How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Marty Your Own Question
Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53153
Experience:  Bosch Certified Master Tech. Over 35 years experience.
13230946
Type Your Mercedes Question Here...
Marty is online now
A new question is answered every 9 seconds

I have an 2000 ML 320 that had signs and symptoms of

Customer Question

hello, i have an 2000 ML 320 that had signs and symptoms of a failing fuel pump. I replaced both the fuel pump and filter and it ran well for 3 days or so and now it appears to have an issue with starting. I checked the pressure valve on the fuel rail
and there's quite a bit of pressure in there (wasn't the case before I replaced the pump). Can I get some help diagnosing the issue?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.
Hi, I think I helped you with this the other day. Is this Howard?
Marty
Customer: replied 1 year ago.
Hey Marty! Yes, everything was running well and now I'm not sure what the issue is.
Expert:  Marty replied 1 year ago.
Sorry to hear that. Can you explain what happened? Did the car just quit while you were driving? Does it make any attempt to start or does it just crank?
Customer: replied 1 year ago.
It just died and I let it sit for a few days because I was busy with work. I looked at the fuel pump lines and noticed that one of them was a little kinked so I straightened it out a bit thinking that was the issue. It started up and ran for about 10 min and stalled. It sat for another day and started no problem. I let it idle for 30-45 min, took it around the block a few times, turned it off and it won't start. I checked the pressure in the fuel rail and there's a fairly strong spray. much more than before. can't figure out what's wrong
Expert:  Marty replied 1 year ago.
Are you able to test for spark?
Customer: replied 1 year ago.
I didn't get a spark tester. Tell me what I should get at the auto parts store to do the tests i need to diagnose the problem. thanks
Expert:  Marty replied 1 year ago.
Just pick up a spark tester and plug it into one of the plug wires. connect the tester to ground and have a helper crank the motor while you check for spark. If you have no spark I'd suspect a bad crankshaft position sensor. I'm assuming that the car makes no attempt to start at all. If it starts and runs for a second or two and then dies I'd try another key.
Let me know what you find out.
Marty
Customer: replied 1 year ago.
the car doesn't run at all...not even for a second or two. do you have any instructions on how i plug the tester into one of the wires? i'm sure it's simple but i've never tried it before. also when you say ground what on the engine or frame would be considered ground? (sorry for the rudimentary questions). Thanks.Howard
Expert:  Marty replied 1 year ago.
Some testers are inline where you just connect them in between the spark plug and the wire and some you just connect to the wire and clamp the other end to a metal bracket or bolt on the engine (ground).
Customer: replied 1 year ago.
Ok, I got a spark plug tester but it maybe i need to have a special one? I got an inline tester that has two male ends (each end about 1.5 inches long. one female end of the tester fits fine over the plug in the block but the other end doesn't go far enough down the boot. is there any trick i'm missing or did i pick up the wrong tester? or what do you suggest?
Expert:  Marty replied 1 year ago.
Where did you purchase it? Do you have a name brand and part number?
Customer: replied 1 year ago.
Lisle Inline Spark Tester - Part Number 20610 - Bought at Napa Auto Parts
Expert:  Marty replied 1 year ago.
Ok, the tester should have come with a short spark plug wire. Disconnect one plug wire from a spark plug and push the rubber boot of the wire that came with the tester over the spark plug in the motor and plug the spark plug wire that you disconnected from the spark plug into the male end of the spark tester. Copy and paste the link.
https://www.youtube.com/watch?v=nWokA2YksPw
Customer: replied 1 year ago.
i get what you're saying but the boot covering the on the spark plug wire is three inches long (metal) and the male end of the tester is only one inch or so...leaving a gap. does that make sense?
Expert:  Marty replied 1 year ago.
I see what you mean now. You will probably need to try a different tester.
Customer: replied 1 year ago.
i did notice that while i had the spark plug disconnected the sound was the same as with it connected. should i go ahead and order the crankshaft sensor and replace it? it doesn't seem to be very expensive and the cost of 2 testers is going to equal what the senor would cost. What do you suggest?
Expert:  Marty replied 1 year ago.
Hi Howard, I know what you mean. First check fuse 26 and make sure it's good and then try a new crank sensor.
Customer: replied 1 year ago.
will do...can you send me instructions on putting in a new crank sensor? i looks like it's a fairly simple thing to do.
Customer: replied 1 year ago.
also, can you look at this part to ensure that I'm ordering the correct one? thanks.
Expert:  Marty replied 1 year ago.
It's fairly simple but can be a little difficult to access. You will need an E8 Torx socket and a long extension. Next remove the E8 torx screw from the sensor then just wiggle the sensor up out of the bell housing and disconnect the plug. Reverse the procedure for installation. Remove the plastic top engine cover to give you more room.
Post the last 8 digits of your vin number and I'll look up the correct part.
Customer: replied 1 year ago.
Last 8 Digits of VIN : YA213241The part number number I'm looking at is Bosch(###) ###-####
Expert:  Marty replied 1 year ago.
That is the correct part number. In case I failed to mention the crank sensor is located at the back of the motor directly behind the driver's side cylinder head.
Customer: replied 1 year ago.
hello Marty,I tested the pressure in the fuel rail, just to be sure. I cranked the engine a good couple of times and there was nothing in there. sorry for the back and forth but it definitely seems as if it's a fuel pump problem. i pulled off the first hose connected to the fuel pump itself (the one closest to the front), and there was hardly any fuel that came out of it. can you tell me again how to test to see if I have a faulty fuel pump? many thanks.
Customer: replied 1 year ago.
btw, because of this, i haven't attempted to try and replace the crankshaft sensor as it truly appears the issue is lack of fuel getting to the engine
Customer: replied 1 year ago.
I did a test on the fuel pump and connected a hose to the front fuel pump line and gas definitely was coming out, so i think the fuel pump is ok. Do you have any other suggestions?
Expert:  Marty replied 1 year ago.
Hi Howard, ideally you should connect a fuel pressure gauge to that test port on the fuel rail so we can confirm that there is 52 psi pressure when cranking the motor. NAPA may loan or rent the pressure gauge to you.
Customer: replied 1 year ago.
right...I can check with NAPA but I took disconnected the fuel lines and reconnected everything just to insure that there were no kinks. I put everything back and there's just a tiny bit of pressure when i test the rail. Definitely not 52 psi or anywhere near that. would you think that it's a faulty fuel pump?
Customer: replied 1 year ago.
when i ran the test with a rubber tube connected to the pump, it wasn't very much fuel that came out. not enough to fill a solo red cup
Expert:  Marty replied 1 year ago.
Yes it does sound like the pump is defective or the pickup in the tank is blocked. I'd remove the pump and check the installation. I would also like to measure the voltage to the pump with a voltmeter. We need to make sure that we have 12 volts to the pump when cranking.
Customer: replied 1 year ago.
Sounds good. I'll check the pickup in the tank and ensure it's not blocked. If I see nothing there, I'll go get a voltmeter. Can you send me some type of guidance on using the voltmeter on the wiring going to the pump?
Expert:  Marty replied 1 year ago.
The green wire at the pump is your power wire. You should measure approximately 12V from the green wire to the brown wire when cranking. Ideally you should take the reading with the plug connected to the pump. You can use a couple of straight pins to pierce through the wires and then touch the voltmeter leads to the pins. Just make sure that the two pins don't touch each other when doing the test.
Customer: replied 1 year ago.
Hello Marty,I tested the wires leading to the pump (without the pump connected) and it tested close to 12V (about 11.5 not piercing the wires). Should I test it with the pump reinstalled?
Expert:  Marty replied 1 year ago.
Chances are you are fine. Next step would be to measure the fuel pressure when cranking.
Customer: replied 1 year ago.
Ok, I used a pressure tester and the pressure barely got 7psi. Suggestions ?
Expert:  Marty replied 1 year ago.
You should have 52 psi cranking. If you only have 7 psi you need to remove and inspect the pump. If you don't see anything wrong I'd replace the pump again.
Customer: replied 1 year ago.
The pump looks fine to me. I can't see any obvious problems. I'll replace it in the next couple days and let you know if that fixes the problem. Thanks Marty
Expert:  Marty replied 1 year ago.
You're welcome Howard.
Customer: replied 1 year ago.
Hello Marty,I installed the new fuel pump and still not starting. I checked the fuel pressure in the rail and there's some gas getting there, but not as much as before when i first installed the pump and the filter. Any suggestions?
Expert:  Marty replied 1 year ago.
Hi Howard, sorry to hear that you are still having trouble. Have you verified that there is plenty of fuel in the tank? Can you perform a fuel pressure test again? Would you like me to call you tomorrow? I can discount the additional service for the phone support if it would help.
Customer: replied 1 year ago.
There is definitely fuel in the tank. I'll call you tomorrow if I get the chance. I may have to wait another day. Could it be the fuel pressure regulator? Just a thought...
Expert:  Marty replied 1 year ago.
Ok, can you get the pressure gauge connected again? Did you test the pressure while cranking the motor? The pressure regulator is built into the fuel filter.