I hope someone can help point me in the right direction here.
I've bought a 96 E300D W210 with an OM606 engine (non turbo).
Basically as soon as you turn the ignition on it fires up and the revs go crazy as if it's a runaway. Luckily the engine shuts down when the ignition is turned off.
I don't want to try and start it again until I've diagnosed what exactly is wrong.
It's got a drive by wire Throttle Possition Sensor which might be worth further investigation but I suspect in may be the pump that's pushing out too much fuel.
Has anyone experienced this before? Does anyone know whether something inside the pump could be sticking open therefore injecting too much fuel?
I guess the TPS could also cause this??? I'm currently awaiting a new engine loom so I'll wait for that before doing anything further with the TPS.
Is there anything else that could be causing the engine to over fuel??
Thanks in advance

Make sure the throttle pedal sensor isn't pulled wide open.

Why is the engine harness being changed?

What is the history of this car?

From under the hood you can see the TPS and the cable to the foot feed. Is everything mechanical connected and working correctly? If so, is the wire harness from TPS connected? Undamaged? If there are wiring harness issues (common in mid-90s cars) you may have a short or open circuit somewhere. The TPS and the electronic circuit it talks to are usually not the problem.

Jeremy

Will unplugging the pedal assembly return it to idle?

__________________

Gone to the dark side

- Jeff

TPS looks fine as does the connector. Can anyone explain exactly how this TPS actually functions? The mechanics are working fine and the cable to the pedal works as is should.
I want to try every other option prior to pulling the diesel pump only to find it's something else causing the problem.
So far I think I need to go in the following order but if anyone spots something I've missed feel free to let me know.
1. TPS and wiring
2. ECU?
Now here I'm thinking that these two could be the problem as the car I believe should return to idle if I put my foot on the brake pedal??? I.e the ECU should over ride the TPS and return to normal idle if it detects the brake pedal is pressed???
3. The Injectors.
4. The Fuel delivery valves (although when the problem started the first thing I did was to change the seals and copper washers on these)
5. The fuel pump. Could something mechanical inside be stuck wide open pushing full fuel? I'm leaning towards this as the fuel seems to be really shooting out of all high pressure lines (I disconnected these to see if I had a problem with just one fuel delivery valve.

As to the history of the car.....
To cut a very long story short.
I'm a part time mechanic and had done quite a bit of work on this car as it wouldn't start. It had been to a number garages etc and the previous owners didn't have a lot of money so tried to get the car up and running on the cheap. The upper engine loom has been replaced but I think my 9 year old could have done a better job! I've ordered a new loom so need that in order to at least have a solid base to work from. Should be here any day now.

The story behind this revving was that it starting doing this then ran fine for a few days. The oil cooler then blew off the car. This was replaced then ever since it's constantly done the high revving.
Engine compression is fine on all cylinders so I don't believe it's running away on oil. Plus it shuts down as soon as the key is turned off.

I'm reluctant to start the car until I've diagnosed the problem but could anyone tell me what would happen if you try to start the car with the TPS disconnected??? I'm prepared to give this a try if it would 100% rule out a problem with the TPS. Would the ECU take over and idle the car or would it just not start.

If you unplug the tps, the car will simply idle. It will start, give a CEL and idlel

Just want to add that you can remove the side cover of the injection pump and observe the rack. You should be able to push it forward with your finger and it will snap back when released.

The rack should move smoothly with no binding.

You can also run the car without the cover on so you can observe it's movements.

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Throttle pedal position is measured by a dual potentiometer, the two have different overall resistances. One sends a decreasing voltage signal and the other a increasing signal. The ECU looks at these and determines pedal position. If the two signals don't match what the ECU is looking for an error code is tripped and engine goes into limp.


The system might not be that advanced to know you are pushing on the brake.

You need to gain a better understanding of how this system works, these are not electronic unit injectors. Delivery valves are just check valves. Neither of these will cause a run away.


More accurately it is called an injection pump, the fuel pump is something that moves fuel from the tank to injector pump.

Given lots of fuel is coming from the injector line, the power transistor / FET in the ECU that controls the fuel solenoid may have failed in a conductive state or the circuitry that drives it has cause it to turn on.

I'd unplug or back probe the fuel control solenoid and measure voltage. I don't know what it should measure.

There is even a chance the harness has rubbed through and the fuel solenoid is being activated.

There is a chance that the crank position sensor isn't sending a RPM signal to the ECU but I don't know the system well enough to say for sure.

The problem may or may not be related to the oil line coming off. What did you do to get it into a running state? The rev might be part of the preexisting condition.

It would be a great help if you had a scan tool with live data.

Unplug the rack actuator - the connector is on the right side of the engine bay. The cable runs from the back of the IP around behind the head and over to the right side. Huge connector on the false firewall.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thanks everyone!
This site is awesome!
I'll try and start without the TPS connected and see what happens.
If its still getting too much fuel I'll try the wiring to the IP. Then failing that I'll take the side of the IP and see whats going on there.
To get it running... The replacement loom (if you could call it that!) was made up out of household earth cable (yet all yellow and green and the same size) I suggested to the previous owners that we buy a new upper engine harness or at least make a one properly but they didn't have the funds for that. I eventually managed to jump the shut off which after cleaning filters etc got the car starting.

When I originally repaired the car (before I actually bought it) it started and idled fine!

The back story for this car for anyone who's interested....

To try to explain it should be noted the previous owners didn't understand a lot about cars and something would only be repaired if totally necessary to just get the car running. Unfortunately prior to bringing the car to me to repair they had been taken advantage of by various garages and dealers and various things had been replaced that I don't think were necessary (including the shoddy job on the loom)

So after I got it running I took it for a run and noticed that oil was mixing with the water. I told them about this and that it would need further investigating which I would do for about 50€. They decided not to do this and took the car back and drove it against my advice. At this time i suspected a head failure but couldn't rule out the oil cooler being at fault. I offered a compression test and to see where we go from there.

After they drove for a few weeks and in this time they had to buy a new radiator and new gear oil as the gear oil was mixing with water inside the rad. This was only repaired as the gears would not engage.

The car then ran fine for a few days with one episode of this revving problem which cleared away. After two days the oil cooler (in their words) exploded therefore this was also replaced.

Since then every time they tried to start it it's on full throttle revs.

I didn't do the work on the rad or the oil cooler which I can only presume is because they felt silly bringing the car back to me when I'd expressly told them not to drive it until we had diagnosed the oil in coolant.

So they then decided to give up on the car completely, got to a point where they needed some cash and offered it to me.

I did a compression test which was fine and accepted. My intention is to repair the car properly and let the wife use it for the school run etc. Therefore I intent to do it properly.

I have the Carsoft system which isn't the best. It's bringing up codes about various things but nothing that I can see that would be related to this revving. MB won't run it through their star diagnostics as it currently doesn't have a MB loom. I live on a small island and only the MB dealer has the STAR system. I think if I can get this runaway problem sorted I'll have to invest in a STAR system as I'm not a great fan of Carsoft.

Thanks again for all the advice. It's greatly appreciated and I'll post back once I've tried a few of the things recommended.

I've now tried disconnecting the TPS but the revving problem didn't go away.
I then tried unplugging the fuel control solenoid or rack actuator. The large connection following the cable from the IP. but with this unplugged it wont start.
Trying to think of a logical reason that this has been made worse with the replacement of the separate oil cooler and my guess would be that the fuel control cable may have been pulled as the separate oil cooler in directly behind the IP.
The cable itself looks ok but I'll get a probe on this later and test continuity. If anyone knows what sort of voltage readings I should be getting from the fuel control solenoid that would certainly help to narrow down whether its a problem from the ECU or if could be a problem with the IP or the connections inside it.
Before I start messing with what I suspect is a loose or broken connection inside the back of the IP can anyone advise whether or not there are any issues with removing the back of the IP (the part where the cable enters) and if I'm likely to be able to see the connections inside there?

So I took the back off the IP to access the wiring connections. It was half full of oil and the electrical connections were also covered in oil. Is this normal? Also I can't see where you could fill the oil once i've put it back together so can only presume the oil would come from the engine???
If there isn't supposed to be oil in this section of the pump then possibly I've got a leaking seal somewhere but surely that would mean I'd be getting diesel in there and not oil! Perhaps I'm barking up the wrong tree here but any advice would be great.
Also I'm trying to get my head around how the IP works. I'm guessing I can't try to start the car with the back off the pump??
I've attached some pictures so hopefully than may help if someone spots something that looks out of place.
On one of the pics you can just see that there is a (thinner than the rest) black cable that looks like it's cut but I can't see anywhere that this would connect to. Any ideas what if anything this is for?
The Square pin that I'm pointing to in the image connects onto the device that looks like it moves in and out to adjust the fuel through the pump. Can anyone confirm if this should be movable? I tried with ignition on but nothing happens. I'm wanting to check nothing is jammed inside the IP.
I've sprayed with electrical cleaner and I'm planning to put the IP back together and see if it works but I'll wait until tomorrow in case anyone has any advice as to what I should be looking for inside the rear case of the IP.

Attached Thumbnails

     

OK, I'll give you a crash course on the IP controls:

Oil in the areas pictured is normal. It flows in from the engine and back through the nose of the IP into the area behind the vacuum pump.

The square part you are indicating is the rack position sensor, it sends position information to the ECU to verify ECU commands. If this information is faulty, the ECU may keep moving the rack open wider and wider. The square thing stays put, the square "hoop" on the rack moves fore and aft over it.

The fuel rack is a rod with a larger round "nub" on it that sticks straight out of the back of the injection pump. You should be able to push if forward and have it spring back when you release pressure on it.

You can actually crank and start the car with the back off the pump but you have to take your finger and mover the rack forward a little to get fuel going. All the way to the rear is shut off or no fuel. You can manipulate the rack just like you would a throttle on a carburrated gas engine, revving it up as you push it forward.

NOTE! Sticking your finger into the back of the pump is VERY, VERY dangerous when cranking! There's a spinning lock and timing plate in there that can catch/break/remove fingers. You must actually look into the back of the pump to verify the position of the plate and make sure it won't get you as it turns.

You should be able to hold the rack forward about 6mm, crank the car and then adjust the engine speed manually by moving the rack back and forth. Again, for heaven's sake, be careful!

Attached Thumbnails

 

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Thanks for that Karkek. I'll hopefully give that a try this afternoon.
I've been changing the upper engine loom today so that I can have peace of mind that it's not a wiring issue in that.
Correct me if I'm wrong but providing the SOV is working (which it is) and the rack sensor is moving smoothly (which it is) and the fuel control Solenoid is OK as well as the ECU I should be able to start and idle the car?? I'm also disconnecting the TPS just to rule out any problems there.

Would any of the sensors need to be connected in order to get an idle?? I'm thinking RPM sensor perhaps??

My next step is to try to rule out everything else before chasing back from the IP to the ECU.