durhamite

My 01 c320 (120k miles) would not start the other night... turned over but not even a sputter!! Sadly, my battery was weak, so I replaced the battery before I proceeded, and lost codes, if any. I spent alot of time with the threads, And as directed, changed the CPS, and cleaned the MAF... nothing. I changed the fuel filter but still no start.

I checked for fuel in the rail, and find that it is dry. I checked the fuse... good, and replaced the relay... still no fuel to the rail.

After turning switch to position 2, I can hear the fuel pump run for several seconds and then stop. Shouldn't the pump run until it reaches pressure?? I get no fuel to engine no matter how many times I switch it on. I've also tried a little gas down throttle body which makes the engine run until the gas is gone... still no fuel delivery.

I pulled pump out and cleaned pickup screen. While out, I bench tested pump in pan of gas and it flowed (but I didn't verify pressure).

Am I missing something? Any thoughts??

Thanks

LILBENZ230

Sounds like the pump is not creating enough pressure to start the engine. I'd replace the pump, seems you've done a great job diagnosing it already.

durhamite

At $300+ I was reluctant to guess at it since the pump does put out some fuel. There WAS some metal in the pickup strainer, though. I was wondering why the pump didn't keep running when switched on, if the pressure wasn't sufficient??

Glyn M Ruck

Pump needs to output >3.8 bar or 55psi while cranking. Have you replaced your fuel filter?

durhamite

yes, replaced filter... and no fuel delivery to the gauge port.

durhamite

I read that you could jump the relay socket and make the pump run in order to test.. Is this true/safe??

Thanks

durhamite

Glyn,

By powering the pump directly, I get 48psi... less than spec, but pressure. I can start the engine, and the pressure drops to zero. The pump doesn't run under operational conditions.

I hear the pump run for a few seconds at switch on. Does anyone know if the pressure sensor at the driver side in-tank unit would stop the pump if it thought it had pressure... and if that could be the problem, how it could be checked??

Thanks

Carsy

Here is the Fuel P/P wiring diagram. Fuel press sensor B4/7 .Hope it helps.

Safety first when checking electrical equipment near fuel fumes .

Glyn M Ruck

I think the problem is the FP sensor or relay or both. A friends green fuel pump relay failed a few weeks back.

durhamite

Thanks... can the sensor be purchased separately? If not, what is the official name of that assembly?

Carsy

Was the wiring diagram of any use !! ??

Glyn M Ruck

See 125

125 A 163 542 28 18 .PRESSURE SENSOR AT TANK

This should be correct for your early car. On newer vehicles it was integrated into on of the fuel level sensors.

durhamite

Glyn and Carsy...First, thanks for sending these diagrams out!! It is awesome that you take this time for us!!

I had to print the four wiring sheets out to see them (which I just got done), and some stuff is still a little fuzzy to read. Is this the wiring specific to the fuel pump?

I have looked at the B4/7 connector, but wasn't sure how to test it.

The diagram that Glyn posted does look exactly like my setup. One question though...it shows sensor 125 out on it's own. It sorta loks like they are made together on my car. Is that a diaphram type sensor??

Glyn M Ruck

I have no idea what kind of sensor that is.

Carsy

Durhamite,

Regarding B4/7

"PU/PI/PIZ Differential Pressure Transmitters

This group of differential transmitters are designed for general applications. The PU gives a Voltage output. The PI has a current output and the PIZ is a 2 wire 4-20mA device. All versions have the option of a digital display."

So you should be able to check its operation with a voltage meter.

N118 the intank fuel pump control module could also be a source of the problem .

So the questions I would ask myself , is the Pressure Sensor B4/7 speaking correctly to the N118 fuel P/P control module & is the N118 control module speaking with fork tongue with the in tank fuel pump?.

You will have to sit down with your voltage meter & nut it all out !!

Check at the bottom of the page ,left hand side for engine types relevent to drawing.

Let us know how you go.

Carsy

From this website the P/U sensor is a diaphram type :-

http://www.halstrup-walcher.com/Deta...mformer&ID=130

durhamite

Wow, that's some heavy duty stuff you guys are laying on me!! Cool... I guess I gotta simulate some pressure to the sensor, and see what it does to voltage

Unfortunately, I had to leave my car about an hour from me (safe location) and I can't just step out and try something, so I have to hit and run as I can. I looked at the sensor today, and it looks like it is bonded with the level sender unit... this the case??

At this point, I would replace the sensor if I can get it.

Once again, I really appreciate your willingness to help.

Glyn M Ruck

Great stuff JC!

I know on some cars you have to buy the whole tank sensor unit. I was hoping yours would not require that.

durhamite

I've garaged this car for two years... Periodically trying new things. I replaced both the fuel pump canister, and the sending unit canister. I've tried virtually everything I could think of, but no luck. Anybody heard of this happening before?

joeyMB

i have a mercedes 2003 C240 .. it runs idle then shuts off, i checked the fuel delivery fuses to fuel pump and the relay the pump turns on and relay clicks and fuse to pump is good. it runs when you put gas in the air filter and stays running feeding it but it stalls if you stop or idles then quits like its starving for gas i also checked the k40 circuit it looks ok i didn`t check the fuel pressure with a gauge yet though .. What else can the problem be? wheres the sensor or sending unit at and how do ya check them? where n what next?

Steve5

Please can anyone help me with a schematic/wiring diagram of the fuel pump on W203 2002 C320.
I am particularly interested in components/sensors which control the fuel pump relay which is fitted on rear SAM.
On another forum I read that when the engine is not running a sensor switches off the fuel pump. Any ideas which sensor that might be? Also someone had found a burnt pin to a connector on rear SAM which made the relay intermittent and hence the pump operation.
The diagrams already published on this page are too small to read. Any help would be much appreciated. Thanks in advance.

Russell Ormerod

The engine ecu drives the relay. And switches it off if the engine stops. There is no sensor

Steve5

Thanks Russel. My car starts and runs for about 5 minutes, till the engine is at normal running temperature. It then shuts off and won't re-start. Cranks but no start. I'm getting engine fault light so hopefully something will be logged in the ECU. Will find out soon.
Schematic diagrams are much better for fault finding and understanding how the system works. I can never get hold of these for Mercs.