Jetronic air flow meter sticky to move - PeachParts Mercedes-Benz Forum

pentoman · #1 07-06-2008, 11:37 AM

I just purchased a complete injection/intake unit for a 2.5-16. It's all still together in one piece, just removed from another 2.5-16 and consists of air flow meter, fuel distributor, most of the fuel pipes, intake pipes, EHA etc. This is because I have a problem with saggy throttle response on my own 2.5-16.

I have noticed the air flow meter flap is very easy to move on the spare unit. A world different from that on my car which is comparatively much stickier. I think that this must be my problem. To explain: Mine comes up to rest position easily enough but requires more pressure to go down. But worse than that when you push the plate down you can feel it's pushing against something else giving it extra resistance (presumably this is the plunger in the distributor sticking). So if you push the plate down with your finger then let the pressure off, the air plate itself will come up very quickly right along with your finger, but the plunger does not - you can feel the delay of 1-2 seconds before the plunger catches up and you feel a 'bump' when it does catch up and hits the air flow meter arm. Also during this period you can very freely operate the air flow flap and the resistance of the plunger against it has disappeared.

Is this normal? Perhaps there's something I'm not understanding, because I'm comparing an air flow meter that's off the car with one that's on the car? I did remove the fuel pressure by unplugging the fuel pump relay and turning the car over(amazingly it ran for a second or two) but it made no difference, it's definitely sticky. While I was there I adjusted the plate to make sure it's central and resting properly.

How would I best fix this stickyness - transfer the whole spare airflowmeter/distributor/etc in one piece over? Or take mine apart to try to diagnose? Lubrication?(!)

Yours excitedly (chasing the prob for 18 months!)

Larry Delor · #2 07-06-2008, 12:14 PM

The plate is part of something that looks like a teeter-toter (sp?). When one side lifts, the other permits a smooth metal pin to slide down - I suspect the metal pin/rod is no longer perfectly smooth. Could be gunk, could be a smidgeon of rust.
Years ago, I unbolted the distributor, and after some fiddling, was able to make the pin come out. There was an area of a rust stain - some good polishing, and it was smooth as new - and working the way it was supposed to.
This was on a K-Jetronic.

pentoman · #3 07-06-2008, 01:21 PM

Hmm.

I just went out and undid the fuel line (the one to the distributor not the pressure regulator - is this the return or the supply?) so that there's definitely no fuel pressure. Then the pin you mention which I thought was the plunger became even less keen to return, most of the time the plate could be moved very freely independent of much return pressure pushing it back - except for its own natural springyness.

I wonder if this is all a red herring and the spare unit I've got merely moves freely because it has no return pressure whatsoever - the pin/plunger is maybe stuck at full deflection since there's no fuel pressure to make it return. And therefore the plate moves freely with nothing impeding it.

Larry Delor - can you tell me how you remove the black rubber bottom half of the AFM? Then I could look to see if the pin/plunger is moving..

Russell

Larry Delor · #4 07-06-2008, 02:19 PM

I honestly don't know how to remove it - the system I was working on, was on an Audi. I do remember unbolting the distributor itself (there was a gasket, and a wavy washer, if memory serves correct). From there you can see where the plunger touches the other end of the arm that connects to the plate. When I would move the plunger is didn't drop right out, but slid out smoothly at a pace you would expect from a piece machined to close tolerances. (it would slide back in the same way.)
Sorry that this is all the help I can give.

pentoman · #5 07-07-2008, 02:52 AM

After investigation it seems you have to separate the AFM body, it splits and there's lots of nuts & bolts holding it together. Unfortunately they're quite tight and my allen keys won't do the allen bolts, so I'll give up on that too.

pentoman · #6 07-07-2008, 08:48 AM

I'm just going to replace the whole air flow meter, boot, fuel distributor, pressure regulator, and even injector lines with this complete spare unit and see what happens. Looks pretty easy, just a few bolts and some fuel lines (remember to depressurize!).

I'll post back if I'm not burned by my exploding car.

pentoman · #7 07-08-2008, 04:28 AM

Quote:

Originally Posted by pentoman

I'm just going to replace the whole air flow meter, boot, fuel distributor, pressure regulator, and even injector lines with this complete spare unit and see what happens. Looks pretty easy, just a few bolts and some fuel lines (remember to depressurize!).

I'll post back if I'm not burned by my exploding car.

Well..

Yesterday took of my air flow meter etc. Looks like the rubber boot that makes up the lower half of the AFM has some smallish splits in it. May well be my problem.

Additionally, the injection unit is really easy to get off. Should have done it sooner perhaps! Nearly had the new one on the same evening (started at 5.30PM and it gets dark at 10 but I couldn't get the rubber boot to sit over the throttle body nicely, then the lady rang me and asked if I wanted to go swimming, so that's what we did. Can't wait to get back today and fit the parts though.
Oh you have to remember to release the pressure from the gas tank or fuel comes out the return line continually!!

pentoman · #8 07-09-2008, 08:46 AM

Spare injection "block" all fitted. Started straight up and from 15 miles driving so far doesn't seem too bad - definitely improved but not by a night and day measure. However I've not even checked the mixture adjustment (its a non O2 car). As for the air flow meter - this one's plunger definitely returns more quickly to rest position. However it does feel equally "stiff" to move.