CIS Air flow sensor calibrations/questions

[47silver]

I read the 42 page bosch tech manual on the K-jetronic CIS and it indicates that a "leaf spring ensures the correct zero position in the switched off stage".

Should the air flow sensor plate rest on this leaf spring? My fuel injectors spray a fine mist when the fuel pump is operating, and the engine is not running but at rest the pate does not rest on the leaf spring. I can pull the plate down but it immediately returns. It does not seem to be the plate itself pushing it back it seems like it is due to either the mixture screw or the fuel piston. I suppose that this is the reason my injectors are operating.

Is there an adjustment to make sure that the sensor plate rests on the leaf spring?
could it be caused by the wur when cold?

[boyt911sc]

Originally Posted by 47silver

I read the 42 page bosch tech manual on the K-jetronic CIS and it indicates that a "leaf spring ensures the correct zero position in the switched off stage".

Should the air flow sensor plate rest on this leaf spring? My fuel injectors spray a fine mist when the fuel pump is operating, and the engine is not running but at rest the pate does not rest on the leaf spring. I can pull the plate down but it immediately returns. It does not seem to be the plate itself pushing it back it seems like it is due to either the mixture screw or the fuel piston. I suppose that this is the reason my injectors are operating.

Is there an adjustment to make sure that the sensor plate rests on the leaf spring?
could it be caused by the wur when cold?

Gary,

Your six (6) fuel injectors should not be spraying fuel until AFS plate moves up. First, inspect the position of the AFS at rest (FP off). The perimeter of the air plate should line up with the narrowest section of the coned-shaped venturi. When you push the air plate up, the resistance should be uniform throughout the range of travel (upwards). Remove your finger and the air plate should drop down quickly and settle back to its original rest position (and properly aligned). Otherwise, there is some resistance or restriction causing it to stop to its mis-aligned position. The air plate should rest on the spring-loaded stop. Adjust it accordingly to get proper aligment at rest.



In your case, I would inspect the air flow sensor plate alignment by re-setting the spring-loaded top. Once you obtained the correct alignment, run the FP.
a). There should be no fuel leaking or spraying at this point. If you observe any fuel delivery, the plunger has been moved up or stucked.
b). Observe for leaking injector/s with the FP running. A good injector should not drip or leak fuel before fuel is injected by the FD.
c). The spray mist pattern should be fine and uniform.
d). The flow rate of the injectors should be almost the same with acceptable variance from individual flow rates.

So this could be the reason why you're having fuel in your cylinders during your early tests. BTW, what year is your car? Pre-'76 or later? Keep us posted.

Tony

[47silver]

tony:
i adjusted the round air flow sensor plate by using rolling paper as a gage.

it moves freely and is at the bottom stop when i raise it and let it go. I have to say it moves perfectly.

However when i run the fuel pump the plate lifts slightly on its own and the injectors begin to operate with a very fine mist not dripping. how is this possible?

Does the cold pressure from the wur cause it to open?

I also tested all of the injectors, volume is equal and the spray patters are great. Also when i pull down on the flow sensor to the stop the injectors stop flowing and do not drip.
My main concern is that the car seems runs rough, i installed 2 new sets of plugs, rotor, cap, re-adjusted the valves and new spark plug wires but when i start it feels like a bad plug.
I want to get the air flow sensor set up before i go any further...
any help is appreciated.
gary

[MatthewBrum]

The fuel pump is not supposed to go on until the AFS plate moves. By turning on the fuel pump on without first lifting the AFS plate may cause the plinger in the fuel distributor to move if you do not have enough control pressure. But the actual AFS plate should not move by just turning on the pump because the linkage only acts in one direction. What I mean by this is that the AFS plate pushes up on the plungerd in the fuel dist. but if the plunger in the fuel dist. gets pulled up it should not pull up the AFS sesnsor with it.

The first thing to do with CIS is to measure your cold CP, hot CP, and fuel pressure before you start adjusting stuff.

[boyt911sc]

Originally Posted by 47silver

tony:
i adjusted the round air flow sensor plate by using rolling paper as a gage.

it moves freely and is at the bottom stop when i raise it and let it go. I have to say it moves perfectly.

However when i run the fuel pump the plate lifts slightly on its own and the injectors begin to operate with a very fine mist not dripping. how is this possible?

Does the cold pressure from the wur cause it to open?

I want to get the air flow sensor set up before i go any further...
any help is appreciated.
gary

Gary,

I can not imagine how the air flow sensor plate could move up when fuel is delivered to the fuel distributor. For the sake of discussion, let say that the fuel pressure inside the FD somehow causes the plunger to move up and causing the injectors to spray. The AFS should remain as is because the lever is not connected to the plunger. Remember that the plunger is resting on the mixture lever and if you physically pull the plunger up, the AFS should stay as is unless there's some physical adhesion presence between their surfaces.

Theoretically speaking, if the internal fuel pressures could cause the plunger to move, it would be going down instead of up because of the control pressure on top of the plunger. Could you do another test for me?

Place an extra weight (like a socket wrench) on the plate to keep the AFS in place and run the FP. This test will isolate the AFS from the plunger. Observe the injectors. I have a suspicion that the plunger does not fully slide down at rest. Keep us posted. Thanks.

Tony

[47silver]

Thank you for the advice, but my 1975 does not have an interlock with the fuel distributor the fuel pump starts when the key is in the on position. I think all 75's are like mine. The 75 FD's do not have any electrical connections.

And the reason that I have to make adjustments is that I had to replace the air box, etc. so had to remove the fd and so on and in the process believe i altered the sensor plate position, and during restart the cold start valve would not work and so the saga began.

luckily I found instructions in Haynes that explains how to set up the air sensor and adjust initial output to the fuel injectors.
The air sensor was out of calibration it would not fall to the leaf spring. I adjusted it by placing cigarette rolling papers on the outer edge and that is the amount of space required. it works very smoothly now.

Haynes said to adjust the idle mixture allen screw until the injectors barely work when the fuel pump operates and then back off 1/2 turn. That gives the initial setp

The engine starts and runs need to set mixture tomorrow.

The miss on my car was caused by a spark plug that was not getting a good ground. I tightened to 21 ft # and it works now on all 6 cylinders.

[boyt911sc]

Originally Posted by MatthewBrum

The fuel pump is not supposed to go on until the AFS plate moves. By turning on the fuel pump on without first lifting the AFS plate may cause the plinger in the fuel distributor to move if you do not have enough control pressure. But the actual AFS plate should not move by just turning on the pump because the linkage only acts in one direction. What I mean by this is that the AFS plate pushes up on the plungerd in the fuel dist. but if the plunger in the fuel dist. gets pulled up it should not pull up the AFS sesnsor with it.

The first thing to do with CIS is to measure your cold CP, hot CP, and fuel pressure before you start adjusting stuff.

Mathew,

The '74-'75 CIS (911) have a different electrical configuration with those of the '76-'77, '78-'79, and '80-'83 CIS cars. For these early cars (CIS), the FP will start to run as you turn the ignition SW to RUN position. I did a couple of test today and found out that as long as the plunger of the FD is fully down at rest, it is not possible to inject fuel to the injectors. One possibility that it could inject fuel at rest is that the plunger is 'set too high or hanging' at rest. Or the AFS is not correctly aligned.

Gary,

Have you fixed the pre-mature fuel injection during FP test? This could be just proper setting of the AFS to prevent it from happening. You did not mention if the problem was corrected. Keep us posted.

Tony

[47silver]

1. I adjusted the round air flow sensor to move freely and rest on the leaf spring when the sensor is at rest.
when i ran the fuel pump the sensor would raise, I dont know how but it did, when i physically pulled down on the sensor it would again rest on the leaf spring.

After reading how to set the initial injector setting, turn the idle mixture ccw to lean, then adjust cw until the fuel injectors barely mist, then turn the idle mixture screw 1/2 turn ccw.
When i did this the sensor plate was at rest and the injectors did not spray.

I did not have time to test anything today so i will check pressures etc tomorrow.

[Paulporsche]

Is the sensor plate resting @ this position?

[boyt911sc]

Originally Posted by 47silver

1. I adjusted the round air flow sensor to move freely and rest on the leaf spring when the sensor is at rest.
when i ran the fuel pump the sensor would raise, I dont know how but it did, when i physically pulled down on the sensor it would again rest on the leaf spring.

After reading how to set the initial injector setting, turn the idle mixture ccw to lean, then adjust cw until the fuel injectors barely mist, then turn the idle mixture screw 1/2 turn ccw.
When i did this the sensor plate was at rest and the injectors did not spray.

I did not have time to test anything today so i will check pressures etc tomorrow.

Gary,

That's was my suspicion that the mixture screw was set too RICH at the beginning. When your old air-box was leaking, the mixture screw was turned CW to compensate for the unmetered air. The mixture adjustment was over-done that caused the injectors to spring mist once you turn the ignition switch ON. I expect to see the car running now and a very well executed troubleshooting.

Please let me know how the new air-box work in the car and keep us posted.

Tony

[47silver]

Yes the sensor is in the position indicated in the diagram.

I'll connect the pressure gauges today and see what i have.

the car does start and run but i know the timing is not spec and the mixture needs set. It is raining so i wont be able to fire it up to do these adjustments.

[47silver]

this ended up in the intake manifold on #4 cylinder.

[T77911S]

nice bag, did someone forget to take it out

i have thought about this and i just dont see how the AFM plate could rise if the engine is off and the FP is on.

here is the ONLY thing i can come up with and it is off the wall, especially if the engine runs.
if th CP is zero, the FP in the chambers could maybe push the plunger up, and IF the plunger is stuck, rusted, or grease has created enough stickum to pull the plate up and cows fly south for the winter, what you are describing could happen. if you did put grease on the roller bearing, that could be enough to lift the plate since it is balanced, but, the plunger would still have to go up, and the plunger just will not do that if you have CP on top, unless there is something physically wrong inside the FD, like perhaps it was taken apart, but even then, i still dont see it happening.

the plunger rides on a roller bearing so it has no solid connection to the AFM plate other than it rests on it. one of the big problems with CIS is when cars sit the plunger will get stuck up inside the FD, but the plate will still fall to its resting position because there is no connection between the 2. even if a plunger gets stuck, the plate will not move unless air is going into the engine.

[47silver]

I really dont know where the bag came from,, i think it fell into the air box before i installed it. I was dumb and did not look into it at all.....I used paper towels to plug the intakes when i had the runners off (to make sure i would see them) so I am thinking it was in the box when i installed it.

On the air plate rising, it does not do it any more, I noticed a slight kink in the warmup regulator line that connects to the return? supply? and straightened that out and have a new line to replace it...perhaps this caused the plunger to move and put force on the sensor arm? It has not happened since I removed the plastic bag and straightened the kink (found when i removed all the intake runners the second time but i may have kinked it when i removed them the second time...

the engine runs better than it has ever run for me.

i did notice that my warmup regulator has a vacuum connection and that the throttle position valve was removed. this does not match the drawing on pelican. Also the warmup regulator is connected to the fd and to the return? supply? with a 3mm id hose via a barbed fitting. The fitting is not the 4 way double tee it is only a tee fitting. I believe that when the engine was rebuilt in 1998 that the mechanic re-piped this system. Farmer auto in indiana did the work on the engine, carrera exhaust, oil tensioners, time certs, new head studs, machining etc. so they knew what they were doing.

[porschedude996]

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