1974 Mercedes 240D Runaway when Started - PeachParts Mercedes-Benz Forum

CJW · #1 02-25-2017, 10:15 PM

So I have been getting my 1974 240D going and a couple of weeks ago I changed all of the fluids and ran it every day in its parking spot for about a week. Ran beautifully. Then, I was busy for a week and was waiting on parts anyway so I did not mess with it. Started working on it today again and have this issue. As soon as it starts it revs up realllllyy high and smokes bad (just like a runaway) and I use the butterfly on the intake to slowly bring it down and then kill it. I spend hours trying to figure out what is going on but I can't. The throttle is completely at idle. The idle adjust knob by the key is all of the way down (it is running way above the high idle anyway). If I take the starter/shut off knob and push it back in (as if to shut the engine off) but not all of the way, I can bring it down to idle if I feather the knob. It almost seems as if the IP rack is stuck but I cannot tell. I know the 300D engines have an ALDA and people say you can look inside it but there is not such a thing on the 240D cars. Any help would be appreciated! Thank you!!!

Diseasel300 · #2 02-26-2017, 12:22 AM

If you push the stop lever in to stop the engine, does it stop? If so you know that the issue is indeed injection related. If it doesn't, what is the oil level? Overfilled?

If the stop lever stops the engine, check your throttle linkages and make sure the injection pump throttle lever is actually moving and resting at idle. Sometimes things go wrong with the linkages and they can jam the throttle in undesirable positions. If everything checks out, you may have an internal problem with the injection pump.

Mike D · #3 02-26-2017, 08:04 AM

Do you have this style of injection pump (post #15)?

74 240d Grey smoke questions

CJW · #4 02-26-2017, 09:56 PM

Diseasel300 yes everything checks out and I believe I have it narrowed down to the IP.

Mike D yes that is the style of IP that I have

CJW · #5 02-27-2017, 11:26 AM

Also, i checked the governor suction this morning and it had good suction for at least 30 seconds because thats when I took my finger off. You could also hear it sucking when moving the lever back and forth. I am going to get a new vacuum line today to run from the venturi on the intake to the governor in case it formed a leak. Other than that I am out of ideas. I know algae and other fungus can form in diesel fuel and cause the ip racks to get stuck but i sucked all the old diesel out, put new in and ran it several times thereafter and then a week later this happened so I am not convinced that could cause the rack to freeze in the full throttle position. Does anyone know how to tell if the ip rack is stuck or not? I do not know of a place where it is accessible to see

Diseasel300 · #6 02-27-2017, 11:54 AM

Out of curiosity, was the car sitting for a long period (years) before you started working on it?

I had the reverse situation as yours on my SDL in it's injection pump saga (you can read all about it in my signature thread). Original IP was toast, replaced with a supposedly "good used" one. Car would start (reluctantly) and run at a fast idle, but would refuse to rev under any circumstance. If you sharply yanked the rack lever it would eventually rev reluctantly, then stall when you let back off. Pulling the IP and taking the side plates off revealed that the oil had turned to a varnish-like goo and everything was gummy and slow to move. Didn't waste my time fixing that, got a refund and a THIRD pump that I'm running on today.

Not sure about the earlier pumps like yours, but the M pump in my SDL has a side plate on it. Taking it off and moving the throttle lever moves the fuel elements inside. On the bad IP, they were very slow to move, if they moved at all.

Diseasel300 · #7 02-27-2017, 12:25 PM

Another point worth mentioning: You might repost this issue in the "Diesel Discussion" forum, you might get better help a lot faster. A lot of the diesel guys don't read the "Tech Help" forum, which is mostly for gas engines.

CJW · #8 02-27-2017, 01:32 PM

Diseasel300 yes the car was sitting for a long time prior to me working on it. Before I attempted to start it I changed all of the fluids including the oil in the IP itself. And it ran beautifully. Revved it up and held it at rpm and let it down and it did not miss a beat. That is why I am perplexed. And I will try moving this to the diesel section. Thank you for the advice

CJW · #9 02-27-2017, 01:40 PM

I started a thread on this issue im having a couple days ago and I am wondering if anyone in this section can help me. All the basic info can be found at this link in my other forum post:
http://www.peachparts.com/shopforum/tech-help/384385-1974-mercedes-240d-runaway-when-started.html

The engine is revving to full throttle as soon as it starts and I cannot figure out why. The throttle is 100% at idle. The vacuum governor holds a vacuum. The injector pump is the source of the issue because if I move the shutoff lever i can manually rev the engine down by starving its fuel supply. Any input will be greatly appreciated!

vstech · #10 02-27-2017, 07:37 PM

Runaway is caused by fuel feeding uncontrolled into the motor.

Motor oil is a fuel to the motor.

Verify oil level, perhaps even have it closer to the low oil mark.

Next, unhook the pcv hose from the intake. If the motor has serious blow by, the vapors can cause this.

Since holding down the stop lever does stop the motor, I am leaning towards a failure in the IP. perhaps a linkage got put back wrong on the engine during service.

Take a picture of the linkage and IP and post it here to compare it to other members setup.

CJW · #11 02-27-2017, 08:44 PM

Thank you all for your help, I found the issue! The line running from the governor to the venturi on the intake had a leak. Replaced the line and it is as good as new!