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Since a few month now i have been chasing idling problems from my '79 euro manual. I basically replaced or let a professional refurbished the whole fuel loop from pump to cis to injectors and wur and all the electronics from green wire, plugkabels, kabels etc. The result has been that since i have been playing with my air/fuel mixture i am pretty lost. I take basically every part and go through the procedures to see if that part causes the problem. Last try was this post: https://rennlist.com/forums/928-foru...ext-steps.html
Anyway i am taking a good look at my air metering plate because when i was lost with the air/fule mixture i had some backfires that might have caused the now strange behavioure. Basically it runs way to rich while it is leaned and when following the 928classics manual it should start easily and run at least. It starts but i cant get it to idle when warming up basically and after that the plugs are black and it smells liek fuel badly (also exhaust is not smelling good).
No i took a good look and made some movies from the plate. My question is has anybody had similar problems that caused this problem? I am going to replace it this weekend but i was wondering if people here can give me some pointers on that. It looks like it is not straight / centered so i hope i found something of course
on the 2 CIS i have here laying around i also noticed that those big top washers are bend . Both in the same way , but the metering plates look flat .
I can only assume this is "not" your problem.....
@Daniel5691 thanks, that will help! Do you think it is possible to replace the air flow plate without taking the whole assembly of like you did? At this point i want to try to only replace and align the plate.
The gap i am measuring in the front int the movie is about a 1 millimeter. If i try to put it in on the sides or the side across it is about 0.14mm. Thats not in the middle, right I hope this could be the problem...
2. The movement of the plate. Again the Fuel distributor has been cleaned and completely refurbished a few months ago, i installed it and it run ok after that. So i would not expect this to influence the fact that i can't get it to run warming up. The movement feel like this: if i gently push the plate down it moves down really easy (feels like no resistance) for about a centimeter or 1/3 inch. Then you start to feel resistance (it feels like it engages the plunger and that gives more resistance). If you let it go it just bounches back. If you push it back further down and let it go its the same it just bounches back. The difference is that if you push it back down further the gap between no resistance while moving down and the moment it starts giving resistance has then moved down too. As if te plunger takes more time to move down and the plate already jumps back. Also look at this movie:
I am wondering if this is "normal" behaviour or not. Maybe it works this way because it has no fuel pressure in the system when i test it? Or is it maybe there is something broke underneath the plate and i need to take it apart like Dan described. I am really considering this, its about the only thing i did not take apart from the engine
Also, another thing which I found and did not anticipate was that my adjustment screw was completely rounded off, and wasn't adjusting anything when it was turned.
Having the meter plate off allows you to get a light source underneath so that you can precisely align the plate. It's like watching the ring of fire around an eclipse...
Please keep us updated with your decision and progress, very interesting.
@Daniel5691 That was the last renewall i did: the adjestment screw I thought that it might have caused the problem. So there is a shiny new one in there It feels way better, but it did not solve it...I think next step could me me following your procedere 1:1
Yes i will keep you posted, it feels like i must There have been so many people helping me already with this one Of course it will be solved, i hope soon, missing the drive already
1. the alignment of the plate in the opening. I think i know it is not aligned correctly. Tried to film this but i am no Jan de Bont https://www.youtube.com/watch?v=aZBE0vKCEpM
The gap i am measuring in the front int the movie is about a 1 millimeter. If i try to put it in on the sides or the side across it is about 0.14mm. Thats not in the middle, right I hope this could be the problem...
2. The movement of the plate. Again the Fuel distributor has been cleaned and completely refurbished a few months ago, i installed it and it run ok after that. So i would not expect this to influence the fact that i can't get it to run warming up. The movement feel like this: if i gently push the plate down it moves down really easy (feels like no resistance) for about a centimeter or 1/3 inch. Then you start to feel resistance (it feels like it engages the plunger and that gives more resistance). If you let it go it just bounches back. If you push it back further down and let it go its the same it just bounches back. The difference is that if you push it back down further the gap between no resistance while moving down and the moment it starts giving resistance has then moved down too. As if te plunger takes more time to move down and the plate already jumps back. Also look at this movie: https://www.youtube.com/watch?v=DP_0rx_JlJY
I am wondering if this is "normal" behaviour or not. Maybe it works this way because it has no fuel pressure in the system when i test it? Or is it maybe there is something broke underneath the plate and i need to take it apart like Dan described. I am really considering this, its about the only thing i did not take apart from the engine
Cheers!
Arie, my plate is freely moving and quite loose when pushing downward by hand. And it is returning smoothly (not that fast as yours) to the upper position. So it is correctly balanced and moving freely. Yours doesn't seem to do that.
The plate appears to be resting too high but it could be the angle of your camera. With control pressure on the Fuel Disti plunger the plate should rest around 0.5mm above the beginning on the upper cone / venturi.
Google 'K Jetronic Workshop Manual' page 15 for details and on how to adjust.
What you describe regarding the plunger catching up when you move the plate back down is normal and shows the plunger is moving freely in its bore:
Hope that helps
Last edited by Chopperharris; 09-10-2020 at 10:25 AM.
I got the plate out, after I took a good movie of the plate movement, I think it is sitting to high in rest position, this is enough to just turn the ignition to “position 1” to test this? Or should I jumper the fuelpump?
If you prime the fuel system by just turning the key it may be enough to test the resting height but i'd jumper the fuel pump relay.
That plate definitely shouldn't be bent like that and would give you some weird results for sure. Install the new plate, centre it and check that the resting position is per the Bosch guidelines. You can adjust the height by moving that pin - be careful doing so as you don't want to do it too many times as wear it so it doesn't hold position. It looks like someone heavy handed has tried to 'fix' the issue before so you may find that pin is already too loose but hopefully not.
I'm pressure you'll need to remove the meter to do this properly - if so you should order a replacement gasket.
I assume you have the Porsche Workshop Manuals? The are available online and will also contain useful info on the meter plate set up. Google 'ligeti 928' if you haven't.
09-08-2020, 03:57 PM
Cis air meter plate check
