I just got this car togethor, it's all stock other than the smog crap taken off. I had another pcm tuned for my stock engine with the emissions tuned out but after it warms up and goes to closed loop it runs horrible. Doesn't idle good and almost wants to die sometimes under real light throttle, just off idle. No codes at all. Have checked all sensors with scan tool and they seem to be in the normal range. It will start to stumble at idle then pick up but when it does smooth out it jumps to open loop just for a couple seconds then back to closed. So I put the original pcm back in that was tuned for a cam and blower. It appears to be an open loop tune because it never does switch to closed loop. Here is the funny part, it runs great. Why would this thing run great with an open loop tune but horrible with a regular stock tune?? I have no idea where to go now.

 

Do the O2 sensors all work?

Are both tunes either MAF mode or Speed density (or is one MAF and the other speed density?)

The ONLY difference in the tunes other than the smog crap is one is open loop the other is closed? No VE table, MAF table, or other fueling or timing adjustments?

You must allow closed loop time to 'learn' fuel trims. It will run like crap until it has developed these fueling corrections. I believe if you disconnect the PCM from the battery it will loose acquired fuel trim information.

When the engine is cold it will run in open loop for about 3 minutes, before going closed. How does the closed loop tune run during this startup time? You might need to drive around for a while to learn the fuel trims, then the next day do a cold startup and see how it runs in open loop.

 

I really can't tell you what all is done in the non stock tune. I don't have any way of reading the calibrations but I was told it was an open loop tune. The stock tune is just all stock other than the smog crap deleted out. The stock tune will run fine while it's in open loop but after it changes to closed it runs really bad. I tried to drive it so it possibly could learn out but it was so bad I could barley drive it. It would pop back through the intake and almost die. It runs good on startup though. But then again it starts in open loop.

 

Vacuum leaks and exhaust leaks as well as Split BLM's caused by intake leaks and certain cams can cause the Oxygen sensors to have false readings and majorly affect the A/F ratio. This could cause way too much fuel to be thrown at one bank and practically none at the other. Check your BLM's. If one is pegged at 108 and one 160 you have a problem. I fixed this in my car and my brothers car by programing in a "blm locker" and put my car in "speed density" mode. I may go back to "MAF" mode when I get more time to tune the car and if that doesn't unlock the BLM's. The BLM's can be locked in the "ECM Constants" table of whatever program you are using. The "ECM Switch" table can put you into "speed density" mode.

O yeah. Try to fix your Split BLM problem first if you have one. Do a search for "Split BLM's" and you will find a lot of information on how to fix your possible split blm issue.

 

Smog taken off? Is there the EGR still there?

Sounds like the tuned blower PCM is setup for your CAM, which if the CAM is big enough any PCM with working 02's will have a problem with.

Are you saying the "closed loop" PCM runs just as good as the stock tuned pcm while in open loop?

 

Closed loop does learn fuel trims, but if the initial base tune runs great, and gets worse as "closed loop" takes over, then this is a sign that the 02's are solely responsible for the damage meaning exhaust leaks, intake leaks, injector leaks, CAM all play a part in throwing 02 readings off.

If the base tune runs crappy, and gets better as 02's take over then the base tune fueling is garbage... 02's cannot adjust timing which makes a world of difference in 95% of the engine driveability range, and can complicate diagnosis.

Gee, hope that helps!

 

Thanks for the info guys. The engine is bone stock other than I removed all the emissions. When I got the car it didn't have an engine. It was a cammed and blown engine so the pcm was tuned open loop for the mods it had. I got the car and put a stock engine in it and bought another pcm and had it tuned for a stock engine but had the tuner just delete the emissions. Started great and ran fine but just as soon as it went out of open loop and in to closed loop it ran like total garbage. So I threw in the original pcm with the open loop tune for the cam and blower and it runs great but it never changes to closed loop. I mean it would probably run better yet if it had the proper tune for the stock engine but you know what I mean. So the facts are that no matter what pcm it has in it as long as it is in open loop it rune perfect, closed loop you about can't drive it.
I did check for intake leaks and found none and it doesn't have any exhaust leaks either. Could the O2s be just total junk?

 

Sounds like the O2 sensors or the wiring going to the O2's. Mine did the same thing. The more I mess with these cars, the more I believe that O2 sensors go bad a lot more than we realize.

 

I agree the 02 sensors do go bad a lot more than we realize but only on a severly modded motor that runs pig rich at WOT,

I personally as a last resort changed my stock 115K 02 sensors after the 383 cam, heads, 650hp hoping that it was just bad 02's even though it ran great right before the removal of the stock cam... yes it ran great for about 20-30 mins (after PCM reset) then started noticing the old signs of what I was hoping was bad 02's... it's really a "bad" cam doing it.