Help me diagnose my fuel issue

[rtrask]

Unlike a lot of you I have been relatively lucky with my fuel issues, I guess it is my turn now. When I bought my SEE, I had it delivered to my house in the city so that I could work on it. At that time it seemed to start and run just fine on the snake oil that was in the tank ( I assume JP8 ) There was not much fuel in there, (maybe 5 gallons), so I just filled it up with #2 diesel that I bought at the pump. Then I added biocide, and anti gel. Well it took me a lot longer to get the majority of my SEEs issues worked out, and it mostly sat at my house in town for 2 years. There is just not that much that I could do with it there, so I never burned through that initial tank of diesel. I finally arranged transport down to my property in Southern Colorado, and wouldn't you know it, the thing would not run continue to run. I took a look at the filters and the diesel seemed to be sticky. I put a new set of filters in and it ran fine. I ran it for a couple of hours after I got it down to my property and it would always start and run immediately when I hit the starter.

So it sat down at my property for ~ 3 months till I could get back down there, and it would start but die after ~ a minute. In one of the times that it was running I tried to use the little hand pump to keep it going (which was probably a huge mistake). After that it would not start at all. I drained the diesel, put in fresh, put in new filters, got the air out of the filters, but it still does not even fire once.

I have a guess, (injectors / metering pump) but before I tear into that I thought I would ask for advice on the best way to diagnose / correct the issue.

 

[frank8003]

Some parts of fuel systems suck and some push ..............
Do Not begin taking a bunch of stuff apart. ... Not the answer probably.

"Fuel" Does not "keep" anymore.
The low sulfur and ULS stupid diesel fuel now sold is not good for our equipment.
It is good for our Grandkids breathing but not good for the few hours We run Our stuff. It is for new Ralph Nader EPA certified engines with lots of money.
They have driven our manufactures nuts so that they will go electric but that is Not your answer .................

There is many things I know to do to make the fuel burn proper and straight diesel form the pump one would get nowadaze is NO good.

Take ever CC of whatever fuel is in there and burn it in the stove or whatever.
Then We start again after all new filter changes. Burn the filters too.

Look up your engine/Unimog year and type and specify to yourself what fuel it was designed to run with.
I would need those particulars to help any further.

 

[rtrask]

Some parts of fuel systems suck and some push ..............
Do Not begin taking a bunch of stuff apart. ... Not the answer probably.

"Fuel" Does not "keep" anymore.
The low sulfur and ULS stupid diesel fuel now sold is not good for our equipment.
It is good for our Grandkids breathing but not good for the few hours We run Our stuff. It is for new Ralph Nader EPA certified engines with lots of money.
They have driven our manufactures nuts so that they will go electric but that is Not your answer .................

There is many things I know to do to make the fuel burn proper and straight diesel form the pump one would get nowadaze is NO good.

Take ever CC of whatever fuel is in there and burn it in the stove or whatever.
Then We start again after all new filter changes. Burn the filters too.

Look up your engine/Unimog year and type and specify to yourself what fuel it was designed to run with.
I would need those particulars to help any further.

OK Frank.
The military runs JP-8, and there are a lot of comments on the quality of that. When I was a kid we ran #1 diesel in our old John Deere tractors, I might be able to source that. I will not argue the quality or merits of #2 Diesel I am sure we can generate a lot of discussion on that. But this really does not help me to diagnose where my current issue is. It ran fine on #2 for a long time. If it was just the #2 diesel and brand new filters that I put in then I think it would at least cough once in awhile when it was turning over. I agree that long term I need a better fuel, but I don't think dumping the new fuel that I put in and putting in another set of filters will make any difference until I can figure out how to get fuel into the cylinder.

 

[frank8003]

Thank You for response.
what is the engine exactly, never had one of them
I need to study to help

 

[Speedwoble]

Unlike a lot of you I have been relatively lucky with my fuel issues, I guess it is my turn now. When I bought my SEE, I had it delivered to my house in the city so that I could work on it. At that time it seemed to start and run just fine on the snake oil that was in the tank ( I assume JP8 ) There was not much fuel in there, (maybe 5 gallons), so I just filled it up with #2 diesel that I bought at the pump. Then I added biocide, and anti gel. Well it took me a lot longer to get the majority of my SEEs issues worked out, and it mostly sat at my house in town for 2 years. There is just not that much that I could do with it there, so I never burned through that initial tank of diesel. I finally arranged transport down to my property in Southern Colorado, and wouldn't you know it, the thing would not run continue to run. I took a look at the filters and the diesel seemed to be sticky. I put a new set of filters in and it ran fine. I ran it for a couple of hours after I got it down to my property and it would always start and run immediately when I hit the starter.

So it sat down at my property for ~ 3 months till I could get back down there, and it would start but die after ~ a minute. In one of the times that it was running I tried to use the little hand pump to keep it going (which was probably a huge mistake). After that it would not start at all. I drained the diesel, put in fresh, put in new filters, got the air out of the filters, but it still does not even fire once.

I have a guess, (injectors / metering pump) but before I tear into that I thought I would ask for advice on the best way to diagnose / correct the issue.

Did you clean the prescreen along the frame rail?
After you replaced the filters, were you able to prime the air from the bleeder screw without much trouble?
Draining the fuel and starting with fresh is going to be a cheap method to start troubleshooting. You can also verify when looking at it whether it is contaminated and you should look at filters/pump/injectors, or if it is clean and you should look at air.

Then remove the primary filters and manually inspect to confirm there is no contamination in them.

Once you are sure there is no contamination, verify control continuity between the throttle and the IP. You want to make sure it isn’t stuck in the cut-off position.

If you suspect air, you can take Peakbagger’s advice and rig up a boat tank with a bulb pump to the IP (don’t bypass the filters. Cleanliness is next to godliness)

Clean then slightly loosen all lines at the IP and turn over the engine to see if fuel comes out of them.

 

[The FLU farm]

I think you're fine with the fuel you have, unless...

Is there any kind of goop at the bottom of the tank? The one I got with JP-8 (or whatever it was) looked like the inside of the tank had a spray-on bedliner on the bottom third.
I got really good at cleaning out the strainer on that one.

And then there's the possibility of minute leaks at every connection, including the copper washers at the fittings.
Oh, and maybe THE suspect: The gasket on the strainer. I ended up using an O-ring instead.

 

[peakbagger]

Most of the normal issues have been covered but here are my thoughts.

There are several issues that can bite you in the butt upstream of the fuel pump. Just in case , you didnt know there are three "pumps" in play, a mechanical fuel pump located behind the primer pump, the primer pump and the injector pump. The mechanical fuel pump needs to pull a suction to pull fuel up from the fuel tank and that means every connection needs to be leak tight. That means the very difficult supply and return line on top of the tank (get your flashlight out), the dreaded fuel strainer gasket, the dreaded Mercedes "plastic" fuel line connectors and the old style fuel primer pump (the one that has to be unscrewed to use). The boat tank method cuts some of the issues out of the picture as it allows things to be pressurized down at the outlet of the strainer and the squeeze bulb will also pump all the way to the injection pump relief valve. It does not cure anything, its a diagnostic tool although I have considered rigging it up so I can burn off road diesel when off road without contaminating the on road tank. It was also a psychological tool, I had a 16,000 pounds of potential scrap iron sitting in my driveway that would not start and after a lot of frustration, I rigged up the boat tank, squeezed the bulb multiple times and then it started. Worth the money to know that there was light at the end of the tunnel.

The dreaded Mercedes "plastic" fuel lines are an issue that are known to other Mercedes owners. The "plastic" used is cross linked polymer that is stretched to fit over hose barbs. As the plastic ages, the connections can loosen up. Counterintuitively, they may not leak under pressure but can leak under suction. The standard fix is buy some fuel line hose and cut it the length of the hose barb, then slit it lengthwise and slide if over the plastic fuel line. Now put a hose clamp over the hose and tighten it up. Fancy fuel injection hose clamps are the best as long as you can open them up to get them over the hose but run of the mill slotted hose clamps work just as well. since they are not cutting into the plastic fuel line.

Its fairly rare that the mechanical fuel pump is the problem, its an ancient design with not a lot of moving parts. On the other hand the original primer pump is a known problem. Spend the bucks and upgrade it to the new Bosch style https://www.amazon.com/Bosch-2447010038-Hand-Primer-Pump/dp/B001CO92F2. If you order from Expedition imports they can sell you this pump and a strainer gasket (another known issue).

Mercedes did not use plastic fuel lines on the ones that are hidden on top of the fuel tank. They are old fashioned neoprene rubber. So time to at least tighten them up.

There is also a hidden fuel strainer on the fuel pick up in the fuel tank. The only way to change it is remove the tank. If its gunked up then any suction issues are just going to get worse. EI also has them in stock. I would hold off on changing it as the tank has to come out to do it. My fuel gauge was not working and when I dropped the tank and pulled the tank suction, I found a very fine wire that was broken off. A bit of solder and my tank gauge started working (the strainer was fine)

So assuming do the smart thing and order and install a Bosch primer pump, a strainer O ring gasket and fuel tank pick up strainer and bring a short length of fuel hose and some hose clamps you are ready to make the first run at it. The bosch primer pump will pull a vacuum on the system all the way from the tank if everything is tight upstream so remove a bleed screw on the dual filter and pump repeatedly until fuel come out of the bleed screw. You want to get ot he point where there are no bubbles and the flow is directly related to a push on the pump. If it doesn't then you got an air leak somewhere upstream or a plugged external strainer or the dreaded strainer in the fuel tank. If you get to the point where you have a steady stream of diesel coming out the bleed holes then its likely you need to prime the injection pump. Hopefully you have good hearing and its quiet nearby as there is an audio diagnostic. With the bleed screw closed (you may need to replace the copper gasket under the screw),pump the Bosch primer pump multiple times, possibly 30 to 50. While doing so listen from the area of the injection pump, at some point you will hear what I would describe as a burp (the guy who told me this trick also call it a burp but its higher frequency). There is some sort of spring loaded relief in the injection pump and once that burps its means you have flooded the injection pump and its ready to pump fuel to the injectors. Others crack the injectors but if the pump is dry its may not clear itself of air. Running the injector pump dry is not good as the diesel acts as lubricant. Note modern low sulfur diesel acts far less as a lubricant so a lubricity additive is recommended.

The tricky part is mine will start first try (as long as I remember to pull the hand throttle out of stop position) all summer. It only loses its prime in the injection pump over the winter so the first start in the spring is the battle.

BTW I think my boat tank trick accidentally does what the fuel injection pump prime with the Bosch pump does. I think the combination of the elevated temporary location of the tank (the passenger seat) and the squeeze bulb actually floods the injector pump and opens the relief valve. Knock on wood I didnt need the boat tank this spring and just used the Bosch primer pump and burped the injection pump after a lot of pumps. The person I bought my 1300L from is quite knowledgeable about Unimogs and buys them from military auctions in Europe, these trucks probably didnt sit for as long but the first thing he does is pour in a full dose of Stanadyne into the fuel filters and then the rest into the tank and then starts the truck. This cleans out the fuel system. I expect this may be a trick for the SEEs except that it also may let loose a pile of crap and dissolve build up causing strainer issues. The 1300L engine does not have the external strainer on the suction side of the fuel pump, it has disposable clear fuel filters on the pressurized side so its easy to see when its crapped up but not as easy to clean. I thought my tank was fairly clean but notice since dosing my truck with a Power Service brand injector cleaner that I have sticky buildup on the big removable strainer on my fuel tank inlet. Its practically sealed right up but I am not seeing it in the strainer. on the frame rail. Good luck and expect you will be smelling of diesel at the end of the day.

 

[Speedwoble]

Some(most) hate the Mercedes fuel line. I happened across the correct Mercedes tool on CL some years back, and I love it now. I have a healthy assortment of fittings and just replace the line with new clear line whenever needed. I get the line and fittings from Belmetric.
When I remove the old banjo, I sandblast and get them replated at work. Now I have a stash to swap out if the need arises.
If anyone needs the tool, I will loan it out with a (healthy)deposit.

 

[peakbagger]

The vice grips are available through any Mercedes part supplier. Thats the good news, the bad news is the price $655.

 

[The FLU farm]

Also good news is that you don't have to use the tool. I've successfully installed all my Belmetric hose without it.

Come to think of it, it wouldn't be hard to make one, especially just for our hose size.

 

[rtrask]

Thank You for response.
what is the engine exactly, never had one of them
I need to study to help

Thanks Frank,

Here is a link to information on it, OM 352 model 353.999.

• Engine Manufacturer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Daimler-Benz
• Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353.999
• Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-stroke diesel, 6 cylinder
• Horsepower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110(81kW

Fuel System

• Fuel Pump Manufacturer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Bosch
• Timing @ 700 rpm +50 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Low idle
• Injection Order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-5-3-6-2-4

 

[frank8003]

Mercedes-Benz OM352 engine - Wikipedia

en.wikipedia.org

 

[rtrask]

Sorry it was a busy day at work and I should have posted more info

Did you clean the prescreen along the frame rail?

I started with the prescreen. There was some stuff in there, but not a lot. Basically enough to know it was serving a purpose, but not enough to makke me believe it was restricting the flow of fuel. I had a spare pre-screen filter so I swapped it out.

After you replaced the filters, were you able to prime the air from the bleeder screw without much trouble?

Yes, I bled the air by pumping on the hand pump until the bubbles stopped, then moved on to the next one. It takes a fair amount of pumping with the hand pump, but I am pretty positive that there are no leaks on the fuel lines.

Draining the fuel and starting with fresh is going to be a cheap method to start troubleshooting. You can also verify when looking at it whether it is contaminated and you should look at filters/pump/injectors, or if it is clean and you should look at air.

I should have done that in March when I shipped it down to my property, but at that time I just changed out the filters and it ran great and started on the first crank. When it would not start a couple of weeks ago and the fuel felt sticky I drained what was in the tank and dumped it ~ 7 gallons. I then put in about 10 gallons of #2 fresh from the pump. I checked the pre-screen and changed the filters.

Then remove the primary filters and manually inspect to confirm there is no contamination in them.

When I pulled the filters out they looked clean, but the fuel that was in them felt sticky like I said. The filters only had ~ 4 hours of use on them, but since changing the filters last time seemed to do the trick, I dumped the fuel and put in new filters.

Once you are sure there is no contamination, verify control continuity between the throttle and the IP. You want to make sure it isn’t stuck in the cut-off position.

If you suspect air, you can take Peakbagger’s advice and rig up a boat tank with a bulb pump to the IP (don’t bypass the filters. Cleanliness is next to godliness)

I am pretty confident that there is no contamination from the tank to the filters. I don't think it is the air filter. One thing I tried was to spray a little either onto the air filter and it fires immediately but does not run.

When you said use Peakbagger's advice, I think I miss understood what you meant by air. I don't think there are any air leaks in the supply lines. I can try the pump bulb idea to confirm that.

My guess is that by using the hand pump while I may have pushed that sticky fuel into the IP and clogged the injectors, or something of that nature.

Clean then slightly loosen all lines at the IP and turn over the engine to see if fuel comes out of them.

This seems like a good idea that may be a diagnostic to either point to clogged injectors or something to do with the pump itself.

 

[frank8003]

NO either No either
Well, unless you wanna rebuild it.
Oh must pull injectors and work on that gummy.
What does it say to do in the TM
Would you like to have a TM?

 

[rtrask]

Also good news is that you don't have to use the tool. I've successfully installed all my Belmetric hose without it.

Come to think of it, it wouldn't be hard to make one, especially just for our hose size.

Yeah I made my own back when I was dealing with the supply lines out of some hardwood and a couple of carriage bolts. I drilled various size holes slightly smaller that the hose between the two pieces of hard wood. It worked OK but the hardwood was too slick and I had to add tape to the lines.

 

[rtrask]

NO either No either
Well, unless you wanna rebuild it.
Oh must pull injectors and work on that gummy.
What does it say to do in the TM
Would you like to have a TM?

There is a either system for cold start, mine is not functional I just gave it a short burst on the air filter to verify that it was getting air. Not to have it run on the stuff.

I have the TMs.
I think this may be the procedure

1. ENGINE CRANKS BUT WILL NOT START OR HARD TO START.

Step 1. Remove fuel injector nozzles. Check for blocked fuel injector spray holes by performing fuel injector spray pattern test (page 13-65).​

• Repair fuel injector nozzle(s) (page 13-65).​

Step 2. Perform compression test as follows:​

a. Run engine until it reaches normal operating temperature of 140°-185°F (60°-85° C). Shut off engine.​

b. Remove six fuel injector nozzles (page 3-41).​

c. Crank engine several times to remove carbon flakes and dirt.​

d. Clean fuel injector nozzle seat base (1) in cylinder head (2).​

e. Place compression tester adapter (P/N 352 589 00 21 00) into protective sleeve. Install nozzle holder nut. Tighten nozzle holder nut to 50 Ib-ft (68 N·m).​

f. Connect compression recorder to compression tester adapter. Crank engine several times until highest reading is obtained. Record highest reading. Minimum acceptable compression reading is 284 psi (20 bar). 2-5 TM 5-2420-224-34 Table 2-1. Troubleshooting (Cont) Malfunction Test or Inspection Corrective Action ENGINE (CONT)​

g. Repeat steps d thru f for remaining cylinders. If minimum compression reading is not 284 psi (20 bar), squirt approximately 1 oz engine oil into cylinder. Crank engine several times and repeat steps d thru f for each cylinder.​

• If compression reading is higher after second test, on any cylinder, excessive bypass of air between piston and cylinder bore is indicated. Replace piston rings (page 13-31).​

• If compression reading remains approximately the same after second test, replace valves and valve guides (page 13-2).​

• If variation between cylinders exceeds 21.3 psi (1.47 bar), replace piston rings (page 13-31). Step 3. Check fuel injection pump timing (page 3-50).​

• If timing is correct and problem persists, replace fuel injection pump (page 3-43).​

• If timing is not correct, time fuel injection pump (page 3-50)​

 

[The FLU farm]

It sounds like you may be over thinking this, Ron.

Primarily, what is it that makes you think that you don't have leaks in the fuel lines, which is so common?
Is the strainer still full when the engine stops, for example?

 

[rtrask]

It sounds like you may be over thinking this, Ron.

Primarily, what is it that makes you think that you don't have leaks in the fuel lines, which is so common?
Is the strainer still full when the engine stops, for example?

Well, I am prone to over thinking things as I am sure you know by now. I have fought air leaks in the past. This seems a lot different as it does not fire at all. I can try the Peakbagger hand pump trick and if that makes it run then I would be convinced it is an air leak. That is easy enough to do and could save a lot of heart ache.

Like I said it does not fire at all, the strainer / pre-filter seems to always be full when I check it, and the filters are full whenever I check.

My biggest problem right now is limited access because it is ~ 180 miles away, and my tools are here.

 

[peakbagger]

Well, I am prone to over thinking things as I am sure you know by now. I have fought air leaks in the past. This seems a lot different as it does not fire at all. I can try the Peakbagger hand pump trick and if that makes it run then I would be convinced it is an air leak. That is easy enough to do and could save a lot of heart ache.

Like I said it does not fire at all, the strainer / pre-filter seems to always be full when I check it, and the filters are full whenever I check.

My biggest problem right now is limited access because it is ~ 180 miles away, and my tools are here.

I looked up an outboard motor fuel tank on Amazon, the price of the them has gone up a lot since they had to be EPA certified. https://www.amazon.com/Scepter-1050...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

and a squeeze bulb https://www.amazon.com/Rubber-Trans...97&sprefix=outboard+motor+squ,aps,159&sr=8-13
(note, I just clicked on a generic fuel bulb, make sure the hose size is correct. I would need to go dig mine out and see what diameter I have.

Now buy some fuel hose and for under a 100 bucks you have a temporary fuel system that cuts out a lot of components that can leak and you fill it with fresh diesel and some injector cleaner. If you know someone with a small outboard motor they can probably use it when you are done. I have a six gallon version and use it to fuel my jet heater. If this does not work then the problem is in the injection pump or injectors. I seriously doubt the injectors are sealed off. Another FYI, the unused fuel to the IP pump recirculates to the main fuel tank, if you run it on the boat tank for very long periods the main fuel tank will slowly gain some fuel. This return line is in a vulnerable place near the engine cover and on occasion its gets pinched or broken leading to a intermittent fuel leak

BTW, if you pull the air filters and spray ether into the intake the engine will "fire" but rarely will start. You need to get fuel to the injectors first.

 

[rtrask]

I looked up an outboard motor fuel tank on Amazon, the price of the them has gone up a lot since they had to be EPA certified. https://www.amazon.com/Scepter-1050...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

and a squeeze bulb https://www.amazon.com/Rubber-Transfer-Vacuum-Gasoline-Accessories/dp/B06X3R9YBN/ref=sr_1_13?crid=2TET7UDPURJQ8&dchild=1&keywords=outboard+motor+squeeze+bulb&qid=1597053197&sprefix=outboard+motor+squ,aps,159&sr=8-13
(note, I just clicked on a generic fuel bulb, make sure the hose size is correct. I would need to go dig mine out and see what diameter I have.

Now buy some fuel hose and for under a 100 bucks you have a temporary fuel system that cuts out a lot of components that can leak and you fill it with fresh diesel and some injector cleaner. If you know someone with a small outboard motor they can probably use it when you are done. I have a six gallon version and use it to fuel my jet heater. If this does not work then the problem is in the injection pump or injectors. I seriously doubt the injectors are sealed off. Another FYI, the unused fuel to the IP pump recirculates to the main fuel tank, if you run it on the boat tank for very long periods the main fuel tank will slowly gain some fuel. This return line is in a vulnerable place near the engine cover and on occasion its gets pinched or broken leading to a intermittent fuel leak

BTW, if you pull the air filters and spray ether into the intake the engine will "fire" but rarely will start. You need to get fuel to the injectors first.

Thanks Peakbagger.

I have an old outboard squeeze bulb that I think will be serviceable for this test.

I just gave a quick spray onto the air filter, I did not remove the air filter, just the outside lid. As Frank8003 said attempting to use a can of either as a fuel source is a really bad idea. I don't know that it was a valid test, but after cranking and cranking without a single fire, I wanted to verify that air was getting to the cylinders. When you do that with no diesel mixed in, it sounds like the engine is going to fall apart or run backwards. I only did it once.