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Discussion Starter #1
Hello ,

On a recent trip my 1999 ML320 developed a major fuel leak in the rear of the car. The leak is only apparent when the car is running and shortly thereafter. It completely stops, apparently after fuel pressure is bled down.
I took out the drivers side wheel well, to expose the fuel filter and the fuel lines. I also took out the rear seat and lifted the carper to expose the top of the fuel tank and the hose connections. All appeared dry and not leaking. I started the car and there was again, a massive fuel leak. It was hard to trace the origin and appeared to be running down the tank from the area of the filler neck inlet. I question whether it is possible for the filler neck to only leak with the car running and the system under pressure. Additionally, I can’t find the end of the small fuel line that runs from the fuel filter to somewhere on top of the tank in the area of the spare tire carrier. I see there are two large lines that run from the filter to the tank, as well as one large line that appears to run to the front of the car. Then there is a small, low pressure mystery line that comes off the filter to an unknown point over the fuel tank.
I replaced the fuel filter with an updated version and lines about 5 years ago without incident. Vehicle has been running fine to this point.
Any ideas? Does the mystery line go to a vent or canister that ‘s clogged? Could the fuel filler neck be defective? Could it be one of the valves in the evap system?

The car has been giving an evap leak CEL for some time. Recently the low fuel light flashed rapidly with a 3/4 full fuel tank.

Thanks for your kind attention
 

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Discussion Starter #3
Hi 43sqd,
Thanks for the suggestion. Unfortunatley, I opened my access panel and though I have the same valve / sensor, I don't have the fuel line plumbing that's apparent in your pic. My 1999, must be different than your 2002.
I'm going to try dropping the spare tire this evening to see if I can get a better look at things where the leak is apparent.
Thank you very much for your kind reply.
Out
 

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My experience with fuel leaking was from the fuel filter. The connector wasn't inserted properly & in time it got loose & slide back resulting in fuel leaking. Just like in your case it would leak while the engine is on & would stop shortly after switching off the car. I had to start the car & leave it running for a few minutes & get under, to see exactly were it was leaking from.
 

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Discussion Starter #5
Hi Art,
I appreciate your comment. When my leak occurred, I was actually hoping it would be a loose fuel line on the filter; because I could find it and fix it. Unfortunately, that isn’t my issue, as all is dry in that area while fuel rains down from above the tank to below when the engine is running.
I’m fairly sure this problem is linked to the evaporative system; that I just don’t understand well enough. Wondering what set of malfunctions could send gas through the system to be purged to the outside. Whatever evaporative calamity this system was set up to prevent has been multiplied tenfold by the spilling of gas from the system.
Thanks,
Out
 

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Discussion Starter #7
MattML430,

YES!! This is pic is very helpful, thank you. I see there’s a lot more going on up there than I expected. More hoses, more opportunities for leaks. This validates my inclination to take out the spare tire carrier to get a better look at things.
Thanks very much!!
Out
 

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Discussion Starter #8
Problem Solved; Maybe?
I removed the spare tire to get a better look at things on the top of the tank. Upon closer inspection, I found that the small mystery line from the fuel filter, AKA, fuel filter vent hose, is supposed to connect to the fuel tank just near the filler neck. Mine was not connected, as the short rubber hose connecting it was torn in half. Interestingly enough, in my further research, I stumbled on a post from 2010, titled; “Fuel leaking driver side rear tire” where a fellow with the same year ML, 1999, had the EXACT same problem; a tear in this small hose at the rear top of the tank. I also learned from this post that this vent hose should be dry; well mine is filled with fuel. Soooooooooo, I’m assuming I have two issues, the torn line that needs repair, as well as a bad fuel pressure regulator in the filter that needs replacing. I will try to get the parts tomorrow from the dealer and report results for reference by future fuel leakers.
Thanks,
Out
 

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When my pressure regulator died in my fuel filter the small rubber hose was leaking fuel until the pressure bled off. The truck took longer to start and then I dug in and found the leak. Replaced the filter and all was well again.
 

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fuel filter to feed line

Thanks to the many previous posters in this and other posts about fuel leaks which really helped.
My ML has a fuel leak. It is hard to see in there even with the wheel well liner removed, but appears to be where the feed line connects to the filter. (see blue circle)
if/when i push up under the connector with a screwdriver the leak seems to worsen - i can see some actual drips. Filter has not been touched in 12 years (changed by dealer in 2005) so sort of unexpected finding.
Based on previous posts I was expecting the small vent line to have been leaking caused by defective pressure regulator. Just goes to show you should try to isolate source of a problem before buying parts.
I did connect my fuel pressure gauge to the fuel rail to see if it bounces (which it would expect to if the pressure regulator has failed) but gauge records zero psi with engine running so seems i must not have the correct fitting, would have been a nice datapoint to aid in decision making but ultimately I am planning on changing the filter anyway ( 163-477-07-01, note 07 not 05) and the feedline 163-470-28-64) to address the leak. Dealer can get both by tomorrow for 131 and 44 Cdn respectively plus tax, so seems the way to go.

Filter not overdue by miles (has 90kkm, ) but due soon i.e. due in 10 km, seems crazy to not just change it while changing the hose (presumably it is the hose that is the problem).
Hoping i can get by with not buying the special pliers as they are expensive and not readily available.

I am hoping once i disconnect both lines at the fuel pump I will be able to pull out the filter enough to access and disconnect the connectors at the filter with the pliers in the picture below (planned purchase).

point of the post; does my plan seem sound: new filter and feed line only? generic pliers? disconnect at pump and pull out assembly?
thanks.
 

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Get both feed line and return line. The lines & lock will likely break & leak due to aging.

The filter isn't so easy to take out & put back in place.

The brand new lines/ hoses I got were probably aftermarket Chinese & wouldn't fit. I almost broke my pump trying to force it on. At the end of the day the seller refused to replace it & I bought one taken off a junk yard filter.

Lest I forget there's this smallest hose connected to the filter, an air hose or something, found mine leaking & just taped it round( I dont know the role of that hose-maybe to maintain pressure??)

I also got similar plain hoses & clips in case of necessity. Couldn't afford spending a lot on lines/ hoses that won't fit, leak or fail prematurely.
 

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thanks for the responses, in the meantime I continued my investigation, might indeed be a leaking pump cover seal. the planned filter and hose will not wasted but seems if one has a leak one must visit the top of the pump. Also seems indeed brittle hoses are a concern.

details: the plot thickens - but not in a good way.
I finally gave up trying to get the rear seats out , and with two bolts to go finally just cut the carpet (in a perfect world with perfect knowledge I should have taken out the seats with car outside, because I have no access in my cramped garage to do so; can barely open the rear driver side door, why am i in the garage? decided to work inside due to the heavy snowfall) ,
Then after much scraping and prying - in the process somewhat bending the cover, i did not want to use any heat to loosen the adhesive - i finally got access to the top of the fuel pump, in anticipation of disconnecting the two fuel lines there the better to undo both lines so filter could be pulled out for access to the connectors and of course was planning to swap the feed line; bad surprise; found a lake of gas on top of the pump sealing cap!

so maybe was not leaking at the pipe to filter interface, maybe fuel was flowing down the pipe and my lifting of that interface with a screwdriver tip just made the flow more obvious....
quickly i ran to the phone to not miss the 4pm cutoff and ordered locking ring and gasket, they will get here tomorrow.

i tapped the locking ring and it seemed loose but rather than tightening it decided i should take a look and try to observe the leak in situ.

then things took a turn for the worse; in the battle to remove the filter i had previously disconnected the fitting from the front of the filter (outlet to engine), so i connected that backup, and having sopped up the lake on the top of the pump, i then cranked the engine to confirm leaking pump cap seal.. turned the key and as ml will continue to crank on its own when you release, I hurried to the back expecting to see the car start and the lake slowly coming back... no lake, car cranked about 10 sec and did not start, it was at that point I noticed there was a lot of fuel under the car, looks like coming from behind the plastic the cover that runs along the bottom of the car, under the left hand sill to the front of the car (also some brake line run in there).
So i suspect that when i was messing around trying to get the filter out, i somehow cracked the fuel line that runs to the front of the car when i eased it out of the way; if so the line must have been rather brittle as i was about as gentle as can be (brittle hoses are mentioned by Dramos, but unfortunately i had not seen his post till after my debacle)

tomorrow i will take off that long cover and see what is underneath. hopefully there is a home mechanic replaceable hose in there. i had second thoughts about starting this job but no garage would take the car before next Wednesday. now the issues are compounding, those nice pliers posted by Art are in the USA so not trivial to get. also the special tool for the cap is also problematic.
Seems i will be learning some good lessons on this little project. :eek
 

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I have a big fuel leak on my 2000 ML. I trace where the leaks was. It was leaking at the fuel line connection on the return fuel line (smaller line) on top of the fuel pump.

Funny thing is that I replaced the fuel filter and and both lines (all Mercedes parts) and it still leak at the same place. I look a the steam sticking out of the fuel pump and I can see any cracks or other defect from the pump steam.

It is unlikely that I got a bad brand new fuel line since it leaks the same way after the installation. At a lost on what is going on.

Any ideas. I suppose I can connect the fuel pump to the filter using old faction fuel lines and hose clamp. But I am not sure I have the room since the steam from pump point straight up and I might not have the room to bend the hose with out kinking it.
 

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thanks for the responses, in the meantime I continued my investigation, might indeed be a leaking pump cover seal. the planned filter and hose will not wasted but seems if one has a leak one must visit the top of the pump. Also seems indeed brittle hoses are a concern.

details: the plot thickens - but not in a good way.
I finally gave up trying to get the rear seats out , and with two bolts to go finally just cut the carpet (in a perfect world with perfect knowledge I should have taken out the seats with car outside, because I have no access in my cramped garage to do so; can barely open the rear driver side door, why am i in the garage? decided to work inside due to the heavy snowfall) ,
Then after much scraping and prying - in the process somewhat bending the cover, i did not want to use any heat to loosen the adhesive - i finally got access to the top of the fuel pump, in anticipation of disconnecting the two fuel lines there the better to undo both lines so filter could be pulled out for access to the connectors and of course was planning to swap the feed line; bad surprise; found a lake of gas on top of the pump sealing cap!

so maybe was not leaking at the pipe to filter interface, maybe fuel was flowing down the pipe and my lifting of that interface with a screwdriver tip just made the flow more obvious....
quickly i ran to the phone to not miss the 4pm cutoff and ordered locking ring and gasket, they will get here tomorrow.

i tapped the locking ring and it seemed loose but rather than tightening it decided i should take a look and try to observe the leak in situ.

then things took a turn for the worse; in the battle to remove the filter i had previously disconnected the fitting from the front of the filter (outlet to engine), so i connected that backup, and having sopped up the lake on the top of the pump, i then cranked the engine to confirm leaking pump cap seal.. turned the key and as ml will continue to crank on its own when you release, I hurried to the back expecting to see the car start and the lake slowly coming back... no lake, car cranked about 10 sec and did not start, it was at that point I noticed there was a lot of fuel under the car, looks like coming from behind the plastic the cover that runs along the bottom of the car, under the left hand sill to the front of the car (also some brake line run in there).
So i suspect that when i was messing around trying to get the filter out, i somehow cracked the fuel line that runs to the front of the car when i eased it out of the way; if so the line must have been rather brittle as i was about as gentle as can be (brittle hoses are mentioned by Dramos, but unfortunately i had not seen his post till after my debacle)

tomorrow i will take off that long cover and see what is underneath. hopefully there is a home mechanic replaceable hose in there. i had second thoughts about starting this job but no garage would take the car before next Wednesday. now the issues are compounding, those nice pliers posted by Art are in the USA so not trivial to get. also the special tool for the cap is also problematic.
Seems i will be learning some good lessons on this little project. :eek
I guess you realise its not a little project. Lolz
I would get all tools & required material plus have a back-up plan(old-school fuel hoses & clips) before starting this job.
You dont want to play with FIRE


I have a big fuel leak on my 2000 ML. I trace where the leaks was. It was leaking at the fuel line connection on the return fuel line (smaller line) on top of the fuel pump.

Funny thing is that I replaced the fuel filter and and both lines (all Mercedes parts) and it still leak at the same place. I look a the steam sticking out of the fuel pump and I can see any cracks or other defect from the pump steam.

It is unlikely that I got a bad brand new fuel line since it leaks the same way after the installation. At a lost on what is going on.

Any ideas. I suppose I can connect the fuel pump to the filter using old faction fuel lines and hose clamp. But I am not sure I have the room since the steam from pump point straight up and I might not have the room to bend the hose with out kinking it.
There are primitive fuel hoses fashioned in curves that won't kink if you search properly. It is most likely the seal-lock of your hose that's defective or the hose has not been fully pushed on the pump connection. You can try swapping those from the old hose i.e the lock/seal part if you still have them & see if you get lucky. I think from design there's a specific pump end & filter end for each fuel hose.(pump end yellow lock, filter end black lock)
 

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Hi All,

Does anyone know if the service loop line 163-470-37-64 should be used with the larger filter 163-477-07-01 and with fuel line (runs from filter outlet to fuel rail) *163-476-01-01*?
Or should the service loop not be used, i.e should be omitted.

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I am back with a new installment so to speak hehe, on fuel lines.
Back in December 2016, I eventually figured out the feed line from the pump to the filter was cracked, and I changed it. I also changed the filter as it seemed like a good idea.
fuel filter 163-477-07-01 ; 117$,
fuel feed line 163-470-28-64 40$

As I has broken the fuel line that runs from the filter to the engine, I ended up replacing this with a 10' section of "rubber" fuel injection line, held in place by fuel injection clamps (two at each end).
It was expedient at the time (car could not be driven, and was in very poor working conditions, time, money, busy with other stuff etc etc).,

Fast forward to last month when the "rubber" fuel injection line failed and started spraying fuel out thru multiple small holes. This occurred in the engine bay. A major fire hazard to be sure (so if anyone is thinking of using fuel injection line as a long term solution I would not recommend it). Not sure if could not handle the heat, the pressure, or both. The factory part is encased in steel mesh in that section of its length.

So I have just gotten the correct fuel line from the dealer, out of Germany, 3 weeks and 220$ later. 163-476-01-01, see picture. Its big, that's a size 12 shoe in the picture for scale. I am researching the install. Looking at the these old posts...

I wonder, is it possible the dealer, when doing the first filter change, jammed in a new larger filter *without* upgrading the fuel lines (even though the new lines were needed) ? is that possible?

data that suggests this is what happened:
-My car is one of the older models (built nov 1998).
-Dealer installed new filter 163-477-07-01. No mention of hoses on the invoice.
- It appears hoses could not have been upgraded because the fuel pump access panel appeared to be factory sealed and the car is not fitted with the service loop, 163-470-37-64.

Is there any possible explanation (other than the dealer to save time and money jammed in the larger filter in place of the small) as to why the car does not have the service loop installed?

this would explain why I broke the line in December 2016 when I was trying to install replacement filter, in the sub zero garage plastic line now much aged, and very cold and brittle broke.

So the past is the past, for now the question is, might I need to get a service loop in hand for the install?
(and I might need to change the return line too, next time if ever I change the filter, if I and the car live that long)

If no one knows, that ok, thought I should share this adventure in case of interest. I will phone dealer for another opinion but that wont be till Monday, and there system is suspect (for example parts fiche shows a fuel return line from engine, which does not exist). I will also get a tap measure, not sure how useful that will be). Nevertheless all inputs welcomed.

Cheers.
p.s Wife said the new VW sportwagon too small - and so the ML took the family from Ottawa to Orlando and Tampa and back without a hickup at Christmas. Impressive for 20 year old klunker. Luckily in retrospect we were not all burnt to death in a fiery immolation. A warm thought.
 

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Hi All,

Does anyone know if the service loop line 163-470-37-64 should be used with the larger filter 163-477-07-01 and with fuel line (runs from filter outlet to fuel rail) *163-476-01-01*?
Or should the service loop not be used, i.e should be omitted.
Yes, you need that loop line. Otherwise fuel feed line will end up with the kink in it.

Lift vehicle by frame. Remove left wheels and left fender liners. Remove left stone guards. Take notes, pictures of line routing. Maneuver towards the front.

Cover ends of new line with rubber glove finger. Keep it clean don't bend or kink. With aid of second person get it in place.
 

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Thanks Witek. I will get me the service loop part in hand prior to trying to install the new long line. Then I will try this in the driveway, not sure will be possible on jackstands, only one way to find out.
And thanks for the PDF instructions.
cheers.
 

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Oh my!; Step 8 and 9 of the PDF instructions seem to be suggesting that the body needs to be lifted off the frame! Sounds unpleasantly challenging =:^o

Can anyone advise what is a ' body suspension unit BA60.80-P-1001-01A
' ?
---------------------------------
for ref:
" 7 Remove the left-hand stone impact protection at the front and rear on the underbody

8 Screw out the screw for the vehicle body on the body suspension unit BA60.80-P-1001-01A

9 Lift up the left-hand side of the vehicle body and remove the three middle body suspension units. Do not remove the front and rear body suspension unit .

10 Detach the fuel line (2) from the fuel filter (3) Clamp 000 589 54 37 00 "
 
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