CIS backfiring
 

I have a 78 SC 3.0 I had to remove the CIS to fix some oil leaks. The car started easy and ran perfectly before I pulled the CIS. While I had it out I replaced injector O rings and all six injector sleeves and O rings. I used all new intake gaskets and replaced the old intake to airbox boots with new ones. I have it all back toegther and it runs but I have 2 problems. First its extremely hard to start cold now. starts easy when warmed up. Also I am getting some backfiring back through the airbox which has a pop off valve. When you start it the thing high idles then drops down to 900 or 1000 rpm just like it should. I have checked timing and searched for vac leaks. Should I drop the motor again to check the backside for air.vac leaks? I have been over everything I can reach a dozen times.
its a vac leak causing the backfire isn't it??? I think the cold start issue is a separate problem. I have done searches and tried about everything i have found.
Thanks for reading all of this. I really am stumped on this one.

Yes, it is important to separate the problems.

If the car starts fine hot, but has to crank a lot cold, suspect the Cold Start Valve. Did you mix up the wiring ? Does the air flow safety switch work ? Check the TTS circuit and if the CSV is getting power during cranking, you need to pull it and test the spray pattern.

When does the backfiring occur ?

Thanks for the reply.
Anything is possible. Everyone makes mistakes. So you're thinking that I might have gotten the plugs mixed up between the cold start valve and the warm up regulator. The Aux Air Valve is correct or it wouldnt work and it does. I will check it as soon as I get back home from work.
I hope that corrects the cold start problem. I'd say you're right.
I still have a bad vac leak to find.

Cold start valve and air flow switch.

You can do some simple tests. Does the fuel pump run with the Key ON (it shouldn't). Does the pump come on when you lift the sensor ? Is there power at the TTS during cranking ? Do the electrical test first before trying to pull the CSV.

I too recently went through this same issue and it took awhile before I got my CIS running right again.

Narrow down the specific leak location while the engine is in the car.

In addition to the above recommendations, double check the AAR hose, mine had a crack in it that separated more from when I had to jam the CIS back into the car because I didn't drop the engine (this created a ginormous vacuum leak), also the right rear manifold nuts are a total pain to tighten. Make sure you have used new gaskets and that they are oriented correctly.

There are two blueish green connections in the back you will know if you got them mixed up if your fuel pump is running before you start the engine it is not connected properly. The WUR and AAV and themovalve have the same power source (red-white stripe =power and Brown =Ground) so even if you got those mixed up it wouldn't matter.

I used starting fluid to narrow down the location of the leak and got it all straightened out just as my box of PMO's arrived in the mail.

The carbs have a little more snap to them (above 3500), for the price and being a street only car I should have stuck with the CIS it is a smooth and powerful system (instant start, warm-up was transparent, and no hesitation anywhere).

I have to caveat this by saying I haven't got my carbs totally dialed in yet or my distributor recurved so I reserve the right to change my opinion at a later date.

Backfire, you might try enrichment, more fuel, less backfire. Could be the injection is tight now.
Do you stumble with the cap off the oil tank?

Bruce

I've been working on the car and i'm making progress. I did verify that the cold start valve and the warm up regulator are correct. I also found another Vac. Leak. Now the car runs smooth but still just barely pops back through the pop off valve once in a while..its not a steady repeating backfire. I'm sure I'v got another leak somewhere. I'll double check the hoses at the AAR as mentioned above. I dont know if it will cold start because i've been running it. I'll know later tonight.
Thanks for all the help but I'm still not done yet.

Keith

Good advise from Flat6pac above.

Did you check to see if the engine speed, rpm's drop when you take the oil cap off? If the rpm's are dropping slightly then it is set up right and you probably don't have a vacuum leak it just may be adjusted too lean.

Try the oil cap. And if you think your oil cap may not be sealing properly then use something else to seal that off and see if your rpm's change.

update:
The engine speed is not affected by removing the oil tank cap it stayed the same....I know that it DID drop a bit before I took it apart.
Does that confirm that I still have a Vac leak?

I found another leak although small its still a leak. there is a short hose with a plug on it connected to a port on top of the rubber CIS boot and its barley leaking. Does anyone know where this goes so I can properly fix it?
I apologize if I used someone's picture. its the only one I could find that showed what I need.

http://forums.pelicanparts.com/uploa...1237511692.jpg

Subscribing

There is a hose that runs from there to the oil tank fillerneck. On an SC the oil system is closed and fumes from the tank go to be burned through that hose.
Bruce

I think I'll be able to get it all corrected after work tomorrow. I'll update to let everyone know the outcome.
Thanks to everyone that replied
Keith

why dont you turn your mix up a 1/4 turn and see if that helps.

I hate to mess with the mixture because the car ran great before I pulled the CIS. Its the same engine and same CIS so why would anything that like change? I'm not saying it can't. I just dont understand why it would. Is the engine running lean now because of air leaks?

CIS Vacuum line.........
 

KM,

The missing vacuum hose in your picture goes to the oil tank. Please refer to the attached picture below. HTH.

http://forums.pelicanparts.com/uploa...1237513904.jpg
Tony

boyt911sc:
Thank you very much. That helps lot. I love the car and want to fix everything right.. ALong the way I am finding where someone in the past has taken short cuts to make repairs. I correct them as I find them.

something has changed, most likely the volume of air, turn it up, test drive, if it doesn't help, put it back. messing with the mixture is no big deal, and necessary at certain times of the year, i change mine from cold days to warm days

CIS troubleshooting.........
 

KM,

Most contributing members try to help diagnose your problem/s but you have to be selective and use some good judgement in implementing those suggestions. I'm completely in agreement in your decision not to disturb the mixture setting because you'll be agravating the situation. Setting your fuel mixture richer is a band-aid remedy and will not solve your problem in the long run. Instead of just having a vacuum leak, your compounding the problem by having an improperly set mixture and a vacuum leak. Just my two-cents.

Tony

put your co meter on it, that will tell you right off.

it will tell him if he is off, but it wont tell him if it is because of an air leak. he says the car ran fine before he did the work, he most likely has something connected wrong or maybe a lose connection. after replacing all the seals, the car should either run the same or run richer because he fixed air leaks, not the other way around.

is the backfiring when cold, hot or both?

check the wires on the thermo time switch for the CSV.

Friday's Update:
I found a couple more small vac leaks last night and fixed them
The car started much easier now but it still pops, but only when its cold. I took the thing for a little drive and it ran better than it did before I started this project. And I thought it ran good then. The car ran fine and did not backfire once it was warmed up.
Here is a pic of the car we are working on..
http://forums.pelicanparts.com/uploa...1237587162.jpg

leaking
 

i was under the assumption that all air leaks were fixed, that was the reason he pulled off the system to begin with, (oil and vacuum leaks) where did you find another vac. leak at?

kmhemi, if you dont know how to set your mix yourself (as per souks method or others) i would get your co checked before any high rpm when warm, i still think your lean, just my opinion.

I removed the CIS because I had to replace the oil switch on the top rear of the engine due to a leak. Also I replaced the crankcase vent gasket and thermostat O ring. Some of the vac leaks are probably my fault. I really didnt know how sensitive this system was. Never had a CIS car before. I'm going to go back over everything again tomorrow and double check clamps, hoses, and recheck my intake runner torque. I'm finding alot of old cracked hoses that leak. They're small but they are still a leak.
I'm in parkersburg West Virgina so its not like there is a Porsche dealer anywhere close by. Columbus Ohio is probably closest and thats 2 hours away and there isnt a mechanic in this town that will ever touch my car...ask me how i know...and the thing may very well be lean as mentioned but I am going to find every air leak first no matter how big or small. If its lean I'll adjust it. I should know tomorrow afternoon if I am going to richen the mixture. I can always put it back where I started if it doesn't help I am starting to agree that its is lean since it only backfired when the engine was cold and needed a richer mixture.
I'm on my own with this. I'll get it sorted out. I never give up

way to go, its fun figuring it out yourself, and you will get to know your cis system personally, yes, the old hoses on the k-jet system are brittle and can be a real pain in the butt, and yes , retourqe everything, esp. the lower runner bolts. if you are going to be a cis master you will need to buy a few inexpensive tools that are a must, the cis fuel gages, dwell meter( If its a lambda car) and a good timing lite, you can get a co meter to, but in my opion, not necessary, i worked at coker bmw in tx from 82-98, and worked on some k-jet 320's, mostly all i remember doing to them was fuel pumps, not many probs at all, the first motronic 318's, different story. keep posting, and get a good cis trouble book, the bently is a must, but ben watsons how to tune and modify cis has more info on isolating probs.

well the bottom line is that if I am going to own these cars I have to learn to service them myself. I've had 914's and 924's 944's in the past. This is my first 911 and I can promise you that it will NOT be my last. I'll get whatever tools I need to keep it healthy. I like buying tools...

You have a nice looking ride there, KM! Good buy. Does the 3.0L still have the air pump?

I'm working on a rebuild of a 78 3.0L with the larger ports which came with air pump and A/C compressor, but am thinking of not using them. Makes things a little lighter, and I noticed the air pump gets in the way when trying to do a tune up.

Good right up on the stuff you are finding and fixing! It helps all of us.

Welcome to the Pelican team and have fun with the car!SmileWavy

yea, nice car, but it looks like the cups have a little backspacing issue on the front, think you can put 1/4 inch spacers on?

Don: Yes I agree that the front wheels could stand to be out a little farther. And I really DO appreciate all of your help. When I tore this thing down I found that the fan housing was broken and the fan itself had a big chip in it. Another board member came forward (Tom Butler) and got me the right housing and fan He even soda blasted them before he sent them to me. He has helped me twice more since then. Lots of great folks on here....

This 3.0 does NOT have the air pump someone must have removed it before I got the car.

Or someone could have replaced the engine with a later SC engine that didn't have the air pump. Lambda controlled car with 02 sensor didn't have an air pump.

yes, this is a handy bunch of people to know, just wish i had found them a few years earlier, but i might have ended up with a rs clone instead of what i have, not that theres anything wrong with that.

True! Only way to tell is via the engine number stamped on the housing, or if the engine has steel fuel lines that would be a tell tale sign. Of course, it is possible they could have plugged the air injection holes in the heads. There's a kit for that.

would be nice if it was an 02 engine, do you know?