CIS backfiring

[kmhemi]

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.

[psalt]

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 ?

[kmhemi]

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.

[psalt]

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.

[snbush67]

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.

[Flat6pac]

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

[kmhemi]

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

[snbush67]

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.

[kmhemi]

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?

[kmhemi]

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.

[TibetanT]

Subscribing

[Flat6pac]

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

[kmhemi]

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

[don gilbert]

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

[kmhemi]

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?

[boyt911sc]

Originally Posted by kmhemi

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.

KM,

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


Tony

[kmhemi]

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.

[don gilbert]

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

[boyt911sc]

Originally Posted by kmhemi

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?

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

[don gilbert]

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