supak111

My dads 04 ml350 wont start on first try, it cranks the engine over just fine (not battery nor starter problem) almost tries to start but it doesn't. Second try it takes a few seconds but it does start everytime. Temp of the engine does not matter, problem always same.

ALSO:

After its starts you can turn the car off and if you try again it will start on first try. But if you turn it OFF and wait more then a few minutes it again takes 2 tries.

I not a Mercedes guy, but I'm thinking it could be a bad fuel pressure regulator, it might be leaking all the fuel pressure back to the gas tank and not building enough pressure for the car to start on first try?? That or possibly a weak fuel pump, not enough pressure??

Anyone have any advice or suggestions to try? I'm also wondering if there are 1 or 2 fuel pressure regulators, I think its a 3.7 v6 in there?

Thank everyone

Maj. Dundee

If the problem occurs in between the span of 30 mins. then it is a fuel pump problem.

supak111

Is there any way to check the pressure that the pump makes is sufficient? I wouldn't want to buy a $300 fuel pump and have it turn out to be something dumb like maybe a fuel pump relay or regulator.

Also there is never a check engine light, wouldn't the car misfire and stuff if the fuel pressure wasn't good enough? Car runs fine, no shaking, has same amount of power as it did before the problem started too.

Thanks again.

Maj. Dundee

You will have to check fuel pressure with a gauge. If it falls below 36psi after 30 mins. then it is the fuel pump.

supak111

Yea I just found that connector and tested the pressure. There is almost no pressure there after the car is OFF for even 1 minute.

Are you sure it couldn't be a faulty pressure regulator though? I will go with the pump, just want to make sure its not something much cheaper that's all.

Thanks Sam

supak111

Hey Maj. Dundee. I just did more testing with the pressure gauge and what I've learned is that when I test pressure on the IN line for the fuel (before fuel rail), when the ignition is ON and the pump primes, I get about 45 psi but as soon as the power goes OFF on the pump the PSI drops fast. I read some place that there is a one way check valve in the fuel line to prevent the fuel from going back after the pump is off, any idea where this inline one way check valve is? If there is such a valve then its definitely failed because my pressure drops as soon as the pump is off. Also since I tested on the inline for fuel before fuel rail its not a leaky injector.

Maj. Dundee

There is no valve in the line. I don't know what I have to do to convince you after I have shown you written proof.

supak111

You were right, the pump is shot. Builds PSI but doesn't hold pressure back once turned OFF. New pump if I try to blow through it air doesn't go through it, it acts like there is a check valve inside it, on the other hand the old damages pump I blow into and the air comes out the bottom (broken check valve). Thank again and sorry I doubted you :-)

Maj. Dundee

Hope you bought a quality pump.

jwhite03

I am having the same problem. Sounds like I only need to install a new fuel pump. Now if I can only find some info on how to replace a center console window switch

Maj. Dundee

If you tell us the year of your ML it would help.

jwhite03

1999 ML320
I found some instructions on removing and repairing but I am buying an after market switch from switch-doctor on eBay for $46. I will keep the old one and maybe try to repair it. I don't have much faith in these instructions.
http://www.grill.org/rodney/mclass/mlswitch/index.html

Maj. Dundee

The instructions are good.

jwhite03

Installed the after market switch according to the posted instructions and Windows work fine now.


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Mercuryprincipl

Hi I am having trouble starting my 2010 ML350 AMG when cold, first thing in morning. It cranks over fine but is hard to start usually starts on the second attempt and will then start fine during the day only an issue when it is cold if I am parked at office until 7 or 8 without driving it. I have replaced both fuel pumps due to wife running out of fuel. Any suggestions would be appreciated.

Maj. Dundee

Have you read post #4?