CIS air censor oscillation.

[allaircooled]

So I pulled my engine to seal up some oil leaks and repair any vacuum leaks. I replaced all the vacuum lines, seals and hoses. I performed a smoke test with about 3 psi of air pressure and I have no vacuum leaks now. Engine is a 77 and I have been trying to tune it for the past week or two. I think I have it pretty close with no exhaust analyzer by using a method I have found here and on the internet. The problem is the air sensor plate arm oscillates rapidly causing the engine to surge. If I lift up on the air sensor arm very slightly I can get the arm to stop oscillating, even after I let it go. The engine will then idle smoothly and everything seems fine...Until I give it some throttle and it will start oscillating again. I can do this over and over again. I took a video and I think you can see and hear the oscillation taking place.

Any ideas? I thought the sensor plate height might need adjusting but it looks close to where it should be according to the Porsche factory manuals.

Video of oscillating sensor arm.

[gazzerr]

That's very strange. Normally there is quite a bit of opposing force acting on the sensor plate arm because of the fuel pressure in the fuel distributor. Is the sensor plate and the assembly it sits on properly attached and all the parts are there? Looks like something is really loose and or missing.

Perhaps the arm pivot where it attaches to the fuel distributor's plunger is worn and loose. Does it wobble around at all when the engine is off and there is no vacuum?

[allaircooled]

No it doesn't wobble around when the engine is off. Moves up and down smoothly. I don't feel any play or feel that anything is off. Hmmm.... one other thing I have noticed and I haven't really got to yet but maybe related. When I try to check fuel pressures, everything is good, 5.2 bar for system, 1.8 bar at 21*c for cold. But when I start the engine and check for warm pressure, the gauge gets to about 3 bar and the engine doesn't want to run at all. Remove the gauge and put the stock fuel line back on, it will run fine. (Except for the problem above of course.)

[john walker's workshop]

Bad fuel distributor.

[gazzerr]

Can it be so loose that the plunger rattles around inside the fuel distributor?

[T77911S]

try leaning it out. if it still runs bad its the FD like JW said.
you can send it off and have it rebuilt.
flowcontrol

[KyMitch]

I noticed on my SC, the plunger moves up and down easily with the fuel pump off. And theres a significant amount of pressure on the plunger when the pump is running. I wanted to question it, thinking it was to stiff, that the engine vacuum wouldn't operate it, till I started it and drove it, runs great, so it should be pretty stiff I suppose.

[T77911S]

that's the way it Is suppose to be.

it should very freely with the pump off, lots of resistance with pump on.
note, with the pump on, if you feel that free play before the resistance then the plunger is not dropping all the way down to its resting point. just a note.

[gazzerr]

Yep it takes a few hours for the residual pressure to bleed off and then the plunger will move up and down freely.

[boyt911sc]

Originally Posted by gazzerr

Yep it takes a few hours for the residual pressure to bleed off and then the plunger will move up and down freely.

After the FP stopped, the plunger would still have control fuel pressure thus a heavy resistance. Gradually the residual fuel pressure drops to zero after a few hours. Then the resistance is gone and you could lightly push the plunger up.

Tony

[allaircooled]

I will take a closer look at that when I get back home from the holiday. Thanks for all your help.

[allaircooled]

Originally Posted by T77911S

that's the way it Is suppose to be.

it should very freely with the pump off, lots of resistance with pump on.
note, with the pump on, if you feel that free play before the resistance then the plunger is not dropping all the way down to its resting point. just a note.

I have been driving all day but thought about this and wanted to mention. With fuel pump on and engine off, if I lift the sensor plate, you can hear the injectors squeal instantly as I lift. No free play.

When I get back home I will do some tests for the heck of it but Mr. walker is probably right.

[T77911S]

that's the way it should be.

if it keeps moving up and down, have the FD rebuilt

[boyt911sc]

Chris,

I received the package containing the FD, WUR, and 6 injectors last Saturday (May 20) and was able to work on the WUR on Tuesday of this week. The WCP (without vacuum) is good and within spec. except when you apply vacuum. The fuel pressure was way too high with vacuum. It needed adjustment and I was surprised you did not observed this problem. Anyway, it has been tested and re-calibrated.

Next, the FD was tested too. There is no problem with his unit. All six (6) ports are good and no drips. I ran the FD without any injectors installed to observe any premature fuel delivery. Dry and no fuel drips during test.

Then installed the six (6) injectors that you have labeled. Only two (2) injectors namely #2 & #4 have good spray patterns. The other 4 injectors have jet-like spray patterns and not the ideal spray pattern you want to have. These fuel injectors will not cause you the problem you are having.

Lastly, the flow rates for individual ports were measured using graduated cylinders. The average flow (3 runs) for each ports were very close and comparable. I will pack them tonight and have it ready for shipment. The service is FREE but you have to take care of the shipping cost back to you. If you could send $20 to cover the postage and insurance fee would be much appreciated.

I could have told you that the FD is bad and needs some work like others have suggested. And make some money from you. CIS troubleshooting is one of my passions and would not sacrifice the integrity of my work. Keep us posted.

Tony

[allaircooled]

Just saw your reply Tony. I am surprised that you found my WUR was out of wack. I have numbers written down somewhere when I did cold and warm control tests and I thought they were good. WUR is one I purchased from you and it only has a few hours of run time. Anyways, car is idleing now. I need to adjust CO to make sure it's correct. I checked for vacuum leaks again but have none. I do have a gunson co meter, and working on understanding these directions. I will update in awhile.

[allaircooled]

Ok so I drove around the neighborhood to warm up my car, seemed to drive ok. Hooked up my gunson meter according to the directions, got a reading of .4. I increased to 2.0 but any richer and she won't idle. I can leave it at 1.5-2.0 but I still have the oscillating sensor plate which increases idle about 400 rpms, until I stop the plate from oscillating. Then it drops back down to my idle setting which was around 980 rpm. If I have an air leak, I am sure having a hard time finding it. I'm using a smoke machine with pressure at about 3 psi and at the same time using soap to see bubbles. I can't find anything.

[fanaudical]

I've read through this and have a couple of questions/suggestions/longshots:

- Which WUR do you have installed?

- Do you have the anti-backfire valve installed? If so, try temporarily disconnecting/plugging the vacuum line to that and see if things improve at idle.

It probably is time to get the FD checked...

[allaircooled]

Originally Posted by fanaudical

I've read through this and have a couple of questions/suggestions/longshots:

- Which WUR do you have installed?

- Do you have the anti-backfire valve installed? If so, try temporarily disconnecting/plugging the vacuum line to that and see if things improve at idle.

It probably is time to get the FD checked...

WUR is a 033, I will post a photo. Not sure what you mean by the anti-backfire valve.
Thanks for the reply.

[fanaudical]

Sorry - I meant "vacuum operated deceleration valve" in Porsche-speak (that would be the item mounted to the throttle body in this picture):

Sorry - Yet another CIS troubleshooting thread...

(I accidentally called it by it's old Audi CIS name.)

The reason I bring this up is that the decel valve does sometimes act like a vacuum leak if faulty or just on the edge of triggering. I had a similar situation (bobbling sensor plate and erratic idle) on an old Audi and the reason turned out to be the decel valve being out of adjustment. Minor adjustment changed the idle behavior. This is a complete longshot and very unlikely, but thought I'd mention it.

For what it's worth, an 033 WUR seems odd to me to be on a '75. Stock engine and CIS? (My '75 has an 009 WUR). It might be useful to get an idea of all the CIS components on your engine.

[allaircooled]

Originally Posted by fanaudical

Sorry - I meant "vacuum operated deceleration valve" in Porsche-speak (that would be the item mounted to the throttle body in this picture):

Sorry - Yet another CIS troubleshooting thread...

(I accidentally called it by it's old Audi CIS name.)

The reason I bring this up is that the decel valve does sometimes act like a vacuum leak if faulty or just on the edge of triggering. I had a similar situation (bobbling sensor plate and erratic idle) on an old Audi and the reason turned out to be the decel valve being out of adjustment. Minor adjustment changed the idle behavior. This is a complete longshot and very unlikely, but thought I'd mention it.

For what it's worth, an 033 WUR seems odd to me to be on a '75. Stock engine and CIS? (My '75 has an 009 WUR). It might be useful to get an idea of all the CIS components on your engine.

I have an engine out of a '77. And we are kind of on the same page, I just removed my AAV to test it for the heck of it and I will do the decel valve too.