Testing the Fuel Pressure Regulator? – Dead engine. - Mercedes-Benz Forum
 
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post #1 of 5 (permalink) Old 11-10-2005, 10:08 AM Thread Starter
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Testing the Fuel Pressure Regulator? – Dead engine.

Can anyone offer some guidance in troubleshooting a potential fuel problem?
My 190E/2.3 will suddenly not start, it has been a little difficult to start lately, but now it's dead. If I keep pumping the gas pedal, it may start, surge in rev. and then die right away.

The rotor & cap looks fine and there is a good spark on the plugs.
Changed the fuel filter.
Checked the fuel relay – it works to spec.
Checked the fuel flow, on the fuel return at the fuel pressure regulator – plenty of fuel.
I don’t have a fuel pressure gauge, but there is significant pressure (at the return line).

One observation, the fuel pump sounds louder than usual (like it runs faster?) – you can hear the fuel coming through the fuel pressure regulator.
I don’t know if this observation is of importance, but if the fuel pressure regulator does not work properly, i.e. letting the gas run back into the gas-tank and not building up the required pressure in the fuel distributor, according to my logic, I will not get any fuel through the fuel distributor and into the engine.
The question is, how do I find out? How can I test the fuel pressure regulator? Is there at all any ‘common’ sense to my logic?

Any suggestions, comments from you all? Even some plain humor – need some cheering-up, can’t get rid of this fuel smell.

Thanks.
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post #2 of 5 (permalink) Old 11-11-2005, 03:59 PM
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RE: Testing the Fuel Pressure Regulator? – Dead engine.

First thing I would check i whether there is pressure at the injectors. Because it is a continuos injection system, there should always be pressure at the injectors once you are cranking.

If there's no pressure, the fault lies in the fuel distributor.

Another suggestion is that you may have a blockage in your fuel return line. To eliminate that, disconnect the fuel return line and divert it into a jug. Then try and start it. If it starts, then fault is in the return line.

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post #3 of 5 (permalink) Old 11-14-2005, 07:46 AM Thread Starter
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RE: Testing the Fuel Pressure Regulator? – Dead engine.

Thanks SPANNERS,

The return line is not blocked, as described above. It looks like I have pressure on the fuel distributor (not proper measured thought, don’t have a gauge yet).
Out of the distributor:
- No fuel/pressure on/to the fuel injector lines.
- Fuel/pressure on the star valve fuel line.

So, summary of the problem; fuel and pressure at the fuel distributor, but no fuel to the fuel injectors.

Question:
Is it the actual fuel distributor that’s the problem?
OR
Is it the ‘mechanism’ that signals the fuel distributor to deliver fuel to the fuel injectors that fails?

The fuel injectors are not electrical, so I assume that the ‘control’ of sending fuel to a specific fuel injector, reside with the fuel distributor AND the CFI module.
I don’t think that I should have a constant fuel pressure at the fuel injector/line, but only at the time the engine needs the fuel injected – IS THAT CORRECT OR AM I WRONG ON THIS?

There are no ‘vacuum lines’ going to/from the distributor, so if the problem is caused by a ‘faulty’ vacuum line, I guess the faulty/missing vacuum - causes somehow – someway the CFI module to NOT sending the right signal to the fuel distributor (to send fuel to the injectors).
INCORRECT? If I am wrong on this and the above, I guess it can only be the fuel distributor it self.

The million dollar questions is to confirm if it’s the:
- Fuel distributor that’s faulty (or not)?
- ICF module function correct or not?
- Any of the ‘other’ modules that influence the fuel delivery system can cause the fuel distributor not to deliver fuel?
- Can a faulty ‘vacuum’ cause the fuel distributor NOT to deliver fuel to the injectors?
AND how can I confirm/ anyway to test each item?

Thanks again for all your help.
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post #4 of 5 (permalink) Old 11-15-2005, 06:15 AM
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RE: Testing the Fuel Pressure Regulator? – Dead engine.

The injectors a permanently under pressure once the ignition has been switched on. It is the suction from the piston withdrawing that opens the injector.

Check out this thread, he had the same symptoms as you.

I would have gone for the a stuck plunger in the distributor or even a bad distributor, but that was not the case here.

https://benzworld.org/forums/forums/thread-view.asp?tid=1230544&posts=7
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post #5 of 5 (permalink) Old 11-23-2005, 10:35 AM Thread Starter
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RE: Testing the Fuel Pressure Regulator? – Dead engine.

[:)]

We got the car back on the road.

Thanks for all pointers and information.

The problem was with the Fuel Distributor and the Start Valve.

To help any fellow DIY, who would face a similar problem, let me try to summarize what we did.

Since there was no fuel on the injector lines (with fuel pump running) BUT plenty of fuel on the Start Valve fuel line, return line and fuel distributor lower chamber (fuel distributor pressure test point), we figured that something got to be wrong with the fuel distributor.

We disconnected the fuel distributor and removed it from the car. Disassembled the distributor, cleaned all the ‘lines’ with carburetor cleaner (and air/compressor), assembled it and re-installed it.
This fixed the problem with fuel to the fuel injector lines (with the fuel pump running – plenty of fuel on the fuel injector lines).

BUT, with the fuel pump running, it sounded like a lot of fuel was running through the distributor!! The engine did not start AND stopped cranking…NOW the engine was flooding.. There was so much fuel in the cylinders that the starter could not turn the engine.
After draining the fuel (by removing the spark plug) a couple of times it was evident that something else was wrong. Actually, the flooding was so severe that we also got fuel in the engine oil.

The next possible problem (the only one left that we could think of) was the Start Valve. So, we swapped out the Start Valve (and the fuel distributor, just to eliminate this as a problem source).

The engine STARTED at the first go - problem solved.

We shut the engine down right away, because of the problem with fuel in the engine oil. Drained the oil-fuel ‘mixture’ and added new/fresh oil. Started the engine to run the oil through the engine and burn off all the excessive fuel (first some fuel came out the exhaust, then a lot of white smoke).

Drained the oil, replaced the filter and added new engine oil.

Drove the car for about 10 miles - Now it starts at the first crank and runs better than ever.

After more that 200 miles, the engine oil looks and feels new (and does not smell of fuel).

Long story, but happy ending.

Just a couple of pointers:
Fuel distributor,
Be extremely careful if you decide to disassemble it. The diaphragm inside the unit breaks easily and it’s difficult to put back together.

Parts,
Considering the possible severity of the problem, we bought a ‘new’ engine (only 80K miles). With the spare engine, we can swap parts in our efforts to find the problems, and if we could not fix the problems by swapping parts, we could always do an engine swap.

Fuel,
Be careful when testing for fuel ‘flow’, i.e. ‘open’ fuel lines, testing pressure and flow, etc. It does not take much to ignite the fuel or the fuel vapors.
If you have to drain fuel from the cylinders, remove the spark plugs, move the cords to the other side of the engine, put towels underneath the sparkplug hole and cover the hole, ALL before you crank the engine (if not, you will have fuel all over the engine, up in the air and maybe you).
Best place to do this: outside!

Thanks again for all the help from you all.
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