911 SC 1980 running bad after CIS rebuild
 

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 SmileWavy tried to start it. So yesterday the engine startet relativly smoothly and died few seconds later :confused:

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





http://forums.pelicanparts.com/uploa...1566147764.JPG
http://forums.pelicanparts.com/uploa...1566147764.JPG

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.

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

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.

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

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.

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.

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

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

WUR spec.........
 

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

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.

Location.........
 

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

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

http://forums.pelicanparts.com/uploa...1566739645.jpg

Warm control fuel pressure.........
 

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

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.

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.

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

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

I would remove the WUR and do a visual. The screen is visible in this pic from a 12 page WUR servicing guide someone wrote to assist all the amateurs like us.

http://b2resource.com/PDFs/wurservicing.pdfhttp://forums.pelicanparts.com/uploa...1566759258.jpg

Of course, you can send it to a rebuilder and have a warrantied WUR. But you still need to verify it's in fact a problem with the WUR and not an obstruction downstream otherwise the problem will remain.

Hey,

i cleaned the WUR, inspected the screen, but looked really good.

ok i think the WUR is defect.

I looked at the cold control pressure again (jumped fuel pump and disconected the heating element on the WUR):
startet at 3 Bar, then i closed the line and control pressure raised to 5 bar, opened, closed,...for about 5 times
so the cold control pressure slowly rised to about 4 bar...

seems there is something wrong.

Regards Philipp

Cold control fuel pressure check.........
 

Philipp,

Try this simple test to evaluate your WUR:
1). Removed the four (4) bolts holding the WUR upper and lower sections of the WUR together.
2). Separate the upper and lower sections. You will find a spring, a cup or “sombrero” and a pin. Remove and save them. You don’t need them for the test.
3). Assemble back the upper and lower sections together. Make sure you put them together the same way they were before. You will notice if they were put together differently. Install back the 4 screws and nuts.
4). Install the WUR back on the car and connect the fuel lines. Do not connect the electrical plug to the WUR. Test run the fuel pump and record the new cold control fuel pressure.

Do not worry about the WUR, I will show you a step by step procedures with pictures for the assembly in case you need them. This particular test will demonstrate the flow restriction if any in your system.

If you have any question or concern, let us know or PM me. Keep us posted. Thanks.

Tony

Hey Tony,

thanks for the good advice!!!! I'm really thankful to this forum.
I have send the WUR to checking ang calibration. I will build a connection to check the pressure if the fuel lines make any blocking...

I replaced all the fuel lines and build them myself by DIN 73378 polyamide tubes. cleaned them carfeully with air.. but yeah i know, everything can happen....

Regards Phil

Hey Tony,

ok i made the analysis. Pressure goes against zero, so there is nothing that restricst the flow to WUR. Do you think too?

Hope to get my WUR back soon. Can't wait too get it done :) Thanks!

Regards Phil

Test result........
 

Philipp,

How did you get zero pressure reading? Could you elaborate how you did the test? It is not obvious to us what was done to get your result. Thanks.

Tony

Hey,

i connected the both fuel lines wich are normally connected to the WUR (One comes from the fuel distributor to WUR, One goes from WUR to the fuel tank)
With the normal pressure gauge in line as to test the control pressure.

So the control pressure goes to zero. When i close the valve, Systempressure 4,9 bar...

Hope is was better explained now.

Regards Phil

Fuel pressure test........
 

Philipp,

One more question. Was the pin inside the WUR removed when you did the above test as I requested earlier? Pin removed or pin installed? Please advise. Thanks.

Tony

Hey Tony,

the WUR as itself was removed. I connected both the lines witch are normaly attached at the WUR with a fitting.

Hope its explained better now?

Regards Phil

Problematic WUR......
 

Phil,

Thanks for explanation and now I fully understand what you did. Keep us posted after you received the WUR back. The WUR needs some work to reduce the flow restriction.

Tony

Hey,

ok i can continue, the WUR is here after rebuild. Put it back in the car.

Cold Control pressure at 15°C: 2.1 bar

warm control pressure 3,8-3,9 bar

;) seems to be good


Car starts fine now. Adjusted the CO at 950 rpm idle to about 0,4- 0,8 % (with the gunson gas tester, engine was hot, Lambda connector off).

Problems:
Duty Cycle at idle is not constant and skips fast from about 10% to 30 % :confused:

when i open the throttle just a few degree, rpm jumps to 2000 rpm and don't goes back to 950... :confused:

To do: Vacuum measure of CIS

Any ideas?

Regards and thank you
Phil

WCP seems at the high side according to factory spec chart.

Did you set your idle with engine fully warmed up?
Maybe the decal valve is sticking.
You can test it with a vacuum pump for proper function.
A quick test to see if it is the culprit is to disconnect the small vacuum line to it and plug the line it to see if the idle drops back down normally.

WUR out of calibration........
 

Philipp,

Contact your WUR rebuilder and have the WCP set @ 52 psi. Second, if your WUR reads 10 Ohms when cold, this is another problem you need to address. There could be more problems with your other CIS components (?).

But let us start one step at a time. Your newly rebuilt or calibrated WUR-072 will always give you an erratic cold idle.

Tony

Incorrect and lack of experience.......
 

PMax,

Why do you say and post something like the above highlighted information? I guess you still don’t understand how WUR-072 & -090 work. The cold control fuel pressures for these types of WUR’s are directly affected by the amount of the heater resistance. You could not achieve a good calibration for both WUR-072 & -090 if you don’t understand the correlation of control fuel pressures with heater resistance values.

The OP has only 10 Ohms reading for his WUR-072 when cold as posted earlier in this thread. Unless this WUR is correctly calibrated, the engine would always experience erratic cold idle. Specially at this time of the year when the ambient temperature is getting colder each day and the problem will be more noticeable.

Tony

There's no causation from the resistance value to the cold control pressure.

Cold control pressure is measured at time 0 from a cold start where resistance does not play any role.

That's what I said and I think we are in agreement there from one engineer to another.

Hi guys,

ok so just to verify: i often read that 10 Ohm for the .072 WUR is correct?
For my thinking the resistance of the heating element of the WUR just leading to a faster heat up of the bimetal.

Ambient Temperatur at every test i did was at around 25°C (Good weather these days :))

Ok did some more analysis:


Jumped 87a and 30 of Fuel pump relay, fuel pump runs. Don't hear and feel the frequency valve buzzling... It should right? in this test case i normaly should measure 50% duty cycle nor?
Edit: I can feel the oxygen relay under passenger seat switching

Next: I will change the oxygen relay under the passenger seat

i think the problem i in the area of the frequency valve...

regards Phil

that's gunna leave a mark.

Maybe even a stain! :D

^^^ Hi there, Raw' and the Profeceteur ^^^

Back to the technical thread !

That's my understanding.
One can remove the WUR heater connector , measure the FP of the cold engine and it will stay at CCP all day long


Yes, the FV should be buzzing.