How to Fine Tune Your Porsche CIS Fuel Injection

[@rg3412]

All this wisdom is invaluable to the Porsche community. Thank you for taking the time to produce it. I hope your channel gets discovered and its number of subscribers explodes.

[@klassikats]

Thanks RG, You had ask a question that I saw but for some reason I was unable to answer it regarding the "Toilet Seat" pop off valve. I do not believe in these valves and feel that for the most part they just destroy a $600 part. I have also found them to be not an effective measure in preventing air box failures due to back fires. I have replaced dozens of air boxes that failed due back fires and had the valve installed. My other issues with them is often the installation is done poorly resulting in vacuum leaks around the valve. The other issue is with the Oring seal at the top of the valve. As the Oring ages it hardens and will also result in a vacuum leak. For these reasons I never install these valves. Thanks for watching Kurt

[@rg3412]

@@klassikats makes sense. I am actually chasing a vacuum leak on my newly acquired SC. I’m using the propane tank and hose method but I still can’t find the damn leak. I suspect it’s harder to do than advertised. Perhaps you could make a video focusing on vacuum leak, where are the usual suspects on the 911 and techniques you might have found to spot them.

[@klassikats]

@@rg3412 RG, the best way to find a vacuum leak is to use a smoke machine. You can pick up one pretty cheaply, here is the link to the one I'm using amzn.to/3DnrVkn . to use you need to remove the air boot and connect the smoke machine to the throttle body. I also use this cap set amzn.to/3oHSzjR to connect to the throttle body. Once connected simply use a flashlight to look for smoke escaping from hoses or gaskets and repair as required. The most common leaks are around the injector buckets, Oil cap gasket, old vacuum and vent hoses, and lastly the airbox seam. I Will work on getting an in-car vacuum leak check video. Kurt

[@rg3412]

@@klassikats Thank you so much for your help! I will give the smoke test a go. Can’t wait for that leak video, as I’m sure it’s going to be good!

[@rg3412]

@@klassikats followed your advice and guess what: the pop-off valve is leaking! I uploaded a video to show it to other owners: kzbin.info/www/bejne/maqkmmuPhMx1f7s Thank you again for your advice! Now I need to figure out how to fix this.

[@henryzeisler8280]

CIS is still my favorite fuel designed for Porsche! It was late and I typed it wrong... Thanks for your time.

[@klassikats]

Actually Bosch invented the system Porsche was just the first manufacturer to use it on the 1973.5 911T models. Thanks Kurt

[@henryzeisler8280]

I remember. I left Ferrari after 7 years to go to work for Porsche/Audi (3 years in Germany) then back in Chicago for another 9@@klassikats

[@johnfreeman1189]

Thanks for the sage advice! Love that nostalgic Porsche.

[@klassikats]

You bet!

[@philjetv8619]

Thanks for sharing, really explaining in detail, I have to do this work on a Carrera 3.0 77 right now :)

[@klassikats]

Glad it helped! Thanks for watching Kurt

[@tomsilbersiepe7594]

Excellent. Learning so much. Thank you

[@klassikats]

Great to hear! Thanks for watching Kurt

[@jasonwright9555]

This is a fantastic video. Thanks so much for posting. I have a 1977 2.7S and I've been having issues for years with no WUR performance during a cold start, even though it has been rebuilt/calibrated, and occasionally some warm start issues too. Once the car is up to temperature it is running smoothly and pulls strongly. I've replaced or rebuilt just about every component on the CIS assembly and the issues are still there. However, I have just seen in your video that my vacuum lines are set up like a 3.0ltr SC! I'll be testing the vacuum lines as per your video. Thanks again.

[@klassikats]

Jason, if your cold control pressures are bad then the vacuum lines will not resolve the hard start/poor cold running conditions. There are only a couple of rebuilders out there and not all are equal. I Use CIS Flowtech in Alabama and have had good results. Kurt

[@jasonwright9555]

Thank you.@@klassikats There are a hell of a lot of CIS "experts" out there on the 'inter-web' and I have found several conflicting diagrams on the CIS assembly layout in just one quick Google search. Sorry, i forgot to mention that my cold control pressures were in spec the last time I checked. Nevertheless, your video has given me renewed enthusiasm to start the investigations again. 🙂

[@klassikats]

Yes reliable information is hard to find on the internet. Good luck with your repair. Kurt

[@mike-wv7vs]

Thanks kurt!. I have 911 Sc 1980 that have surges idle during coldstart and it takes a minute to run smoothly.

[@klassikats]

Mike look at your control pressures and the aux air slide. Also check the fuel mixture settings with the engine hot and using a CO meter Kurt

[@saint_pyre]

great video. Thank you. The clock isnt working.

[@klassikats]

Thats not unusual for these cars Kurt

[@JamesGolomb]

Kurt, I am so grateful for these instructional videos on the CIS. I am the original owner of a 1976 2.7L 911S. It was initially bought in the US but has been living in Switzerland for the past 35 years. The engine was recently completely rebuilt and is now running better than ever. For the past 48 years I was always completely baffled by the CIS. It was the one aspect of the engine that for me was essentially a black box. After some exhaustive reading and watching your videos I now have a good understanding of what it is doing. Thank you very much! Only one question: Still not sure I get why the manifold pressures differ reciprocally with changes in engine speed between the WUR intake and the deceleration valve intake as both seem to be below the throttle butterfly (although on different sides). A few more words of explanation here would be great.

[@klassikats]

James, Manifold vacuum is an indication of load not engine speed. when the engine is has a High manifold there is minimal load and therefore less fuel is required. When manifold vacuum is low there is more load on the engine and it requires more fuel. The decel valve connection and WUR can both be below the throttle plate although port sizes can also vary which will vary the amount of vacuum placed on each unit. Kurt

[@02powertube]

Fantastic videos 👍🏻👍🏻👍🏻

[@klassikats]

Glad you like them!

[@peterdefranceschi]

Hello Kurt, this is a very good video with lots of information! Can you tell me what brand and size the vacuum-lines are that you are using here? I like the idea of running different colors... Thanks, Peter

[@klassikats]

The Red and Blue lines are actually a BMW vacuum hose used on the 1980's models. Not sure of the part number off the top of head, but if you look up a 3, 5, 6,or 7 series car you should find them pretty quickly. Kurt

[@danieljourney8188]

Very cool stuff it’s really surprising how much the vacuum signal varied from one port to the next…a reminder that everything on these cars were designed in a specific way for good reason. How long did you run the new engine for before the first valve adjustment?

[@klassikats]

I generally run the engine on the test stand for about 3 - 4 hours. This allows for the assembly lubes and initial parts beding debris to become completely washed down into the oil, through the filter and anything left will come out in the oil when its nice and hot. It also allows for the valves to bed to the seats and the engine to completely expand then contract once cooled. This allows me to retension the head studs, do my valve adjustment and get it ready to go into the car. Once in the car first service is done at 2000 miles with another valve adjustment. After that the car goes back to its regular maintenance schedule. Kurt

[@TandrupWS]

Hi Kurt, I really enjoy your videos and have a question, I have a 1974 2.7 with CIS the car starts well and drives great under load (both cold and warm) but driving it in town is a different topic, it’s studders and kind of like a car with a wild camshaft - it does not have that, do you have a clue what this could be? Best regards Lars

[@klassikats]

Thats a tough one being that I cant see the car. I would start with the basics. Engine mechanical condition, ignition system and lastly fuel pressures and mixture settings. I know its not a great answer but its the the way that you have to work though any drive-ability issue. Kurt

[@diederickzeelenberg6867]

Hi Kurt, this is very informative, thank you! I have a 1977 2.7 as well. I had the fuel distributor and 033 WUR rebuilt. I have double checked and the fuel pressures are in spec. This vacuum hoses are hooked up identical to the engine in your video. The engine will start up cold, get to an idle but when I rev the engine it immediately dies and then refuses to start again. I have smoke tested and found no leaks. Now I'm at the end of my wits. Do you have any suggestions?

[@klassikats]

Diederick, If the fuel pressures and fuel volume is good then the issue is not fuel. With an issue like this I will always look at the big picture. Have you looked at the ignition side of things yet? Its possible that you are losing spark and hence the reason for the no start after stalling. I would start with checking all of my connections throughout the engine compartment to make sure that the CDI box is getting good grounds, power signal, and trigger signal. Hope that helps Kurt

[@RustyRatchetGarage]

Is it possible to back date a 81 CIS unit to a 78 79. Deleting the lambda and o2 sensor

[@klassikats]

It is possible to back date, although you would need to change the fuel distributor and warm up regulator to the ones used in 1978-79 models. If you dont want the O2 sensor to control your fuel trims you can just unplug it. This will keep the system in open loop and the frequency valve will remain at a constant 50% duty cycle. Kurt

[@RichieRich845]

👍

[@klassikats]

Thanks. Kurt

[@alexlerner2608]

I actually had a question. What would cause the car to start and Immediately stall over and over again 1977 targa 2.7

[@klassikats]

usually that is a fuel pressure issue. The car starts on the cold start fuel injector but is unable to get enough fuel to keep running. Check your control pressure Kurt

[@jasonwright9555]

Hi. A year late but just wondering if you got this problem sorted? I had the same issue after an engine rebuild and I managed to fix it. I'm not an expert and not even in the same league as Kurt, but let me know and I will tell you what I had to do. (It's a long one)

[@user-gl2eq2ly4g]

Kurt just had a 3.0 Carrera engine rebuilt by local Porsche tech/dealer ...... it smokes like crazy on start up with milky brown fluid coming from exhaust .....any initial thoughts?

[@klassikats]

Thats not good, a small puff of smoke on start on is normal but it should not smoke like crazy. The milky Brown fluid sounds like oil in the exhaust. First thing i would do is check the engine oil level and make sure that it is not over filled. If that is not the case then it needs to go back and come apart again as it wont fix itself.

[@user-gl2eq2ly4g]

@@klassikats Thank you ...... .....I did bring it back to the dealer.... They said it's fine just drive it ..... My own thought was overfill too so I'll drain it and see ...... Thanks for your insight.