CIS issues

[a239947]

Does anybody in Brisbane have a CIS test kit i could borrow?

Or alternatively, does anybody know a place in Brisbane where i can buy the metric fittings, hoses and guage to make one. 

I would like to test the system pressure on my 924. I'm trying to troubleshoot a cold running issue and a hissing and gurgling fuel distributor.

The car starts easy but wont idle, it just dies but if i give it a few good revs it seems to idle fine. Its also has a missfire until warm but is sluggish at lower revs. Once warmed up the car runs pretty good but is still a bit sluggish down low.

Im not sure if the issue is with the fuel pump or if its the distributor. I need to test my system pressure before i look at buying a rebuild kit for the dizzy.

Any help would be appreciated guys.

cheers

Dylan

 

[tazzieman]

Yes those 924s are hard to get perfect! When did the car start to behave badly? What has been done so far e.g. have you inherited a car that has needed work? 

The hissing & gurgling sounds possibly like there's too much fuel running into the FD.  From memory the quick check is to jumper the FP on and turn the mixture screw until the gurgling just stops. Assuming the noise is coming from the FD. Of course there are many components and you probably should get hold of a CIS test kit. Online troubleshooting often takes longer!

Some O rings in the FD can be replaced easily. The Haynes manual has plenty of system checks too.

Just a quick cut & paste from a doc I have handy. The car is pretty sensitive to mixture control in my experience. Doesn't take much to make it run badly! 

[a239947]

I recieved the car with the issue. Ive been doing a lot of research into the CIS and even spoke to a guy locally who rebuids them, he suggested i may have a pump issue and to check the system pressure before i start pulling things apart.

The noise is definitely coming from the FD, i stood over the engine with only the ignition on and pump running and it was easily noticeable. I also need to check to ensure there is no air being sucked into the system somewhere and also check the filter. 

Bit of work ahead of me but nothing im afraid to do myself. I just want to get it running properly until i can get everything i need to throw an efi system on it and do away with this overly complicated CIS.

[tazzieman]

I recieved the car with the issue. Ive been doing a lot of research into the CIS and even spoke to a guy locally who rebuids them, he suggested i may have a pump issue and to check the system pressure before i start pulling things apart.

The noise is definitely coming from the FD, i stood over the engine with only the ignition on and pump running and it was easily noticeable. I also need to check to ensure there is no air being sucked into the system somewhere and also check the filter. 

Bit of work ahead of me but nothing im afraid to do myself. I just want to get it running properly until i can get everything i need to throw an efi system on it and do away with this overly complicated CIS.

CIS isn't that complicated but you can't expect 30+ year old components to work as well as when they left the factory! 

Once sorted , CIS is as reliable as EFI in my experience - freezing cold winters and 40C summer days  But as parts prices often carry the Porsche Tax , EFI may be more wallet friendly.

[a239947]

So i was able to source the parts to check the system pressure today.

The guys at Industrial Fitting Supplies were a great help and pieced it together for me.

All seems within the specs of the haynes manual and other sources i found online. Control pressure and system pressue all within limits. Hot and cold aswell.

i guess i might look at the mixture like you suggested and see if it makes a difference. It does smell as though its a little rich.

Following that ill get a rebuild kit for the FD and and also check the injectors.

The car seems to run fine but the missfire when cold seems to be why it wont idle. If i give it a rev to clear its throat it idles just fine, even cold.

 

[Shady Speedway]

The CIS hates any air leaks.

The quick way to find them is with a can of WD40. If WD40 is sprayed at an air leak at idle, the leak will suck it in temporarily changing the air fuel ratio. You will then hear a change in RPM. Use the precision straw that the can comes with and methodically check each hose, gasket, injector and anything else around the inlet manifold.

Another cheap tool is a length of hose. One end in your ear, then hunt around with the other end. You will be surprised with what you can hear.

If the miss at idle is constant enough and you suspect injectors. You may be able to eliminate the cylinder missing by running it on 3 cylinders by way of dropping plug leads one at a time. If you (for example) find that the miss is coming from cylinder #2. Then move the injector from #2 and swap it with injector #3. Repeat the first test and see if the miss follows the injector.

[a239947]

Thank Shady,

They are some great techniques, ill give them a try. 

The missfire is definitely consistent when cold. Its smooth as a kitten when warm.

[tazzieman]

924s generally start on 2 cylinders and need the throat cleared. Is the vac advance unit working? Agree with Shady ,  check for any vac leaks. Is there any black smoke when you blip when cold? 

One other thing , the piston in the FD can get a bit gummed up . Rebuilding the whole FD is a bit tricky (not that I have tackled that) but O rings and checking that "do not drop" piston are easy jobs and peace of mind to boot.

My car is also very sensitive to moisture which gets in and around the distributor - which is poorly positioned near the cowl. 

It's well worth going through all the ignition checks in the Haynes manual with a multimeter. Sometimes people put the wrong coils in etc.

Sounds like you're getting there! I drove mine today and they great cars , real underdogs of the Porsche clan.

[a239947]

Cheers Taz ill look into those things. 

Im going to pull the dizzy just for piece of mind like you say. Rulling it out of the equation makes it easier to look elsewhere.