Greeting Forum Members,

Today I tested the fuel pressures on my poorly running 1985 280sl.
I now need help in interpreting the results, CIS Kjetronic II system.
My control pressure at idle of .5 bar @ 25 degrees Farenheit I think is correct as the acceptable minimum.
My system pressure @ 20 degrees Farenheit reads only 1 bar.
The system pressure should read 5 -5.6 bar engine at idle warm or cold.
My control pressure topped out at 1.2 bar with the engine warm and begining to die due to running rich.
The control pressure should read 3.6 - 4.0 bar with the engine warm
and warm up compensator stabilized.
System maintains good constant rest pressure(engine off).
Could a worn or damaged system pressure valve be responsible for these poor pressure readings and/or does this look like a warm up regulator problem?
I suspect the former.
Any experienced help with this matter would be most appreciated.
I'd hate to order a part I don't need.

Thanks,

Knarf

__________________
72 350SL #69
73 450SL Parts Car?
78 450sl Parts Car
79 450SLC - Sold
1985 280sl
87 190E 2.6 - Donated
90 300E-Junked
97 E420

but my 84 280e euro was running very rich. like 10 mpg rich. and it was the warm up compensator.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

53 psi warm idle.
Cold will be 26 to 29 psi.
Pump pressure must be above 75 psi.

Look at the CPR...there's a pin sunk slightly in the body.
Drill a 5mm hole 10mm deep in center of pin (Dowel.).
Tap drilled hole with 6x1mm bottom tap.

Fit a 6mm nut on a 6x1mm 30mm machine bolt and a washer to go between the CPR and the nut and run nut up to the bolt head.
Screw machine screw into pin on CPR with Loctite.
Run nut down to CPR and continue to tighten it until pin begines to rise.

Bridge fuel pump contacts.
With pressure guage fitted, adjust nut or tap down bolt after backing off the nut a turn until pressure correct cold. You are changing the pin height in the CPR that directly affects the fuel pressure cold.

If the warm pressure is not correct, you need a CPR.
You may find you need to tap the bolt past its origonal point if fuel pressure was way off.


.


.

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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

What about the low system pressure though? Does that need to be correct before tackling the control pressure values?

__________________
1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

What type of fuel pressure gauge are you using? If you are using a pressure gauge that has a shutoff valve, how are you connecting the two ends to the system.

When the valve is in the closed position the gauge should be reading pressure from the upper chamber of the fuel distributor, this is system pressure. When the vavle is open then it will read pressure from the warm up regulator, this is control pressure. If memory serves me correctly;
Cotrol Pressure--(.8 to 1.2 bar @10 C [11.5 to 17.5 psi]) and (3.2 to 3.8 @80 C [47 to 56 psi]).
System pressure--(5.0 to 5.8 bar [74 to 85 psi]).

Mind you, each vehicle is slightly different so you may need to adjust one or all of these values up or down to obtain optimum efficiency and optimum performance from your engine.

First determine pump stalls out at over 75 psi(Dead head.)
If not you need to find out why pressure is lower.
Filter.
Line kink, etc.
The pressures MrCjames quoted are correct, except California emmisions cars.

.

__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Thanks to all for replying.
dkveuro,
I see that my warm up regulator is already set for this adjustment proceedure.
Will this adjustment also increase my system pressure? My fuel pump and filter are new. I have no vacuum leaks.
For the record the poor performance at operating temperature came on "all of a sudden", right after a fuel fill up. Maybe it was coincidential that it just started manifesting itself at its current level. Actually for some time I had been noticing a sooty exhaust but no noticable performance problems.
What do you mean by "First determine pump stall over 75 psi"?

raymr,
Good question.
I've ordered a system pressure valve repair kit from Phil at Fastlane I hope that this contributes to the cure.
What happens to these valves when they fail?

Cjames,
I'm testing my pressures with a Bosch CIS fuel pressure tester by ATD.
I do have the MB shop manual spec values for my 990 engine.
How does the fuel pressure damper effect pressures? I see an adjustment screw at one end.

Knarf

__________________
72 350SL #69
73 450SL Parts Car?
78 450sl Parts Car
79 450SLC - Sold
1985 280sl
87 190E 2.6 - Donated
90 300E-Junked
97 E420

Pump pressure against closed line should max out above 75 psi...most will go to 100+ psi.
Don't fully understand your comment on I see that my warm up regulator is already set for this adjustment proceedure.

Rich indicates a non functioning O2 system.

May be coincedental....check tank for venting properly. A sucked on tank will collapse .

Other than that...no other ideas.

.

__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

That adjustment will not fix the system pressure issue. The control pressure cannot exceed the system pressure, and can't bleed off enough fuel to kill the system pressure unless you have a real problem (elsewhere).

You aren't measuring the system pressure correctly! System pressure has to be at least 4bar or the injectors won't even OPEN! You did say the engine runs!??

0.5bar control pressure is too low for 25F & control pressure must be between 3.4-3.8bar WARM.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

dkveuro,
My warm up regulator has the adjustment screw and lock nut installed by the a previous owner.
M.B. DOC,
I think you're correct, something's wrong with my readings if the car is running fine cold below injector opening pressure.
I suspect air in my tester line.
The guage does not have a bleed off screw to bleed air from the guage and lines after installing.
The manual describes a proceedure to purge air from from the lines that I followed but I suspect I didn't get it all out.
I'll try purging the lines again and take new readings.
P.S.
I received a system pressure valve repair kit from Fastlane today.
Ordered after 6:30 PM EST 1/16/06


Thanks to all.
I'll keep you updated.

Knarf

__________________
72 350SL #69
73 450SL Parts Car?
78 450sl Parts Car
79 450SLC - Sold
1985 280sl
87 190E 2.6 - Donated
90 300E-Junked
97 E420

I don't think you need a system pressure regulator. I agree with the previous post, if the system pressure really was 1 bar the engine wouldn't run. This may be a measurement error. Before putting in the pressure regulator I would measure the output of the pump, both pressure and volume tests, then re-run the system pressure test.

Once the system pressure is verified OK then and only then will the control pressure test be meaningful. Control pressure should be in the range of 3.1 to 3.5 bar (engine warm).

If the control pressure is low with engine warm then your warmup regulator will probably have to be replaced. It's possible to adjust the wamup regulator but the range of adjustability is very small. If the control pressure is 1.2 bar with the engine warm then your chances of a successful adjustment are very low. If your control pressure is a few tenths low then your chances are better. Remember that your car left the factory with the control pressure just right. If it's low now that means that something is wrong, usually (but not always!) with the warmup regulator itself. That's why our company makes lots of warmup regulator upgrades.

BTW, if the control pressure really is 1.2 bar then DON'T run the car for an extended period of time. We lost an engine in one of our test vehicles due to scuffed cylinder walls because of this problem.

Steve
UnwiredTools Support Team
www.unwiredtools.com

You might want to refer back to my first post, mainly how you’re connecting the gauge to the FI system. What will help us better understand your test values may be explaining where the gauge is connected in relation to certain fittings as well as knowing the placement of the shutoff valve. If memory serves me correctly the shutoff valve is placed between the gauge and the warm up regulator. If the shutoff is valve is placed between the gauge and the fuel distributor you will get erroneous readings.

Again and again I have measured the system and control pressures and they read low, 1.2 - 1.5 bar max with 2 different guages.
When I turn the engine off the guage pressure rises to a resting pressure of 3 bar.
The car runs fine showing a system pressure of 1.2 bar until the engine reaches operating temperature, then the engine begins to stumble, runs rich and shuts down.
I can drive the car as long as I keep the rpms above approximately 1,000 rpms and feather the throttle at stops.
So theoretically the system pressure is actually at least 3 bar if this is the minimum pressure required to open the fuel injectors.
The fuel distributor does have a frequency valve installed.
Could this be bleeding off pressure to the guage readings?
How does the on/off ratio of the frequency valve function effect fuel pressure readings? Faulty valve?

Thanks to all for your responses,

Knarf

__________________
72 350SL #69
73 450SL Parts Car?
78 450sl Parts Car
79 450SLC - Sold
1985 280sl
87 190E 2.6 - Donated
90 300E-Junked
97 E420

As has been pointed out your pressure readings are implausible. The posibilities for such are that you have a defective gauge or you are testing at the wrong point. Use the image included and indicate where your fuel preesure reading are taken at. For control pressure you should be reading pressure inside pipe #776. Because I don't like to mess with the running that using the tee valve does to get system pressure I use two gauges or one gauge two times to read the two pressures. (In other words the mechanism for reading system pressure with the valve is to block off control pressure till it reaches system pressure to achieve a reading. This cause the engine to run very poorly as during that moment system pressure equals control pressure not good for fuel mixture preperation)

For system pressure I have a tee fitting that reads the pressure as it enters the distributer.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician