Very basic question for W108. - PeachParts Mercedes-Benz Forum

W108 · #1 09-22-2006, 09:59 PM

I know this seems like a basic question but what is the difference between the Fuel Injection Pump, and the Gasoline Injection Pump?

The replacement prices for the two are completely different although neither are really cheap.

The reason I ask is that I suspect my Fuel Pump needs to be replaced as it's running quite rich, possibly due to wear. However the screws on the Fuel Pump itself can't really be adjusted to any signifigance.

Shab · #2 09-22-2006, 10:11 PM

If it's a 6 cyl SE, you have an electric fuel pump in the rear under the car, driver's side near the tank behind a shield (Turn the key on and you’ll hear it whirring). Then you have a mechanical fuel injection (MFI) pump at the engine, on the driver's side as well. You will see the 6 rails coming from it to your fuel injectors.

That’s about the breadth of my knowledge. Others here are expert and the posts with procedures to test these components are voluminous and thorough, before you spend $$.

Emmerich · #3 09-22-2006, 10:12 PM

The fuel pump pumps the gas from the tank to the engine. All cars have one, be it mechanical or electric.

The injection pump is part of the fuel injection system on the engine. It is the way the fuel is distributed to the cylinders. In fact, on the later CIS cars, there is a device on top of the motor called the fuel distributor.

On a mechanical fuel injection system (same as a diesel) the injection pump is turned by the engine and sends fuel to the cylinders. It is actually a little engine run backwards. The camshaft in the pump is turned and the pistons are used as little pumps to send the fuel out the fuel lines to the cylinders. The diesel cars have a cam inside the injection pump to control mixture, it is like a regular camshaft in a car. The gas cars have a 3 dimensional camshaft-it is tapered in addition to having cam lobes.

Hope that helps, I understand how it works but i am not sure I described it very well.

W108 · #4 09-22-2006, 10:20 PM

Here is a link to a picture:

http://www.pbase.com/slidevalve911rsr/911rsr_factory_parts_bosch_mfi_pump

I suspect having it rebuilt would be a wiser "purchase".

Arthur Dalton · #5 09-22-2006, 10:34 PM

Rich running on MFI can be as simple as an adjustment to the linkage or pump to a Bad/leaking Cold Start valve and stuck Warm Running Device.

A quick test is to see if you can stall the engine by running the idle air screw in..
Post those results and I will walk you through it.

W108 · #6 09-22-2006, 10:48 PM

Quote:

Originally Posted by Arthur Dalton

Rich running on MFI can be as simple as an adjustment to the linkage or pump to a Bad/leaking Cold Start valve and stuck Warm Running Device.

A quick test is to see if you can stall the engine by running the idle air screw in..
Post those results and I will walk you through it.

Thank you for the advice. I will try that, and see.

The car itself runs fine, and drives well but it's obviously running rich from the exhaust smells to the very low MPG.

Arthur Dalton · #7 09-22-2006, 11:02 PM

...then I would check the CSV test port for leakby..
It has a 5 mm hex cap just below the CSV.. Take it off when car is running
or when the key is in the Run position. There should be no gas coming out this test port.. if there is, the CSV is always leaking gas into the intake, causing your rich condition.
The only time gas should come out that port is when the starter circuit is energized on a cold engine. [ less than 36C]

W108 · #8 09-23-2006, 02:26 AM

So, is #5 is the CSV?

http://www.peachparts.com/shopforum/attachments/tech-help/34206d1151362624-cold-start-valve-voltage-coldstart.gif

Tomguy · #9 09-23-2006, 11:16 AM

That's the CSV for the 4.5.
The 4.5 has D-Jet EFI. The 6-cyl has mechanical fuel injection. Completely different systems!

Arthur Dalton · #10 09-23-2006, 02:33 PM

.. Before we can help any further, you may want to tell us exactly what you have here ..
Is it an IL-6 /M130 engine [ which I assume it is b/c your other post say 280sel] .. or is it a 4.5 , as you are showing us a picture of a V8.. and you also show us a Injection pump from a 911..which is not applicable at all to my diagnosis.

What is the chassis/model??? ...please......

If it is the IL6 , then the CSV is the single wired solinoid at the center of the engines intake plenium, on the right side [passenger] of the car. The test port/hex is just below the CSV.

W108 · #11 09-23-2006, 03:46 PM

Yes, it's the straight inline 6 liter 130 engine.

Today, when I opened up the hex screw, and started the engine, a sizeable spray of gasoline came out, which I suppose points to the leaking Cold Start Valve. How do I proceed?

Arthur Dalton · #12 09-23-2006, 04:16 PM

Quote:

Originally Posted by W108

Yes, it's the straight inline 6 liter 130 engine.

Today, when I opened up the hex screw, and started the engine, a sizeable spray of gasoline came out, which I suppose points to the leaking Cold Start Valve. How do I proceed?

OK

One more test
Retry , but this time with the feed wire disconnected. This will differentiate if you have an electrical problem [ stuck relay, etc] or a mechanical prob w/CSV.
If it still leaks w/wire removed, the valve is leaking from a bad seat or dirt. Take it apart and see what you have..

PS .. be aware that you mention gas came out as you started the engine.
You do not take the plug off until after the engine is running , as gas will squirt out the port when the starter is cranking...so do not test the port while cranking, only after it is running [ you can also just turn the key to run position and check it w/o running the engine, as the fuel pressure going to the CSV is from the electric fuel pump and does not require engine to run, just electric pump to be running

W108 · #13 09-23-2006, 09:56 PM

Quote:

Originally Posted by Arthur Dalton

OK

One more test
Retry , but this time with the feed wire disconnected. This will differentiate if you have an electrical problem [ stuck relay, etc] or a mechanical prob w/CSV.
If it still leaks w/wire removed, the valve is leaking from a bad seat or dirt. Take it apart and see what you have..

PS .. be aware that you mention gas came out as you started the engine.
You do not take the plug off until after the engine is running , as gas will squirt out the port when the starter is cranking...so do not test the port while cranking, only after it is running [ you can also just turn the key to run position and check it w/o running the engine, as the fuel pressure going to the CSV is from the electric fuel pump and does not require engine to run, just electric pump to be running

I see; I had first removed the hex plug then started the engine, which resulted in a spray of gasoline. However, when starting the engine first, and then removing the screw, no gasoline came out.

I presume this means that the CSV is working fine?

I also unscrewed the CSV device, and it looked clean with some sort of a cork gasket attached. There is a thin piston rod, which didn't look dirty. As well, the air filter on top of the Injection Pump was recently changed; the old one was clogged.

I'm hoping this running rich problem is not due to a faulty Bosch Injection Pump.

Arthur Dalton · #14 09-24-2006, 03:34 AM

Then CSV is working as it is supposed to.

Take a small hose and put one end at that air filter on the IP and listen to the other end in your ear. You will hear air entering the filter as the engine warms up.. once the engine coolant is up to temp, the air should stop. If it does not , then the warm Running Device [WRD] and air slide valve is dirty and sticking. this causes rich running. Try that test.

W108 · #15 09-24-2006, 03:59 AM

I'll try that as well. Thank you.

Also, I heard rich running could be due to a faulty Fuel Pressure Regulator.