throttle "lunge" of approx 1-2hz - PeachParts Mercedes-Benz Forum

bricktron · #1 08-29-2014, 01:45 AM

i try to change the throttle position on the om617 slowly, because when i do it quickly the engine seems to roar or lunge once or twice before settling at the new level of throttle. it's kind of embarrassing when i have a passenger. the feel gives me the impression of an eccentric weight, out of balance. i can't think of anything that rotates about 1.5hz in the engine, though since it affects engine speed i'm guessing this has to do with the IP. (unfortunately no tach installed yet.) will this mean my rack damper spring is worn out? - other thoughts? cheers!

leathermang · #2 08-29-2014, 01:54 AM

First be sure your throttle linkage is not binding..
and take apart every ball joint in it... one at a time... clean and lube with trans fluid.
Then try it again...

cooljjay · #3 08-29-2014, 03:18 AM

huh throttle position?

What are you talking about? The throttle control on the dash? or the linkage from the ip to the valve cover?

You don't have a rack damper bolt on a 240D just a fuel pressure relief valve...

Skippy · #4 08-29-2014, 07:03 AM

According to his sig he's got a 617.952 in there. That does have a rack damper, and I kind of suspect it may be involved. Mine doesn't behave anything like that, but I've experienced something like he described in early model GM 6.2 diesels. Most of the 6.2's I've drive from before about '85 did it. Newer ones seemed to have that sorted out.

Diesel911 · #5 08-29-2014, 08:36 AM

Quote:

Originally Posted by bricktron

i try to change the throttle position on the om617 slowly, because when i do it quickly the engine seems to roar or lunge once or twice before settling at the new level of throttle. it's kind of embarrassing when i have a passenger. the feel gives me the impression of an eccentric weight, out of balance. i can't think of anything that rotates about 1.5hz in the engine, though since it affects engine speed i'm guessing this has to do with the IP. (unfortunately no tach installed yet.) will this mean my rack damper spring is worn out? - other thoughts? cheers!

None of the below has been spell checked.
You did not say if that symptom is when the Engine is in Drive or not. If that is happening in drive I had a similar symptom before My B2 Piston Broke. After the B2 Piston Broke I figured the symptom must have been from the B2 Piston Sticking.

On the other hand if someone has cranked the Rack Damper/Governor Idle Pin in too far or the Idle adjusment screw is cranked down to far (to compensate for some other issue on the Engine that is keeping it from idling properly) it can put the Governor it a place that is beyond the range of the Governor.
In the Manual it has that the Gorvernor works at idle and at the high end. Some where inbetween the Governor is not in control of the Fuel Injection Pump and it is your Foot in control
This is a guess but it could be your Governor is right on the edge of where it is control and not incontrol.

So as the other member said check yout Linkages and the Bell Crank on the Fire Wall (that connects the Pedal Linkages to the Throttle Linkages). The Throttle Linkages are supposed to have specific lengths.

After that back out the Rack Damper/Governor Idle Pin and set your Idle within the normal Idle speed range (on mine it is 750-800 rpms). The adjust the Rack Damper/Governor Idle Pin. The Adjustment should barely raise yoru idle speed or not raise the idles speed at all.
Even if your Engine is shaking more then you would like see if your symptom is gone.

If you symptom is gone and you are shaking too much you need to look look up the DIYs on excessive Shaking

bricktron · #6 08-29-2014, 11:19 PM

OK. will review the linkage leathermang, which i don't think is sticking, but worth double-checking. cooljjay, i just mean the accelerator pedal... and the engine is turbo. skippy, thank you for validating my complaint by understanding it!! 300DMan, i have a manual transmission. i think you're right about the governor, intriguing theory. i will adjust idle and damper and report back - presumably after i install the damn tach.

cooljjay · #7 08-30-2014, 03:41 AM

AHHH ok, makes more sense.....I assume they transferred the throttle pivot bushing to the 77? It may be bad, or something they did during the adaption....also look at the knee panel.....the black portion above the pedals may have came lose...

bricktron · #8 08-30-2014, 12:40 PM

cooljjay, honestly i do not know. i can say i'm glad i'm missing all the machinery that some people have bolted onto their valve covers. here is a view of the linkage mechanism after the swap. what i can say with certainty is that i have no knee panels

cooljjay · #9 08-30-2014, 07:02 PM

Hmmm odd, they added the pivot mount but it looks like they left the original linkage...

I would remove all the older linkage and keep the new one, and install the throttle pivot mount correct and see where you are at....very very possible it is binding on the older linkage..

This shows the rod going through the fire wall on a 240D

This is a 300d, and show the linkage running along the valve cover

leathermang · #10 08-30-2014, 07:08 PM

That 300D is missing several of the metal clips on its fuel lines... makes them subject to cracking from vibration...

Diesel911 · #11 08-31-2014, 12:40 AM

On the normal linkage setup the Blue circled Part is not bent like that and more importantly the Red Circled Part dost not have a Bolt that sticks out that far and makes contact with the other parts.

As it is now that Bolt that stick out is what is phusing the Linkage around when you rotate that shaft.