Intermittent Fuel Issue - PeachParts Mercedes-Benz Forum

reinventthewheel · #1 04-03-2012, 02:48 AM

Low miles 82 300SD
Has great compression, brand new fuel lines.
I just converted it to veggie oil, its about 2/3 wvo and 1/3 dino diesel
(single tank with heat exchanger, injector line heaters, inline electric heater and boost pump).
I changed the fuel filters right before the conversion.

It was running fine with no problems. Then it started having trouble starting, where I'd have to crank it a lot to get it started and it wouldn't start if facing uphill.
Then it started having major power loss, going up hills especially but also at lower speeds on flat roads sometimes.
This was short lived. Changed the fuel filters again, cleaned the alda banjo fitting (wasn't very dirty) and didn't drive it much after. Started right away and drove fine a few times over the last couple weeks.

Then today I started it and drove it for about ten minutes. Then it sat for half an hour and then wouldn't start. Took about half an hour to get it going. The engine was still warm and it was facing downhill. I opened up all the injector lines and had a friend crank to see how much fuel was coming out and all the lines were barely dripping at all.
After it finally started I drove it for half an hour and it ran fine the whole time, with good power up hills.

All the fuel lines are clamped on tight and I don't think any air is getting into the system. (it's not accumulating in the primary filter and it's getting good power)

When I pump the primer pump I can hear a small amount of hissing that's coming from the fuel filter housing, maybe one of the banjo fittings. They are all tight and I don't see fuel leaking from any of them.

It just seems very strange that this is happening intermittently. I have a 300d with a tank full of algae and a majorly clogged tank screen and it consistently has trouble starting but will start ok if you give it a lot of throttle and keep on the pedal a little until it's warm.

Tomorrow my plan is to:
-Check the fuel filter housing o-rings (or copper seal)
-If it won't start again, make a fuel tank in a bottle and see if that does the trick. Or, maybe swap the supply and return lines, I have about a half a tank in there. If that gets it started, then I'll drain the tank and clean the screen

Not really sure what else it could be. Any thoughts/ideas?

Stretch · #2 04-03-2012, 03:16 AM

How viscous is the fuel mixture you are using compared with normal diesel?

reinventthewheel · #3 04-03-2012, 03:49 AM

It's definitely a little thicker, but I don't see how that could be causing the problem. A friend's 300sd is running on 100% wvo with a lovecrap system that is only coolant heated (so it starts on cold wvo).

The oil is only canola, which doesn't gel until 20 deg F. And today was a particularly warm day here in the NW, where it rarely gets below 40 even in the winter.

layback40 · #4 04-03-2012, 07:13 AM

You will probably get more responses if you post in the alternative fuels sub forum. Or ask a mod to move your thread there.

Phillytwotank · #5 04-03-2012, 08:23 AM

sounds like you are "loosing prime" from something gone wrong in the primerpump or the lift pump because of pumping the thick stuff. I have had the same problem.

Renntag · #6 04-03-2012, 09:40 AM

Quote:

Originally Posted by lacolocho

...I just converted it to veggie oil, its about 2/3 wvo and 1/3 dino diesel

Change the filters again. Once you introduce a bio fuel, you have to change hoses and then continually change filters until the system is clean.

Quote:

Originally Posted by lacolocho

I have a 300d with a tank full of algae and a majorly clogged tank screen and it consistently has trouble starting but will start ok if you give it a lot of throttle and keep on the pedal a little until it's warm.

This makes no sense. Why not fix the problem?

Phillytwotank · #7 04-03-2012, 10:06 AM

Quote:

Originally Posted by Renntag

Change the filters again. Once you introduce a bio fuel, you have to change hoses and then continually change filters until the system is clean.

With Bio-Diesel YES but with SVO and #2 Diesel mixed, degradation of the fuel lines is not an issue.

reinventthewheel · #8 04-03-2012, 02:48 PM

Quote:

sounds like you are "loosing prime" from something gone wrong in the primerpump or the lift pump because of pumping the thick stuff. I have had the same problem.

If I was losing the prime then there would be air in the system (visible in the primary filter), right?

Quote:

Change the filters again.

After 20 miles of driving? I doubt it

Quote:

This makes no sense. Why not fix the problem?

Because I haven't had the time and haven't been driving the car. I'm doing it this week

reinventthewheel · #9 04-03-2012, 02:56 PM

How much air in the primary filter is an indicator of a problem?

Biodiesel300TD · #10 04-03-2012, 03:12 PM

I put my money on the tank screen. I've experienced intermittent problems with clogged tank screens. I'd try the fresh bottle of fuel trick and see if it solves the issue. Sometimes when you switch the lines you end up pushing all or some of the gunk off the tank screen which can mean you get to clean it again later.

Also try pulling the vac line off the shut-off valve on the IP, I've experienced hard starting and fuel starvation issues due to the vac system not bleeding out all the vac at the shut-off valve. This usually happens when you've been driving and shut the engine off, then try to start it again within a short time period. But it's an easy check.

Biodiesel300TD · #11 04-03-2012, 03:17 PM

Quote:

Originally Posted by lacolocho

I have a 300d with a tank full of algae....

No you don't, it's full of fungus or bacteria.

As a Biologist this is one of my pet peeves.
Algae are photosynthetic and require light to grow, where as fungus and bacteria do not. They can grow in the dark depth of your diesel tank. With that said there are algae that can grow in diesel, particularly biodiesel, but it must be exposed to sunlight to grow for them to grow.

reinventthewheel · #12 04-03-2012, 03:25 PM

Thanks for chiming in on the fresh bottle. I definitely want to fix the screen this week if it does end up being the problem.

Quote:

Also try pulling the vac line off the shut-off valve on the IP, I've experienced hard starting and fuel starvation issues due to the vac system not bleeding out all the vac at the shut-off valve. This usually happens when you've been driving and shut the engine off, then try to start it again within a short time period. But it's an easy check.

If this does end up being the issue, how would I keep it from happening again?

And thanks for the info about algae vs fungus/bacteria! I will keep it in mind when posting on other forums so I can spread the word

Biodiesel300TD · #13 04-03-2012, 03:34 PM

The vac issue is usually caused by the shut-off valve that is on the ignition.

cho · #14 04-03-2012, 03:50 PM

.

recheck the return lines all the way...sounds like air issue

.

reinventthewheel · #15 04-04-2012, 03:44 PM

Ok, so it started fine this morning. Stopped ten blocks later for a quick errand on my way to my garage. Wouldn't start back up.

The battery died shortly after so I didn't have much time for diagnosis. I'm hoping that when I head back one of the parking spots next to it will be open so I can get some jumper cables on it.

I didn't have enough fuel lines on me to make a fuel-tank-in-a-bottle, so I put the rubber supply line on the metal return line, and the rubber return line into an empty bottle (leaving the metal supply line open). I realized that I didn't prime it after this (oops). Will prime it first when I try again.

Also, I pulled the vac line off the shutoff valve at the IP and there was still vacuum in it. I put it back on before starting and later thought that I should have left it open. Will try to start again with this line off.

I'm thinking it could be ignition related, but never made the connection before Biodiesel300td mentioned it. When it has trouble starting, the engine will continue to crank for 5+ seconds after shutting the key off. Also, the car came with another ignition in a box.
Could a faulty ignition have a shut off valve that is failing intermittently?