mikey

iTrader: (6)

Hey guys, have you had any luck tuning very large cams in the 246/254/108 range on a stock CI LS1? The only way I can get it to work is by tuning the PCM open loop. Closed loop a/f control just does not work. This is the way I tuned my race car but I wanted to actually try to get this cam to run on the street. I know its the LS thats killing me.

Mikey

Bink

After screwing with it for quite awhile I pulled the plug and went open loop. NoGo told me I'd be better off open loop- and of course he was right
The oxygen that sneaks by, due to overlap, really confuses the sensors - the PCM thinks you're lean and adds fuel.
I'm not sure how the boys Down Under get around the overlap problem but I think they run the O2 sensors MAFLESS.
Oh....My cam 239/251, 106, 0.570. FWIW.
joel

NoGo

iTrader: (2)

That's correct. Once you throw a P0101, the LTerm Learn gets turned off.

mikey

iTrader: (6)

LOL, I threw that 101 code right away but modified the table and got around it. I'll just tune it open loop as I thought I would need to do. Thanks!

JimMueller

iTrader: (9)

So under which condition do you know it's better to switch to open loop? Only if you get the P0101? A certain number of degrees of overlap?..?

mikey

iTrader: (6)

When the PCM has a tendancy to overcorrect the fueling (adds too much fuel) and sends the LTFTs +xx but the a/f meter shows otherwise. I tune open loop using the injector flow rate to get the steady state fueling right then the PE for WOT. Just disconnect the O2 sensors and deletes the codes. It's actually quite simple to do. The only down side is that you have no part throttle correction so it can adversley affect driveability and fuel economy. But then again, if you use a cam of this size, you better not be concerned about either of therse ...

GrannySShifting

iTrader: (10)

you can get open loop driveability as good if not a good bit better with an open loop tune with the cams causing lotsa reversion

Cmarsh93z

Mikey, once you are in open loop...log the map reading, and rpm. Then just adjust the VE table in that area, and bam! I have tuned a 251/247 107lsa cam in a stock head 346..and it drives perfect at 15.0:1 at part throttle..13.9 under moderate load, and 12.9 at wot. Just takes alot of playing.

Chris
AMS Racing

NoGo

iTrader: (2)

I'm glad this open loop thing is finally catching on. Most people used to cringe or throw up arguments when we were tuning open loop. My personal car has not had O2 sensors on it for over a year and the majority of our BIG cam cars have been running open loop for over a year. Just to provide some legitimacy to the long term effects of running the car without oxygen sensors. Basically, there aren't any long term adverse effects.

Bink

And it would have remained Voodoo if you hadn't shown us how to do it!! How are you, NoGo?? Staying very busy I hope.

joel

NoGo

iTrader: (2)

This site has been keeping me pretty busy.......which is good and bad rolled into one.

The tuning has been going nuts lately. The PM box gets full in about 2-3 days now.

Bink

Busy is VERY Good!! Keeps us out of trouble.

joel

gameover

well i have a big cam and MAFless tune and my LTFT's work fine.

NoGo

iTrader: (2)

LTFT Learn is disabled, not the LTFTs, as I have seen it.

If you know otherwise, please correct me.

Additionally, the type of exhaust that you are running plays a big factor into this. Some exhaust / cam combinations just simply won't report LTerms correctly (with the stock O2 offset).

iateyourcat

Can I turn off P0101 Mass or Volume Air Flow Circuit Range/Performance Problem in order to keep LTerm learn from being disabled or are there other codes that will also disable it?

HumpinSS

iTrader: (1)

How does the LTFT's work if the O2 sensors are taken out of the loop and running in open loop?