I have a 2.7L with CIS in my '75. The car starts with a touch of the key when cold and immediately idles at 1100.

When the car gets warm (about 190 degrees) the car surges at idle between 900 and 1200 rpm. It never stalls but it is annoying.

Is there something obvious about this symptom or can I do something to provide more information?

Thanks in advance!

Could be really rich. Do you have a CO meter?

Hi Ferg,

I have access to a wide band AFR.

First check for vacuum leaks. The check again. Do not let anyone mess with the senor plate adjustment!

Absolutely check the fuel pressure Second then second. The most common issues are vacuum leaks and fuel pressure.

If the pressure is wrong going to the WUR it will cause a rich condition. Check the fuel pump flow rate for volume and the pressure at the WUR.

If you can't find someone local that knows the 2.7 find an old Volvo guy. If they walk out to the car with a little allan wrench close the hood quick and find someone else.

check the timing they will hunt if the timing is off

Thanks Rick,

Great information.

Are you and Sandy back home yet?

Thanks, I wouldn't have thought of that.

If you still have points ..set them first
Ricks right never throttle plate stop or sensor plate stop ,,,
mixture screw and air bypass..simple tweeks no big deal..

https://www.youtube.com/watch?v=8TcAzqKxWgY

Thanks Jeff, interesting video. I wish the video had a few minutes of the issue but it sounds very similar to my issue. This car has had about 2000 miles put on it since it was rebuilt over 5 years ago so limited use struck a chord with me in the video.

PS: MSD electronic ignition

What's your elevation? 7k?

It was at about 5k, did you notice the issue when you picked it up?

Hi Ferg,

My elevation is 6600'. The car was cold when I picked it up and first noticed it on the drive home when I stopped for gas a few hours later in Monte Vista (elevation 7600').

The car is perfect when cold - only notice it when warm. I thought the fuel injection would compensate for elevation but I am new to CIS.

I did see this article on Pelican that echos everything mentioned before in this thread: http://forums.pelicanparts.com/porsche-911...cis-engine.html

There are several threads on the Bird Board about this and how to adjust - most starting with "Get a 5mm Allen wrench"...

Thanks for your help on this.

Your symptoms sound a lot like what I had with my '75 911S with CIS. Get yourself the fuel pressure testing kit (HF as one that is fairly decent) and check your pressures. My problem was cured with a replacement WUR. You may find more useful information in the 911 forum on the Bird.

Keith

Thanks Keith.

Yes I think a fuel pressure gauge needs to be on my tool box...

The CIS Testing setup is not just a gauge.

Thanks Ron - is there one in particular you like? I have seen several for sale.

Mike,

I have a CIS tester ... I'll shoot an image of the setup. If you want to borrow it, I can mail it to you.

All the instructions for use are in the 911 manual as the fuel pressures are checked while the engine is cold and then warmed up. You need the temperature / pressure chart contained within the manual.

You can play with the idle mixture with the long allen wrench, but do it one click at a time. Clockwise = richer and Counterclockwise = leaner. Playing with the adjustment slightly alters the position of the airflow plate (and commensurately, the position of the piston in the Fuel Distributor).

Thanks Ron,

When you get a chance (no hurry) shoot me an image and I will see if there is one in town (slim chance but there are a few 911 guys here).

I am going through my manuals and Tech Spec booklets now to make sure I have the right data.

Need it ... send me a PM with your address. Being an asshole, I will charge you for the cost of sending it.

This setup is plumbed between the center of the Fuel Distributor and Control Pressure Regulator (WUR). The fuel pump puts out 65+ psig and pressure is regulated into the Fuel distributor. The control pressure regulator (WUR) bleeds off fuel pressure depending upon the temperature of the (engine) bimetalic spring in the WUR. There are specific values based on ambient (cold) and warm engine (hot).

That makes perfect sense when you say it.

I found the specs in a 911 Tech Spec book I have so I think I have the numbers. It shows a graph with control pressure cold corresponding to ambient and then numbers for warm based on throttle position:

Idle = 2.9-3.1 BAR
Partial = 3.4-3.9 BAR
Full = 2.7-3.1 BAR

Am I on the right page?

Yes ....

With your 2.7L you will either have an 017 or 033 WUR. For these WURs, the (ambient) cold pressure is:

50 F ....1.2 - 1.6 bar (17,64 - 23.52 psig)
68 F ....1.8 - 2.1 bar (26.46 - 30.87 psig)
86 F ....2.4 - 2.8 bar (35,38 - 41,16 psig)
104 F .... 3.0 - 3.4 bar (44.1 - 49.98 paig)

Control pressure warm (engine hot)
2.7 - 3.1 bar (39,69 - 45.57 psig)
High idle speed (1800 rpm) 3.4 - 3.8 bar (49.98 - 55.86 psig)

Your initial system pressure (from fuel pump) is regulated between 4.5 - 5.2 bar (66.15 - 76.44 psig)

Leak down test (engine shutdown)
10 minutes - 1.3 bar (19.11 psig)
20 minutes - 1.1 bar (14.7 psig)

If you have any other WUR the control ranges are different.
Bosh WUR numbers are 0 438 140 XXX

Great info - thanks for taking the time to document this.

PS: "Fireball" says hello...

Hi Fireball ...... wish I were in Durango right now ... it snowed 5" last night while I was asleep.

Mike, remember when you are testing "cold" you must remove the electrical connector to the WUR so it won't heat up for the test. After that you plug it back in 'cause it has constant power when the key is on. Between the heating of the bi-metallic strip and the heat of the engine, the fuel pressure will vary.

Got it - good info as I would probably have failed to do that.

Denver is getting snow this weekend. Durango is gorgeous today - but that stuff you got last night is moving our way. Looks like a shitty weekend here.

It took me years to finally learn CIS. I couldn't get the old Volvo guys to touch it with anything but an allen wrench. It was so screwed up! I ended up reading enough about it to figure out that the sensor plate is never the issue. I was offered a Volvo turbo WUR for parts. I ended up gutting mine and the Volvo unit and swapping in the 928 bi-metal spring setup as the Volvo unit has an adjustable plunger. You will read about "knocking or tapping" the plunger to adjust the bi-metal spring.

An old Volvo mechanic that wouldn't touch the car borrowed me his gauge setup. I set the cold and warm pressures ( they were way off) and then went about undoing the inaccurate adjustments to the sensor plate. I cranked the allen out about a full turn. If you have ever adjusted a sensor plate you are sitting there with your jaw in your lap. The allen adjustment is a verrrry fine movement. Not turns, just movements by a hair.

Oh and were home now.

Glad you guys are home safe!

Was there's book you read on CIS that helped you? I learned a ton from Ron just today.

simple easy to try , make note of wich way you turn 1/8 turn is a lot ...
then if needed you can become an expert..

http://rennlist.com/forums/928-forum/60228...-the-wur-2.html

http://jimsbasementworkshop.com/CIS/

Thanks Jeff,

I have more reading to do. This CIS is so new to this old carb guy!

Thanks Rick,

Looks some great information. I will dig into the data right after the Formula 1 race this morning.

Cheers!

UPDATE:

I borrowed CIS fuel gauges from a friend and here is what I get.

I have a 033 WUR.

Ambient Temperature was 68 degrees F.

Cold Control Pressure = 21PSI (Range 26 to 30)

Warm System Pressure = 69PSI (Range 65 to 75)

Control Pressure at Idle = 42psi (Range 39 to 45)
Control Pressure at Partial throttle = 42psi (Range 39 to 45)
Control Pressure WOT = 42psi (Range 39 to 45)

Rest Pressure was 21psi after 20 minutes

After the car warmed (temp above 120) the car started surging like it always does. What I discovered was if I pinched the return line from the fuel distributor the idle would smooth out perfectly - no more surging. What would I be doing by crimping the return from the fuel distributor? It is obviously changing pressure at the fuel head but what else?

I don't have an O2 gauge. Is that the next piece of important data?

If you crimp the return line, you are adding full fuel pump pressure to the fuel distributor. Maybe the fuel pump is weak even though the pressures you obtained are in the range.

With the 5mm allen tool, try going richer by turning it ONE CLICK at a time clockwise. Remember to remove the tool and let the engine stabilize prior to making any further adjustment.

My 80 911 did the exact same thing. There was a broken wire inside the control box/computer. Shop soldered it up and it was fine. Need to find a porsche shop comfortable opening that up.

I agree with Slits except it should be a 3mm allen wrench and I don't recall any clicks in the adjustment. I make a very small adjustments (maybe an 1/8 of a turn) and blip the throttle after removing the allen wrench.

Jim, good info on the control unit wire, except it does not apply to a 2.7 with CIS. In 1980 the 911 w/CIS an Oxygen sensor and electronic controls, earlier cars did not have this.

Jim

Thanks Ron - I will give it a try tomorrow!

Mike did you check vacuum now that you pressures checked out? is the vacuum gauge in the range of 15-20 steady? regardless if it is 17 or 19 it should be fairly steady. If you are getting low readings or a funny tick in the gauge you need to look there before adjusting the sensor plate.

Not intended to challenge the master I just wouldn't jump on that plate until I was sure I ruled out everything else.

This is how I would proceed. Pressures, Vacuum, Valve adjustment, vacuum again then Timing, Then Sensor plate

Hi Rick

I haven't seen any mention of testing vacuum in the documents I have read. Do you have a link to the procedure?

Sounds like another gauge to borrow...

Thanks!

http://www.tuneruniversity.com/blog/2011/0...a-vacuum-gauge/

http://www.gregsengine.com/using-a-vacuum-gauge.html

A vacuum leak will cause your sensor plate to pulse.

OK - this makes sense. It is a $30 part so I will go get one today.

As long as I am connected to a vacuum line below the throttle plate I should be good right?

Thanks again!

I had a 79 with 3.0 cis......vacuum and seasonal changes drive it crazy.. What little I know I'm going with rick....check for vacuum leaks first.