300E m103/w124 accelerator sensors
 

I read a post a few days ago about an accelerator "dead spot".

well my 300e (which has just had a new engine installed at 306'000ks with an engine done 80'000ks) has exactly the same problem.

New wires, plugs, injectors, coil etc. EVERYTHING.

Mechanic thinks is may be a sensor in the intake area playing up?

Pushing the pedal 20% is fine and drives perfectly, after that there is nothing. Especially sitting on 100kmhr, to get to 110 is close to impossible. Yet I know that is not the case with this engine.


Any info is much appreciated, cheers :)

No real sensors in the intake area on the M103-12V....
Everything from the pedal to the throttle body is mechanical...

Have you remove the air cleaner assembly to see if the accelerator linkage allows the throttle body to fully open ?

did you use an engine with everything on it or transfer your old intake?

the new engine has everything minus a few pulleys from the front and the injection pump.

i only assumed the sensors as thats what my mechanic suggested... hmm...

is there a likely culprate? or is this going to be a larger issue...

I have a gut feel the dead spot on my m103 is due to the accelerator cable. Mine has 221k miles on it and probably is on original cable.

But my mechanic who is very knowledgeable on m103's, and who also has an m103 MB (300E) says he too feels a dead spot at times. Especially at cold start and first time you try to accelerate in the morning. Like you step on it, and it feels like it bogs down, then will quickly regain power and off you go.

Check the cable for binding. Second take a multimeter and measure the sensor on the air pentimeter.

i have a multimeter but what is the "air pentimeter" and what am i measuring.

i have checked cable under air filter and everything is fine, movement is nice and even.

i noticed when i step on the gas (air filter off) the flappy thing that lets the air in goes down rather irregularly, then suddenly opens? well not suddenly, but not even really. just the only thing that seamed odd.

idle speed is 900, 750 in reverse or drive.

Potentiometer. On the front of the throttle body, measures the position of the throttle. There is a resistance test in the FSM, but I don't recall it offhand. Won't be hard to find under the electrical troubleshooting section, if you can put your hands on a copy of the FSM.

My bad about the spelling. Anyway that flap should drop easily with one finger with no bind and come back up to resting position with some resistance. The test for this sensor goes like this:
Pull off the plug enough were you can up hook up your leads from the multimeter (engine off)
Terminal 1 to 3 4.6-5.1 volts
Start engine terminal 1 to 2 should read .57-.81 volts at idle

Terminal 1 is on the top of the plug terminal 2 middle and 3 is the bottom.

If your car has fault readings it should show 10 percent when you measure the cars lambda reading if its bad. Have you checked to see if the x11 jack is throwning any codes?

The key reading is to test between pins 2 and 3 with key on. Depress the sensor plate, and you should see an increasing reading, then decreasing as it nears the end of its travel.

sorry folks but i'm used to a W108 - this is a big step up from that! haha!

1. how do you measure the lambda reading

the car seems to be much better when warm. ie first up on the highway of a morning it takes atleast 30 seconds to reach 100km hr. coming home when warm, it takes 15.

also this is more than just a dead spot, only 10% of the accelerator is working...

Well, if you are having enrichment problems, then they would be worse with a cold engine. Did you test the output of the potentiometer as advised? That is the most likely problem.

You measure the on-off ratio with a dwell meter or a DVM with a duty cycle reading from Pin 3 at the diagnostic socket. There must be at least a hundred posts on this. Have you tried a Search?

assuming i am testing the correct plug (the ONLY three point adaptor on the front of the fuel distributor pump) then the top, is 0v, the middle fluctuates between 1.1 when idle - to 1.4 when accelerating, then .9 when taking your foot off. and the bottom (which I thought should be 12v) is only 4.76 v.

now Im just confused.

At idle, the key reading is between pins 1 and 2. That's where you should see .7V. 1 - 3 should be about 4.7V.

M103-12V uses KE-Jetronic III CIS-E.
No potentiometer to monitor throttle position.
Just a simple SPDT switch ( wiring diagram reference S29/2 which plugs into X56 ) that merely detects full load and idle.

RE:Service Manual Engine M103 S-2421-103, page 07.3.11 I-121/24

The "potentiometer " is the air volume meter sensor ( wiring diagram reference B2 )

Ed A.