Fuel Distributor rebuild kit?

[zedster]

All I know is that I mentioned to Larry that my car runs good but when I come up to a stop sign apply the brakes it will sometimes die from low idle. Not always. It will not turn over until the third key crank. My mechanic says he wants to replace the fuel distributor. Larry said, "I'm gonna make your day! Your problem is more than likely the rest position of the air flow sensor."

[etmerritt33]

Any of you that think the sensor plate rest position is not critical are DEAD WRONG!. If you consider how the air intake funnel is shaped it is engineered that way for a reason. That reason is each one of those graduations and the position of the sensor plate is mechanically tied to the position of the plunger in the fuel distributor and that establishes your air/fuel ratio. If that relationship is off even by a little (.5 mm is the factory tolerance) the air fuel mixture will be out of sync based on air flow with the demands of the engine and the car will never run right. Will it run? Yes! But, it will not run as intended by MB. You will be too lean or too rich under different driving conditions and there is no idle CO adjustment or control pressure adjustment that will put things right.

How do I know this? I also thought at one time that the adjustment was not critical so I didn't pay enough attention until Larry Fletcher stressed it to me. I change WUR's and control pressures like most people change underware and I've also had a number of the Unwired Tools WUR's and have the latest one on my 6.9 that allows the control pressures and engine vaccuum and warm up control pressure cycle to be precisely adjusted via a laptop. I've adjusted the hell out of my system and replaced almost all the components. Lowering that rest position for the sensor plate made a big seat of the pants difference because mine was 3.5 mm too high. The improvement you realize is directly related to how far off the rest position is for the sensor plate.

Trust me on this one. If you don't you will be leaving some nice improvement with respect to driveability on the table.

[etmerritt33]

Also, the comment about the air sensor plate always being down when the car is idling is also incorrect. I also thought that to be true until recently. During the warm up cycle when the auxiliary air valve is open and the control pressure is low to richen the mixture, the air sensor plate will deflect noticeably, perhaps 2/3 to3/4 of an inch. After the engine warms up and the auxiliary air valve closes and the control pressure rises, the air sensor plate will only deflect very slightly at idle. If you do not believe this pull the air cleaner housing off and observe this for yourself. This does assume that all the components in your fuel system are working correctly.

I, like most people, learned these things over time as it is human nature to not begin the process by studying and understanding how the system was engineered before touching it. So, I've had to delve into different aspects of the system as problems have occurred and learn the surrounding components. I'm still not sure I know everything about it as every time I think that, someone more experienced teaches me something that I did not know.  I do know this. I know a hell of a lot more about K-Jet than I did when I started the 6.9 sorting over 5 years ago now. I admit I'm a pretty slow learner.

Hope this helps.

[zedster]

Great info etmerritt33! I sent the pdf to my mechanic and he hasn't responded to me yet. I hope to get mine working properly.

[TJ 450]

That sounds very reasonable, etmerritt33.

Regarding the deflection, that is what I mean in my previous post.

Maybe this is the problem I'm having with my 6.9, as I paid no attention to the rest position when I pulled apart the airflow meter. It has run very lean ever since. I can't drive it until I fix it because when it warms up, it pings like crazy... the last thing I want is to have to deal with is major engine damage.

Tim

[koan]

Any of you that think the sensor plate rest position is not critical are DEAD WRONG!. If you consider how the air intake funnel is shaped it is engineered that way for a reason...

I'm going to be quite dogmatic about this because your explanation doesn't hold up.

It matters not one iota where the sensor plate sits when the engine is not running. What does matter is where the sensor plate sits in the funnel when the engine IS running.

The position of the sensor plate when running is determined by airflow and control pressure, not it's rest position.

The idle mixture is adjusted with the engine running and once that's set the mixtures at various throttle openings and engine RPM are determined by funnel shape and control pressure (which includes vacuum controlled enrichment applied to the warm up regulator) and that's it, there is nothing else to adjust. Rest position of the sensor plate doesn't come into it.

The only danger is if the sensor plate is too high is that it might not pull down when cranking. If your sensor plate was way too high this might have been the cause of stalling at lights but it won't affect running under open throttle.

"TJ 450", Have a look in the Library at a 450 SEL (which uses the same fuel distributor and air meter as 6.9) Job 00-245, "Replacing, centering of air flow sensor plate, checking and adjusting of zero position of air flow sensor plate.

Agree with you TJ  regarding sensor plate deflection at idle

I've followed your trials and tribulations on m-100.cc, I may have contributed when you were given inaccurate information by another poster.

You say you "change WURs like underwear" or "adjusted the hell out of your system", that's suggest to me there is something wrong somewhere, have you replaced the fuel distributor itself?

Also puzzled about the linking of aux air valve to control pressure, they operate independently, there is no connection between them, it's just that they operate simultaneously as the engine warms up.

I'm always a bit concerned when authorities are quoted and there appears to be holes in the argument.  I'm always willing to be corrected with rational argument though.

We are all going to have to learn more about our aging machines and work in the areas we wouldn't have delved into before because there are fewer and fewer capable people around.

At the moment I'm collecting fuel distributors and pondering the effects of age on the springs in the flow equalising chambers, how they might affect the mixture under various operating conditions.

Please "etmerritt33" have a think about the way I believe it works and point out where the flaw is.

koan

[zedster]

Job 00-245 where is that?

[TJ 450]

Thanks Koan, I'll have a good look at the manual.

Tim

[koan]

Job 00-245 where is that?

Sorry, error on my part, in the library but it's "Engine Manual", 07.3-245.

koan

[etmerritt33]

Koan,

I stand by everything I said and have no real interest in arguing with you. It's all in the manuals. Just to be clear I have a brand new aluminum fuel distributor, two new WUR's (Bosch and UT), all new bronze fuel injectors, new fuel damper, new fuel pump, and new auxilary air valve. You adjust the rest or zero position of the air sensor plate by pressurizing the system and with the engine OFF! I was just trying to share some info with you guys that I have learned the hard way so you could avoid some of the frustration I've gone through. If you refuse to believe that the rest position of the air sensor plate matters that's fine with me.

- Tom   

[zedster]

Tom, I believe you and will pass this info on to my mechanic. koan, I also respect your knowledge on these cars. I bought a new fuel distributor yesterday from AutohausAZ. Larry called me today just check to see if I had gotten it squared away (what a guy!). I told him I bought a new one (one of his) and would keep him posted.

[koan]

I bought a new fuel distributor yesterday from AutohausAZ.

Nice, is it alloy or cast iron? And it is actually new or a rebuilt unit?

On related (!) matters, there's too much voodoo and black magic surrounding our cars. I particularly fire up when I read the words "my mechanic said..." and what he says don't stand up to scrutiny. pretty common with fuel system and hydro suspension. All I want are logical and coherent explanations of how things work. Always willing to be corrected but only with rational argument.

koan

[s class]

Agreed koan.  In my opinion, when one has actually worked through a 6.9 suspension, one should have a proper understanding of it, and what follows is the realisation that it is actually pretty simple.  I'd like to think the same is true of K-jet - but I think though that the initial learning curve of getting to grips with it is steeper. 

[zedster]

Mine is the cast iron part # 0438100012
FD29X        Rebuilt Fuel Distributor

Bill

[koan]

Mine is the cast iron part # 0438100012
FD29X        Rebuilt Fuel Distributor

Let us know how it goes. I'm thinking I might be in the market for one.

I'll try a rebuild of my spare, I have some ideas, if it doesn't work out I might have to spend money.

koan