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1999 ML320
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319 Posts
Discussion Starter #1
I tried to start the ML this morning. It wound over but wouldn't start. I've had no problems lately and its been running well. I tried the spare key but with the same result. When I checked the fuel pressure at the rail, there was no pressure at all. I swapped the pump relay and fuse (and banged the tank) but no difference. I'm measuring battery voltage at the pump connector when I crank the engine so strongly suspect that the pump is faulty. Fuel pumps in Australia are $1400 from the dealer and the best I can do is $1100. I don't want to double the value of the vehicle so will ship one from the states but that means the car will be off the road for awhile.

What troubles me a little is that because the car was running fine yesterday, I would have thought that there should have been pressure in the fuel lines even if the pump wasn't working. I would expect that the engine shouldn't have started and then died.

The fuel filter was replaced about three years ago. Anything else to try before ordering the pump?
 

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Premium Member
02 ML320 06 ML500
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16,866 Posts
Before condemning the p7mp, do the following:

1. check to see that fuse #38 is good.

2. swap relay #3 with similar one and see, if not.....

3. remove relay #3 and with a 6" , 10 gauge jumper wire with spade terminals attached, bridge slots 30 & 87 at the fuse box and see if the pump runs. If not replace relay and....

4. remove the left rear wheel and fender liner, and access the X18/3 connector. Separate and check for corrosion. If not.........

5. while the connector is still separated, have someone hold the key to start while you check for voltage at position "D", GREEN wire at the main harness side and check for ground at position "C", BROWN wire

6. then reconnect the harness and try again. If not replace the pump.
 

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1999 ML320
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319 Posts
Discussion Starter #3
Thanks 43sqd for the tips. I tried swapping the relay and fuse this morning without any difference. I measured the voltage across green and brown at the pump while turning the key and measured battery voltage. I have since removed the pump and found a few pieces of broken plastic floating around inside the housing so figure that not all is well. I've ordered a new genuine pump from the states for $350 so will wait until it arrives. Thanks again for the advice. I'll post again after the pump arrives.
 

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1999 ML320
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319 Posts
Discussion Starter #4
I removed the broken pieces of plastic from the pump and tested it by applying 12V direct to the motor. The motor ran. I re-installed it thinking that one of the broken pieces of plastic had jammed the motor. Still no go. Although I had measured voltage at the plug, I decided to do it again but with a headlight bulb to provide a load. This time, no voltage. I tried 43sqd's shorting spades and eliminated the relay. I traced back to the connector in the wheel well and discovered that the dodgy brothers had been at work. The green and brown wires had been cut off either side if the connector and "bullet" connectors had been substituted. I removed these, soldered the wires together and covered with heatshrink. The engine started first time.

I'll look into getting a new X18 connector and pins. The soldered joint is probably better than any connection so it may not be worth the effort. In any case, I have a new pump on the way which I'll fit because of the broken pieces of plastic I found in the old one. (see pic). I now know a bit more about my truck and consider myself lucky that this happened at home. (This must be the best place to break down.)
 

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Purple Moderator
99 ML430, 00 ML320, 05 E500 4matic Wagon
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Glad it is running.

You did a great job tracing the problem and thank you for letting us know so other members can learn.
 

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02 ML320 06 ML500
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16,866 Posts
I'll look into getting a new X18 connector and pins.
If only the wires were damaged, the soldering is the way to go. Buying a new X18/3 connector is not necessary if it isn't damaged. M/B only sells the small pins that attach to the wires and special M/B release tools are necessary to remove them.

Just leave it as is.
 

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1999 ML320
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Discussion Starter #7
I've already come to the same conclusion. I can't see any circumstance where I would need to undo this plug. I think that it must have been designed for when the body mated with the chassis during assembly.
 

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02 ML320 06 ML500
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16,866 Posts
I've already come to the same conclusion. I can't see any circumstance where I would need to undo this plug. I think that it must have been designed for when the body mated with the chassis during assembly.
Not really Raya. It is there as a test connector. Otherwise you would have to go to the top of the tank to do so.
 

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Before condemning the p7mp, do the following:
3. remove relay #3 and with a 6" , 10 gauge jumper wire with spade terminals attached, bridge slots 30 & 87 at the fuse box and see if the pump runs. If not replace relay and....

4. remove the left rear wheel and fender liner, and access the X18/3 connector. Separate and check for corrosion. If not.........

5. while the connector is still separated, have someone hold the key to start while you check for voltage at position "D", GREEN wire at the main harness side and check for ground at position "C", BROWN wire

6. then reconnect the harness and try again. If not replace the pump.
What do I need to get to do this? . was having other issues(so I thought) and car(98 ml320) ran great for 2 days.. Then last night NOTHING. No pressure at rail, has spark, 1/2 tank gas but "coughs" instead of turning over. Tried attach but says video too big. Thanks so much in advance. I'm at wits end. . -- am the one who had move today... All belongings, myself,and cat stuck out front
 

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Premium Member
2002 ML320, 2003 A160, 2002 ML500, 2018 GLS350d
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If by ‘coughs’, you mean it makes a coughing noise when you turn the key instead of cranking, then you might have low battery voltage. You could try jump starting it.
 

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Sorry my mistake. It has plenty of umph. It cranks. Turn key and cranks for about 7 seconds on its own then stops. All indicator lights except SRS stay on.
 

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Dallas, Texas
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What do I need to get to do this? . was having other issues(so I thought) and car(98 ml320) ran great for 2 days.. Then last night NOTHING. No pressure at rail, has spark, 1/2 tank gas but "coughs" instead of turning over. Tried attach but says video too big. Thanks so much in advance. I'm at wits end. . -- am the one who had move today... All belongings, myself,and cat stuck out front
You have found right post to follow.

In front engine compartment fuse box locate fuel pump relay and remove it. On the fuse box there are terminals 30 and 87. Clearly marked. Make sure you can identify them. If you jump other terminals 85/86 you will destroy engine control module. With 30/87 jumped check fuel pressure. If none go back to fuel tank and using piece of 2x4 whack bottom of the tank.

Take care of the cat.

5S9A7455.jpg
 

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But with no fuel coming out of the brass fitting doesn't that mean no pressure anyway? So even still jump them? Thanks. He thinks hes a dog. Lol. Likes swimming, playing fetch. Weirdo Kitty if ever..
 

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But with no fuel coming out of the brass fitting doesn't that mean no pressure anyway? So even still jump them? Thanks. He thinks hes a dog. Lol. Likes swimming, playing fetch. Weirdo Kitty if ever..
I am responding to thread "No start, no fuel pressure" so if you get nothing at test port depressing schrader valve there is no pressure. I am not going to tell you to connect pressure gauge.
 

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Yes to whack the tank if you have no fuel pressure. CPS has nothing to do with this.
 

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Oh.. Someone told me CPS controlled if the fuel would come out of the rail. I whacked it . didn't work. Landlord just said I better have fixed and gone tomorrow or else.. Just what need..more friggin stress. People are so uncaring anymore... If not cps???
 

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Oh.. Someone told me CPS controlled if the fuel would come out of the rail. I whacked it . didn't work. Landlord just said I better have fixed and gone tomorrow or else.. Just what need..more friggin stress. People are so uncaring anymore... If not cps???
CPS is used to determine engine speed and position of cylinder #1.

Feel pump relay is activated for 1 second after key is in position 2, cranking, and of course running.
 
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