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1999 ML320 and 1985 300SD
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18 Posts
Discussion Starter #1 (Edited)
I just wanted inform the next guy, who may have the exact same symptoms, what fixed the problem for me. My Ml320 was doing the following:

1) Hard to start if it sat for anything more than 10 minutes. It would take at least two tries to fire it up.
2) Once started, it would run fine like nothing was wrong.
3) It also had no loss in power, even under full load up to the rev limit, everything was fine.
4) After sitting overnight, i would take the shraeder valve cap for the fuel rail off and push open the valve to see if it's holding any pressure and there was nothing, not even a few drops.

When doing a search, i found that most had to replace the fuel pump to fix similar issues. However, most of them also had a loss in power when under load, which i did not. So, since i have two vehicles, i decide to put this one on stands and order a fuel filter (which has the integrated pressure regulator) and try that first before i replace the pump. If it didn't work, oh well the filter probably needed to be replaced anyway, and then i would order and replace the pump.

Well there was no need because it was the fuel filter, i'm assuming through the pressure regulator, that was leaking fuel back out and causing a loss in pressure. Not only does it now hold pressure over night, it also fixed my throttle hesitation that the truck had when leaving from a stop. I also noticed that the vacuum hose that connects to the pressure regulator had quite a bit of fuel in it which i didn't expect. I guess it's possible that the diaphragm in the regulator ruptured and leaked into the vacuum hose. Is that a common failure for these regulators because i've never seen that before in other cars i've worked on?

Anyway, if you have these exact symptoms listed above, don't go throwing money at the pump until you've tried just replacing the filter first.
 

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2001 ML320
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43 Posts
My 2001 ML320 is having the same problem, hard start in the morning or when cold. On the first start, the engine would be cranking and keep on cranking but will not start. Then
it would start immediately on the second crank. I am trying the fuel filter now, hopefully it will fix the issue. Buying it on EBAY for $55.
 

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2001 ML320
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43 Posts
It costed me another $50 for the hoses connecting to the filter. Even after this, still same problem. Looks like I will have to replace the fuel pump also., another $200. Hopefully, it will fix the problem.
 

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'00 ML 430
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235 Posts
It was a bad, leaking check valve. After shutdown the hot engine will cause the fuel in the rails to boil and push it out of the rails. Once cold the rails are filled with vapor. Cranking takes so long because the vapor is purged through the injectors before real fuel follows.

Ingo
 

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Registered
2001 ML320
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43 Posts
Well, after replacing the filter, the engine starting problem improved somewhat. It still takes 3 to 4 seconds before it starts, when the engine is cold. I lived with it for a few months. Then the car started hesitating some time. Eventually, it misfired, lost power after driving about 10 minutes. Replaced the fuel pump, now everything worked! $100 for the pump on ebay, and $200 labor.
My truck now always starts immediately!!

Now I am onto the next problem, the remote keyfobs are failing.
 
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