Surging at cold low throttle....

[evadllig]

Dear Team of Experts,

I have a 2006 Trailblazer SS. Ever since I have owned this car I SOMETIMES get a surging effect when pulling away at low throttle. The surging happens almost only in first gear, and mostly when the car is cold.

I have heard of many different explanations for this situation (open vs. cold loop - running rich at low rpm - vacum leak - bad mass air flow or O2 sensor).

I would like to try and eliminate as many of these items as possible and was wondering if I am able to log or monitor A/F ratio right at start up. If so how exactly do I do this....

Thanks
Dave

[mikel]

To see A/F you will need a wideband, the Predator cant show it.

[evadllig]

Mike,

Here is an update on my situation.

I restored the truck to factory tune and the dealership reflashed the tune with a new update.

I tried to load the Diablo back in and it did not recognize the truck.

I upgraded the Diablo to the latest version and then uploaded the Diablo tune and actually logged and fine tuned using Diablo Redux.

The surging came back. I reloaded the factory tune and the surging is gone.

Can you give me any ideas on what to do or is this something you can correct?

Thanks
Dave

[johan]

Does the surge appear right away after installing a tune? We do not touch anything in that area tune wise in the canned tunes.

[evadllig]

It seems pretty quick after the install. Maybe I will try and install again and test again today.

FYI - I do have a K&N intake installed which has a very big effect on the leaning the truck out. Using the Diablo Redux I have had to adjust the LTFT as much as 15%.

[06MonteSS]

wow!

make sure there are no intake or exhaust leaks anywhere....

[evadllig]

I am fairly confident that there are no exhaust leak or intake leaks. Although I am not sure how to double check this.

I do know that the K&N intake removes a substantial "neck down" in the original intake tube. I believe this is what causes the big jump in air volume and hense the leaning condition.

[evadllig]

I am heading out this afternoon and will try the Diablo tune again...

[evadllig]

OK Here is an update:

Running Diablo tune with K&N Intake:
LTFT at idle = 0% +/-
LTFT at cruising = 17% +/-
No surging at cold low throttle

Running Diablo with LTFT adjusted by -15% and K&N Intake
LTFT at idle = -15% +/-
LTFT at cruising = 1% +/-
Surging happens at cold low throttle

Running Diablo with LTFT adjusted -5% and K&N Intake
LTFT at idle = -5%+/-
LTFT at cruising = 10% +/-
NO surging at low cold throttle

I have not experienced any other ill effects (throwing codes etc.) when running any of the configurations.

If anyone can shed any light on this please let me know.
I got to believe that the K&N Intake has something to do with it. As mentioned before the intake does eliminate a sever neck down in the original intake plumbing.

Thanks
for any help
Dave

[05Z71]

It sounds like on or a few of your injectors are dumping more or less fuel for some reason making you run rich. You could rule out the O2 sensors because they don't actually go online until you are up to operating temperature and at that point they are closed loop, but here is the other side of that argument. Your O2 sensors could be reading wrong once they do actually go online and are giving you a false reading which would explain your ECM telling you that you are running SOOOO lean. That would also explain why when you only make a -5% adjustment you aren't having any problems. Bottom line is you are running rich once you make the -15% adjustment.

I'm not real familiar with the Trailblazers. Do they come stock with duals like a truck? Are you able to run a log on bank 1 from one side and bank 2 from the other? If so, are the numbers different by a substantial margin? If so, then that would explain quite a bit.

Try adjusting to -10% and see what happens.

[CANUCKPREDATOR]

When was the last time your MAF was cleaned?

[evadllig]

The MAF sesor has been cleaned recently along with cleaning a re-oiling the K&N Filter. I am resonable sure that that is not the problem.

The trailblazer does not have a dual exhaust. I will check to see if there are two O2 sensors. I am pretty sure there is.

At idle there is a difference between the left and right bank LTFT readings - as much as 5%. There is as much as 5% difference during acceleration but during cruise they are closer - 1-2% difference.

Should these be equal at all times? Should they be within 1-2% at all times?

How do I tell if an O2 sensor is bad?

How do I tell if an injector is bad?

Thanks for the comments
dave

[05Z71]

Well if you don't have duals then you don't need to be logging 2 banks. You just need to log "long term fuel trim bank 1" and that is it. Look and see if you have 2 cats.

When you are logging, what is your speed and rpm?

How many miles do you have on the rig?

Are you able to save a log and post the file here? If so, post up your log and maybe some sugestions can be made.

As far as there being 2 o2 sensors there will be...one before the cat and one after the cat if you don't have dual exhast,a nd when I say dual exhaust I don't mean 2 tailpipes. I mean 2 cats.

[Ill_Born_SS]

Reading through this, I understand you have this primary problem when cold without the tune. then on top of it you removed the tune and had it re-flashed at the dealer. Then reinstalled the tune and proceeded with the LTFT adjustment.

Highly recommended:
Return to the original factory tune, drive at least 4 complete cycles (cold to full temp) (on/off) each being at least 50 miles in duration. If it was reflashed it has to learn everything, even trans parameters.

Your DiabloSport what revision are you on ( physically check it )

List Anything else done to the truck ( screen removed, oil residue in the intake neck between filter and MAF, aftermarket anything)

The intake system (TB thru to and including the filter)If you are not sure remove it and clean it all again before you start off fresh again with the factory tune.

Get yourself a aerosol can of Throttle Body Cleaner (any cheap brand) and a can of Mass Airflo Sensor cleaner (I like CRC) an old tooth brush,lint free rag, Q-tips and a small tray. Remove the Throttle body but while you have it off clean the rest it`s easy. be gentle with the throttle body and be sure to excerise the butterfly to the max limits in your hand because it only travels 80%-89% with the TPM, get in the small port with the spray and dry it good and apply a little vasaline or simular to the flange before reinstalling. While your there remove and clean the purge sol with (TBC) throtle body cleaner and Q-tips and rinse with TBC and lubricate the o-rings.

Once this is done If you want post back and I will try to give you directions on how to test and find problems using your predator.
Chances are your trims stock were about -8 to -9 before the intake was installed.

[evadllig]

Gentlemen,

Just as clarification I have had this problem when cold on the original factory tune, the original factory tune with the Diablo and the original factory tune with the Diablo modified. Since the reflashed factory tune was installed I have only had the problem when I installed a heavily (-15%) modified Diablo tune. With the lightly modified Diablo tune (-5%) I don't seem to have the problem.

It would appear that I have 2 cats that flow into 1 cat back system. I do get readings on both banks when I log.

When I log I normally set the cruise at about 65 and the rpm is about 2200.

I have almost 50,000 miles and I have used the Diablo since about 15,000 miles.

I am on Diablo U7191 revision 9r01. I just checked and Diablo just posted a revision 9r02 yesterday. It said "internal changes."

I recently (a couple of weeks ago) cleaned the K&N filter and the mass airflow sensor. The filter was very dirty but there was no dirt or oil residue on the MAF sensor or on the intake tube. I cleaned them anyways and reinstalled. Surging at cold happened again both in tuned and untuned conditions. It was after this that I was reflashed at the dealer.

I have not cleaned the throttle body yet. I should put that on my to do list. Or have the dealer do it next time I am in.

After reflashing I ran the car about a week before tuning it again and then ran the unmodified tune for about 4 days before adjusting the tune.

As far as mods the the truck I have the Diablo, the K&N AirCharger system and a Corsa Touring Catback system. Nothing else.

It is good to know that the factory tune without the intake is probably running about -8 or -9. That means my lightly modified Diablo trims are about the same ball park. If the surging does not reoccur I might just run the truck as is.

Thanks guys for your insight and if you have any other suggestions please post them.

Dave

PS - I will try to log and post the file. If I do should I be logging at cruise on the highway or from a cold start with normal stop and go driving?

Thanks Again.