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rpmdiag
rpmdiag, Tech and Instructor
Category: Mercedes
Satisfied Customers: 7744
Experience:  Since 1975
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2002 mercedes ml320. Wife drove to store in the morning.

Customer Question

Hello. 2002 mercedes ml320. Wife drove to store in the morning. Came out an hour later and car cranks (tries to turn over) wont start. I am pretty handy with vehicles but having trouble diagnosing this one. I have read all sorts of things that this could be. I need someone that will help me systematically troubleshoot this issue. Thanks.
Submitted: 11 months ago.
Category: Mercedes
Expert:  rpmdiag replied 11 months ago.

Hi, welcome to Just Answer. I’m Ron and I’ll be helping you
today.
Before we get started though, Please understand that I don't know
your skill level or tools you have to assist us. Also understand that
I can't see, smell, hear, or touch the vehicle either, so patience is
appreciated. JA is a great Q/A site, but it does NOT replace a
repair shop.
My goal is to make you happy and get a great rating in return for
my time. Sometimes I have to give you bad news that I know you
didn’t want to hear, so please don’t shoot the messenger.

Okay, no problem. We do need to check the fuel pressure with a gauge as well as check for spark at the plugs with a spark tester to see what we are missing. keep me posted of your results.

Thanks, Ron

Customer: replied 11 months ago.
Hi Ron. I just checked spark with a spark tester and light is popping on and off when cranking. Looks good to me. I went and purchased a fuel pressure tester, connected to the rail, turned on key and zero pressure. Cranked and zero pressure.
Expert:  rpmdiag replied 11 months ago.

Okay, then check to see if we have power to the pump. Check fuses first, then power at the pump. If we have power, then the pump is bad.

Thanks again and please remember to rate me 5 stars and keep this link in case you need me again later on.

Ron

Customer: replied 11 months ago.
Ron. Opened my fuse and relay box and there is no fuse in F38's spot and no relay in K3's spot. Is this normal? I dont see any other area listed in the box for relay or fuse for fuel pump.
Customer: replied 11 months ago.
Hi Ron, I found the correct location of the relay and fuse. It's under the passenger side kick panel. The one in the engine compartment is for diesel. So, I place my meter on the fuse and when I turn the key all the way on I feel the relay click and see ~11.7v for about 2 seconds and then the relay clicks again and power to the fuse drops out to 0. Before I found out where the fuse and relay was I decided to remove my back seat to expose the access panel for the pump. I disconnected the connector and am not getting any power. I did this before I found the correct fuse and relay.
Expert:  rpmdiag replied 11 months ago.

The power is only continuous for a couple of seconds when you turn on the key then it stops. It appears to be working right then. Sounds like you do have a bad pump.

Thanks, Ron

Customer: replied 11 months ago.
Ok. Thanks Ron. I am just a bit hesitant. Can you explain why the power doesn't stay constant? I can understand this if the pump turns on, builds pressure snd then shuts off. In this case the pump isnt turning on and creating pressure. Wouldnt it just stay on?
Expert:  rpmdiag replied 11 months ago.

Sure, the engine isn't running, that's why.

It will stay on when the engine is running, but if the pump is bad, how cam it stay running?

Thanks again and please remember to rate me my 5 stars and keep this link in case you need me again later on.

Ron

Customer: replied 11 months ago.
Ok. Sounds good. Picking up fuel pump.
Expert:  rpmdiag replied 11 months ago.

Thanks,

Ron

Expert:  rpmdiag replied 11 months ago.

Just following up to see if you had any more questions.

Thanks, Ron

Customer: replied 11 months ago.
Will be installing fuel pump Friday. Will give updste then. Thanks.
Expert:  rpmdiag replied 11 months ago.

Thanks