CIS pressures - stumbling

[dede911]

Dear All,

My 82 ROW porsche starts very good (cold or hot), but on cold starts idle is sometimes irregular.

Hot or cold, I have a stumble around 2000RPM.

Today I started checking CIS pressures :

Cold system pressure 5.1 bar
Cold control pressure WUR disconnected 0.75 bar (T ambient 9°C)
Cold control pressure WUR connected 2.8 bar

To perform these test I jumped the FP relay

Before the "real test" I forced the FP by lifting the air sensor in the air box...By doing that, have I pumped fuel in the oil/engine? Me silly????

CCP seems very low...could be very rich...

How to proceed???

Thx,

André
Belgium - foggy - cold

[stlrj]

Start with an ignition tuneup- new wires, cap, rotor and plugs.

[schamp]

Along with the ignition tuneup start with a new fuel filter. Actually a fuel filter would be the first thing I would do. The tuneup won't hurt. Valves next, not for the stumbling but will make it run better and right. You might check for play in your distributor. Let us know. Spencer

[dede911]

Fuel filter has been replaced 2000 Km ago, Valves adjusted 300 km ago, Injectors replaced ca 2000 Km ago...

The ignition check is something I still have to do, but I have concern about the low ccp, that the mixture will be to rich...

What is your opinion?

André

[Gunter]

Originally Posted by dede911

Before the "real test" I forced the FP by lifting the air sensor in the air box...By doing that, have I pumped fuel in the oil/engine? Me silly????

CCP seems very low...could be very rich...

How to proceed???

André
Belgium - foggy - cold

Lifting the Air Sensor Plate (ASP) briefly with Ignition ON will send fuel through the injectors and that's o.k. for a short burst.
You could check delivery from the FD by placing all injectors into 6 glass jars and lifting the ASP briefly. (2 Seconds)
Volume of gas should be the same in all jars.
You can try and adjust the WUR for cold pressure by moving the plug but first, I would check the small screen in the line. Open the line on the WUR; you'll see the small screen that sometimes gets clogged.
The "plug" can be made adjustable or get a spare WUR for your year.

WUR Adjustment Plug

Modified my WUR

[dweymer]

Andre-you are checking two systems at one time. Stop doing that, check one system fuel or ignition, all the way through. Then move on to the next.

For the ignition-
1) Replace distributor rotor and cap-keep the old as spares.

2) Remove and inspect the spark plugs, clean and re-gap as neccesary.

3) Start the car at night no lights on and look into the engine compartment to check for sparks from the spark plug wires. You can also check the resistance of the wires(specs can be found by a search).

4) Get a timing light and check your timing, adjust as neccesary.

That should do it for ignition.

Then move on to fuel system, checking pressures and fuel delivery using procedures outlined here: http://members.rennlist.com/jimwms/CIS/CIShome.html

Once you have confirmed CIS is working properly you can move on to idle speed and air/fuel mixture.

[dweymer]

Gunter-I was not sure on when he lifted the sensor plate, but if he did that before reading anything wouldn't it alter the cold pressure numbers by releasing system pressure?

[dede911]

Thanks for the replies

I forgot to mention that the plugs were replaced and gaped ca 2000 km ago...
Cap and wires are not replaced during my ownership (> 1 year)

I do not excluded ignition issues, but I first want to cleare the fuel pressures (so that I can play with my diy gauge set up)


I repeated the fuel cold control pressure test, and discovered that after switching off the ignition switch and fuel pump, pressure went up to ca 2 bar...
(when FP was running, again I measured 0.75 bar)

How can the pressure increase when pump is switched off???

definitely need advice .....

André

[dede911]

Is no CIS guru who can help reading these pressure values???

Help would be very welcome

André

[boyt911sc]

Originally Posted by dede911

Today I started checking CIS pressures :

Cold system pressure 5.1 bar
Cold control pressure WUR disconnected 0.75 bar (T ambient 9°C)
Cold control pressure WUR connected 2.8 bar

Thx,

André
Belgium - foggy - cold

Andre,

Your cold control pressure was too high for ambient temp. of 9°C. What do mean by 'CCP WUR disconnected 0.75 bar' ??? Could you elaborate a little bit on this subject? System pressure very good. From cold start have you observed the rate by which the CCP increases over a period of time? Your WUR should show a gradual increase in fuel pressure over time (from cold start to say 10 mins). Keep us posted.

Tony

[dede911]

Dear Tony,

With WUR disconnected I mean electrical power to WUR disconnected

2.8 bar is the pressure engine cold, WUR electrical power connected, after some minutes...

I think that because my WUR has a vac port, I can only measure the exact pressure with vacuum (hand pump)...

André

[T77911S]

i dont know much about 82 cis, but, here is what i had for a 77.
cold- .8 bar
i have a thermo time valve that blocks the vacuum when cold to richen it even more. once the TTV opens,(20sec), cold=1.8bar.
hot with vacuum=3.7 bar ? (from memory, i have the values at home).
with vacuum removed it was about 2.8 bar.
it looks like your presurres may be ok. also check hot with vacuum. i hope this helps.