CIS fuel distrib. individual fuel line adjustment HELP..Fixed?
05-22-2011, 07:59 AM
#61
Rennlist Member
Thread Starter
The injector pressure is NOT the system pressure minus the control pressure; it is about 0.1 bar below system pressure. The only relevance of the injector opening pressure is that it has to be below this pressure. The fuel distributor is designed to keep this pressure drop (the 0.1 bar) constant, regardless of the deflection of the control plunger, which meters the flow rate of fuel to the injectors.
You are messing about unproductively until you correct the system pressure. I call the K-Jetronic a hydraulic fuel injection system, rather than mechanical. It requires a known fuel flow rate (delivered by the fuel pump) at within-tolerance system pressure (as controlled by the system pressure regulator in the fuel distributor) to produce the correct pressures and flow rates within the system.
The cold control pressure will vary with ambient temperature (logically, more enrichment will be required when the ambient temp is lower, so the cold control pressure had to be lower, allowing the control plunger to rise higher and deliver a higher flow rate). At what temperature did you measure your control pressure? Your cold control pressure is at the upper limit (19 psi = 1.3 bar; spec is 1.1+/-0.2 bar or 16.0 +/- 2.9psi) at an ambient temperature of 20 degrees C (68 deg F) and without vacuum. The warm control pressure (44psi = 3.0 bar) is on spec (3.0+/-0.2 bar = 43.5+/-2.9psi without vacuum).
The lower than spec system pressure, with correct control pressures, will produce a lower flow rate to the injectors ie your engine will be tending to run lean (hence the backfire through the intake when you open the throttle).
Surely there must be a fuel injection specialist somewhere who will have a variety of shims for the system pressure regulator. They are just little washers, after all. You should use the proper Bosch ones as a Walmart special may corrode in gasoline. Porsche, Mercedes, BMW, Volvo and Saab used K-Jetronic from about 1974 to 1984, so parts should not be that hard to get.
You are messing about unproductively until you correct the system pressure. I call the K-Jetronic a hydraulic fuel injection system, rather than mechanical. It requires a known fuel flow rate (delivered by the fuel pump) at within-tolerance system pressure (as controlled by the system pressure regulator in the fuel distributor) to produce the correct pressures and flow rates within the system.
The cold control pressure will vary with ambient temperature (logically, more enrichment will be required when the ambient temp is lower, so the cold control pressure had to be lower, allowing the control plunger to rise higher and deliver a higher flow rate). At what temperature did you measure your control pressure? Your cold control pressure is at the upper limit (19 psi = 1.3 bar; spec is 1.1+/-0.2 bar or 16.0 +/- 2.9psi) at an ambient temperature of 20 degrees C (68 deg F) and without vacuum. The warm control pressure (44psi = 3.0 bar) is on spec (3.0+/-0.2 bar = 43.5+/-2.9psi without vacuum).
The lower than spec system pressure, with correct control pressures, will produce a lower flow rate to the injectors ie your engine will be tending to run lean (hence the backfire through the intake when you open the throttle).
Surely there must be a fuel injection specialist somewhere who will have a variety of shims for the system pressure regulator. They are just little washers, after all. You should use the proper Bosch ones as a Walmart special may corrode in gasoline. Porsche, Mercedes, BMW, Volvo and Saab used K-Jetronic from about 1974 to 1984, so parts should not be that hard to get.
05-22-2011, 12:51 PM
#62
The injector pressure is NOT the system pressure minus the control pressure; it is about 0.1 bar below system pressure. The only relevance of the injector opening pressure is that it has to be below this pressure. The fuel distributor is designed to keep this pressure drop (the 0.1 bar) constant, regardless of the deflection of the control plunger, which meters the flow rate of fuel to the injectors.
If you are going to quote what I say, please include the whole statement. My statement was "The injector pressure should be equal to the system pressure, minus the control pressure, as adjusted by the position of the air sensor plate."
The point I was trying to make was that if control pressure is too high or system pressure too low, the piston will not meter enough fuel to the injectors. Yes simple hydraulics.
Have a good day.
Dennis
05-23-2011, 01:29 PM
#63
Developer
That's a Mercedes-Benz fuel distributor. It will work fine on your 928.
The little Allen screws underneath the caps are needle-and-seat valves. Turning in will reduce the amount of fuel going to that pot, and also raise the pressure going into the other pots (a double-edged sword). Backing the needles out increases the flow to this pot, and lowers the pressure to the other pots. Be careful!
This "port flow balancing" is normally done on a bench by a tech, where the process can be controlled with a common and known fuel supply input. Its hard to do right on a car, but it can be done.
The little Allen screws underneath the caps are needle-and-seat valves. Turning in will reduce the amount of fuel going to that pot, and also raise the pressure going into the other pots (a double-edged sword). Backing the needles out increases the flow to this pot, and lowers the pressure to the other pots. Be careful!
This "port flow balancing" is normally done on a bench by a tech, where the process can be controlled with a common and known fuel supply input. Its hard to do right on a car, but it can be done.
05-23-2011, 01:50 PM
#64
Rennlist Member
Thread Starter
That's a Mercedes-Benz fuel distributor. It will work fine on your 928.
The little Allen screws underneath the caps are needle-and-seat valves. Turning in will reduce the amount of fuel going to that pot, and also raise the pressure going into the other pots (a double-edged sword). Backing the needles out increases the flow to this pot, and lowers the pressure to the other pots. Be careful!
This "port flow balancing" is normally done on a bench by a tech, where the process can be controlled with a common and known fuel supply input. Its hard to do right on a car, but it can be done.
The little Allen screws underneath the caps are needle-and-seat valves. Turning in will reduce the amount of fuel going to that pot, and also raise the pressure going into the other pots (a double-edged sword). Backing the needles out increases the flow to this pot, and lowers the pressure to the other pots. Be careful!
This "port flow balancing" is normally done on a bench by a tech, where the process can be controlled with a common and known fuel supply input. Its hard to do right on a car, but it can be done.
I thought that CW increased the flow through that port and CCW reduced it but what you are saying is reverese of that. Correct? Gunar
05-23-2011, 01:55 PM
#65
Rennlist Member
Thread Starter
How she ran today with a low control pressure WUR I have and A/F adjusted so rich it barely starts.http://www.youtube.com/watch?v=D68EY...etailpage#t=6s
05-23-2011, 06:53 PM
#66
finally getting there,did you check the strobe timing i mentioned before?also it seems to me your centrifugal and or vac advance may be seized/not working, causing you not to be able to accelerate.both of these could be checked with the strobe gun!it sounds like its on all cylinders now?
05-23-2011, 08:19 PM
#67
Rennlist Member
"I thought that CW increased the flow through that port and CCW reduced it but what you are saying is reverese of that. Correct? Gunar "
I read what he said as being -- adjusting any of the screws affects them ALL to some degree - the more you open one port, the less there is for the others, and vice versa. Think of it as a garden sprinkler with 8 outlets - block one, the other 7 get more; open one up, the less all the others get. Once you play with one, ALL will need some adjustment.
jp 83 Euro S AT 53k
I read what he said as being -- adjusting any of the screws affects them ALL to some degree - the more you open one port, the less there is for the others, and vice versa. Think of it as a garden sprinkler with 8 outlets - block one, the other 7 get more; open one up, the less all the others get. Once you play with one, ALL will need some adjustment.
jp 83 Euro S AT 53k
05-23-2011, 08:47 PM
#68
Rennlist Member
Thread Starter
"I thought that CW increased the flow through that port and CCW reduced it but what you are saying is reverese of that. Correct? Gunar "
I read what he said as being -- adjusting any of the screws affects them ALL to some degree - the more you open one port, the less there is for the others, and vice versa. Think of it as a garden sprinkler with 8 outlets - block one, the other 7 get more; open one up, the less all the others get. Once you play with one, ALL will need some adjustment.
jp 83 Euro S AT 53k
I read what he said as being -- adjusting any of the screws affects them ALL to some degree - the more you open one port, the less there is for the others, and vice versa. Think of it as a garden sprinkler with 8 outlets - block one, the other 7 get more; open one up, the less all the others get. Once you play with one, ALL will need some adjustment.
jp 83 Euro S AT 53k
05-23-2011, 08:53 PM
#69
Rennlist Member
Thread Starter
finally getting there,did you check the strobe timing i mentioned before?also it seems to me your centrifugal and or vac advance may be seized/not working, causing you not to be able to accelerate.both of these could be checked with the strobe gun!it sounds like its on all cylinders now?
for the car to get the plate down far enough to counter control. I have balanced the flow to each injector on my Mercedes(individual fuel line adjustable) fuel distributor. This fixed the cylinders that were missing and had clean plugs. I pulled the injectors and but little Gatorade bottles underneath them to measure volume and watch the spray pattern. I replaced ones that looked bad with some of my extra injectors. Once the flow was even and good spray patterns I was satisfied and put it back together. I now have a problem with low system pressure(68 psi). I know I have the correct new fuel pump in so I am going to try to get it up to at least 78 psi by replacing the FD pressure regulator valve , the right size new o-rings and add shims to increase the system pressure. I am compensating as much as I can for that now by using an experimental WUR I have that the cold and warm control pressure stays around 26 psi which is low therefore making the mix rich by applying less counter pressure on the top of the fuel distrib. piston which allows the air meter plate to go down further and push the FD piston up more and allow more fuel to injectors. I have also set the idle up and when I set the A/F mix way rich it brings the idle back down. Doing this A/F and idle adjustment just barely allows the car to start. I have to pump the accelerator pedal a little when it catches to get it started. This setup results in a rich idle/low rpm mix but at higher rpm I don't have enough fuel pressure so it runs lean then. By the way I may be wrong on all this but this is my most educated setup/guess. Gunar
05-23-2011, 09:21 PM
#71
Rennlist Member
This has been one of the most engaging saves by a new owner I've ever followed.
Good work.
Gotta be satisfying to hear that engine, which you built from parts, running that well.
Good work.
Gotta be satisfying to hear that engine, which you built from parts, running that well.
05-24-2011, 04:16 AM
#72
i may be wrong but i dont think your current running issue is fuel pressure.if you can manually rev the engine by the plate and the trottle flap what you are compensating for is air pressure at the plate.nothing to do with fuel.i think you have a torn rubber connecting hose on the intake losing vac.dont think the engine would run as good as it is now, ie up to 3k rpms with the wrong fuel pressure.
Last edited by dogleg; 05-28-2011 at 11:03 AM.
05-28-2011, 07:02 AM
#73
havent read back through your tread but had you replaced all vac and intake rubbers hoses.i have recently done all of mine and cant tell you how much it helps on start up and running in general.
05-28-2011, 07:31 AM
#74
Rennlist Member
Thread Starter
Yes I did. I put a new FUEL DISTRIBUTOR VALVE KIT in and got the system pressure up from 68 to 79 psi using the shims but I am still having stumble on acceleration problems. Gunar
05-28-2011, 07:50 AM
#75
not sure were on the same page, i think your talking about the fuel delivery side of the system.im talking the air side of the equation.