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Old 06-04-2011, 06:27 PM
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w210 Fuel pressure

Anyone here know what the fuel pressure should be on a w210 1999 e320 4matic? i tried searching the forum but no luck. i tested with a gauge and got only 28-30 psi (200 kpa).

trying to narrow problem before ordering a $300 pump. problem is wont start when warm. cleared all codes by replacing mas, egr, egr tube, plugs, cam sensor, crank sensor. now i'm stumped and think it may be a fuel pressure problem.

Any help would be greatly appreciated.
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Old 06-04-2011, 08:11 PM
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The spec at idle is 3.7 to 4.2 bar (53.6-60.9 psi). Also the delivery test is 1 liter of fuel in a maximum of 35 secs.

-From WIS procedures for Repair and Maintenance of Service Manual DVD
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Old 06-04-2011, 08:30 PM
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Thanks RchardM98! Looks like a new fuel pump is in order huh? I was also concerned about how quickly it lost pressure after powering down. thinking there's a check valve inside the pump thats bad.
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Old 06-04-2011, 10:51 PM
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There's also a pressure test -

1) Turn off engine
2) Pressure should be about 3 bar (43.5 psi)
3) After 30 min pressure should be no less than 2.5 bar (37.5 psi)
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Old 06-05-2011, 12:15 AM
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ok. i replaced the fuel pump just now. still only getting about 32-35 psi running and no pressure at all after shutting engine off. details of what started all of this are:

06-02-2011, 09:37 PM
1999 E320 4Matic. Started this morning fine. Then had a hard time starting like it was "sputtering" to life. I replaced the crank pos sensor in January, so i put another new one in. That didnt work. Had someone read the codes and they were p0170 and p0173 (mass air) and p0301 (missfire cylinder 1) and p0400 (i think is egr). Replaced the mass air sensor and it fired right up. Drove it and it was cutting out under acceleration. Started it a number of times ok. now it wont start again. if its not the cps or the mas, what would be next? Thanks in advance for any advice.

06-03-2011, 06:38 PM
Thanks for the replies guys! It was the EGR valve. Replaced it and changed the plugs at the same time. Also cleaned the Bosch MAS and took back the Autozone one. So far so good, however, i have a vacuum line left over that i cant figure out. I posted pic's if anyone wants to see.

Interestingly, the old plugs were gapped at app. .052 from a tune up 3 years ago. They were pretty fouled up. I am pissed that they were so far out of gap. I won't take it back to that shop again.

Thanks again for the replies.

Yesterday, 08:49 AM
No codes now. no need to swap the coil as it is no longer misfiring (i think it was fouled plugs). it will start cold, accelerate sort of jerky, start immediatly after shutdown. if you wait 5 minutes after warm shutdown, youre stuck. it will start warm sometimes, but it takes forever turning over and then will sputter to life. i did change the fuel filter back in Jan with a good one. Friend of mine that works on Audis frequently said if it were an Audi, first thing he'd check would be Camshaft (not crankshaft) position indicator. Many people seem to be getting those 2 confused. Any thoughts?

Yesterday, 12:06 PM
Have now put in a new cam position sensor. that didnt fix it either. i am truly stumped. it may be going to stealer on monday for diagnostic if i cant fix this.

So now i've replaced fuel pump @ $300 to no avail. Getting pretty stumped. Guess i might try a new fuel filter tomorrow. Any help would be greatly appreciated.

Last edited by MichaelMorris; 06-05-2011 at 12:23 AM. Reason: left out info
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Old 06-05-2011, 07:41 AM
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Did the fuel pressure increase with the new pump? 35 lbs is awfully low. Regulator stuck open?
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Old 06-05-2011, 08:59 AM
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I think it is difficult to diagnose these electro-mechanical systems without access to the fault codes stored by the ECU.

There is also the purge 'MOT' valve which could not be holding pressure. Mostly it makes a ticking sound when the engine is not warmed up yet.

Hope that helps some.
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Old 06-05-2011, 10:06 AM
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Fuel pressure did not increase with the new pump but definitely comes on stronger(gets up to that wopping 35 lbs faster). I thought pressure regulator too and that is going to lead me to change the fuel filter this morning (i already changed it in January but maybe i got a bad one). I guess the MOT valve is def on the list. What about trash or water in lines? Also, i would think that leaking lines would produce visible and smellable leaks, yes?
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Old 06-05-2011, 04:57 PM
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New fuel filter did the trick. I just replaced the thing in January but guess i got a bad one. Tried to figure out how to get to the tank screen but couldnt and i have had enough of this car for awhile anyhow. If anyone knows of a simple way, please let me know.

Thanks for all your posts. I will definitely keep coming back here for advice as well as to try and help. The value of this blog to Benz owners and DIY'ers is limitless. You are all very kind. THANKS!

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Old 06-07-2011, 07:57 PM
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There is no easy way to get the tank screen out. Usually the the pipe elbow sticks in the strainer. If you apply enough force it will loosen the strainer but you won't be able to turn it more than a few degrees before it binds due to lack of space. Sooooo unless there is an indication of a problem, don't mess with it.
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