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This one is a treat. I’m not a diesel technician, so I could use a little help on this one. I’m at the shop and the customer complaint was the transmission wasn’t shifting into any gear. We tried a few things like rolling start, things of that nature. It was still stuck. So I was the one who had to take the transmission out. 2 hours later, it’s out. We send it out to get rebuilt. It was locked up due to a bearing failure. Now the transmission is perfectly fine. Put it back in with no problem. I go to start it yesterday after putting in the transmission and it starts up with no problem. It was running great. However, I forgot to put gear oil in it. I usually would put it in before putting the transmission in, but we had to wait for the oil, so I did the install in the mean time. So, 2 minutes went by before I realized that there was no gear oil. I turn the key to turn the truck off and it won’t shut off. I couldn’t figure out how to turn it off. So I just put it into first gear and braked to stall it out. We left it like that for the night because the gear oil came in today. Put it in, and the truck won’t start. We figured out that the truck will start if you pump the brake. It will stay on for as long as you pump the brake. It then stalls out 4 seconds after letting go of the brake. I know it is some kind of vac leak (I’m guessing). From the looks of it, this has a hydroboost unit. Oh and the weird thing is it has 3 brake fluid reservoirs. Can anybody shed some light on this problem? Thanks.
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First off, I don’t know if you realize this but you have to turn the key to the “glow plug” position. Let the glow plugs get hot(there should be an indicator light), then start it. Be careful cranking that thing a whole lot cause the high compression of the engine can wear your starter out pretty quick.
You have a vacuum leak. The fuel pump and injector timing are mechanical. The engine really only needs the battery to turn the starter, after that everything is operated by vacuum or mechanically driven.
So in order to stop the engine the fuel is cut off by a vacuum actuated valve right near where all the injectors feed from.
In order to test if that shut off valve is working you need to use a vacuum hand pump where the vacuum line typically connects to the shut off valve.
Because of the brake pumping thing you were talking about, you may want to check the “vacuum check valve” that leads to the vacuum reservoir. It will most likely be a yellow cylinder about the size of a $3 stack of quarters. There should be two or three vacuum lines plugged into it. REMEMBER WHAT DIRECTION IT IS PLUGGED IN BEFORE YOU DISCONNECT IT! After you disconnect it blow then suck through it. It should only allow air to move one direction.
Don’t confuse the yellow check valve with the green “buffer valve”. The buffer valve is supposed to allow air both ways.Another thing that could be ailing the old girl is a leaking fuel pre-filter. If the fuel filter or pre-filter are leaking (which I have found is very common) they can suck in air if the engine is stalled out. If this is the case you will have to bleed the system. I am not sure exactly how to do it on that Merc, but for the one I was just working on today: Look on the driver’s side of the engine down near the engine mount, you will see the fuel pre-filter (it looks like a standard in-line filter) You will see the fuel line go to a block with a primer pump (looks like a roll of quarters) then the fuel line will go up to a canister (this is the fuel filter). You should see a bolt that drives straight down into the top of the fuel filter, this is your bleeder point. open the screw a bit and push on the primer until a bit of fuel comes out.
Thanks for the reply man. The fuel pre-filter is where you said it will be. However, there is no yellow or green valves of any kind. In fact, the only thing yellow is the writing on the junkyard engine that it has.
They don’t look like valves, they look more like in-line filters (little cylindrical things about an inch long), but they are on the vacuum lines. I will admit I am not really well versed in Mercedes so it may not have them. If it does have them even if they are bad it should run. try going to http://www.mercedessource.com this site helped me alot.
Thanks for pointing me to that site. I actually knew about it but just completely forgot. When I went on it I realized it was Kent. Anyway, it helped me to figure out that the truck shuts off with a fuel cut-off valve or something of that name. I saw that there were 2 vac lines under the steering column that had both ends together. This looked odd to me. So I pulled them apart and the truck started up and stayed on. This led me to investigate further. I tried to see if by putting my thumb over each line would stall it out. It didn’t. Then I tried both lines at the same time. It still didn’t stall. So I put the lines back together and it stalled. That told me that one of those lines was the fuel cut-off vac line. So I followed each line through the firewall. They were 2 different colors. The brown one went into the vac pump and the off-white with blue stripe went to the fuel cut-off valve. So I thought, there has to be some way that these 2 lead to the ignition switch. Sure enough, I pull out the ignition switch and there were 2 small hoses that were cut. I connected the 2 vac lines and it was stalling immediately after start-up. This told me that there was a problem with the switch, which is probably the reason why the previous owner of the truck used the 2 lines together to turn off the truck. This owner just bought the truck as a project and it turned out to have too many issues for him to tackle. I took apart the switch and there was a kind of lobe that turned when the key turned. I adjusted it and connected the lines and the truck started. I turned the key off and the truck turned off. I took it out for a test drive and all four gears and reverse are shifting perfectly. I am not a diesel tech, but this job actually turned out to be so much easier than any other job that I had to tackle. Thanks again for your input.
[quote=”LJ11194″ post=41948]I didn’t think they even sold that in the states! Glad you got it figured out.[/quote]
Yeah man, it was weird when this thing came into the shop. It is real cool though.
I want one! As far as I can tell it really wasn’t sold here, except by importers who bought them and made them DOT compliant. And sold them for over $100,000.
My friend just bought a mercedes and I have been fixing it up for the last week or so. I have experience working on diesel construction equipment but have never worked on a diesel car before. I’m actually enjoying it. It’s nice to work on a vehicle that doesn’t have computer controlled shit everywhere. Thanks for posting your resolution.
Yeah, it was real nice to just fix it without any computers. I really enjoyed working on it because it wasn’t hard at all. Once I heard about the fuel cut-off, it was pretty much all me from then on.
Thank you very much for keeping us up to date on this one. We don’t have a lot of diesel info here on the forum so this will help a great deal. Thanks also for using the ETCG forum.
Those old MB diesels are heavily reliant on vacuum.
The first thing I always do when I buy one is replace all the vacuum lines.
Before you said that the tranny had a bad bearing I was going to chime in about the importance of adjusting the transmission vacuum controls.
I assume the G-class transmission is the same one in the W123 sedans as well as the engine.
There should be a vacuum line going into the driver side of the transmission and there is a rubber-plug-covered adjustment wheel/gear just below it. You can turn it with a coin/screwdriver IIRC and then test drive it until it is shifting the way you want it to.
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