Doesnt start on Deisel but dies on WVO??? - PeachParts Mercedes-Benz Forum

NC Benz · #1 02-01-2009, 10:25 AM

**EDIT** Dies was supposed to be DOES. My typing skills SUCK.

OK riddle me this batman.......

We run WVO during the summer on our 300Ds. They run just fine, combined have put on about 30,000 on wvo.

During the winter, we change over to diesel. No surprise here.

But we find when we are straight diesel, we cannot start one of the 300s, and the other one starts hard.

The one that doesnt start doesnt even fire at all. I have changed out filters, did a valve adjustment on both. Changed out bad glow plugs, changed out a few return fuel lines that were leaking...

With the one that doesnt fire, when we go out and buy a bottle of Canola oil and put it in. After a little priming, the car starts up.

One would think with the much lower flash point of diesel, compared to canoloa oil, that the diesel would start in a (eh hem) flash. But it appears both cars like to have a little oil in them to run well or even start.

Is this strange or what?

Astroman · #2 02-01-2009, 10:44 AM

I've seen this problem a couple times before, and what it indicates is worn out plungers in the injection pump. The more viscous VO helps seal between the plungers and the barrels in the IP, but the much thinner diesel doesn't and really exposes the problem, especially when the engine is hot and it's even thinner. This is why adding in the VO to the mix and priming it up helps solve the problem. The result is that due to the "blow by" in the IP, you're not getting much fuel into the cylinder. Probably doesn't even blow any smoke or unburnt fuel when cranking. When it does start, the higher rpm masks the problem, just like low compression in the engine cylinders.
I won't speculate as to the cause of the wear, but inadequately filtered fuel (whatever that fuel may be) and/or water can and has done it.
Swap the IP on the problem car with one from the yard, and scrutinize for air leaks in the system.

NC Benz · #3 02-01-2009, 11:20 AM

Quote:

Originally Posted by Astroman

I've seen this problem a couple times before, and what it indicates is worn out plungers in the injection pump. The more viscous VO helps seal between the plungers and the barrels in the IP, but the much thinner diesel doesn't and really exposes the problem, especially when the engine is hot and it's even thinner. This is why adding in the VO to the mix and priming it up helps solve the problem. The result is that due to the "blow by" in the IP, you're not getting much fuel into the cylinder. Probably doesn't even blow any smoke or unburnt fuel when cranking. When it does start, the higher rpm masks the problem, just like low compression in the engine cylinders.
I won't speculate as to the cause of the wear, but inadequately filtered fuel (whatever that fuel may be) and/or water can and has done it.
Swap the IP on the problem car with one from the yard, and scrutinize for air leaks in the system.

We actually have a problem with the RPM being LOWER, where we need to keep our foot on the accelerator until it warms up.

I am still barking up the air leaks tree with this too.

Astroman · #4 02-01-2009, 12:24 PM

Quote:

Originally Posted by NC Benz

We actually have a problem with the RPM being LOWER, where we need to keep our foot on the accelerator until it warms up.

I am still barking up the air leaks tree with this too.

Right, until the car warms up enough for the idle to be high enough. I stand by my diagnosis.

NC Benz · #5 02-01-2009, 03:17 PM

Quote:

Originally Posted by Astroman

Right, until the car warms up enough for the idle to be high enough. I stand by my diagnosis.

The only problem is that it will start WARM on Diesel. It will not start COLD with diesel. But will start cold when we add a little VO.

Wouldnt that negate the plunger issue then?

Just to make sure.... I am NOT arguing, just trying to understand.

turbobenz · #6 02-01-2009, 03:46 PM

I agree to the second poster, you probably destroyed your plungers with the VO.

Or your timings off and the slower combustion or flash point gets it started

Biodiesel300TD · #7 02-01-2009, 11:24 AM

Have you cleaned the tank strainer? If you can run on a bottle of VO but not the diesel from your tank, the only thing different other than that fuels themselves is the tank strainer.

Astroman · #8 02-01-2009, 12:23 PM

He has to mix in a bottle of VO and prime to get it to start. He's not running from the separate VO bottle.

NC Benz · #9 02-01-2009, 03:14 PM

Quote:

Originally Posted by Biodiesel300TD

Have you cleaned the tank strainer? If you can run on a bottle of VO but not the diesel from your tank, the only thing different other than that fuels themselves is the tank strainer.

Pulled the tank strainer. It was spotless.

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