BlackbirdWS6

I had my car tuned a very long time ago by Julio at Cartek. Overall I am happy with my tune but he informed me that I'm running very rich at idle and it could not be leaned out any farther within the limits of the stock computer. BS or not? I think my car has very typical mods and I would think that it should be do-able.

The car runs very strong and puts down respectable numbers for the mods but I can sit and let the car idle away a tank of gas if I let it.

-brian

Injuneer

The closed loop A/F ratio is hard coded into the PCM, so there's not much you can do to change it, unless you have the PCM set up to run in PE mode at idle. But getting it to idle decent in closed loop shouldn't be that much of a problem with the CC306. High overlap is what screws up the idle A/F ratio, since the O2 sensors pick up the air that leaks into the exhaust via the overlap, and the PCM adds fuel the engine doesn't need. Probably be a good idea to run a data log, to see what is happening. The 58mm TB often causes "split" BLM's, which can result in one side of the engine running rich and the other lean. Other causes of excessive fuel can be exhaust leaks before the O2 sensors, misfires, or faulty O2 sensors.

Was Cartek able to tell you exactly how rich it was running? As I recall, they gave up working on LT1 engine several years ago.

BlackbirdWS6

Thanks for the input. The car idles just fine when it warms up. No stumbling or any other bad tendencies. It just runs rich.

I doubt they would be able to tell me how rich it's running unless I took a ride back there. They hardly do any work on LT1's but they occasionally do the LT1 tune here and there. They were the only guys in my relative area that would tune the car after I did the heads/cam to it.

After the dyno, I had some header bolts come loose which led to the gaskets going south. They were replaced shortly after and no problems since.

mdacton

With your mods you should be able do do something about it.

Do like fred said and get some data logged and we can kind of firgure where the problem is. Has it always done this or just started?

Plenty of others run similar set-ups with no issues

BlackbirdWS6

Nah it has always done this but it just is an annoying trait than anything else. It has no drivability issues but the cold start is usually entertaining. It bogs then the idle goes up, bogs then the idle goes up not to stall over and over. Once its warm no problems.

I will get it datalogged. Btw, this may not mean much but my 02 mV readings are usually in the 120-150 range on both sides at idle.

Injuneer

120-150 "milliVolts"? If so, its indicating lean, not rich. If its so rich that its stalling and the smell is extreme, you have your problem.... incorrect O2 sensor readings.

If it only does this when the engine is cold, how long does it take before it clears up? Does is clear up when the PCM goes into closed loop?

On cold start, with no AIR, the O2 sensors should read 450mV, then gradually move higher or lower as the sensors warm up. With an AIR pump, they will drop as low as 004mV before the PCM kicks into closed loop. With !AIR, as you indicate, they should push up to the rich side as the sensors warm up, then gradually drop back closer to 450mV as the PCM senses that the coolant is warming up, and reduces the cold start fuel enrichment. After about 3 minutes, and with the coolant temp over 120*, it should be kicking into closed loop. Does your scanner indicate this is happening?

FASTFATBOY

He may have went too far on leaning it down.

WHen I started my car for the first time with a fair size solid roller I also thought it was rich. WHen I towed the car to Ed wright to get it tuned he explained to me that rich and lean have similar smells out the exhaust.

Lean will burn your eyes and rich will not.


You need a datalog.


WHere is the O2 voltage in closed loop idling?


David

BlackbirdWS6

The 02's read 450mV at start-up when cold. They gradually work their way down in the 100's once the car is fully warmed up and idling. The smell does not burn my eyes. It cruises in the 800mv range on both side when going down the road at usually a little above 2k rpm.

-Brian

FASTFATBOY

What is the MAP voltage?

David

Stl94LT1

Adding "Closed TPS" timing will clean up the combustion at idle.

Injuneer

Your O2 sensors are telling the PCM its lean on cold start, and after it warms up. You need to do a scan and see what the long term fuel corrections look like.

If the O2 sensors read a somewhat steady 800mV at cruise, it is running rich, and since they are not cycling rapidly (~9 times per second) from 0xx - 9xx mV its not going into closed loop. Apparently he did an open loop tune, which also should not be a requirement with your setup.

BlackbirdWS6

Thanks for the info. I am actually scanning the car with an interceptor scan gauge. It may not be reading fast enough to notice the rapid cycling. I will see if I can get it to read faster and see if there is the rapid cycling you are talking about. If I don't see any difference or I am unable to do that I will get a proper scan gauge on it.

More or less it's a poor tune then? I don't want to waste any of your time until I get the info you guys need so I will report back when I have the info.

Thanks again.

-Brian