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2000 E320
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18 Posts
Discussion Starter #1
Hello Everyone!

I have had a problem for over a year I am just finally looking for a possible solution.

My car has had a hard time starting when hot, on occasion. If I've been driving for a wile then turn the car off for a bit, upon starting it cranks and cranks then finally starts to sputter to life. It does not start up instantly but it sounds like a firing here and there till it eventually roars to life. Sometimes an entire crank cycle (turn the key then about 5 seconds or so of cranking) will pass and the engine will not start. I could be imagining this...but if I turn the key to position 2 and wait for the hiss of the fuel pump to finish (about 2 seconds after turning to position 2), it will almost never have the issues. Again, this could just be my imagination.

Now, I've had the CPS fail on me before. I changed it with a brand new one from the dealer 4 years ago. This issue started happening over a year ago. It is possible the CPS could be bad again but after only 3 years of use, I don't think it's likely. I also don't really know how to test the CPS.

In my head, waiting with the key in position 2 before cranking allows "pressure in the fuel system to build". This was just a hypothesis, so I decided to pressure test the fuel system. I got a loaner fuel pressure kit from the auto store. When I hook it up I get 55psi when the engine is running. When I turn the engine off the gauge instantly goes to 0psi. It is possible I'm not using the fuel pressure tester correctly, but I think I am.

Based on my testing and what I've read on the forums here, the check valve in my fuel pump has failed. But I have a big problem with this answer: When the fuel pressure goes to zero after turning the car off, I can restart it with no issues. It is only once the engine is hot that sometimes the issue occurs. So if the check valve is the cause of the problem, why does it only cause issues when the engine is hot?

Am I on the right track? Any advice is appreciated.
 

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Premium Member
1998 E320 base sedan @ 160kmiles
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7,215 Posts
Hello :)

When the engine is cold you wait for the fuel pressure to build up, start the car and then turn the engine off, and the pressure goes to 0. This shows that the check valve is bad. After it goes to zero, do you still wait for few seconds to before you start the engine for the fuel pressure to build up ?

Cranking but not starting when the engine is hot may point to leak in one or more of the fuel injectors due to fuel evaporation.

This is for the fuel pressure test:
Note : 1 bar is 14.5 psi
STAR TekInfo

This is for the fuel pump test:
STAR TekInfo

This is for the fuel injector test:
STAR TekInfo

A bad CPS will not cause the fuel pressure to go to zero when the engine is turned off :).
 

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2000 E320
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18 Posts
Discussion Starter #3
Hello :)

When the engine is cold you wait for the fuel pressure to build up, start the car and then turn the engine off, and the pressure goes to 0. This shows that the check valve is bad. After it goes to zero, do you still wait for few seconds to before you start the engine for the fuel pressure to build up ?
Hi MrBoca!
No, when the pressure goes to zero, I did not wait for pressure to build and start the cold engine again with no issue.
 

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Premium Member
1998 E320 base sedan @ 160kmiles
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7,215 Posts
You really need to make the measurements again. The car will not run when fuel pressure is zero. it must have built up quickly. Just observe the pressure when someone turns the engine off and on.
 

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2000 E320
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18 Posts
Discussion Starter #5
You really need to make the measurements again. The car will not run when fuel pressure is zero. it must have built up quickly. Just observe the pressure when someone turns the engine off and on.
Okay. I'll retest it again and have someone crank it for me. I'll post a video tomorrow
 

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2000 E320
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18 Posts
Discussion Starter #6
I must be doing something wrong because I am getting inconsistent test results

In this first video, the pressure does not build up in position 2, only when starting does the pressure increase. However on the second start in this video, the pressure rises then falls before starting.

In this second video, pressure builds while the key is in position 2

in both videos, the pressure returns to 0psi after turning the engine off. However, I did not get it on video, but the very first time i started the car today, the pressure was held after turning it off. The videos i have linked are from subsequent starts.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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4,343 Posts
Change the fuel filter. It has check valve built in.
 
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Premium Member
1998 E320 base sedan @ 160kmiles
Joined
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7,215 Posts
Change the fuel filter. It has check valve built in.
Fuel filter or fuel pump ? I thought the fuel pump has the check valve and fuel filter has the regulation valve (excess pressure fuel goes back to the tank).
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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4,343 Posts
Hmm, I'm confusing 163 with 210. 163 have check valve built in filter.

You're correct that the filter has regulator built in, and pump has check valve built in.

Change fuel pump, OP.
 
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Premium Member
1998 E320 base sedan @ 160kmiles
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7,215 Posts
What seems to be happening is when your assistant turns the key to position 2, the ECU turns the pump relay on for 1 to 2 seconds to build up pressure, If the fuel lines are completely drained, this will not be enough to build the pressure up. When she subsequently stopped the engine and turned the key to position 2, there was still some fuel in the fuel line and filter, and the pump built up the pressure and then lost it. When you start the engine the pump gets constant power, but not when the ignition on and engine off. In the second video , it looks like the fuel pump held the pressure, so the check valve issue is intermittent. I agree with Deplore. I would change the pump, and the filter to ensure proper operation.
 

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1989 W124 260E
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1,897 Posts
I have the very same problem,, only on the M103 engine and i put it down to the fuel pumps in my case First of all .the filter was replaced,, along with a new acumulator .It only leaves me to think is is poor fuel pumps or check valves .And as the new pumps will come with new check valves i will replace them both pumps ..
 

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2000 E320
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18 Posts
Discussion Starter #12 (Edited)
So I just got around the changing the fuel pump and filter. Looks like that solved the issue! I hooked up the fuel pressure tester and the pressure was held after turning off the car. No more hard starts.

Intermittent problems like these are so tricky to solve. Thank you all for your help with this!
 

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2008 E350 110k, 2000 E320 143k, 1983 380SEC 240k
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965 Posts
So was it the pump, or the filter? My money is on the filter. Will it hold back pressure? Then crack it open.
 

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Premium Member
1998 E320 base sedan @ 160kmiles
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7,215 Posts
The only valve in the filter is the regulator valve which keeps the pressure at a constant level. If it goes bad, you would have variable fuel pressure, and the car would have problems when demand is high, because of insufficient fuel pressure.
 
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