How to test fuel pressure

[Karl W]

Hi,

I don't have a fuel pressure testing guage and neither does the local garage, Is it possible to read the fuel pressure through the 16 pin diagnostic port. I can fault code read the system using a power scope.

My local garage has various old testing equipment and they are sure they'll have something that works but they and me don't know what pins to connect to on the diagonstic port to find what the fuel pressure is at the injectors.

The car is a 95 e200, thanks for reading.

 

[jaymanek]

I dont think you can measure the fuel pressure electronically on that car..

You will need a fuel pressure gauge.. only specialist garages will keep them. We normally borrow one from our local injector specialist.

You can buy cheapo ones on ebay but not sure how accurate they are.

 

[Karl W]

I've got a problem with lean mixture when it's warm, but just need to check the pressure before I start fiddling around changinf stuff that doesn't need changing. It's fueling problem I've ruled out any ignition faults.

 

[jaymanek]

air leaks?

 

[Karl W]

Checked and double checked, even checked the PMS unit and ECU ect. It's fine from cold as it warms the mixture leans you can spray some of what I call easy start spray and that richens the mixture gives a quick fix.

 

[kth286]

I find it incredible that there are two examples above of garages not having
fuel pressure gauges.

It is an absolutely basic requirement of all cars to have the correct fuel pressure to perform correctly.

Without the measuring kit, how will you ever know?

The poster needs to find another garage.

 

[kth286]

I would suspect the coolant temp sensor may have gone out of spec.

It is a key component for feedback to the ECU to inform how much fuel
to inject.

As you will know the amount of fuel an engine requires is dependent on its
operating temp.

At cold it needs more and when hot, less.

The coolant sensor may not be following the correct curve with temp change.

Try and measure the resistance change with it being heated up.

You will need to know the expected values to be able to determine any
deviance from spec.

 

[powerfulml270]

Hi,

I don't have a fuel pressure testing guage and neither does the local garage, Is it possible to read the fuel pressure through the 16 pin diagnostic port. I can fault code read the system using a power scope.

My local garage has various old testing equipment and they are sure they'll have something that works but they and me don't know what pins to connect to on the diagonstic port to find what the fuel pressure is at the injectors.

The car is a 95 e200, thanks for reading.

Hi,
Yes if you can read all fuel pressure and fuel volume going through your system, plug in a proper computer, like a Snap on Solus Pro or similar and you can read all its live data. It will tell you what the rail pressure is and injector pressures and injection volume on fuel.

 

[mazza]

I've got a problem with lean mixture when it's warm,

Have you checked the Lambda signal??

I could be wrong but, if you had fuel pressure problems, you would have serious cold starting issues.

mazza

 

[tor_ake]

I have not seen a rail pressure sensor on the M111 engine in my wifes CLK200 -99. It is not at all common on petrol engines. No pressure sensor = no way for the computer to know.

 

[Karl W]

I'll test the ristance on the temp sensor. I replaced it last year with one from the MB dealer so unless it's faulty. I wasn't too happy when they hasn't got a pressure tester.

 

[Karl W]

Lambda sensor reading is what the book say's. It starts up fine from cold, when you give it some revs it'll start popping, when you spray some fuel straight in the intake it runs smooth again. I've checked all the conectors and put the voltage meter over the rest of the sensors and they are all ok. The main pump doesn't run as smooth as I'd have thought it would. I'm hoping when I can get the pressure tested it's low at the injectors.

 

[Terry_]

I cannot see your problem being fuel pressure. You need to get the car on a star machine and have the codes read
There will be stored / current codes. It could well be wiring related