CIS backfiring - Page 2

T77911S · 03-20-2009, 05:52 AM

Quote:

Originally Posted by don gilbert

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.

T77911S · 03-20-2009, 06:04 AM

is the backfiring when cold, hot or both?

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

kmhemi · 03-20-2009, 02:13 PM

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..

don gilbert · don gilbert's Garage

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?

don gilbert · don gilbert's Garage

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.

kmhemi · 04:03 PM

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

don gilbert · don gilbert's Garage

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.

kmhemi · 03-20-2009, 04:08 PM

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...

TibetanT · TibetanT's Garage

Quote:

Originally Posted by kmhemi

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..

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!

don gilbert · don gilbert's Garage

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?

kmhemi · 03-20-2009, 06:09 PM

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.

ruf-porsche · ruf-porsche's Garage

Quote:

Originally Posted by kmhemi

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.

don gilbert · don gilbert's Garage

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.

TibetanT · TibetanT's Garage

Quote:

Originally Posted by ruf-porsche

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.

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.

don gilbert · don gilbert's Garage

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