Fuel starvation issues with my 6.3

[abl567]

When I bought Six 3 back in '06 it had been fitted with a W108 fuel tank to provide clearance for the tow bar, the correct W109 6.3 specific 105 litre tank is about 50mm deeper than the 80 litre tank.

So I found a 109 tank, 2 in fact, and put them aside for the day I would get around to swapping tanks, which came not so long ago when Styria phoned me looking for a 108 tank. The tanks were swapped and foolishly I didn't have the 109 tank professionally cleaned as a visual inspection came up clean, which of course it wasn't so it promptly blocked the fuel filter and in tank strainer with sediment. I drained the tank completely, cleaned the strainer and replaced the fuel filter and went for a drive, after about 100 miles the main fuel filter appeared to block again, but when I changed it it was dirty but didn't appear clogged.
Started it up and it ran fine so I took it to work the next day, got about 15 miles from home and you guessed it, fuel starvation issues again

My next theory was that as the fuel pump was now mounted 50mm higher than the tanks outlet it was starving as the level of fuel in the tank dropped so I fabricated some brackets and dropped the pump so the pump inlet was level with the tank outlet, started it up and let it warm up..
Until it stalled again. Kicked the cat, threw a stick at the dog and sent the children to their rooms then tried to restart it, started right up, idled for a couple of minutes and of course died again.

I removed the sender unit and had a peek inside and it looked clean and plenty of fuel appeared to be returning to the tank and the main filter looks clean.

My question, after all that, is has anyone experienced a fuel system "blocking up" then returning to normal as pressures equalise? This is what seems to be happening and I'm wondering if sediment has got into one of the fuel dampers, causing a build up of pressure that relieves itself when the pump turns off?

Any ideas appreciated

Ant

 

[motec 6.9]

Hi Abl567 i had a similiar problem when i fitted a 460 big block to my XB fairmont after changing everything several time it turned out to be the tank breather line was blocked causing vacume lock when the pressure built up. Causing the car to stall through fuel starvation . The car then restated 20 minutes later as if nothing had happened . Geoff

 

[BenzBoy]

And if Motec is right, can you tell if there is a vacuum by taking off the filler cap when the car stalls to see if you get a rush of air into the tank? I've had that happen. A simple but poor solution (you loose petrol through vapour) is to take off the filler cap seal. And then a passer buy strikes a match and you are back to first base - although no more blockages...
Regards,
Brian

 

[abl567]

I have considered that but it displayed the same problem with the sender unit out, exposing the contents to atmosphere. I will however run a whipper snipper line through the vent lines to ensure that is not the problem.
I'll also remove the tank cap when it stops next to check for negative pressure build up.
Thanks guys, keep the ideas coming

 

[Helmet]

There is a small gauze filter in the fuel pump inlet , I bet it got blocked as well. You need to remove the hose first and then unscrew the fitting that has the gauze in it and try blowing through it. If its blocked just punch it out and think about maybe adding extra filter it the tank is still suspect.

 

[abl567]

Helmet,
My 6.3 has a 116 style pump fitted, not the vertical style long/short body W111-W108/9 pump, I don't think these had that gauze screen but am happy to be contradicted.
I have a new, W116 style, fuel pump I can try but would rather find a logical explanation to the issue than simple use the process of elimination method
Ant

 

[CraigS]

You don't mention if you checked/cleaned the front filter.

 

[abl567]

You don't mention if you checked/cleaned the front filter.

Replaced it 3 times now Craig, and have the bruises and grazed knuckles to prove it, the first time it was replaced it was dirty/black but not full of muck or solids, the second time it was also dirty but not as black, the third time it looked slightly used but I changed in anyway.
Put simply it is a sod of a job, Waxenburger must have hated mechanics

 

[BenzBoy]

Do you have a vapour trap or charcoal canister that is blocked?
There must be a simple reason for this...
Regards,
Brian

 

[abl567]

Exactly Brian, I am missing something elementary I'm sure

 

[BenzBoy]

OK - so you start and one end and work to the other...
Time consuming but is there an alternative?
I've just done that with the hydraulics on the Spirit searching for a mystery leak. And what did I find? A non-original seal in hydraluic pump #1. It looked OK but under pressure it deformed and allowed the prssure to drop. Clearly not the correct rubber compund even if the size was right. With the motor off a vacuum was created pulling air into the system - and no matter how many times I bled it the air returned. The only way I found it was to start at one end and work to the other and that was a pain in the proverbial...
End result was worth it.
Regards,
Brian

 

[Styria]

Hi Anthony, just not quite sure how to best tackle this situation. Given that you experienced no problems with the smaller tank, it should be taken for granted that the non-standard CIS fuel pump was working satisfactorily in conjunction with the standard 6.3 filter and other associated fittings that are part of the fuel system. There are two fuel dampers as part of the original system - one is located just below the suspension pump, and the other is located at the back of the valley right on the bottom. Now, I don't know if they can get clogged up at all, nor do I really know what their functions are, and I presume they are in fact fuel dampers. Obviously, neither of the two are easily accessible. So, I do think it is important that some attempts should be made to measure the fuel system pressure and for that you will need some testing equipment.

I suspect that perhaps an appointment with one of our learned friends may become a necessity. I have Helmet in mind (although I am uncertain of his calling nor do I know whether or not he'd want to be part of the investigation), and the others would be Silver Star Motors at Kingsgrove, certainly very experienced mechanics with all matters pertaining to Mercedes. The testing equipment is of importance as it takes the guess work out of the equation. If you had the equipment, readings could be taken with engine cold, and also at the precise time when you are experiencing the starvation problems. Mind you, you can do without that when stuck at the roadside. I am hoping to make Helmet's acquaintance at the ####tail party this coming Friday. Maybe in the meantime, you might get your mechanic friend to fit the new fuel pump - it may just solve your problem. Regards Styria

 

[kunbarrie]

from memory when i was a boy,hook a fuel gauge to left hand starting valve,ignition on engine stopped.at least 11volts to pump,should have 0.8 to 1.1atu.if to its normally one of three things,
fuel filter insert
overflow valve in return flow damper,
blocked strainer in closing plug in tank,
hope this helps,it is a very basic system,nothing elaberate,but i dought any one in australia would remember how to overhaul one of these,let alone still have the gear,last injector pump i needed came from a mb club member he had three in his collection,that was a 1967 250sl,had seized elements in the pump,buts thats another story.

 

[abl567]

Thanks kunbarrie

"overflow valve in return flow damper"

I'll bet that is the issue, after it stalls I can hear flow/cavitation noises from this area with the pump still running.

If you're right there will be a bottle of single malt on its way to you

 

[Styria]

Hi Kunbarrie, grateful to get your input. It's a name that doesn't crop up very often. The damper you are talking about, is this the one situated at the back of the V8 gully...you know, the one difficult to get to, or service ? It's a long time since I opened up one of those dampers, but in reality there is not a lot to them. Are you a member of the Club and, if so, are you coming to the concours this Sunday at Parramatta Park ? (Sorry, I haven't looked up your location). Regards Styria

 

[kunbarrie]

no not a club member,started work at local mb dealer in 1970,been out on my own 12years,if you work on these cars 6days week,i am not really fussed on looking at them on time off,rather go sailing,still have my training notes from early days benz training,if you need any info,will see what i have.

 

[Helmet]

Just reread this thread as it has me intrigued. Firstly have you confirmed good fuel pressure and flow rate . The pump may have been damaged whilst working against a clogged strainer and fuel filter. Secondly, maybe good idea to check the tank strainer again. And thirdly pray that not to much dirt has made it's way into the injection pump.

 

[Styria]

.......especially considering that it was rebuilt only about six months ago. BTW Anthony, any further news or are you closer to finding the problem ? Regards Styria

 

[abl567]

I have done nothing other than walk past it on the way too and the way back from work Styria. Sorting out my pool/big bowl of green water is my priority at the moment and that is a big job. Gotta get it right for summer for the children
I do however intend to attack it as soon as that is done, and the next Lodestar is at the printers, and the patio floor is painted, and the......................

 

[abl567]

I cannot believe it is over 18 months since I last posted on this, the shame

So, in that time I had the tank boiled and cleaned, dropped the pump to below the tank level, changed filters a number of times, checked the pressures and flow at idle and the problem remained, all would be ok for 5-6 miles and the problem returned.
In frustration and simply fed up with it I nursed it from home to my factory, pulling over every 5 miles let it settle down, and gave it to my mechanic who looks after the boring daily drivers.

He to, assuming the tank was cleaned properly, (I had him send it out to be cleaned 1st time), changed filters, blew out lines etc a number of times to no avail, it would still starve and stutter after 5 or so miles.

Around this time the fuel gauge ceased to function, thinking there may be a build up of sediment in the sender I asked him to check and clean it. Thinking he had to drain the tank to get to it he did, and was greeted with 50 litres of fuel and 10 litres of rust sediment and a strainer blocked solid.

Tank out and sent to another tank cleaner and 300 odd miles and a refill later all seems well, Six 3 is back!!!

I'll change the fuel filter again after the next fill and hopefully it will be happy days.