Topic: WOT Hesitation Above 5k RPMS With Intermittent Boost On Stock Tune

[MattM]

I'm posting a new one here, because I think I'm narrowing down part of my problem.

So when I turn the tune off and run on stock tune and then go WOT I get that same hesitation above 5000rpms as previously described, but with the stock tune my boost will jump around intermittently (like go from 16psi down to 12psi up to 14 then 16 etc.).

This is all happening at the same 5000rpm plus hesitation point I described in a previous thread. 

I'm wondering if that sounds like a boost leak/intercooler problem/wastegate issue to anyone?  The boost doesn't fluctuate nearly has badly when the trifecta tune is enabled it stays between 23 to 20 psi. 

Has anyone else had anything similar happen?

[Sly Bob]

I had the hesitation over 5000 rpm and boost was erratic for 4 or 5 tank fulls after bad gas I bought in an out of the way gas station one time. Was afraid I had a real issue but it went away on it's own and I hope the hell it never comes back.

[Uranium-238]

Forgive me if this has already been covered in your troubleshooting saga, but have you checked the spark plugs?

[MattM]

Yes.  Replaced them a few times now as well.

[Uranium-238]

I can't remember, are LNF's coil packs or coil on plugs? Could be a bad plug wire, if LNFs have them.

An ignition issue seems one of the simlest explanations for this issue, that's why I'm harping on it.

[MattM]

Hmmm.  Just for shits I could buy 4 new coils and try I guys. 

Would that cause the boost to go from 16 to 12 to 14 etc though?

[Sol Asylum]

If you are getting pulses in the exhaust gas pressure, yes.

[MattM]

That makes sense.

Luckily the coils aren't terribly expensive and easy to replace..  I'll check those out.

[elff]

I can't remember, are LNF's coil packs or coil on plugs? Could be a bad plug wire, if LNFs have them.

An ignition issue seems one of the simlest explanations for this issue, that's why I'm harping on it.

They are individual Coils per spark plug.   


It also sounds like you may have a leak.  I had issues in the past with the couplers that connected the IC Pipes to the intercooler.   

You can use something like this  and hook it up to the Passenger IC pipe on the Turbo end

[MattM]

I had someone else review logs and...the one thing he also pointed out is that the throttle position fluctuated even though I had it floored.  It's not a lot but it does fluctuate.  Is that normal?

[MattM]

I had someone else review logs and...the one thing he also pointed out is that the throttle position fluctuated even though I had it floored.  It's not a lot but it does fluctuate.  Is that normal?

Sorry,  To better explain this.

On the datalogs (even the earlier ones I've posted).  At WOT instead of just reading 69% or 68% or 67% the relative throttle position will read between those values with seemingly no reason for the change even though I've floored it.

I'm wondering if when any of you do datalogs in HP tuners or anything else do you see a fluctuating relative throttle position?  If not, I'm almost thinking this could potentially be what's causing my problem!  If the computer doesn't think I'm flooring it then it would let up some to try to match what it thinks I'm trying to do right? 

Hmmmm....The other thing is that I don't think it's just a tps sensor going bad because it's only a fluctuation of 3% or so.  I might have to chase down some wires somewhere.

Anyway, anyone that is familiar with datalogs and tuning.....If your ecu sees those number fluctuating at WOT would it cause the symptoms I'm describing?

[Sol Asylum]

I think you should start by seeing if there is an issue between what the pedal position sensor is reading and what the throttle position sensor is actually doing.  Because it's drive by wire, you position the pedal the computer reads that and then commands a throttle position the computer reads the throttle position and adjusts as needed to get to the desired position.  I don't know how much of the nanny controls are tied into throttle position but I would start by looking to make sure that the pedal sensor is not giving erratic readings.

This is where the added scan parameters of HP tuners will come in handy.

[MattM]

That was my thought took....maybe an issue with the pedal position sensor.

[Steelmesh]

Just throwing it out there, some rev limiters on drive by wire cars will close the throttle to limit engine speed (in addition to spark or fuel cut).  Also, torque management could override the throttle too.  Don't know if those are related to your issues.

[MattM]

Hmm..I would have thought trifecta would have turned that off..

[Uranium-238]

I think you should start by seeing if there is an issue between what the pedal position sensor is reading and what the throttle position sensor is actually doing.  Because it's drive by wire, you position the pedal the computer reads that and then commands a throttle position the computer reads the throttle position and adjusts as needed to get to the desired position.  I don't know how much of the nanny controls are tied into throttle position but I would start by looking to make sure that the pedal sensor is not giving erratic readings.

This is where the added scan parameters of HP tuners will come in handy.

A commanded vs actual delta on a GM drive by wire throttle will usually result in limp mode. I'd wager that it's being commanded to fluctuate, but why?

[Sol Asylum]

A commanded vs actual delta on a GM drive by wire throttle will usually result in limp mode. I'd wager that it's being commanded to fluctuate, but why?

Have to trouble shoot to isolate the problem source, bad pedal sensor, bad throttle actuator/sensor, wire, or software.

[MattM]

I have it in getting the IC piping and intercooler inspected for leaks and cracks in the intercooler.  Once I've eliminated that as a possible issue I'm thinking I might just by the datalogging custom tune from Trifecta and send a logged run to them (where I paid for them to actually look at it).  Maybe they will see the problem and let me know what it could be/how to fix it. 

I did also turn the traction control completely off before I dropped the car off yesterday and did a few pulls (the hesitation issue was inconclusive).  Essentially, by that I mean that one time I felt the hesitation and one time I really don't think I did.

It might also be caused by how I push the accelerator pedal down as well.  It seems I get more "hesitation" when I have my foot fully covering the accelerator pedal and floor it (maybe the side of my foot gets caught and doesn't push the pedal full-full down). 

When I put the tip of my foot onto the accelerator pedal and push harder down I don't seem to feel "hesitation" or as much "hesitation." 

What's wierd is that from what Uranium is saying....If it were a pedal position sensor or wiring it would probably throw a code, but I've never gotten one. 

This does however explain how in my datalogs during this "hesitation" event I could never log a misfire or anything that would tell me an actual hesitation was occuring. 

Makes perfect sense now though...in the ecu's mind everything was functioning perfectly and it was just letting up on the WOT parameters because it thought I wasn't flooring it....That's also literally what the "hesitation" i've been describing feels like too...Basically like someone is flooring it then lets off some then floors it again....Pretty crazy!

[Uranium-238]

Keep in mind, I abandoned the LNF for LS power almost 8 years ago. Most of what I know is a comes from both powerplants, but definitely more from the LS side.

On an LS ECM, I'm pretty sure there's a separate parameter for pedal position and throttle position. If the same is true on an LNF, (GM doesn't like to reinvent the wheel when they don't have to...) identifying that parameter and plotting it next to throttle position would be a good step. Of course the software may offset the pedal input, but then there would be a relevant table back on the tuner side where you can get the data needed to calculate whatever that offset is.

[elff]

At one point I had to replace the sensor in the foot well.
HPT scanner can log the following parameters to confirm if this is your problem

[ Guests cannot view attachments ]

[MattM]

At one point I had to replace the sensor in the foot well.
HPT scanner can log the following parameters to confirm if this is your problem

(Attachment Link)

Did it show the same sort of symptoms as I'm describing?  Like the wot hesitation?

[elff]

Not really.
On mine it just felt like I was only pressing the pedal about 3/4 of the way and not really hitting it.
I noticed it in my 60-100mph times, and then someone else pointed it out to me that my Pedal was not hitting 100% even though the desired was.

[elff]

I do remember there being a pause and then it hitting hard, but that was solved with fixing a leak with new clamps.

[MattM]

Ok new wrinkle to my stupid issue.  So I take the car out on Sat for the first time in a week and I get a check engine light with a p0107 which is barametric map sensor etc.  Well I hook torque pro up and monitor boost since the dic won't show it now.  Car hits like a ton of bricks...I see between 26 and 23 psi through third.  What's weirder still...There is NO hesitation type let up feel like I was getting.

So now I just got this pending code and I'm assuming the map sensor either works or doesn't right bc if it wasn't working it would have thrown a code earlier.

My question now is that the map sensor couldn't have been causing the car to have the hesitating feel right?  Wouldn't that have thrown a code?

[TomatoSoup]

This sounds like the kind of issues you get with The GMPP tune, when the new T/MAP sensors are crimped and getting poor contact.

You said a Trifecta tune, but do you have 3-bars sensors too (from before, maybe)?  In any case, check the wiring to the MAP sensors.  Clean the connect contacts, etc.

Worth a try.