I've been trying to get my car tuned for my CC306 383 and I noticed that every time I upload a tune the car runs ALOT stronger and then slowly falls on it face after driving it for a while.
Even if I upload the same tune it had already.

What do you guys think could be the problem??

 

Do you have a closed loop tune? If so, it might be bad feedback from the O2 sensors. With a new upload, the long term fuel corrections are probably reset to 128. As the PCM "learns" the long term fuel corrections, its may reduce the power because its running too rich or too lean. Use some free scan software to watch the long term fuel corrections (BLM's) as the PCM learns. That will tell you if this theory is correct.

Your "open" long tubes could be screwing up you O2 sensors pretty badly.

 

yes, Its a closed loop tune. I had a bad split blm problem that I somewhat fixed with VE Master, and now my BLMs seem to be OK. Here is the latest log after about 70 miles on the tune.

oh and I'm running an X pipe now, Just haven't changed my sig.

 

I was wondering if by making my car run in open loop all the time, the problem goes away. If it does, I need new O2 sensors right?

Can I keep my current tune and just set it to open loop? or will I have to modify anything else?

Thanks for the help.

 

I fought this one until the very end including months of tuning and changing 02 sensors, then end in my case was switching to Open Loop.

Trust me, the quality and improvement keeping it open loop is worth it.

I was getting lean readings on my wideband so I decided to use that signal to feed the PCM (both sides) but with the WB02 in only one side of the exhaust the right side was going crazy since it never saw a change in fuel.

Long story, in my case the stock 02's were reading rich and the PCM was pulling fuel creating slight weak surges on accell and cruise, Switched to open loop and it's consistently smooth.

 

Have you also confirmed this issue by just unplugging the batt to let the PCM reset?

Just sounds like simple tuning issues, honestly. All of my rebuilds required MAF calibration. I was having similar problems until I learned to calibrate.

I respect those going open loop but take a look at my sig. Even a more radical cam than yours and I have my car running almost stock (part throttle) in closed loop. You should be able to do the same.

Take a look at the stick up top for what I mean specifically on MAF calibration under WOT tuning without a wideband.

You confuse me with the discussion of split BLM's and VE Master. In closed loop, VE is not used.

 

Your trace looks good, L/R short term BLMs' at cell 16 near the beginning of the trace look out of balance 106/129 but they clean up 126/130 by record 310. The Long terms at cell 16 look crappy 122/150 maybe some old stuff needs a PCM reset or more learning to clean up. Otherwise your drive ability short term BLM Cells2,3,4,7,11 all look good in the 120-130 ranges, really doesn't look like an O2 mixture lean/rich fueling problem and both the O2 switching voltages look normal 0.200-0.860 . Although you are within specs for stock fans, you are running this thing pretty hot. It starts out at 195*F and is running 230-235*F at 30-48 MPH (you got the air dam installed ?) does you dash gauge look the same ? Your OP said "car runs ALOT stronger and then slowly falls on it face after driving it for a while." Was it running bad during the trace you posted 0-48 MPH, sluggish or missing ?

 

Well, before I even messed with anything else other than closed tps timing, My BLMs use to be way off of each other. I ran VE Master twice and my BLMs came closer together. So it looks like it helped a bit

No I do not have the air dam installed yet. But I'll install it today.

My dash gauge reads fine.

The log was After it started to run sluggish.

Thanks for all the help guys!

 

This is exactly the problem with 02's and cams, they pick up the excess unburnt fuel from the cam overlap and throws the reading off... you wont see it in the 02 readings because the ECU does what it can to get what it "thinks" 14.7afr, some people say it makes the car run richer but mine was definately lean, no doubt about it, start getting that slight lean cruise stumble (under 1900rpm) and slight waves of ueven power accelling slightly in the low gears under 1900rpm. Switching to Open Loop with the proper VE's it's buttery smooth and crisp, the same low speed bucking/surging is just about eliminated.

side note - I was assuming everythings working properly and he knows what he's talking about and is why I jumped straight to the 02's/closed loop being the problem.
Now, the reason I think he know's what he's talking about is because this behavior after PCM reset is exactly what happens when the 02's are reading improperly.. it starts off great and progressively gets worse until you notice it and goes away if you reset the PCM. If you have the 02's working there will be nothing you can do to fix it permanenly unless you have exhaust leaks or bad 02's. You could disable Long Term correction and run purely off Short term correction or remove power to the PCM every time the key is turned off to force a reset, this all might be ok if you mainly drive short trips but it will catch up to you on long trips. 02's will never read right with large cams when the engine is in the lower RPM's.

For me, I didnt really care/notice the stumbles until I turned off closed loop (ran in open loop) after dialing in VE tables with VE master and noticed the nice smooth clean part throttle/cruise power almost felt like a different cam was installed. When I re-enabled 02's after driving in OL for awhile is when I started paying attention to the cycle of degredation closed loop caused over time and tried everything to stop if from happening, finally gave up like everybody else has.

A quick test: unplug the 02's or program it to stay open loop and drive it for a while see what happens however you'll need a good MAF and good VE calibrations to prove this out since if those are off it could run bad, but based off your close on BLM's.. worse case you might have one or two spots needing adjustment but worth trying anyway.

 

Minor point, but an O2 sensor can't "pick up the excess unburnt fuel". It can only "see" O2. Same cause.... overlap.

 

Since we're on that topic, curious why alot of people say it makes it run rich when infact on mine it makes it run lean.

Is it then safe to say 02 sensors dont work well because cam overlap creates excess unburnt fuel (vapor) which results in less 02 in the exhaust than there was in the cylinder during combustion which makes the PCM think it's running rich and pulls fuel?

Or, is the 02 sensor simply not able to detect the presence of the 02 since there's so much unburnt fuel (vapor)? Seems like my WB02 reads lean while the stock NB02's read spot on (effectively leaning out the motor). I did try to connect the single WB02 sensor to my PCM 02 input but I only had one, I would need two units like someone else did.

Either way, yes overlap is the problem for lean running conditions.. this is assuming exhaust leaks make it run rich and cam overlap make it run lean (that's they way I look at 02 sensor problems based on what I see with my setup.. sealed exhaust with lean running engine with cam overlap, NB02's reading right on while WB02 reading lean).

 

The data logs I've reviewed often show a pronounced rich condition (elevated BLM's - in response to a "false" lean O2 reading) as a result of overlap. The sensors are reading lean.... and the PCM is bumping the fuel in response - fuel the engine doesn't need.

Fuel vapor in the exhaust will affect the O2 sensor readings. Wet fuel could seriously screw them up. The O2 voltage is driven by the partial pressure of O2 in the exhaust on one side of the thimble and the partial pressure of the O2 in the air on the other side. Increasing the HC vapor reduces the partial pressure or the O2 in the exhaust, and would tend to buffer the magnitude of the voltage developed. Partial pressure is a function of the mole fraction of each component in the gas. Increase the mole fraction (or "%" for simplicity) of HC and the mole fraction of the O2 falls. But there is so much raw O2 flowing through the open valve during overlap, that the O2 % in the exhaust is going to rise dramatically, in spite of the HC content. The results will be affected to some extent by how hot the exhaust is running. As temperature increases, there will be more of the HC vapor combining with some of the excess O2, in the headers.

 

So I uploaded an open loop tune,drove it, and it runs good. Didn't really notice any drop in power. Then I loaded up the closed loop tune, drove it, and I didn't feel any drop in power either. its just that sometimes it feels alot slower than normal i guess.
I have both datalogs of both open and closed loop if anyone would like to see them.

I don't know, maybe its all in my head

 

It takes awhile for the 02's to mess up the tune, you wont see it right away. On the other hand the open loop tune should run the same all the time.

 

I dont completly understand this, since BLMs are based on your base VE tables (or whatever calculates fuel in open loop mode be it MAF or SD mode).. so if your having elevated BLM's that means you are increasing fuel based off preset values, and if you installed a cam with overlap that also means these values should be adjusted to suit, so your BLM's are back to 128. If you compare stock cam BLMs to overlap cam BLMs because yes you will see a bunch of adjustment going on, just because the PCM is trying to compensate back to 14.7 and acheiving what it thinks is 14.7 it could also mean (since the 02's dont read correctly) that it could be adding all that fuel due to the new cam and still be lean or rich in reality.

So, if you run some of VE master adjustments like I did to get the BLMs hovering around 128 based on what the 02's see (perfect - neither rich or lean) then there shouldnt be much drift from 128 assuming everythings setup right. At this point if the 02's were reading proplerly then the motor should run A-ok.. in my case it was too lean.. any adjustments to richen it up simply gets cancelled out by the 02 BLM (Lterm adjustment).

My point.. there's no way to know if your overall lean or rich based on stock 02 values since if you tune according to the 02's and they cant read right then once you do tune it all your BLM's *should* be tuned and close to what the 02's think are OK - that's all we can do when tuning the stock PCM since we cant change the 02 target setpoint (cant change target 14.7 to 14.2 or 15.3 to fix this problem).

All the lean I tried to fix was off-idle, below 1900-2000rpm and closed loop mode (light throttle)... it would get leaner (and slightly surge) the more I drove it... it gets to the point you can tell the instant you enter PE mode since it's suddently completely smooth and surge free (much like when you reset the PCM and before 02 adjustments set in).

I hear alot about Rich Idle with 02's and cams, just curious if anybody really looks at the rest of the rpm/load ranges, maybe it's different off-idle than it is at idle.