PeachParts Mercedes-Benz Forum - View Single Post - IP issues - won't throttle up until 80 percent open -possible hole in ALDA diaphragm?

JimSmith · #15 06-19-2010, 06:14 PM

The throttle linkage from the firewall to the injection pump has a couple of devices that change linear motion (the accelerator pedal motion) to rotational motion and then back to linear motion (what you look for at the injection pump linkage). It all requires the bushings and fittings have nice, tight clearances or some of the pedal movement gets lost in slop between the pedal and the injection pump. On a 240D (1982 and 1983 models, at least) there is a male pronged connector at the bracket that hangs off the valve cover that requires a rubber block be bonded to the sheet metal at the female receptors. Between heat and Diesel fuel and other dirt and grime in the area, after 25 years one can expect the rubber to disappear. At which point the slop between the female slots and male prongs takes up about 80% of the travel at the injection pump and you can't make it up a hill.

Not sure about the 300TD you have, but it would not surprise me if the same chunk is used. The ALDA is a method of pneumatically adjusting the stroke of the injection pump based on intake manifold pressure - when the turbo compresses the air you need more fuel, and the amount more is dependent on throttle position and manifold pressure. The throttle position control is up to you, the adjustment for manifold pressure happens outside your direct control. If the linkage to the injection pump is losing 80% of its travel it is, in my opinion, unrelated to the ALDA - that device works inside injection pump housing. My guess is you have the same or similar problem I described for the same vintage 240D. Or, on older 240D's the problem would happen at the bearing support on the firewall - a plastic device that would split and let the rod the accelerator pedal was supposed to twist, just move up and down.

So, have someone step on the throttle pedal, and watch every one of the bearings, couplings and especially the places where the linear travel turns to rotational motion or rotational motion turns to linear motion. If it is the device I noted earlier, I "fix" mine with popsicle sticks stuffed and then wired in the slots of the female part that snug up the male prongs against the edges of their slots. There is also a travel adjustment at that joint on the bracket for the male parts - I adjust it to get the most travel.

Good luck, but don't mess with the ALDA. I don't believe it can address the fact that the accelerator pedal is not actually connected to the injection pump.

Jim