CIS K-Jet Help needed
 

Hi All,

IF anyone can help me get the R107 back running I would be very appreciative.

I bought the car knowing that the previous owner said it needs a fuel distributor rebuilt. My buddy tried,,,

So fuel distributor leaked from one of the screws that holds it together. I disassembled and reassembled the fd (following CIS fuel distributer cleanout w/pics - Page 2 - Pelican Parts Technical BBS ) and the leak is gone, but the car still doesn't run.

When I crank, she fires right up, runs about 3-5 seconds and dies. So I know that the ignition is OK and that the Cold Start valve is spitting fuel for the start.

I tired half throttle, full throttle, no dif.

I am suspecting a block fuel return (when I took the fd apart most of the small O rings were torn, so there might be a chunk of rubber blocking the return. Problem is, I don't know which is the return. Also notice the messed up blue connector. I have no idea what that thing is for, or what it doe, but I don't want to keep messing with the fuel lines if the blue connector can cause a no run situation.

Any suggestions?

The car is a 1976 450SL with 86K miles.

m:

The blue connector is to a safety switch ("rollover" switch). With it unplugged, the fuel pump should run continuously. If the safety switch is defective, the fuel pump will run only when the starter motor is cranking.

Thank you Frank,

I know that it's a purely mechanical injection, so I couldn't figure out what it could possibly be for.

There are some other controls involved. This video is for VWs, but the operation is the same. Sure helped me get a handle on how the system works....

https://youtu.be/a4fJAfXYxWk

I recommend doing a proper rebuild of the fuel distributor. You can get the parts for it here: Fuel Metering Distributor repair kit for Bosch K - Jetronic 8 Cylinder - salvox

There's a guide on benzworld's r107 subforum on how to do it. Link: http://www.benzworld.org/forums/r-c107-sl-slc-class/2205337-cis-fuel-distributor-rebuild.html

The diaphragm that rests between the heads of the distributor can go bad. The act of separating it for the cleaning most likely destroyed it.

It's very easy to do and there isn't any need to keep the ceramic hats and springs together. You just need to make sure you keep it clean.

Try that first and report back. You may have to invest in a KJET fuel pressure kit to diagnose further.

m:

Just a word of caution:
The post above by "oyab" contains two links; both of them are for the aluminum FDs, not the earlier iron version which you have. Not only are the castings of different metals, the internal components are also quite different.

Thanks Frank.

The correct part is on this page.
Mercedes 450 SL Rebuild kit to repair Bosch Fuel Distributor 0438100012 - salvox

For the sake of records, I edited the last link to direct to their homepage. Penalties of posting on a mobile phone!

OH, I failed to mention that I have a 79 450SLC (rusted out parts car) that was running. So I pulled the FD and put it in the SL. Same thing, starts runs a few seconds and dies.

When I got the car the FD was leaking. I tore it apart and it was dry. Then it started leaking. So I'm wondering if the pressure is too high.

Plans are to pull the warm up regulator and pressure regulator from the SLC and install as a pair.

Frank, after some research, I think that blue connector on the mixture controller might be control the overrun solenoid, which energizes an air bypass around the sensor plate.

I noticed that the warm up regulator has a vacuum line going to it. That line was loose, didn't seem to change much when I tightened it.

Found this site VERY helpful,,,

https://www.slideshare.net/guestceff35/bosch-k-jetronic-fuel-injection-manual

It's not for a Benz, but I've found this site very helpful with my 911:

911 CIS Primer - Index

To the extent that any air bypass is present, it will be around the throttle plate (rather than the sensor plate), and would function as an anti-backfire valve. The electrical signal for that valve would come from a switch on the throttle shaft.

the blue connector is not for what you mention. it is the fuel pump switch. it has to be plugged in to run the fuel pump. good luck, chuck.

pf:

Quite correct, thank you; as stated in post #3.

I have the same problem with my 280SL (did not run for many years) and the problem was return fuel line to tank.
For testing disconnect return line and catch fuel to the bottle and engine should run.
God luck,

I think I found my problem!!!


First off, when I got the car she didn't run, and fuel leaked out from the FD where someone had tried to r&r the fuel distributor.

So I removed and tore apart the fuel distributor, bought some permatex tacky gasket sealer, thinned it with lacquer thinner and proceeded to paint to two halves before I put it back together.

IT didn't leak! but still no start. After many cranking attempts the fd started leaking. This led me to believe that the fuel pressure was high. I checked the return to the tank, and it passed air without much effort.

So, I decided to pull the pressure regulator and warm up regulator, and mixture control and swap out. THAT's when i noticed that the warm up regulator had a second vacuum port on the bottom. At which point I immediately realized that someone had swapped vacuum lines. The one labeled atmosphere was going to the intake, and the one labeled intake was going to the atmosphere (atmosphere being the 25mm air lines)

So, as soon as the car starts, vacuum is applied to the atmosphere port of the warmup regulator, and the diaphragm is pulled to the lower stop, thereby increasing fuel pressure.

So I went to swap vacuum lines, but they are different sizes and it "Looks" like it's supposed to be that way. So I'm going to swap the two vacuum lines going to the warmup reg from the SLC to the SL.

MAybe later today.

Here's the way I got the car.

Been a long time since I messed with it, but I think the aviation Form-a-gasket was the only one that was fuel proof. Unless you used that particular sealer, the sealer probably failed and caused the leak, not excessive pressure. If it was excessive pressure there would be fuel spraying everywhere.

Thanks, but since I had a spare fuel distributor from a known good 450SLC I just swapped it, and will worry about the FD later.

I really don't think the fault is the k-jet. I'm starting to think that the only reason it has started is because the fuel pump is on during start. And doesn't stay on in "Run" So I'm gonna start by looking for the fuse and go from there.

Not sure about the vacuum going to the warmup regulator. And swapping them had no effect. So I'm confused, 1976 hooked up one way, 1979 hooked up the other possible way. Now, the 79 didn't really run all to well, so maybe I should put it back the way I found it, something my parents always told me to do. Anyone know which way it's supposed to be hooked up?

The attached schematic. When the switch is in Start position, the relay labeled A/C starter relay is energized. When this happens the fuel pump is getting 12v through the A/C starter relay (which I believe also disconnects the A/C compressor) But when the ignition switch is in "Run" position, if the fuse is blown, the car will start and stall after consuming the fuel from the cold start valve.

See post #3, again. Unplug the safety switch.

It's been unplugged. Someone messed with the wires and did a bit of sloppy splicing.

I decided to wait a day because of the cold weather and snow. I am working in a garage, but I didn't want to go out in the miserable weather.

Digging further I discovered that the brown/white wire going to the Fuel Pump relay got fried and the insulation melted off. I couldn't figure out why the brown/white wire at the baffle switch was grounded all the time.

So For a test I cut the brown/white wire by the fuel pump relay, and tried the car.

Same thing, start, runs a few seconds and dies.

Next troubleshooting step, I wired the fuel pump directly to the black/white/green wire (hot when ignition is in run) and same thing, runs a few seconds and dies. So the problem has got to be either mixture control, pressure regulator, air by-pass, or warmup regulator. It's supposed to warm up a little tomorrow, so I might swap those out.

Does the fuel pump actually run continuously when the key switch is in "run"?
If not, remove the pump relay and jumper the hot socket (87a/#2) to the pump socket (30/#3).
Once the pump is actually running continuously, then go thru the starting sequence.
It is possible that the engine is running only on the cold start injector.

Pump runs continuously.

That is exactly what I did, and got same results. Yes I agree, car is only running on cold start injector.

I pulled the mixture control unit today, as I have a replacement (along with pressure regulator and warm up regulator. I noticed some melted vacuum lines and all the rubber connections are hard and loose. So before I go any further, gonna replace all the rubber vacuum parts and the melted line. Will also inspect for other vacuum leaks since the mixture control unit is off.

Currently the fuel pump relay connection 85 has no wire going to it (Brown/white stripe) it got so hot that the insulation melted away inside the fuse box. That same wire outside the fuse box looks ok, but is very hard.

You probably realize this, but the fuel pressure regulator is not a separate device. Fuel pressure is regulated inside the fuel distributor (FD).

The pressure regulator that is connected to the warm up regulator and the FD.

Chanced up this
http://www.taunusfinland.com/tiedostot/ford/K-Jetronic/K-Jetronic-schema+troubleshoot.jpg

hard to read that jpeg, but it say for when starts and immediately dies,, fuel pump, excessive fuel delivery, warm pressure to hi/lo, or primary system pressure out of tolerance.

So by replacing the FD, mixture control unit, warm up regulator, pressure regulator, the only other parts suspect parts should be fuel pump and accumulator (and for those I gotta crawl under the car.)

But for now, I must wait to get some vacuum lines. Went to a VW dealership and he told me all their lines are custom made. Oriely's wanted $6 for about a foot of the plastic vac line, I need about 2 meters,,, so when I get to my shop, I scrounge some up.

It sure got hot in there, as a couple vacuum lines actually melted.

The fuel pressure regulator, item #5 in the schematic, is actually inside the FD.

this thing
 

whatever this thing is,,,

Is that in the line that runs from the top center of the FD to the control pressure regulator (WUR)?

If not, what is connected to it?

That last part is a fuel pressure damper.

Day late and a dollar short, but a CIS fuel pressure test gauge would have been essential in configuring the system to proper spec instead of throwing parts at the problem.

You still have to modify the air fuel metering screw after swapping out so much. Your no start may be caused by this being crazy out of whack.

Here's a trick to get you in the ballpark:

1. Remove one of the injector hardlines.
2. Jump the fuel pump to pressurize the system.
3. Look at the open injector hardline port. If gas is coming out of the top of the port, turn the metering screw counterclockwise until it just barely stops. If nothing is coming out, turn it clockwise until fuel just barely starts to come out of the hole.

Have a bunch of shop towels handy to wipe away the fuel. This will get you close enough to "running". From there, you will need to bring out the duty cycle number on pins 16 and 17 within the jetronic ECU that lives behind the passenger kick panel.

You cannot use pins 3/2 on the x11 port unless you have an oscilloscope or multimeter that filters out the PWM portion of the signal.

There is no ECU; 1976 is K-basic.

My bad, looks like a CO2 sniffer is what is required next.

TY, knew it was fuel pressure something or other.

It's been a few days since I've had time to play with the 450sl, but I started replacing rubber vacuum lines that were hard, and all the hard plastic lines started breaking,,, the I had trouble removing the warm up regulator.
After busting the nipples off one of the temperature sensors (and repairing with hard plastic vacuum line and JB weld, I'm close to the point of putting the new mixture control unit, pressure damper, and warm up regulator on the car.

Thank you. When I get everything back together, and she still doesn't start I will do that.
When I first got the car, the Fuel Distributor was leaking, seems like someone took it apart once already. After replacing that, and having the same exact issues, I decided to swap out the parts from my part car (which I know runs)


i do wish I had the Bosch equipment, but I do not. I will probably take it to a friend who has all teh necessary tools to tune up the fuel system.

How long had it been since it had run? On every old gasser I've ever resurrected I had to go through complete fuel system from tank to engine. How does the screen in the tank look?

I've had good luck purchasing good, used fuel distributors. I have not seen a FD taken apart and put back together successfully.

OK, So, I replaced the fuel distributor, mixture control unit, presure damper and warm up regulator, but still have the same problem. If I disconnect the cold start, then I get no start.

You can hear the fuel pump running in this video,,

https://youtu.be/cHdEij5X3UM

So, maybe the fuel pump isn't delivering enough fuel, or the accumulator is stuck, or the pickup screen is blocked and restricting fuel flow.

I adjusted the mixture control unit two 360 degree turns in both directions, didn't notice any change.

The above parts were pulled from a known running 450SLC 1976.

Did you try my suggestion above?

The air mixture screw is like a regular old screw. Think like a regular old wood phillips head screw. Turning it 360* in either direction won't reveal anything if the screw has to be turned 440* clockwise to get it into spec.

Another trick you can try if you don't want to go through all that is have a helper try to start the car while you push down on the air horn in front of the distributor. If the car tries and stumbles and runs a bit longer after cranking, you're running rich and need to keep turning the scew counterclockwise in MINOR increments while a helper cranks.

If it dies instantly then turn it clockwise in increments until it runs.

I have no idea how long she sat. But the PO had taken her to a mechanic who had tried getting it running. New ignition coil, plugs, wires,,, I'm thinking he replaced the fuel filter and maybe pump.

The mixture screw I am aware of is I think 4mm hex

Since the FD works on the other car, you can pretty well rule it out. I'd be looking at fuel pressure at this point to find out what's going on. Just because the pump is running doesn't mean it's any good!

M:

As Diseasel has pointed out, if the parts which you have taken from another car were working there, they are unlikely to be part of your problem.
You might also exchange the nozzles; the original ones may very well be completely plugged. Also, loosen the injection lines at the nozzles, run the fuel pump, and press down on the air flow sensor plate. There should be fuel flow from the lines at each nozzle.