Euro 500SEL / Can I remove the add on K-Jetronic? - PeachParts Mercedes-Benz Forum

MJM · #1 01-15-2007, 02:20 AM

Hello,

I'm not new to Mercedes but I am new to older Mercedes, especially Euro spec. I just purchased an '85 500SEL and had some issues that were because of a faulty warm up regulator.

I'm waiting for a new warm up regulator to arrive so I can get the car on the road again. While I've been waiting I have been cleaning things / investigating. To get the car federalized they added an O2 sensor and K-Jetronic. I found the K-Jetronic control box in the passenger foot well. What I'm trying to figure out is can I remove it from the car?

I am removing the cat and trying to get this car back to the way it was in Germany, removing any remains of US tampering.

Some other things they did under the hood with fuel / vacuum lines are a bit confusing to me. I figured I'd ask the question and see if someone has been through my situation.

Attached is a picture of the box I found.

Thank you for any input.

Matthew

Hit Man X · #2 01-15-2007, 02:31 AM

I've dealt with that on Euro cars, "Johnson Box" is another one I've seen.

Just start tracing wires and removing, it should be apparent the hack job that was done and where they lead to be removed. The O2 sensor is probably a one wire jobber.

MJM · #3 01-15-2007, 02:47 AM

Hit Man X,

You hit the nail on the head with the one wire O2 sensor. The electrical side of things doesn't scare me too much, however the damn vacuum lines do. I'll have to snap some pictures.

I'm just a little gun shy and don't want to back myself into a corner.

Thanks.

Hit Man X · #4 01-15-2007, 02:51 AM

Doesn't look like vac runs through the unit, just power, ground, the associated sensors.

Take a pic, I'd be curious what has been done.

MJM · #5 01-15-2007, 03:01 AM

Hit Man X,

Could you maybe give me a brief overview of what exactly that K-Jetronic is feeding and controlling? I've read about the Jetronic system, but I haven't seen how the O2 sensor and control boxes like this fit into the system.

Thank you for the help.

Hit Man X · #6 01-15-2007, 03:11 AM

When they're hacked in, no telling honestly. One I cut out of one of the 380 wasn't even hooked up! For one of my BMWs, it was tapped into a few pins on the Motronic, used the O2 sensor, and I think that was it.

BUT what they should be doing is making the vehicle go into closed loop fueling and try to maintain 14.7:1 A/F at cruise.

Most of the US cars had the computer to drive the O2 sensor and EGR/AIR injection bits.

MJM · #7 01-15-2007, 03:16 AM

Hit Man X,

That makes more sense. Thank you for the input.

I'll take some pictures of the under hood things that I think might be issues. I'll try and draw some arrows on the pictures with vac lines I'm really unsure about.

Thanks!

Hit Man X · #8 01-15-2007, 03:19 AM

Hope it helps! If it's not factory, it's junk to me when hacked into place.

There are some Euro vac diagrams around I'm sure, just have to do some hunting.

RunningTooHot · #9 01-15-2007, 10:35 AM

You will most likely find that the add-on box also connects to what may look like an electric fuel injector that is tapped into the control pressure line to the warm-up regulator. That would be the frequency valve that is acting to bleed off pressure & regulate the mixture when in closed-loop mode (when the O2 sensor is hot enough to output some voltage signal).

Not that I'm recommending removing anything, but let's just say that that it wasn't there when your car left the factory. In fact, if it was/is malfunctioning, it may have been the cause of your warm-up regulator 'problem' - I'd try resolving that before trying your new part; may save you some $$$.

Matt L · #10 01-15-2007, 10:43 AM

The adjustment of the warm up regulator is different when the lambda feedback is used. It's set to a higher pressure (leaner mixture) and fuel is bled off by the extra valve.

MJM · #11 01-15-2007, 11:56 PM

Ellington,

I'm from Wisconsin, we're very lucky in that we have no emission testing. Very few areas in Wisconsin have testing requirements.

I figure I should enjoy it while it lasts.

MJM · #12 01-16-2007, 12:00 AM

RunningTooHot,

You are exactly correct about the wiring from the O2 sensor to the Frequency Valve after the Warm Up Regulator.

Please excuse my lack of knowledge on this topic, I'm trying to learn as much as possible but it takes time to put together the big picture from bits and pieces.

If say I were to remove the frequency valve do I just reconnect the hose without the valve? Or does the entire tap off of the Warm Up Regulator to the fuel distributor go away?

Thank you everyone for the input.

RunningTooHot · #13 01-16-2007, 12:59 AM

Quote:

Originally Posted by MJM

If say I were to remove the frequency valve do I just reconnect the hose without the valve? Or does the entire tap off of the Warm Up Regulator to the fuel distributor go away?

The line between the warm-up regulator & the fuel distributor must remain intact; that is how the control pressure is normally routed.

I would STRONGLY suggest reading up on the basic functioning of the K-jetronic system, so that you will understand how they work; it’s not as complicated as some people seem to think. Bosch published a really good book about it.

Once you understand how the warm-up regulator normally varies the control pressure on top of the central plunger in the fuel distributor, you will also ‘have a light bulb go on’ in your head as to how the frequency valve controls the mixture by bleeding off varying amounts of pressure. The factory did it using a frequency valve plumbed in with a special port on the fuel distributor; the grey-market cars usually had the control pressure line butchered to allow a bleed-off valve to alter the control pressure. Don’t ask how I know…

ALSO: Matt L (posted above) points out the correct theory – that the system is set to run lean, so that when pressure is bled off by the frequency valve, the control plunger rises & the mixture is enriched. However, it is not necessarily done by adjusting the warm-up regulator, it is normally set lean (while the frequency valve is unplugged) via the mixture adjustment screw. Remember that the lambda system is not functioning when the O2 sensor is cold, so no pressure is being bled off…

Bottom line would be to remove the non-factory garbage, and set the mixture correctly via the normal methods – then see where things are at.

OH - DON'T FORGET: The pressures in this system are high - use the right fuel hose (not the normal low-pressure hose for carburetor cars) and proper hose clamps (non-serrated bands)

Hit Man X · #14 01-16-2007, 01:35 AM

Interesting info on the wiring.

RunningTooHot · #15 01-16-2007, 08:59 AM

On second thought, you could just leave the hacked-in frequency valve in place - it will not affect the mixture if there is no power being fed into it (assuming that it does not leak internally). This way, you will not need to mess with any of the fuel line connections...