I have been searching for weeks and am at my wits end here. Here's the deal. I installed LT's and a LS6 intake with a P/P TB. I drove the car a few days with open headers until my ORY arrived. That's when my problem started. My car started backfiring and stumbling really bad. So I naturally did some forum searching to figure out why it could be doing that. First thing I came across was bad O2's (typical with running open headers) so I replaced them. This did not fix my problem. So I dug even further and found other things to check. (i.e. vaccum leak, spark plugs, plug wires, fuel pressure). No vaccum leaks. So I talk to a buddy of mine and he tells me it probably just needs a tune "too much air with those mods for your stock tune to handle" he says. I tell him that I could buy that if so many other guys on here didn't do basic bolt-ons and have their cars run fine on the stock tune (not to mention the countless "will my car need a tune after LT's?" threads I read during my searching where it has been stated time and time again that the car will run fine with basic bolt-ons). So I buy some credits for HPT (my buddy has the software) and we hook my car up. Turns out one of the O2's I bought wasn't working. So I put one of my old O2's in there and it just so happens that it worked fine. So he tells me he wants to set some time up to tune my VE tables. No problem. Meanwhile I decide to just replace my spark plugs and plug wires just to eliminate that as a cause. My car runs a little better after this but is still doing the same thing.
Oh I forgot to mention that at this point I had my ORY hooked up. I've been running that open though since I had to hack my stock cat-back to get it out.
So last Sat. my buddy comes over and we go out to start tuning my VE tables. My LTFT's were really high, like in the +20's. he had read that to if they are that high to start you can multiply the whole LTFT table by 1.18 to get them to a more workable level. So we did that and most cells dropped to around 10 so we flash my PCM and went out driving to log my STFT's. Added them to the VE table by "add paste special by % half" smoothed it out and flashed my PCM. We then took it back out and the car seemd to be running worse. After doing some tuning research (i knew absolutely nothing about tuning before starting this whole process) i realized we had missed a lot of steps in the tuning process. My car did drive better when we had adjusted the LTFT's by X 1.18 so we refleashed the PCM with that and gave up for the night (after having spent 12 hours trying to tune my car with very little progress)
During the course of the day of tuning we decided to check my fuel pressure to eliminate that and it was good.
And so here i am now. About to set my car on fire and collect insurance money. I'm so unbelievably frustrated right now. The stress is eating away at me. I have cleaned the MAF, replaced plugs and wires, checked fuel pressure, checked for vaccum leaks, replaced O2's, checked my injectors to ensure they were all working, added 2 bottles of injector cleaner to 2 seperate tanks of gas and I don't know what else to do. My PCM has thrown no codes other than my EGR and rear O2's.

Oh, 1 thing. when we went out logging we decided to check my LTFT's and the cells from 60k/Pa on and 1200-about 2800 rpms are the most lean with readings of about 11-12's. and this is when my backfiring and stumbles are the worst/most noticeable.

Could it just be that my car is running like crap because it needs a good tune? Is there anything else I can check? Could it be that the EGR hasn't been tuned out after my !EGR? I know my buddy turned the codes off but I'm not sure if he actually "tuned" it out.


I'm sorry for the long read but I wanted to give the most information possible to get the best help possible. I have started 2 other threads similar to this and the only responses I keep getting are "vaccum leak" or "plugs wires" etc. I've checked all of that! what else is there? please help.

Also, if someone could help me find a good write up on MAF tuning for dummies that would be great. I've found a couple of write-ups that were just way too confusing for me to understand. thanks

 

Have your buddy put the original tune back in it, but put it in open loop. Then clear the LTFTs and see how it runs.

If it is still popping and running bad, then it is likely to be actually lean and you will need to figure out why... first thing I would check is your intake - how did you check for vacuum leaks? You can use carb cleaner with the engine idling and see if the idle goes up.

If it runs good in open loop, then your O2 sensors are seeing a lean condition that doesn't exist - i.e. you have an exhaust leak that is making them "think" the car is lean because of the air getting into the exhaust, and the O2s are adding a bunch of fuel that it doesn't need (as seen by your high +LTFT readings)...

Follow the logic?? Hope that helps...

 

Yeah, I used carb cleaner....used a whole big can of it actually...i was thinking though that if one of the intake port gaskets didn't seal right that might be causing it and the carb cleaner just isn't reaching the spot of the leak. but the car ran fine for the first few days after the install which kind of tells me it couldn't be an intake gasket.

but i will try what you suggested though. it does seem like a logical way to help narrow down the problem

 

Bear with me on this...

In closed loop:

1) Air comes in through the MAF. Expected airflow is looked up in the MAF table.
2) Fueling is calculated from the expected airflow and blended with VE, LT, and ST trims
3) O2 sensors measurements are taken and compared to the O2 switch point for that airflow level.
4) If the O2 shows lean, the trims are bumped up. If the o2 shows rich, the trims are bumped down.
5) Rinse and repeat

In open loop:

1) Air comes in through the MAF. Expected airflow is looked up in the MAF table.
2) Fueling is calculated from the expected airflow and VE

So you have multiple things that have changed. Air intakes throw off the MAF calibration. Headers throw off the narrowband O2s so that the stock switchpoint table is off. I saw this after putting headers on. Idle became rich as heck and my mileage dropped 3 mpg. The most crucial thing when running in closed loop is the o2 sensor calibration. The PCM expects those measurements to get it to 14.63 AFR. If the switchpoint is wrong then the PCM will continue to trim as it thinks its hitting 14.63. In my case it was adding fuel and trimming to 12.9 AFR at idle.

So to fix this you'll need access to a wideband O2 sensor that you can log the actual AFR. You can't use your existing trims/o2 info because they're off.

First fix the MAF calibration.
1) Turn off narrowband O2
2) Log at various airflows.
3) Correct the MAF calibration to 14.63

Second adjust the O2 switchpoint table.
1) Reset fuel trims.
2) Log at different airflow levels. You want to hit as many as possible.
3) Filter on the different airflow ranges (CL Mode)
4) Find the average AFR for an airflow range. Adjust switchpoint V lower to lean out, higher to make richer
5) Continue until each range produces a 14.5-14.7 AFR. I like to go a little richer than 14.7 because it seams to run smoother. Also, 10% ethanol blends lowers stoich.

Here's my switch point table you can use as a starting point:

CL Mode Bank-1 Bank-2
0 365 365
8 403 403
16 407 407
24 411 411
32 450 450
40 485 485
48 495 495
56 550 550
64 560 560


Lastly, look at your trims.
1) Reset all fuel trims.
2) Adjust MAF/VE until trims are within +/- 5%
3) This will vary every time you log car so just get it close

 

white01ss - that is really more of a fine tuning of the O2 sensors - they aren't off enough to cause the problems he is seeing... like you said, your idle was trimming to 12.9 - that is not off enough to cause popping and running rough like he is describing... he has something else going on!

 

Just relax. Better to park your car for a month than to 'blow it up'.

Look, this is where 'friends' and 'buddies' can do more harm than good. If you are still running the MAF (closed-loop), you are just chasing your tail attempting to do the VE Table first and expecting it to effect Trims and fueling.

First adjust your MAF frequencies vs LTFTS using the HPT website. I am sure they pages of information on it. Get rid of those +LTFTS using the MAF. Then adjust your Idle Trims (per website) and tweak your VE Table.

You just need to slow down and systematically apply good tuning principles. The information on MAF tuning is all there. Do it first through the MAF. I would hold off on an open-loop tune unless you have a wild cam and only if you have a good working wideband.

Slow down and enjoy your car!

 

All the car has is a freakin set of headers and an LS6 intake... it should run just fine on a stock tune!

Like I said before - put the stock tune back in it, but force it into open loop. Clear the LTFTs. If the car runs like **** still, then you have a real problem such as the intake leaking. If the car runs good, then you are getting the problem from the O2 sensor feedback, which would indicate that you likely have an exhaust leak, bad O2 sensor wires, etc...

Its not rocket science...

 

You're right. Guess I just had some time to kill. Being a little rich only wastes fuel and foul plugs. My car ran great on the stock tune w/headers, if you didn't mind the fuel smell. Something else is up. Did the front/rear O2 plugs get mixed up, perhaps?

Barring any mechanical issues, bucking can be caused by a lean condition. If you have access to a wideband if would strongly encourage it.

 

Actually white01ss, I think you had a pretty nice version of 'cliff notes' on tuning. It was good material.

Problem is that you can never really tell where people are getting hung up on tuning. They may say they are tuning 'open-loop', but either they have not successfully failed the MAF or they have the nomenclature confused as to what open-loop really is.

To the OP, having a reliable and accurate wideband always helps. Posting a tune and log always helps. I have the 'other' software, but I am sure someone can look it over and advise. Best of luck..

 

well....i went out yesterday and did some logging....somehow my LTFT's are rich now all around -8 or so....I'm not sure what caused this change....maybe the change my buddy did to my VE tables did it and it just took me driving around for a week to see the effect? i don't know, i'm just learning about this tuning stuff. i haven't had a chance to change back to my stock tune yet because it is saved on his computer. When we were trying to tune it that day though we did run it in open loop and it was still running the same way. I'm going to pull the intake off this coming weekend and check the gaskets on it as well as the MAP sensor in the back and all the vaccum lines behind the intake. I might even put the stock LS1 intake back on and see if that makes any difference. My guess is it's either the MAP sensor not sealing right or a crushed gasket or something under the intake. Like i said, i sprayed down the entire engine bay with carb cleaner and the idle didn't move...i did my best to spray behind the intake but it's tight back there. It has to be an intake leak somewhere though. BTW i drove my car to work today and it seems like its running a little better....it's not stumbling nearly as much and only backfired once. i just gave it enough throttle just to see if the problem still existed though...i'm not like beating on the car or anything...atleast not until i get it fixed