911 SC 1980 running bad after CIS rebuild

[Philipp1988]

Hi everyone,

i need the help of this great forum.

so to me: i own a 1980 911 SC US. I put the engine out and made a complete rebuild of the injection system (new seals everywhere, new fuel lines, fuel filter, spark plugs, valve adjustment) . It should be vakuum leakproof.
Before the rebuild the engine was running smooth idle but it was nececarry to do the rebuild...

ok..
the engine is now in the car tried to start it. So yesterday the engine startet relativly smoothly and died few seconds later

today i tried again. the engine starts but it runs like tractor (not smooth, sounds horible) and dies if i don't move the throttle My first thought was a wrong ignition timing or less fuel...

So what i checked:

I checket all injectors, Fuel is cooming and all injectors spray at same level,
I put cylinder one to tdc, then the rotor points exacly to the marking of cylinder one (i also market the position of the distributor bevor removing, fits perfect)
i checket the position of all ignition wires to the firing order, fits

so ok. I ordered a CIS Manometer to check the system pressure

Any ideas ot tips what it could be (i read a lot in the forum but i'm not getting into the problem)? i'm really confused and a bit down...

Sorry for my bad english.
Best regards and thanks. Philipp

[mike sampsel]

I’m no expert but:

Maybe the idle screw (on the throttle body 1,2,3,side) is too far in and the car dies from lack of air?
With the idle screw all the way in the car should die unless you have vacuum leaks.

I’d check your plug wires to be sure they are connected.

[RDM]

Originally Posted by mike sampsel

I’m no expert but:

Maybe the idle screw (on the throttle body 1,2,3,side) is too far in and the car dies from lack of air?
With the idle screw all the way in the car should die unless you have vacuum leaks.

I’d check your plug wires to be sure they are connected.

If you eliminated a lot of air leaks when you replaced all your seals, it would make sense that you would need to open the idle screw a bit to make up for it.

[Philipp1988]

Ok, thanks for the reply.

folowing things i checked and did:

1. I found a bad "green cable" from the distributor and fixed it with a new one. Ckeck

2. I removed all spark plugs and checked the ignition with all Sparks. --> Good spark and all plugs work fine.


For me the summary: No ignition problems, seems to be a fuel problem.

Car starts fine everytime. But 3- 10 seconds later it runs terrible and goes off. Maybe its not loosing spark but fuel?


Next: Check the system pressure, Check if the duty cycle vent

regards Phil

[pmax]

Phil,
It's probably not the problem here since it appears rich but check the Lambda relay and FV anyway, feel or listen to the latter if it's buzzing. I would also unplug the O2 sensor to eliminate another variable. Another possibility is the thermo switch not shutting off the CSV.

[walt]

If you sealed up all the vacuum leaks maybe your air/fuel mixture is way off.

[targa80]

Since you worked on the fuel injection system, did you mess with the fuel distributor? You really need to use the fuel pressure gauges to establish a base line of the fuel pressure at each stage, cold pressure, warm up and running. The posts on cis for dummies is a great resource along with the Bosch fuel injection manual.

[47silver]

1. Set your timing with a light as it is more than likely way off. The rotor pointing to the spark plug at tdc is only for getting it to start and is called static timing.
2. if you fixed air leaks you are probably running very rich so may need to lean out the enrichment screw CCW. turn it one click and keep track of what you are doing. May need a gunson tester to get it set properly.

[Philipp1988]

Hey everyone,

Thanks for all of your ideas.

So ok, the analyse goes on:

System pressure: 4,9 bar --> Check
pressure cold (28°C) warm up regulator: 3,2 bar --> seems too high
pressure WUR engine warm: 4,5 bar
Lambda cycle vent is working (can feel it clicking)

ignition set to 5° at 950 RPM --> Check

ok i played a little bit with the air/fuel mixture and now the engine is running. sounds very good to me. I made the mixture richer (screwed the 3mm allen screw clockwise).

Lets see tomorrow if the engine starts again

Do you think the WUR could be the problem??

Regards Philipp

[Flat6pac]

In order to make changes in the lambda system you need to un plug the oxygen sensor while you’re changing settings on the system.
The relay next to the lambda box, if defective, mimics a bad WUR
Bruce

[boyt911sc]

Originally Posted by Philipp1988

Hey everyone,

Thanks for all of your ideas.

So ok, the analyse goes on:

System pressure: 4,9 bar --> Check
pressure cold (28°C) warm up regulator: 3,2 bar --> seems too high
pressure WUR engine warm: 4,5 bar
Lambda cycle vent is working (can feel it clicking)

ignition set to 5° at 950 RPM --> Check

ok i played a little bit with the air/fuel mixture and now the engine is running. sounds very good to me. I made the mixture richer (screwed the 3mm allen screw clockwise).

Lets see tomorrow if the engine starts again

Do you think the WUR could be the problem??

Regards Philipp

Philipp,

You should have a WUR-072 on your motor. Please check the heater resistance (Ohms) when the engine is cold and keep us posted. BTW, your starting problem is caused by your too high cold control fuel pressure and the warm control pressure is way too high. Setting the mixture RICHER as you did would help get it to start. But it is a band-aid remedy. Get your WUR calibrated if you want it to perform satisfactorily.

Tony

[Philipp1988]

Hey,

WUR 0438.140.072 with 10 Ohm resistance cold.

i agree, i think i have to let the WUR calibrate. Ok i try again tomorrow morning and check the pressure again.

Regards Philipp

[pmax]

Originally Posted by Philipp1988

Hey,

WUR 0438.140.072 with 10 Ohm resistance cold.

i agree, i think i have to let the WUR calibrate. Ok i try again tomorrow morning and check the pressure again.

Regards Philipp

Phillip,

The resistance doesn't affect the cold control pressure which is a tad high (lean) in your case.

The CCP can be made adjustable using a simple well known mod to the WUR (Search for adjustable WUR). That's what I did to the 072 unit in my 80. Bring the CCP to spec and it will start better.

[boyt911sc]

Philipp,

Where are you located? Are you in Europe? I am going back to Europe next month (September) and could lend you one for you to test in your car. Then sent it back to me after the test. PM me if you need one. Thanks.

Tony

[Philipp1988]

Hey,

what a cool idea with the adjustable WUR. i will do that!!

@boyt911sc: in southern Germany, Stuttgart . Thanks for the great offer I will first try the mod.

So my control pressure is about 3,2 bar at around 25°C. What do you expect would be the right pressure to adjust? The control pressure withwarm engine was high (4,5 bar)!

Regards Philipp

[boyt911sc]

Philipp,

The first thing you need to do is adjust the WCP (warm control pressure) to 3.6 bar/52 psi. followed by CCP. Or install a calibrated WUR-072.

Tony

[pmax]

Originally Posted by Philipp1988

Hey,

what a cool idea with the adjustable WUR. i will do that!!

Adding control mods to these ancient gadgets is always good and fun too !! In my no start case, the CCP was 1 bar off if I recall correctly.

So my control pressure is about 3,2 bar at around 25°C. What do you expect would be the right pressure to adjust? The control pressure withwarm engine was high (4,5 bar)!

Ah, didn't notice the WCP numbers being high as well. I would first look for a blockage first somewhere from the WUR "intake" to the return. If that's causing the high WCP, it will also lead to the high CCP.

[Philipp1988]

Originally Posted by boyt911sc

Philipp,

The first thing you need to do is adjust the WCP (warm control pressure) to 3.6 bar/52 psi. followed by CCP. Or install a calibrated WUR-072.

Tony

Hey Tony,
Ok, but when i adjust WCP to 3.6 bar the CCP pressure can‘t be adjusted independently?

Ok i will Look for some blocking but i don‘t think there is one. Bevor the mounting of the fuel lines i cleaned them with air (Not the WUR)

Regards Phil

[pmax]

Phil,
The WUR has little screens which can be blocked if crud gets in there. I would check those first ... then move on to the next possibility etc. The WUR is like a valve which regulates the control pressure by controlling the return.

[Philipp1988]

Originally Posted by pmax

Phil,
The WUR has little screens which can be blocked if crud gets in there. I would check those first ... then move on to the next possibility etc. The WUR is like a valve which regulates the control pressure by controlling the return.

Hey,

Ok seems logic or a possible failure source.
How would you ckeck or clean that? Open the WUR? Clean with brake cleaner?

Regards and thanks a lot
Phil