Fuel pump not getting fuel after filter replacement?
Thread Starter
Newbie
Joined: Apr 2007
Posts: 24
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From: Virginia US
95 C36 AMG
Fuel pump not getting fuel after filter replacement?
I'm hoping that someone here can help! I had a small hole in my 95 C36 fuel filter. When I discovered it, the car was running and gas was dripping significantly out of the botton of the filter. I replaced the fuel filter, and now the car will start (after cranking for at least a minute) but only runs for 2 seconds before it cuts out. It acts like it isn't getting any fuel, so I checked to make sure the filter was going the right way (it is) and checked to see if the pump was running (it is). I took off the filter - no fuel in it! I started the car (with an assistant) to see if any fuel came out of the fuel pump - nothing. The pump seems to be running, and didn't have any problems before replacing the fuel filter. Now I have no clue where to go. Any suggestions? 
Junior Member
Joined: May 2008
Posts: 71
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n/a
It might be possible that the pump needs to be primed with fuel now that the system has been opened and air allowed into the pump.
When you turn the key ON (ignition) the pump should run until the car has fuel pressure, and then shut off until the engine starts and the fuel pressure drops below the threshold again. Does your fuel pump run incessantly with the ignition ON? or does it run for a moment and stop?
If it was me having this problem, I would fill the tank completely up using a gas can. Next I would turn the ignition on and leave it on for up to 5 full minutes. Then crank the car without turning the ignition off and see if that works!
If that still didn't work, I would re-install the old fuel filter and see if starts.
If it starts, then the new FF is plugged.
If it doesn't start, there may still be air in the system, OR something unrelated has broken while working on the car.
How are you confirming that the FP is running, btw?
When you turn the key ON (ignition) the pump should run until the car has fuel pressure, and then shut off until the engine starts and the fuel pressure drops below the threshold again. Does your fuel pump run incessantly with the ignition ON? or does it run for a moment and stop?
If it was me having this problem, I would fill the tank completely up using a gas can. Next I would turn the ignition on and leave it on for up to 5 full minutes. Then crank the car without turning the ignition off and see if that works!
If that still didn't work, I would re-install the old fuel filter and see if starts.
If it starts, then the new FF is plugged.
If it doesn't start, there may still be air in the system, OR something unrelated has broken while working on the car.
How are you confirming that the FP is running, btw?
Almost a Member!
Joined: Sep 2006
Posts: 32
Likes: 1
ive got similar problem,when you full the tank(only wen i go on a long distance trip.wen the car says 1/2 tank it cuts out.if u put a little fuel in the it stars up again but its annoying wen you go on a long trip?
Thread Starter
Newbie
Joined: Apr 2007
Posts: 24
Likes: 0
From: Virginia US
95 C36 AMG
Thanks so much for the info - put more gas in the tank and pressurized the system. Apparently that was the issue - it didn't have enough gas in there to pressurize. I discovered that I also have a multitude of dry rot cracks in the return line, so I have gas leaking out of that, too, which may have accounted for there being less gas in the tank than I thought.
To answer your question, I have an assistant turn the key while I have my hand on the pump - I can feel the pump turn on and off.
Thanks again for your help!
To answer your question, I have an assistant turn the key while I have my hand on the pump - I can feel the pump turn on and off.
Thanks again for your help!
Junior Member
Joined: Dec 2008
Posts: 17
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From: Canterbury, New Zealand
W202 C280 94
Can o worms
Hi, found your story very interesting, I decided to change my fuel filter and used an aftermarket filter.
I had the same experience exactly.
I found that when I poured about 2-3 litres in the tank it started promptly.
It was later when I took it for a drive I knew something was wrong so went to my auto sparky and he read my fault codes, it registered Emergency fuel shutoff had registered a fault but he didn't know why, at idle, it would drop to 300rpm then over correct to 1200+rpm, straining against the brakes at intersections and sometimes refusing to accelerate as if out of fuel.
I first replaced the engine loom as it was cracked and wouldn't survive the diagnosis then had VAF(MAF) tested as easily damaged by the occasional backfire during its dead starts and it gave dodgy readings, have ordered a new one.
It seems I may have not de-pressurised the fuel system enough/properly before opening the system and the sudden pressure drop triggered a safety fuel shutoff in the system
.
Anyone know much about this??????
I had the same experience exactly.
I found that when I poured about 2-3 litres in the tank it started promptly.
It was later when I took it for a drive I knew something was wrong so went to my auto sparky and he read my fault codes, it registered Emergency fuel shutoff had registered a fault but he didn't know why, at idle, it would drop to 300rpm then over correct to 1200+rpm, straining against the brakes at intersections and sometimes refusing to accelerate as if out of fuel.
I first replaced the engine loom as it was cracked and wouldn't survive the diagnosis then had VAF(MAF) tested as easily damaged by the occasional backfire during its dead starts and it gave dodgy readings, have ordered a new one.
It seems I may have not de-pressurised the fuel system enough/properly before opening the system and the sudden pressure drop triggered a safety fuel shutoff in the system
.Anyone know much about this??????
Super Member
Joined: Oct 2008
Posts: 837
Likes: 25
From: seattle
1990 300ce supercharged and intercooled
I do not know for sure what your guys problem is, but it sounds like if your problem is at a half tank that your siphon system is bad. The c-class uses saddle tanks and a siphon-jet system to move fuel around between the tank halves and a pick-up section. The pump should get fuel from the gas tank by gravity. The start up cycle of the pump does not read pressure, it is simply a time pulse of the pump. I do not know why changing the filter would cause a problem. I have never heard of this happening. I would put five gallons in and if there continues to be a problem then your gauges are bad or your tank has some problems.
