Warm up regulator question - Page 2 - PeachParts Mercedes-Benz Forum

knarf · #16 01-22-2006, 12:24 PM

Thanks for the reply Steve,

That is where I've been taking my readings, between the fuel line #776 as indicated in your diagram and the fuel distributor head with the shut off valve between the guage and line #776.
I'll take readings again today.

Knarf

knarf · #17 01-29-2006, 02:09 PM

Between dealing wth the weather and finding the time,
I have just completed a fuel pressure test of the fuel pump pressure delivered to the fuel distributor.
My new pump and filter maxed out at 65psi.
The car is running no differently with the new pump and filter than it did with the old pump and filter.
Assuming the new pump and filter are both good, what could cause such a low reading?
Could an obstructed fuel damper located between the tank and pump?
Bad fuel accumlator?
I know that any obstruction in the lines is another possibility.
I guess this explains my erroneous system and control pressure readings.

Thanks,

Knarf

stevebfl · #18 01-29-2006, 02:22 PM

That pressure is low, but not critically low. I could make a car work just fine with that pressure for system pressure. Since it is so close to right I assume the fuel pressure regulator is shimmed improperly. Since that pressure isn't the problem with a car that is performing poorly, I deal with it after fixing the real problem. What is your control pressure cold and warm?

knarf · #19 01-29-2006, 02:53 PM

Thanks for respondjing so quickly Steve. I think I'm close to finding the cause of my problem.
But let me clarify the source of my pressure reading.
That 65psi is the fuel pump pressure only.
This reading was taken directly from the fuel supply line that leads from the fuel pump to the fuel distributor.
I've read that this pressure should be at least 75pis.
The reading was taken with the line removed from the distributor and attached to the pressure guage.
The only readings that I get when attaching the fuel pressure guage to take system and control pressure readings have been the 1.2 bar warm system pressure reading and .5-1.2 bar cold control pressure readings previously mentioned..
The engine runs worst as engine temp rises, eventually stalling.
I'm suspecting a clogged fuel damper.

Thanks,

Knarf

stevebfl · #20 01-29-2006, 03:28 PM

Well generally speaking that pressure is meaningless, EXCEPT it is definitely TOO low. The fuel pump has an internal pressure relief for instances where it is deadheaded like you are doing. They don't exactly publish that pressure but I would guess that it was somewhere over 120psi.

The fuel pump DOES not determine the system pressure the pressure regulator does. A proper test of a fuel pump will be to measure the inlet pressure (determined by the regulator) while catching the fuel flowing through the regulator headed back to the tank. A critcal specification is the volume that flows back to the tank. On your car the pump should maintain system pressure about 75psi as you state while a liter a minute is returning to the tank.

Sounds like a fuel delivery problem. That usually means fuel pump. They way you are testing it restrictions shouldn't matter as you are not allowing flow. Even if the pump was pumping through a .020in hole it would eventually fill and pressurize the line to the blow off pressure. Is this the same gauge that read less than two bar on a running motor. I'm beginning to distrust it. No way a motor can run below 49psi. That is what it takes to open the injectors.

The other possibility is that you have no fuel in the tank or can't get it out.

raymr · #21 01-29-2006, 03:43 PM

If 2 different gauges were used and they both show the same reading, then that rules out a defective gauge.

But why would the system pressure INCREASE after shutting down the engine?

Did you take apart the pressure regulator and change the number of shims to see if that changes your readings? I think you add shims to increase pressure.

knarf · #22 01-29-2006, 08:18 PM

raymr,

I'm not sure why the pressure rises after the engine shuts down.
I theorize that the 42 psi rest pressure represents most of the low system pressure that was just enough to open the fuel injectors to run the engine cold and register a guage reading of only 17-19 psi until the engine stalled.
It was as if the injectors or something else is bleeding off pressure or I'm not getting enough fuel pressure to the distributor from the pump.
Would a dirty tank screen give such results?
I did add a couple shims to the pressure regulator. They caused no change in the pressure readings.

Knarf

stevebfl · #23 01-29-2006, 08:35 PM

Pressure rises because all flow stops??

Based on your test, your problem is before the fuel distributer. Do the fuel delivery test as I described. It is the factory test to evaluate what your system is doing. You can not control fuel pressure and distribution in this system unless you have a huge fuel flow. It needs to have sufficient quantity that with all manner of control and distribution the system stills puts more fuel back to the tank than it uses. Quantitatively it needs to flow a liter or more to the tank while maintaining 5 bar.

Do the test with the engine off by jumping the fuel pump relay. Read the pressure and collect the fuel exiting the fuel distributer back to the tank. My guess is you won't have any return at all, because you can't even meet the regulated pressure with a dead headed pump. make it pass the test and you will go a good ways to fixing your problems is my guess.

knarf · #24 01-31-2006, 07:14 PM

Good Evening (6:45 PM EST),

Today I removed the fuel tank screen.
I was hopping that it would reveal an obvious cause for my poor pressure readings.
I think it did, but it wasn't the screen itself. The removal of the screen , which looked fine I might add, revealed an empty gas tank. Albeit the rear of the car is raised about 8 inches, but no gas spilled out as I removed the screen.
I think I lost the last bit of gas in the tank while changing out and adding shims to the new system pressure regulator a few days ago.
That same day the low fuel indicator light was on so I added a few gallons of gas to the tank.
I guess that I've probably been testing pressures with 2-4 gallons of gas in a tilted tank.
What' the minimum gallon requirement in a gas tank to maintain propper fuel presures in a CIS system, 1985 280sl specifically.
Might it be a percentage of the total tank volume?

Thanks,

Knarf

stevebfl · #25 01-31-2006, 07:39 PM

Out a gas is out a gas, anything else functions. If it is there it will be pumped through the system appropriately. The quantity of gas in the tank has absolutely nothing to do with the pressure up front UNLESS internal restrictions require gravity to force fuel to the pump. A cup of fuel available will pressurize the system for a few seconds, not many.

knarf · #26 02-03-2006, 03:20 PM

Greeting Forum Members,

The saga continues!
This weekend I'm going to disconnect and check the fuel supply and return lines for blockages.
Is blowing them out with compressed air ok?
I would like to clean the screen in the warm up regulator.
Can that be done without removing the regulator, i.e. back flushing the regulator with Techtron or something simular?
It's located in a real tough spot to remove on the 110 engine or would this be premature given my previous pressure readings?.

Thanks,
Knarf

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