Africa...C250 TD 1999 NO accelerator function
 

I hope one of you can you help this fellow.



Mercedes Benz C250 TD 1999 model, only 52,000 miles, full service record.....
Difficult starting after parked for about hour with heavy diesel fumes under engine hood, caused by worn seals on fuel line system at inlet to diesel filter. After replaced original rubber seals from MB dealer - problem solved - started by the flick of the key, idle smooth like sleeping baby BUT touch the accelerator pedal, EDC warning light comes on - NO accelerator functioning.
This happened miles away from any dealer in the country side of South Africa, to expensive to load and transport to any MB dealer. Swap accelerator control unit (rheostat) with another car - no difference. I urgently need technical support with schematic and values because Mercedes South Africa do not assist with any.... The person working on the car is a retired Electro Technical Engineer. Much appreciated

Hennie Hattingh
hennhatt@gmail.com

Sorry, I don't have access to the information you have requested, and I am not familiar with the C250TD. By "normal" MB nomenclature practice that would be a 2.5 liter, in-line 5 cylinder Diesel in what we call a station wagon over here. It may be turbocharged, but the "T" designation is for the wagon chassis.

However, if the engine is laid out similarly to the E300D Turbo of the same year (in-line six with a turbo), the intake manifold covers the area of interest. It is actually easily removed (do a search here for a great step by step procedure for the E300D of 1998 and 1999), and if you changed all those fuel lines without taking the intake manifold off, I would suspect you removed either an electrical or vacuum line of importance, or possibly have jammed a mechanical device.

Anyway, it would seem the problem is related to the previous repair, and I would check the work done at that time first. I hope someone else jumps in who may actually know something specific about your model. Good luck, and I hope this helps somewhat. Jim

My brain is not working today...whats EDC?

Sounds like they replaced the pre-filter oring (3 x 18mm)

May be that when the throttle is touched they are getting a massive influx of air that kills it.

First, I'd check the pre-filter again and make certain it and the fuel line entering it have a good seal.

Next I'd comfirm the filters arent clogged restricting fuel delivery under load. Fuel in Africa would be suspect.

Electronic Diesel Control. The computer.

My 99 doesnt have a "EDC" light or if it does its never been on before, perhaps they mean the CEL is on? Would be nice to know what code is present regardless.

Quite posible during the no start phase the key was turned with no glow period and PO380 popped up on CEL. Notes attempted/failed start on cold GP's. Will turn itself off after 3 cold start cycles (Usually a day and a half).

Not much you can do about codes out in the boonies. Still think the problem is related to lack of fuel delivery/air intrusion and would concentrate on that. About the only whoosh of air big enough to kill it when running would be from the pre-filter area.

I guess a better description of the problem is in order. I understood the problem to be the engine will run, but pressing the accelerator pedal does nothing. That, to me, means the mechanical connection from the pedal to the injection pump has been made non-functional. In the old days that would be a cable or the mechanical linkage failing. In new machines it may be related to a vacuum reading that, via the engine control computer, disables the throttle or an electrical sensor connection that can do the same.

I am not familiar with the engine and controls, however, it seems something was done when the new fuel lines were installed to address a leakage issue we are all pretty familiar with on the 1998 and 1999 E300D. I know on the 190E 2.3-16 gas car a vacuum hose being disconnected can make the car ok to start but it won't run when you step on the gas. It was my understanding that as soon as the leaks were fixed, the unresponsive throttle pedal appeared. To me that makes the fix and the new problem related to what was done.

If there is a huge air leak, I cannot imagine no fuel leaks with the engine idling or right after shutting down. Jim

This car has a 605 right?

One possibility:
 

Let's assume the 1999 C250 has the OM605 (5cyl 20-valver), brother to the OM606 (6cyl 24-valver) which was produced during the same time.

If the 1999 C250 with the 605 is anything like my 1999 E300 with the 606, it has an electronically-controlled IP, and the throttle linkage terminates in a Position Sensor behind the engine bay firewall. There is no physical connection between the pedal and the IP.

It has been mentioned that the owner installed a new Position Sensor, so we can safely assume that is not the problem.

This leaves the fault at either the ECU or the wires plugging into the IP. It has also been mentioned that items around the IP were replaced, which makes it extremely possible that one of the harnesses was disconnected.

Now for an understanding of the wires leading to the IP: there are two harnesses, one connecting to the shutoff solenoid (on the side of the IP) and one connecting to the IP controller (on the rear of the IP). The shutoff solenoid is opened when the ignition is switched ON, and closed when ignition is switched OFF. The IP controller electronically performs the functions of a mechanical throttle linkage, ALDA, etc.

Here's my thinking: the harness connecting the IP controller to the ECU could have accidentally been disconnected, while the harness connecting the shutoff solenoid to the ECU could still be in place, causing a situation where the enigne will RUN but not ACCELERATE. It is logical that the engine could START and IDLE without the functions of the throttle, ALDA, etc--the functions performed by the IP controller. The engine is able to run with a fuel supply (shutoff solenoid) and a starter; the IP's internals are still mechanical despite its electronic controls.

Thus, the engine would be able to run with a working shutoff solenoid, yet with a disconnected IP controller pressing the accelerator would produce no increase in RPM.

All of this, of course, assuming the car has an OM605.
:D

Thank you
 

I am forwarding this thread to the vehicle owner.

Closed issue
 

Thanx for your response. The problem is solved!! 6 Pin Wire connector on Accelerator Rheostat - Pin (1) 5volt, Pin (2) Earth / Ground ( This was missing ) Pin (3) 5volt, Pin (4) 2.4volt, Pins (5&6) At engine not running

Regards

Your car is US-spec, and thus the MIL is labeled "Check Engine" as are all others here.