W639 Cutting Out - Out of Fuel?

[schneckster]

Hi,

I don't know if there is something similar on the forum. I have searched, but couldn't find anything. Apologies if there is and I'm too dumb to see it!

The missus was oop north this afternoon and got onto the motorway to head back to Brum. All of a sudden, the battery light started flashing at her and then the engine stopped. She also said the fuel gauge went from 1/4 tank to red light and zero like a switch had been flicked. £20 of diesel later and she's going again (she has run cars out of fuel before so I put it down to that)

60 miles later, the red light is on again and the engine feels like it's being held back. £10 more diesel and she can get home... just! The red light was on again by the time she got on the drive.

I checked the engine bay and could see no leaks. Rev it and I can still see nothing. However I had noticed a few days ago that there seemed to be diesel residue around the filler cap and the bottom of the hatch spreading along the door sills just below it (for those that aren't sure, the Viano filler cap is between the front and rear passenger doors behind a hatch held shut by the front passenger door).

So I got underneath, and again couldn't see any leaks. Tapping the tank, however, and I got a hollow sound. The damn thing was definitely empty.

The car, though, thinks it did 35 mpg so there should be a good 1/3 or more left in the tank after £30 of diesel put in. She only did 100 miles.

So, my questions are:
1. Am I right in thinking the fuel system is pressurised?
2. Am I right in thinking that if there is a seal on the fuel filler cap, and it's faulty, it could be enough to empty the tank under pressure? If so, how do I fix it?
3. If I'm wrong, can you suggest other options I can investigate?

Many thanks for your help,

Schneckster

 

[Danny DeVito]

how did she get the diesel in after it stopped ? The system will be pressurised and it should cut out instantly if the fuel gets too low. my car then lights an EDC light not battery light

 

[schneckster]

how did she get the diesel in after it stopped ?

Err... walked to the nearest petrol station with a can, bought some diesel, and then she just put it in. Shouldn't she have been able to do that for some reason?

It may well have been the EDC light, but she just told me it was the battery light. She could easily have mistaken it. It's a relatively new car to us both (our first Merc) so this could be the sort of light we haven't seen/noticed before. Other lights were probably lit, too. Unfortunately, I wasn't there... I just get the bill!!

The sight of diesel all over the filler flap and door sills is making me think so I thought I'd see if anyone on here has seen it before. I've never seen that on any other car I've owned.

Schneckster

 

[Danny DeVito]

I cant imagine it's forcing itself out of the cap really, more likely it would blow the cap off if pressure built up. Most likely a leak someplace. HAve you tried driving it yourself yet ?

 

[schneckster]

No, not yet. With one thing and another, I haven't had the chance. It hasn't been driven since the missus got it back on the drive. I need to get some diesel in it anyway... a trip in the other car and a fuel can!

So am I right in thinking the pressure could force it out through a leak? It only seems to lose anything when driving. There's no evidence on the drive underneath the car, just diesel all over the filler flap... unless it's the filler hose that's leaking and there's now a new tank in the door sills!

Thanks for the help,

Schneckster

 

[Dieselman]

The diesel stain will be either from filling it or it slopping when going round bends, Check the cap seal as it is crucial due to the low filler position.

If your Wife bought fuel on the Motorway she only got about 2.9 gallons, so the usage seems about right for her journey.

The light will come on with about 9 litres left, so 2.9 gallons used less than 2 gallons left after 100 miles, seems pretty good to me.

The battery light will come on when the engine stalls, so again sounds right.

 

[schneckster]

She put a total of £35 in to do 100 miles, only £10 from motorway services. Using £1.41 (local services) and £1.51 (motorway) a litre giving about 4.5 gallons. With the car reporting it did 34.8 mpg on that run, that's 160 miles (110 & 50) worth of fuel, yet the needle was almost on the peg after 60 miles (£25), and there again after another 40 (further £10).

Also, the diesel around the filler only started to appear in the last week and it looks like it has been soaked rather than the small amounts you get from sloshing on corners. I'll have to post a picture of it. Before that, it would remain dry even when chucking it round bends - well, as much as you can chuck these cars. I will check the seal on the cap, though .

Are there any Haynes manuals or equivalent for these cars? My local indie MB garage can't get it in this side of the Royal Wedding (no staff and too much work!) so I want to see if I can spot it, and maybe fix it, myself.

Thanks again,

Schneckster

 

[Danny DeVito]

Does your car have an mpg readout ? Maybe fill it up and go for a drive and see what you think then. I think if that much diesel is leaking it would also have to be before the high pressure pump. i.e. between the tank and the pump. I might also suggest that you dis-connect your battery for a short while and allow the ecu to reset itself and see if that helps. And maybe you could ask your mb stealer to read out your fault codes ? Surely that would only take a few mins they might do it if you ask nicely then report back we may be able to help more. I don't thin theres a haynes for it but i there are others that make manuals cant remember the name though. Or else buy or download a copy of MB wis which is as much info as the dealer has.

 

[schneckster]

Danny,

Good suggestions, thank you.

Had a chance to have a good look round on the car after giving it a (much needed!) clean. No leaks whilst sitting on the drive at idle or revving. No leaks on the tank or visible parts of the fuel lines. A short, err... "vigorous" drive didn't put a noticable amount of fuel out of the filler cap or that general area. There was a tiny amount, but nowhere near the sort of amount I'm losing. I do think I need a new cap but I doubt it's the root cause.

Whilst driving it I could visibly see the fuel needle getting lower. Performance seemed OK, though a touch rougher than we're used to, but it accelerates OK and seems to pull OK, too. It's getting the fuel, but it just seems to be using way too much. I'm going to check the mpg again in a bit, but I had only done about 3 miles to get fuel in.

Someone suggested a potential cause could be faulty injectors. The rationale is that if they pass too much fuel through to the engine, it'll just blow it out the exhaust making it appear like a leak. Is that a possibility?

Tuesday, I'll get it to a dealer (love the name "stealer"!) and see if they can do anything. My local indie is fully booked next week.

Oh, and where can I get the WIS and does it cost much?

Thanks for all your help. It's very much appreciated.

Schneckster

 

[Danny DeVito]

Wis can bought from ebay or download via torrent etc. I think the inj holes get bigger as they get worn and so allow more fuel to pass through, but i would expect that to be a slow process. I wonder if your car has a faulty maf sensor or something like that. I suggested the ecu reset by disconnect the battery because it will reset the ecu to default and relearn and maybe this will help. Oh also look at the colour of the exhaust fumes. this may indicate the fault too ! Give it welly and have a look. And sorry i can only suggest things i have only exp of my own merc model

 

[schneckster]

I bought access to EPC, but the price of the WIS from the same place surprised me! I'll have a look for it on torrent tomorrow. Too late to be starting a 20GB download!

Looking at EPC, it seems the fuel pump is in the tank (called a "Delivery Unit"?) with the filter bolted to the engine. The engine isn't starved of fuel, so I think the pump is fine... I hope!

OK, exhaust fumes are sooty (on start up) or clear. The car has done 94k so I expect stuff to be worn and in need of some TLC. If that means the injectors, then I guess it has had enough time to wear and cause an issue.

As for the MAF... I've heard of this before, but I don't know how it works or what the symptoms would be. Would it act like my car is now? Generally it feels OK, just using way too much fuel? And is it expensive to put right?

 

[Danny DeVito]

google the maf. it is most likely just behind the air filter box. ur epc should show it. Sometimes if it's faulty it can mess up the fuel/air mixture. Fuel pump is probably okay because pressure should be regulated by the high pressure pump/ fuel rail. It seems you may need to have the garage check fuel pressure etc on a STAR diagnostic machine. Maf price varies a lot, i think my old volvo wanted €120 but cheaper on ebay. sooty black is probably ok too. I'm kind of out of ideas so unless any of the big wigs know more you may wait for the garage sorry

 

[schneckster]

I'll have a look on EPC now and get the garage to investigate it, too.

I also had a chance conversation with my Uncle. He asked about the car and how it was... so I told him. I got halfway through my description of the problem (excess consumption, no evidence of leaks) when he interrupted with one word: Injectors. My Uncle was a mechanic until he retired and worked on diesels of one description or another his whole career. He reckons that at this mileage, they may well be worn and could cause what I'm seeing.

So, when I get the MAF checked and the car read by STAR, I'll get them to look at the injectors, too.

Thanks for your ideas, Danny. Much appreciated.

Schneckster

 

[Danny DeVito]

No problem, please remember to report back !! Best of luck with it

 

[schneckster]

Update: I just got off the phone to my local MB indie - still can't get me in till late next week. I told him of the symptoms and he also suggested the injectors. I asked how much that could cost... I should have remembered that old saying of "If you have to ask the price, you can't afford it!". £350 per injector (from Merc) plus labour! He said they fit them once and forget them hence the price, which seems odd considering the number of people on this forum that need to replace them. They did say the engine would smoke if over-fuelled, which it isn't doing.

Summary of the problem:
1. Excessive fuel consumption
2. No leaks on pipes or tank
3. No smoking from exhaust
4. Engine feels a little rougher, but otherwise pulls OK

Bad injectors, I believe, give worse performance and smoke as well as bad consumption.

However, leaking injectors leak fuel into the engine bay which may be hiding in places I haven't yet seen. It's never running on the drive long enough for a puddle to appear. And these are apparently known for having leaking injectors.

What do you reckon, guys? Leaking injectors? And could I fix that myself?

Cheers,

Schneckster

 

[Danny DeVito]

tony russell had a post about his viano concerning injs. He thinks he should have got the garage to do it in the first place. I did mine never having done them before and it was simple enough. my inj overhaul cost 150 euro. so it's an expensive job even without being robbed by dealers