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> 2.7L CIS surges at idle when warm, UPDATED with pressure readings 7/6/15
Kansas 914
post May 6 2015, 11:10 AM
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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!
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Ferg
post May 6 2015, 11:14 AM
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Could be really rich. Do you have a CO meter?
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Kansas 914
post May 6 2015, 11:17 AM
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QUOTE(Ferg @ May 6 2015, 11:14 AM) *

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

Hi Ferg,

I have access to a wide band AFR.
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rick 918-S
post May 6 2015, 11:36 AM
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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.
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white1975
post May 6 2015, 12:04 PM
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check the timing they will hunt if the timing is off
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Kansas 914
post May 6 2015, 12:05 PM
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QUOTE(rick 918-S @ May 6 2015, 11:36 AM) *

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.

Thanks Rick,

Great information.

Are you and Sandy back home yet?
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Kansas 914
post May 6 2015, 12:07 PM
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QUOTE(white1975 @ May 6 2015, 12:04 PM) *

check the timing they will hunt if the timing is off

Thanks, I wouldn't have thought of that.
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sixnotfour
post May 6 2015, 04:43 PM
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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
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Kansas 914
post May 6 2015, 05:03 PM
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QUOTE(sixnotfour @ May 6 2015, 04:43 PM) *

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
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Ferg
post May 6 2015, 07:30 PM
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What's your elevation? 7k?

It was at about 5k, did you notice the issue when you picked it up?
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Kansas 914
post May 7 2015, 08:32 AM
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QUOTE(Ferg @ May 6 2015, 07:30 PM) *

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"... (IMG:style_emoticons/default/dry.gif)

Thanks for your help on this.
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luskesq
post May 7 2015, 08:52 AM
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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
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Kansas 914
post May 7 2015, 08:57 AM
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QUOTE(luskesq @ May 7 2015, 08:52 AM) *

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...
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SLITS
post May 8 2015, 08:55 AM
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The CIS Testing setup is not just a gauge.
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Kansas 914
post May 8 2015, 08:59 AM
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QUOTE(SLITS @ May 8 2015, 08:55 AM) *

The CIS Testing setup is not just a gauge.

Thanks Ron - is there one in particular you like? I have seen several for sale.
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SLITS
post May 8 2015, 09:05 AM
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QUOTE(Kansas 914 @ May 8 2015, 07:59 AM) *

QUOTE(SLITS @ May 8 2015, 08:55 AM) *

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).
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Kansas 914
post May 8 2015, 09:10 AM
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QUOTE(SLITS @ May 8 2015, 09:05 AM) *


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.
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SLITS
post May 8 2015, 09:22 AM
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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).
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Kansas 914
post May 8 2015, 10:01 AM
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QUOTE(SLITS @ May 8 2015, 09:22 AM) *

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?
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SLITS
post May 8 2015, 10:25 AM
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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
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