Do fuel distributors just stop working???

Stuck fuel metering plunger in the distributor would be my guess.

 

You need more than fuel pressure being present at the inlet to the fuel distributor -- you also need a pressure difference between the upper chambers and the lower chambers of the fuel distributor. Things I would do (after getting that fuel line fixed/replaced) -- not running the engine, just running the fuel pump by jumping 30-to-87 in the fuel pump relay socket:

1. Confirm the system regulated supply pressure is ~5.4 bar when the fuel pump is running -- measured where the cold start injector line connects to the KE-Jet fuel distributor (you can just remove the line going to the cold start injector and attach the pressure gauge there). If OK:

2. Measure the amount of fuel flowing in the small return line going from the fuel distributor back to the pressure regulator (i.e., the line connected to port 5 of the fuel pressure regulator as shown in Fig 56 on page D78 of the TR WSM). This should be about 130~150 mL per minute if the small fixed orifice at the end of the lower chambers (#10 in Fig 54 on page D75) is not blocked. If that orifice is blocked (and the flow is zero or near zero), the lower chamber pressure will not be lower than the upper chamber pressure = diff pressure valves closed = no fuel flow to injectors. The thing here is that when you remove the small line from port 5 to put in a jar to collect the fuel in 1 minute, you need to block port 5 -- I use a 17/64" metal ball and a brass 1/8" NPT pipe cap that I've drilled and retapped to M10 x 1P. If that lower chamber orifice is blocked, you can try blowing back up the small line (when not running the fuel pump) to try to dislodge any debris out of the orifice, but no guarantee that it won't block the orifice again.

Those are the relatively easy diagnostic things that I'd recommend you confirm/deny before going deeper -- Good Hunting!

 

Hey Joe,

the brass nut on your picture -which the fuel line connects to- contains a small filter element. This almost always contains dirt and can get clogged. Easy to clean. Cheap to replace. Your local Mercedes dealer has them available for a few $$ (part no A 000 074 60 86).

You may also apply ample amounts of throttle cleaner several times in all areas under the plate (move the plate manually). Try this also with the engine running.

If Steve's (excellent as always!!) analysis process results in stuck valves, then you can try to pressure wash from inside using throttle/carburettor cleaner instead of fuel. Simply connect it instead of the fuel line. That's cheaper than having it rebuild....

Have fun hunting!

 

Did you mis-type? 4.5 bar is low.

Certainly a good sign for the fuel distributor that you had that flow coming out of the small port 5 line into the jar. You can always check to see if the fuel return line from port 8 of the pressure regulator going back to the tank is blocked (it shouldn't be). If the pressure regulator has failed in the closed state (or the line from port 8 back to the tank was blocked), that would block flow in the small port 5 line, too, but that should show too much pressure at the cold start injector port of the fuel distributor (not the 4.5 bar you report). You can always put everything back, and see if you still have the trouble -- sometimes an issue caused by debris moving around might come and go. If still bad with everything assembled, but the engine runs fine when the port 5 line is vented into the jar = certainly justifies further investigation of the fuel pressure regulator function and its lines (you might have something blocking port 5 on the fuel distributor).

 

Those results make me think that you pressure gauge is just not accurate -- like measuring about 0.9 bar low. When you turn off the pump, the fuel pressure should immediately fall to something like 2.8~3 bar -- a pressure lower than the opening pressure of the injectors, but high enough to keep the (hot) liquid fuel from vaporizing. Your measurement of 4.5 bar might actually be closer to 5.4 bar.

Yes, that's the KE-Jet fuel pressure regulator (they got "smarter", and made it a separate unit rather than integrating it into the fuel distributor like on K-Jet). No warm-up regulator on KE-Jet.

 

Steve M, I wanted to let you know that your post # 3 above was extremely beneficial in my recent case. Upon bringing back to life my '86 Testarossa after an extended engine out service and restoration, she started right up, but I found my 7-12 bank did not appear to be running on idle. After disconnection of the small black plastic fuel return banjo fitting on the 7-12 fuel distributor (and main fuel line), I used a little carb cleaner into a clear vinyl hose in the open port to hopefully soak the orifice IF IN FACT IT WAS PLUGGED. There did not appear to be much backflow into the port that I wanted, but upon reconnection of the hoses and restart, the 7-12 bank now runs as normal. Steve, your knowledge saved me time here as usual so THANKS! EDoug.

 

Glad to hear that it helped you. The Achilles Heel of these Bosch CIS systems is just way too many very small clearances and small orifices that don't tolerate debris at all (so disuse is a killer) -- I believe that that particular orifice is something like only .008" or .010" in diameter. Larry Fletcher at CISFlowTech.com gets the credit for giving me that spec for the (correct) fuel flow in the small KE-Jet return line. I've never seen that specification appear in any F or Bosch documentation, and it's absolutely critical for proper KE-Jet operation as fuel has to be able to exit the Lower Chambers to create the Upper-Lower pressure difference to eventually get fuel to flow thru the FD slits.

 

Thank you Steve. To let you know, I had the TR down for a long time. After reinstalling the engine, and getting to fuel delivery, I found that both fuel pumps did not run. Jumped them directly off a battery and nothing. Removed both and put a little TechRon into the suctions. Shook it around followed by light taps on the lower case of each with a soft rubber mallet. They both ran fine after that as each wanted to violently suck my finger into the suction, so all good. Because of this, I was expecting more blockages elsewhere, but only this so far. I think that BG-44 in the fuel tanks will address anything else fuel wise. EDoug

PS, as a side note, I see that there is other FChat dialog now going on with a BBi that is running on only one bank, but is focused on the distributor/spark. I am not a Boxer guy, but as that car was not run for a long time the same as mine, have they dismissed this fuel return orifice plugging as the possible cause?