KE fuel system help needed. - PeachParts Mercedes-Benz Forum

MAGV5 · #1 01-30-2009, 06:38 PM

1986 500SL KE system

Problem to solve: Engine looses power above 3000 rpm and will not exceed 3500
rpm.
In the remainder of this document this condition is referred to as “stall
condition”.
The engine starts fine hot or cold and idles ok.

Ignition:
Replaced the rotor and cap (new), tested the ignition wires, replaced the coil
and EZL with units from salvage yard (symptom did not change, so I assuming they
are in good condition). Measured voltage at ignition pickup (at flywheel) with
and it checks ok (possible that at higher rpm this might still fail). The ignition
timing is correct and the advance is working. Plugs clean and gaped. If the ignition
failed when the "stall condition" occurs the 02 sensor should go rich voltage, instead
it goes to a lean voltage.

Fuel system:
The “stall condition” is encounter with or without the EHA
connected, therefore the electrical inputs to the ECU are not causing the “stall
condition” Is this correct?
Replaced the FD with a used unit and encountered the same “stall condition”.
This does not eliminate the FD as the cause, but does increase the odds on it
not being the problem. Replaced intake manifold gaskets,the eight rubber coupling
rings and inspected all the remaining rubber idle tubes for crackes.
Fuel pumps have passed the fuel deliver (quantity) test.
F.D. upper pressure (at 80C) is 93.5 psi, lower pressure is 87 psi and gages
have been calibrated against each other.
These pressures remain constant up to and after the “stall condition”.
CO adjustment can be set for the 02 sensor to read .6v at idle, but any throttle
advance will result in 02 reading drop to .2V or lower depending on rpm. In “stall
condition” the 02 sensor reading jumps between .1V and .4v

Personal analysis: Suspect that the problem is fuel starvation, but don't know a
definitive test to prove starvation and the cause.

Anyone with an analysis?

duxthe1 · #2 01-30-2009, 07:13 PM

Fuel starvation is a definate possibility but I would rule out exhaust restriction before digging too deep into the fuel system. Your symptoms sound a lot like exhaust restriction and car that age could easily have the internal baffling falling apart in the muffler.

saumil · #3 01-30-2009, 07:55 PM

did you check intake vaccum ? it could be on the exhaust side, catalytic converter...

tinypanzer · #4 01-30-2009, 08:19 PM

Check the air meter plate for free operation.

Also, I agree it does sound like it could be exhaust restriction. Could also be a fuel filter.

-tp

Oracle12345 · #5 01-30-2009, 09:36 PM

Are you sure you got the right system for your car?

There were no 500Sl for the w126 chassis.

http://www.benzworld.org/modelguide.html?action=chassisguide

http://en.wikipedia.org/wiki/Mercedes-Benz_W126

If you have a 500Sl then you dont have KE K jetronic fuel injection

slk230red · #6 01-30-2009, 11:13 PM

Did you check the resistance and voltage measurements of the Air Flow Potentiometer Sensor?

wbain5280 · #7 01-31-2009, 12:16 AM

Maybe you meant 500SEL.

Make sure your fuel pumps are properly connected, it's a 500 and like my 420 should have 2 pumps in series. The screen in the bottom of the tank needs to be checked, so drain the tanl and remove the strainer. Make sure the wires are connected because on my 420 one pump was disconnected when I bought it.

There are small strainers at the fuel distributor input too so check those.

I don't have the number handy but the fuel system must deliver a certain volume of fuel during one minute. Someone should know that value.

The FPR may be bad so bridge the pins and drive the car. This will turn the pumps on all the time.

The fuel pressure regulator may be bad, so in order:

1. wires
2. volume test
3. filters/screens
4. voltage test at FPR/pumps

Does this problem happen only when driving or also when driving and parked and revving the engine.

el sea · #8 01-31-2009, 09:13 AM

This sounds like another "Ethanol Related Incident". Mechanics are seeing more and more ERI's. Spoke with eight yesterday here in the St Petersburg Florida area, all are telling the same stories. They are rebuilding carbs, replacing pumps and working overtime.

Good Luck,

Oracle12345 · #9 01-31-2009, 10:11 AM

the fuel delivery is the ability to fill a 1 liter bottle in 40 seconds

the fpr on ke jetronic is vacuum controlled.

MAGV5 · #10 02-01-2009, 03:18 PM

Duxthe1
I have considered exhaust restrictions but have moved the testing further down the list. Thanks for the input

Saumil
At idle the vacuum reading is 17.5, exhaust and converter are on the to be checked list.

Thanks of the input.

Tinypanzer
The air meter plate check ok to spec. Thanks

Slk230red
I have checked the resistance and voltage measurements and they are to spec. Thanks for the input

Wbain5280
I need to perform several of the items you have listed. The FD strainers have been checked. I need to look in more detail near the pumps. I hope my trouble may be in that area. Also need to test the pressure regulator. The “stall condition” happens parked and driving. Good input thanks.

Oracle12345
Car is 1986 500 SL. You are right it is not a w126 chassis, it is a 107. It has a Bosch injection system that contains a separate pressure regulator, an EHA, mass air potentiometer, 02 sensor and engine temp sensor. The publications I have read make this a KE system. The engine and fuel system parts are very similar or identical to the 420 of the same years 86,87,88.

Thanks for the fuel delivery spec of 1 liter bottle in 40 seconds. Do you know exactly where I should disconnect the system to make this test? The vacuum hose that is connected to my pressure regulator is run to the top of the passenger side valve cover and connected to a fitting at the top. Is this correct? Thanks of the input.

el sea

I will look into the ERI situation. I suppose I can find information on the net. Thanks.

sbourg · #11 02-01-2009, 04:22 PM

I don't know much about your engine, but looking at responses, I see no mention of testing the ignition advance curve - or at least checking vacuum/mechanical advance, if there is any.

Steve

MAGV5 · #12 02-01-2009, 05:44 PM

Steve
Ignition:
Replaced the rotor and cap (new), tested the ignition wires, replaced the coil
and EZL with units from salvage yard (symptom did not change, so I assuming they
are in good condition). Measured voltage at ignition pickup (at flywheel) with Oscope
and it checks ok (possible that at higher rpm this might still fail). The ignition
timing is correct and the advance is working. Plugs clean and gaped. If the ignition
failed when the "stall condition" occurs the 02 sensor should go rich voltage, instead
it goes to a lean voltage.

el sea · #13 02-01-2009, 09:11 PM

MAGV5,. ON

When I clean out a gas fuel tank, I pull out what looks like oatmeal from my filtration unit. On autos and pickups I am forced to remove the fuel then flush the tank serveral times until clean. On larger vehicles I can recirculate at a high velocity until the tanks are clean. The biggest difficulty today is intruducing drivers to 'Predictive Maintenance'.
This being to repeatedly check and analyzing the systems on a regular bases rather than relying on performing preventive maintenance on a pre-determined schedule. The Department of Energy has an excellent piece on Predictive Maintenance which I may be able to forward.

I test for the present of water in all tanks, if water is detected the source is determined than a corrective action is taken. Then a test for microbial contaminates is performed and depending on the resolutes a corrective action is taken for this.

As I first noted, talking to the mechanics on Friday, they are seeing a rapid degrading in the fuel and a drastic increase in common repairs. When I am called to clean a tank I am seeing a major breakdown in both diesel and gas fuels today.

Good Luck,

El Sea/LC