Carrera 3,0 WUR and fuel pressures

[Michael - 69E]

Hi CIS gurus.
Please forgive the long post.

After having completely overhauled the CIS system to eliminate (a lot) of vacuum leaks my 1977 Carrera 3,0 now starts and runs great. Warm starts used to be a problem but that seems to have been corrected now
In the past, I had a slight studder/hesitation at neutral throttle around 3000 - 3500 rpm which seems to have been eliminated as well.
The mixture had to be adjusted after the overhaul and I set it to 13,9 AFR / app. 1,5% CO. I prefer a little rich to lean.

My idle does not drop when I remove the oil fill cap. I keep reading that it should, but I cannot get my head around why. Can someone please explain why it gets unmetered air?

I found some discrepancies between the CIS primer and the spec. book for the 76 - 77 cars. Which is correct?

Acc. to the spec. book the control pressure should be:
0-6 - 1,1 bar @ 10 deg. C
2,2 - 2,6 bar @ 35 deg. C
Not specified with vacuum

The CIS primer lists two different types of WUR for the C3:

Carrera:
Control pressure
0,8 bar @ 10 deg. C
2,4 bar @ 35 deg.C
Not specified with vacuum
(Looks like average values of the pressures stated in the spec. book)

0,33 type WUR:
1,4 bar @ 10 deg. C
3,2 bar @ 40 deg. C
3,6 bar @ 40 deg. C with vacuum

911 CIS Primer - Testing: Pressures


I checked my fuel pressures today:

Type of WUR: 033
Type of fuel distributor: 0438 100 010
10 deg. C ambient
Cold control press: 0,75 bar (spot on acc. to spec. book, 0,65 bar too low for 0,33 WUR)
System press: 4,8 bar
1 min : 1,4 bar
2 mins: 2,0 bar
3 mins: 2,6 bar
4 mins: 2,9 bar (0,3 bar too high acc. to spec. book, 0,3 bar too low for 033 WUR)
No further increase in pressure

With vacuum:
1 min : 1,7 bar
2 mins: 2,7 bar
3 mins: 2,9 bar
4 mins: 3,8 bar (0,2 bar too high for 0,33 WUR)
No further increase in pressure

Residual pressure: 2,5 bar
After more than 30 mins. I still have 1,5 bar

Is my 033 WUR correct for my car or is it a replacement adjusted acc. to the spec. book?
I know the WUR and the fuel distributor are a matched pair, so I tend to believe the control pressures should be adjusted as per the spec book.

What is the verdict on my pressures? Would fine-adjusting the warm pressure have any influence on the running of the car - is it worth messing with?

[soren.911]

Hi Michael.

I don't think is is worth to try to adjust your pressures. They are pretty close to specs and it is af big fiddle to adjust though.

As far as I know it is on the 3.2 motronic engines you will se a drop i RPM when removing Oil cap.

[Bob Kontak]

Originally Posted by Michael - 69E

My idle does not drop when I remove the oil fill cap. I keep reading that it should, but I cannot get my head around why. Can someone please explain why it gets unmetered air?

In the 3.0 SC's there is a hose from the top of the oil tank to the back of the accordion bellows thing between the TB and air sensor. Must be for sucking in crank case blow-by.

Open the oil cap and air sensor drops from reduced vacuum.

[Bill Jennings]

Michael,

I also have a 1977 Carrera 3.0 and my rpm has never dropped when I remove the cap from the oil tank.
However it did drop on my old 1979 SC.
I always thought the vacuum plumbing was different on our cars as what I have does not match any drawings I have seen.
I am also unsure if I have original parts on my car.
Does anyone have a vacuum drawing specifically for the Carrera 3.0 and original part numbers for the CIS?
Cheers
Bill

[Walt Fricke]

Michael and Bill

I bet if you look at your hoses you will see that two connect to the oil tank console by the filler tube and cap. The big one goes around the front of the engine where you can't see it and connects to the engine breather.

The other one, rubber and not fabric covered, goes from its connection onto the tank oil tube right over to the right side of the air box, and connects to a fitting there. When you pop off the air filter, you will see where it empties, so to speak, into the air box behind the air filter but before where air flows upward into the intake system.

Thus any effects of taking off the oil cap don't affect the air which has already passed through the air sensor plate.

My '77 2.7 was set up this way, and I suspect the same is the case with your Euro 3.0 Carrera of that year.

In later cars (looks like starting in '78 from the posts) had this hose (whose job is to allow the oil tank and engine to breath, but only filtered air) connected to the left front of the bellows boot. Thus any air admitted there is going to lean the mixture from what the air sensor plate is seeing, hence the change in rpm when you remove this cap.

I think this change had to do with emissions or something. A common thing for a new 911 owner to do is read the oil level on a cold engine. Good golly, it is a quart or more low, better add oil. Then you go and autocross or otherwise fling the car around, and you puke some oil from the now overfilled tank (which is why you always check oil levels hot and soon after running the car). In the 1974-7 configuration, this oil slops into the air box. Some may get sucked up, but most runs out a hole provided for that purpose at the front (relative to the car) of the box, and down a tube which dribbles it out on the highway or wherever).

In the later configuration, this oil (and fumes from the tank under normal oil levels) enters the boot. Perhaps, because the boot is up high enough, oil doesn't slop up there? Anyway, it doesn't spill on the ground.

So your rpm shouldn't drop, and all is well.

[Michael - 69E]

Originally Posted by Walt Fricke

Michael and Bill

I bet if you look at your hoses you will see that two connect to the oil tank console by the filler tube and cap. The big one goes around the front of the engine where you can't see it and connects to the engine breather.

The other one, rubber and not fabric covered, goes from its connection onto the tank oil tube right over to the right side of the air box, and connects to a fitting there. When you pop off the air filter, you will see where it empties, so to speak, into the air box behind the air filter but before where air flows upward into the intake system.

Thus any effects of taking off the oil cap don't affect the air which has already passed through the air sensor plate.


So your rpm shouldn't drop, and all is well.

That is exactly why it never made sense to me. Thanks for clarifying

Hi Søren :-)
The car runs really well now and I sort of decided not to mess around with it any more. Cruising is very nice without stumbling/bucking at 13,9 AFR. Above 14,0 it starts to stumble/buck at neutral throttle.

However, my AFR drops to 11,9 - 12,0 at WOT so I may be leaving a little hp on the table. Ideally I would like to see 12,5 at WOT.

[Michael - 69E]

Originally Posted by Bill Jennings

Michael,

I also have a 1977 Carrera 3.0 and my rpm has never dropped when I remove the cap from the oil tank.
However it did drop on my old 1979 SC.
I always thought the vacuum plumbing was different on our cars as what I have does not match any drawings I have seen.
I am also unsure if I have original parts on my car.
Does anyone have a vacuum drawing specifically for the Carrera 3.0 and original part numbers for the CIS?
Cheers
Bill

Bill.

When I removed my CIS to take care of vacuum leaks I carefully labelled the vacuum lines and reconnected them the same way and.......the car ran like crap. Searched extensively on the net but could not find any vacuum drawings for the 76-77 year models. They seem to be nonexistent. Found some PET drawings on various vendors' web sites - they were all different. With the help of the CIS primer component description (great resource) it turned out the line for the thermal valve was routed incorrectly.
I know two other owners of C3s here in Denmark. Will compare our cars' components when we meet.

[soren.911]

It is a Nice thing with a AFR meter in the car
Mine starts to stumble above 13.6 between 2-3000rpm light throttle and goes down to 10.5 - 11 at WOT.
I don't know if it is adjustable in some way. Maybe the vacuum diaphragm in the buttom of the WUR?

[Bill Jennings]

Walt,
Yest that describes exactly the setup on my car.

Michael,
I would be interested in hearing from you regarding the vacuum line routes on your and your friends cars.
One issue I have is low rpm on cold start up and I think it has to do with not getting any vacuum at the distributer. I have it rigged at the moment that the line from the the distributer is teed off to the WUR and the base of the throttle body. I cannot feel and vacuum at the base of the throttle body however.
Cheers
Bill

[Michael - 69E]

Bill,

I have sent inquiring e-mails to compare vacuum lines

My vacuum line routing is as follows:
Upper stud (on the rear of the throttle body):
Runs to the bottom / base of the WUR.
T'ed with the distributor.

Lower stud (on the rear of the throttle body):
Runs to the thermo valve "in" port.
From thermo valve "out" port to the top of WUR.

Based on the CIS primer components description, I firmly believe this is the correct routing.

What is your idle timing?
Since I do not have any vacuum in the distributor line I set my idle timing to TDC. That way I will still have full advance at 6000 rpm. The idle retard is only for smooth idle and emissions I guess. I am not too concerned about that.

I also face an issue with low rpm on cold starts. So far I have just used the hand throttle (does your car have that too?). I think it is an issue with the automatic air regulator (AAR). I believe it does not open enough when cold. I have bench tested mine and it does open and close as intended - less than 50% open at 10 deg. C

There is a current thread on adjustment of the AAR I am following.

[Michael - 69E]

Originally Posted by soren.911

It is a Nice thing with a AFR meter in the car
Mine starts to stumble above 13.6 between 2-3000rpm light throttle and goes down to 10.5 - 11 at WOT.
I don't know if it is adjustable in some way. Maybe the vacuum diaphragm in the buttom of the WUR?

Sure is nice. Saves a lot of expensive dyno time

10,5 - 11,0 at WOT - guess mine is not that rich then

I don't know either. There must be a way to do it......

[Bill Jennings]

Michael,
Sorry for the delay life got in the way of doing anything with the car I will look at my lines tomorrow.
I think I am running with about 8 degrees advance on the timing.
My car has a hand throttle but I believe it is not connected.
My WUR is a 033 is yours the same?
Cheers
Bill

[Jubbie]

Subscribed...

My C3 has a:
- 033 Regulator which was a replacement and I don't recall what the original one was
- 006 Distributor which came with the engine when I got it.

Ever since I rebuilt and run the engine it has been cold natured and bucks a bit at mid-range. Now is time to make it right. Also realized my vacuum thermal time switch is missing.

I am interested too in the interchangeability of the 033 and 017 WURs

Thanks

[Walt Fricke]

What's a C3?

[timmy2]

Originally Posted by Walt Fricke

What's a C3?

Carerra 3.0 as opposed to the 2.7 variety '74-'77

[Michael - 69E]

Originally Posted by Bill Jennings

Michael,
Sorry for the delay life got in the way of doing anything with the car I will look at my lines tomorrow.
I think I am running with about 8 degrees advance on the timing.
My car has a hand throttle but I believe it is not connected.
My WUR is a 033 is yours the same?
Cheers
Bill

Bill,

I have the 033 WUR and it is correct for the C3 as per the PET.

[Bill Jennings]

Michael,
Thanks for the reply and info.
I am wondering if one of my main issues is that my hand throttle is not connected.
In fact I think it has been removed apart from the lever.
My car always starts from cold with 1000rpm max and sometimes only just catches.
The hand throttle would remedy that from what I have read.
I am planning on making a drawing of my vac lines tomorrow.
Will report back.
Cheers
Bill

[boyt911sc]

Originally Posted by Bill Jennings

Michael,
Thanks for the reply and info.
I am wondering if one of my main issues is that my hand throttle is not connected.
In fact I think it has been removed apart from the lever.
My car always starts from cold with 1000rpm max and sometimes only just catches.
The hand throttle would remedy that from what I have read.
I am planning on making a drawing of my vac lines tomorrow.
Will report back.
Cheers
Bill

Bill,

The original WUR for '76-'77 Euro cars was WUR-017 and later superceded by WUR-033. Cars destined for USA/CAN were using WUR-033. They are not identical in properties as far as heating/warm up is concerned. They have different heating resistances.

If you are using WUR-017 or -033, you don't need the TPR (throttle pressure regulator) because these later WUR's are vacuum assisted. Why do you have a hand throttle for the '77 C3? Is this standard on these cars? My familiarity with C3 configuration and components is very limited unlike with those of the US/CAN models which I work on these days. Thanks.

Tony

[carrera30]

Nice to see so many ID's I've had contact thru this forum. Tony, the hand throttle is standard in the Carrera 3.0.
Happy Spring all>
Mill

[Walt Fricke]

Tony
My SC started life in 1976 as a 1977 model Euro 2.7. Among other quirks, it did not have boosted brakes, but it did have the hand throttle. That's a really handy thing for a race motor, or just for working on a motor which is having idle issues, though hardly essential. The 2.7 and most of its components is long gone, though.

So I am not surprised that the early Euro 3.0s - of the same era - retained the hand throttle.

Mill - did these early Euros also retain the non-boosted brakes?