SC lean above 4k rpm

[MaRu]

Hello everybody,

I´m having issues with a freshly rebuild SC. It runs very nice. Cold start, idle,... everything is good. But as soon as I have WOT the AFR is getting way to lean above 4k. And a little to lean beyond. ( I used an AFR tester during the drive) Adjusting idle CO is no problem. There is no vacuum leak and I already swapped out WUR, fuel distributor, and the auxiliary air device on the right side. Oh, and fuel pressure and quantity is spot on, too.

Any ideas what I might be missing? The engine is stock.

The only thing I haven´t swapped so far is this golden 3" "thing" in the right rear of the engine bay. What does this do and how can I test this.

Many thanks in advance, Malte

[MaRu]

Number 39 is what I´m referring to.

[Zuffenwerker]

What year SC?
I know you said f/p is good but have you checked it according to the manual? CCP, WCP, SYS. Press, etc.?
How lean are you getting?

Do you have the correct WUR?

The 3” gold thingy is the Aux Air Valve. Probably not your issue. If you want to test it then remove it from the engine and record at what vacuum does the valve open. Should be around 8” depending on the part #. When they fail open you’ll notice a high idle speed or bouncing idle.

[MaRu]

Thanks for your answer. Yes I did check it correctly.

I also installed a second set of WUR, valve and Fuel distributor from another car. Same issues.

AFR with full throttle

3500 13,1

4000 13,8

4500 15

5000 16,7

I barely hit the 5k because I didn´t want to have hole in a piston.

I was wondering if this Aux air valve stays open the entire time but I somehow adjusted the engine at idle to a point where it does run smooth if I this might cause the lean mixture at higher revs...?


Again, thank you!

[AndrewCologne]

The Aux Air Valve passes "metered" air, so I don't think this will lean out your mixture. And if it's flawed, then a typical symptom is a high idle.

Maybe your air sensor plate is not adjusted properly, you should check that.

And! Check if you did not forget pull and remove the hexagon key from the Fuel dizzy hen you did set the CO – that happened once to me ;-)

[MaRu]

Unfortunately this indeed wasn´t the cause...

Also the flow plate is working correct, but I anyway swapped this one, too.

The hex key thing happend to me, too

Do you by any chance have some numbers how much fuel the injectors should deliver at Wot?

[MaRu]

I forgot to mention. I check pressure today with a more accurate meter and while my system pressure is at 5.1 bar, the control pressure is at 4. Not 3.8 what it should be when it´s warm. Could this cause the issue?

[Zuffenwerker]

What rear is your car? Does it have full throttle enrichment? Which warm up regulator are you using?

[MaRu]

Engine is 1978 I think (it´s not the original to the car so I´m not 100% sure).
Yes, with throttle enrichment. I´ll check the numbers tomorrow when I´m in the garage.

[boyt911sc]

Originally Posted by Zuffenwerker

What year SC?
I know you said f/p is good but have you checked it according to the manual? CCP, WCP, SYS. Press, etc.?
How lean are you getting?

Do you have the correct WUR?

The 3” gold thingy is the Aux Air Valve. Probably not your issue. If you want to test it then remove it from the engine and record at what vacuum does the valve open. Should be around 8” depending on the part #. When they fail open you’ll notice a high idle speed or bouncing idle.

The AAV (auxiliary air valve) is NO (normally open) and will close when engine vacuum is created during the initial start and will stay closed until engine stops. The failure mode is AAV fails to close when vacuum is applied. Not the other way around.

Tony

[safe]

Originally Posted by MaRu

I forgot to mention. I check pressure today with a more accurate meter and while my system pressure is at 5.1 bar, the control pressure is at 4. Not 3.8 what it should be when it´s warm. Could this cause the issue?

Too high control pressure. Get it down near 3. Wher did you get 3.8? That seems high.
Some specs.
https://jimsbasementworkshop.com/CIS/pages/test_pressures.html

[MaRu]

Sorry for my late reply.
I got another Fuel distributor (the third) and this one seems to be working better.
But I´m still wondering about the high pressure. Is there a way to lower it?

Thanks again!

[safe]

Originally Posted by MaRu

Sorry for my late reply.
I got another Fuel distributor (the third) and this one seems to be working better.
But I´m still wondering about the high pressure. Is there a way to lower it?

Thanks again!

The WUR determines the control pressure. Yours might be clogged or out of spec in some other way. It can be cleaned and or adjusted.
CIS is very sensitive to debris in the fuel, lots of small passages and filter screens.
Fresh fuel filter and clean tank is essential. New ethanol fuel might dissolve old fuel deposits in the system too.

[Reiver]

Originally Posted by MaRu

Unfortunately this indeed wasn´t the cause...

Also the flow plate is working correct, but I anyway swapped this one, too.

The hex key thing happend to me, too

Do you by any chance have some numbers how much fuel the injectors should deliver at Wot?

I have a 930-10 '83 SC with AFR in the dash. I run it a bit rich due to the 9.8-1 compression and our heat in Az....and 91 octane.

At normal idle 13.2....cruise at 75, 13.7/14.00 , and at WOT 11.5/8 but I have set it up for that exact AFR.

In the Euro the WUR controls the AFR by vacuum. I don't think you said what engine you run....16 or 10?

I had the same issue a few years ago.... it was the WUR and it was out of spec.... rebuilt and now runs as I set it up.

[MaRu]

Thank you. I didn´t had time so far to check again.
The engine is a big port SC. But not with the 204hp pistons.
I think I´ll try to get more into the WUR and how to "manipulate" it in terms of cold start and pressures in general over the winter. That seems very interesting!