoms than i did.


Dave, didn't you install a good A/F ratio meter?

Crumpler

I did and it's where my ashtray used to live. And I can move AFR around fairly well by adjusting MAF Ohms from the out side of the sensor....just trying to wrap my brain around the spring method and how it is different?

The Fixer

We have an earlier Bosche AFM (up to '84) different than yours.

Definition Air Flow meter:

Our early L-Jetronic system has a movable flap connected to a potentiometer which measures the amount of air being inducted into the system. The more air entering the system, the farther the flap is forced open.


At the same time the signal is being sent by the air flow meter, other signals are coming to the ECU from the throttle position switch and the air temperature sensor. All of these signals are integrated by the ECU to to determine how long the injectors should be held open. Along w/ the flap of the air flow meter, there is a small bypass port which controls idle speed by increasing (or decreasing) the amount of air which passes through the air flow meter at idle.

Because the measurement of the amount of air flowing into the engine determines the amount of fuel injected, it is critical that only air passing through the flow meter be allowed into the engine. Any leaks in the system will not be accounted for by the air flow meter, which can cause the engine to run lean (or not run at all).

Crumpler

Thanks Matt, that makes a lot more sense.
Now that you mention it, I remember you guys don't have a hot wire and can use a K&N filter (if you wanted).
I didn't realize how different the sensors were. That really does help me.
I'm having fun learning, appreciate the time to bring me up to speed.

granprixweiss928

AFM spring loosened today by 10 notches (recomendation from GB) and this made no improvement with regards to the slight bucking problem. inside my AFM the circuit board was VERY clean, no noticeable marks from the needle.

I drove it today about 100 miles- and sometimes hard, and had the pulse in power (drop) pretty commonly around 2600 rpm (but not only at)

it is more noticeable (seat of pants) when under more load, such as going uphill

granprixweiss928

I actually think the adjustments made to the AFM have exaggerated the issue. It feels worse now.