Idling after rebuild FIP

[Rob12345]

HI. I have a 280sl and after rebuil injection pump by the workshop I have a problem with idling(when the engine is working, idle are going up and down), when I try turn left air screw on the intake mainfold. There is no diference on cold or warm engine. I set timing ignition to 4 degrees BTDC, but on 8 degrees situation was the same. I have two scales on my pulley and when I installed my FIP, there was 20/60 degrees. I checked every hose with vacuum, I have second distributor and nothing change. I do not know where is the problem. Linkage is disconnected right now, turning the fuel mixture on FIP make changes, but turning air screw ccv make idle problem

[stickandrudderman]

Do the split linkage test:
Plenty of info here in the tech manual if you're a member or here:
https://www.youtube.com/watch?v=28uD3JVbQ-I

[Rob12345]

I did. When I give the air engine is gowing down and stop. When I give a fuel on fuel pump idle increse. After this test I turn mixture screw on Fuel Injection Pump to the right 3 clicks, and the 3 a and 3 for example, but on AFR I have 10-11 so its to much(13 on AFR is 4 CO). Othervise, when I give to much to the right on fuel pump, the engine is shooting off on 800 RPM. I notice that there is option to set up warm engine to good idling on 750-800 RPM, and AFR is 12,5 but when I start cold engine there is a problem-idle are going up and down

[mrfatboy]

What year is your 280sl? Auto or manual?

[Rob12345]

1968, Automatic transmission. When the engine is working good:
https://www.youtube.com/watch?v=ND6gQzwu0Rw
Problem is when engine is cold.
I do not know is it good but when I close air screw engine is working(low RPM but still working)

[Rob12345]

https://youtu.be/dxG1A2pH77I

[mrfatboy]

I would first suggest that your WRD is working properly. You can take off the little air filter on the back of the FIP and feel for suction. There should be very little or no suction when engine is at operating temperature. Do a search here for exact procedure. There is much info on it.

Once you verified that it does shut off when the car is at operating temperature adjust your AFR to spec.

When the engine is cold tell us what your AFR is and then we can suggest how to adjust the oval shims under the WRD to make leaner or richer during warm up.

[Rob12345]

Here you are

[mrfatboy]

You are going to have to give us a little more info   

Is that the AFR when car is cold? Hot? Did you verify if the WRD shut off when car is at operating temperature?

Also does your gas tester display CO instead of AFR? It’s just easier for at least me 🤣 so I don’t have to do conversions in my head.

[Rob12345]

This picture above was na example.  Now I have correct reading. RPM 740 AFR 13,20. Engine warm. https://youtu.be/YbIFPreszKU

[mrfatboy]

So it seems the car is running nicely and has correct AFR when running at operating temperature, correct?

is the car only running poorly during warm up? Have you checked if the WRD is working properly?

If so, what is the AFR during warm up?

[Rob12345]

Yes,  the car is running nicely and has correct AFR when running at operating temperature. Thats correct. WRD is working propertly, There is suction on cold engine, and after warm up there is no suction. I will send you AFR reading for a moment because my engine is little bit hot now

[mrfatboy]

Good. Making progress👍

While you are waiting for the engine to get cold you can experiment with this FIP app.

https://www.sl113.org/fip/index.html

[Rob12345]

What is it?

[mrfatboy]

Check it out. A FIP Simulator.

[Rob12345]

Engine was almost cold. There was idling on the begining a few times. You will see on video.  https://youtu.be/8GyYDZbXld8

[Pawel66]

With the usual disclaimer: I am not a mechanic nor any kind of expert, so be careful.

I think there are, in essence, 4 ways for the air to get to combustion chambers:

1. Throttle, only if opened
2. Idle channel, where the idle screw is
3. WRD (when engine is below operating temperature, warm up cycle only)
4. Leaks in manifold and/or anything that is attached to it

Let's make assumption that screwing idle screw all the way down cuts air completely (I do not know that). This air channel can be plugged easily if need be (the hose there).

If you are saying that your engine runs idle despite idle air screw screwed tight WHEN COLD, although I never checked it, it may be possible, I think that it just runs on WRD air. Easy way to check it is to unscrew FIP air filter and plug the opening with your thumb. The engine should die. If it does not then either the assumption above is not correct or there is another way air gets to engine.

In any condition - warm or cold, if you plug idle channel and plug the WRD with your thumb and engine is still running - you either have the throttle not closing fully or there is a leak somewhere (e.g. brake booster is typical). If that is the case, you need to get rid of it first as you will not set/adjust anything.

There are ways to test both that even I can do.

So this is for your question from your first post.

Then there is a discussion about warm up cycle rich or lean, long or short - this is mrfatboy lead and the FIP simulator topic.

[Rob12345]

1, 3 and 4 checked OK. 2 I will check tomorrow. I notice that, when I gave one more gasket under BC(1 mm), engine is working better when cold(AFR 11,8 Cold RPM 900, warm RPM 720). Maybe there is some vacumm leak but only when cold? Strange. When warm engine is working properly.

[mrfatboy]

The BC changes mixture at all temps and ranges.

It sounds like your pump is too lean during warm. I can even hear it in your videos. It is “hunting”.

Remove WRD and add some oval shims so you are only enriching the mixture during warm up.

A even quicker test would be loosening very slightly and evenly the two screws bolting the WRD to the FIP.

This will act like adding shims temporarily. It it works added in real shims.

[Rob12345]

Yes, my pump look like lean at the beginning.  When I loose two screws from WRD engine was working stable. But there is I think something like 4-5mm. Is it not too much?

[mrfatboy]

I think 4-5mm is too much. I think typically the average oval shim thickness is about .6mm.

How thick are the shims under your BC? I believe 2mm is normal.

It now sounds like you need increase your the BC to enrich the pump at all ranges and temps AND then adjust idle mixture screw leaner during normal operating temperature to achieve correct APR.

Once you have that set, adjust your WRD oval shims to have APR correct for cold start and warm up.

[Rob12345]

Under BC was 3,8 mm, and I add 1mm so now is 4,8. Ormaybe I should give him 1 click more on full load screw (inside the pump)?

[mrfatboy]

Have you verified that the BC is working properly? If I remember correctly 😜 when they fail they make the pump go leaner which would explain why you have so many shims under the BC.

Remove the BC and measure pin length. Post a picture of it here. You can also read about it in the tech manual.

[Rob12345]

Ok. I will send you pictures tomorrow

[col320ce]

Make sure the wrd filter is not blocked... It should be very easy to suck through.
I'd do cold start tests with it off completely.