17 Sierra 6.2L 8L90 BTR stage 2 cam, headers, idle surge.

[Dominatorstang]

2017 Silverado E92A L86 8L90 3.42gears only tuning ECM (TCM still locked and stock converter)
Cam: 210/223, .540"/.540", 111(+6?) LSA, 14% fuel lobe (stock springs, push rods, rockers, 20deg limiter)
Speed Engineering 1-7/8 long tubes with catless Y pipe (stock muffler)
Hone on stock bore, new Speed pro stock replacement pistons and GM rings
194deg thermostat

I have been dialing in the VVE, VT, MAF, and Idle settings. But I feel like I am missing something or I have an engine issue or sensor issue that is not allowing things to line out. I have sprayed around for vacuum leaks, but none showing up around intake or throttle body.

Tuning VVE I get a surge at idle, but timing is staying positive. If I blip the throttle then it comes back down to idle somewhat okay, but if I slowly let out then zero pedal goes negative and it dies on the way down.

MAF is typically idling with less surge for me than SD, but it can get to surging pretty heavy at times too and it does show some negative timing when surging.

MAF tuning.hpt
MAF idle stable, blip throttle, slow throttle, surge.hpl
VVE idle surge, blip throttle, slow throttle.hpl
VVE tuning.hpt
stock ECM.hpt

[Ben Charles]

If I get a moment I’ll take a look…

[SultanHassanMasTuning]

your "MAF" tuning file is stock curve

check this out2017 sierra 6.2 cammed MAF tuning test.hpt

[Dominatorstang]

Thanks Ben

[Dominatorstang]

Thanks SultanHassanMasTuning. Funny thing is that just a moment ago I was comparing the changes you put in a file for someone else with a similar setup.
https://forum.hptuners.com/showthrea...hlight=btr+cam

Yes my MAF tuning file was just to start MAF tuning as I honestly was mostly tuning VVE first and having a rough (literally and also pun intended) time with that idle, so I started MAF to see how it acted there too.

Here are a couple logs after pulling in the changes you made for the file above. Thanks for that.

with SultanHassanMasTuning at idle.hpl
with SultanHassanMasTuning couple revs, blip, then slow throttle let off and dies.hpl

[Dominatorstang]

SultanHassanMasTuning, those changes did great for the surging issue. Thanks again for that!

I am tuning VVE more now and I do not notice the type of surge I had on my original MAF or SD tune I posted. Just trying to work through the slow pedal release allowing RPM to drop and die.


SultanHassanMasTuning VVE tuning.hpt
SultanHassanMasTuning VVE tuning idle start.hpl
SultanHassanMasTuning VVE tuning slow rev, blup, slow let off until die.hpl

[Dominatorstang]

I still must be just missing something.... I have not changed anything on the tune since the last post that did not surge. I gave it a break for a bit and then come back to it to log trims and dial in VVE more but now it is surging again and showing I am heavily lean all the sudden. Yesterday when tuning VVE table then something similar happened to where it all the sudden was saying the whole table was lean and needing more fuel even though I had not made any changes since the previous log that was looking pretty good.

no changes but now commanding richer and surging again.hpl

[Dominatorstang]

I cant tell for sure if this is a problem but I keep coming back in the logs to reviewing the fuel rail pressure actual vs desired. Sometimes it looks like it is just all over the place and the two are not very in sync. Installing the HPFP I verified I had contact at the lowest point on lobe and had clearance even without a gasket at the highest point of the lobe. No changes to lash cap or anything. Scaled the Y axis of leading edge angle x1.14 for 14% fuel lobe too.

I reviewed the logs from some other posts and the pressure look to vary much less than mine. Or my brain is just to fried at the moment.

[GHuggins]

If you can see it, take a look and see if the pump is still in one piece and bolted down. Only seen it once, but still worth a check. Also just looking at your VE table - it's way off and should be very lean around idle. You shouldn't have it that low and taper up that steeply in really any setup. I didn't look at any of the hpfp settings, so can't comment on that at the moment. Just for reference though compare your current ve table to your stock and look at how different it is.

[pisces_0]

I just went thru this exact situation, chasing idle and surge, on my '16 Suburban. Took a lot of polishing on the tune, but it'll now sit rock-steady at 720 RPM all day (even in -15* MN weather).

Relevant mods: GPI Stg 1 cam, Whipple, NW 103 throttle body, LT4 injectors.

Process that worked for me:
1. Lower Virtual Torque in idle areas (MAP & Airflow maps, both gas & E85)
2. Smooth Virtual Torque maps
3. Tune MAF via fuel trims and wideband
4. Tune VVE via fuel trims and wideband
5. Rest LTFT
6. Wash, rinse & repeat many, many, many, many more times.

I had to get the MAF curve and VVE dead-nuts on (+/- 2%) before I could polish the VT tables, idle torque External Load and Speed Control Reserve. If your fueling isn't right you'll chase your tail with torque, and torque controls idle.

[Dominatorstang]

I checked the pump mounting and the pump is nice and secure, not showing an issue there. I had seen too where the bolts broke on someone because of using a thicker lash cap and not verifying stroke has clearance for it. That is why I was very meticulous in verifying mine when assembling. I make enough of my own mistakes, so I 100% like to learn from others when I can.

Trying more to understand what is causing my fuel trims to swing far rich or far lean out of the blue with no tune changes I came across the below information. It could also explain my pressure not staying smooth and why I have leaned out my VVE tables so far while tuning. This truck has 186k on it and I do not believe the pump has ever been changed. Now with the cam then the stroke has changed position from that 186k wear it had been riding in before too. I am not sure how much I will have time tonight for the truck, but this is my next thing to try and prove is or is not happening.

This bulletin applies to 2014-2019 Chevy Silverado trucks. The vehicle may have a concern with a Service Engine Soon (SES) lamp on and a rich running condition DTC P0172 and P0175. The cause may be the high pressure fuel pump. If routine diagnostics do not isolate the cause, the following may be helpful:

Disconnect the dirty air side of the PCV system.

Plug the vacuum supply.

Start the engine and monitor the fuel trim in closed loop.

If the fuel trims return to normal, this is a good indicator that the high pressure fuel pump is leaking. Chevrolet reports that with this concern, they do not see a lot of fuel in the crankcase, so changing the oil may not isolate the concern. When the high pressure fuel pump leaks, the PCV will pull the fuel mist straight into the intake, causing the concern.

[Dominatorstang]

Thanks for the tips pisces_0. Soon as I get back to the tuning, I hope to get it dialed in as good as it sounds you have.

[Dominatorstang]

Okay, so I checked fuel trims with PCV unhooked and hooked up but did not find much difference.

I am still puzzled by the way the HPFP rail pressure does not follow smoothly to the desired pressure. Some error I figure is normal, but I do not have much experience with these Gen5 or logs to compare. I did find a log from another L86 with a cam in the forum group and it honestly looks pretty smooth and following well. I have attached the comparison log along with a high freq log of mine and standard freq log.

The thing is I hate to throw parts at it and honestly I am not 100% the pump has an issue or possibly the pressure sensor. The reason I question the pressure sensor because my fuel trims are not consistent. Sometimes it is way rich and other times it is way lean with no reason I can find. Fuel pressure not being what it shows could do this though. And an injector issue could cause uncontrolled fuel pressure, but it is hard to tell if I am seeing the an injector causing the issue, or being effected by the issue...

Any experience anyone has in HPFP, HP sensor, and DI issues please chime in. Any of the logs in my above posts will show this too.

(bottom graph on each photo is fuel pressure)

High Freq log from my truck
High freq log.jpg

Low Freq log from my truck
low freq log.jpg

Log from another truck on forum.
good pressure log.jpg

[Dominatorstang]

https://www.ebay.com/itm/124809834985

I have a complete low mile HP fuel system coming. So fuel rails with injectors, sensors, wiring, and HPFP. FP appears to be from a 2019+ but comes with wiring so I hear that should be fine and the injectors show to have the same exact part number as mine. I will inspect the lifter when I pull the pump to make sure nothing odd is happening with it either. The more I look at the fuel pressure bouncing, the more it does look like an issue. Hopefully this resolves it.

The parts were going to be here today, but with the weather I am not sure I will even get them tomorrow. I will update more once I have something.

[GHuggins]

Don't know if your parts showed or if you've gotten them swapped out or not, but I made a lot of changes to hopefully help with your problem.

[Dominatorstang]

Thanks GHuggins, I will load it and take a log to see how it does. So far the parts still show to have never left Austin TX, so guessing Monday or Tuesday.
I did a quick review of the changes I noticed on the tune file, to try and understand what I should be doing a little better. Below is what I came up with.

Idle RPM - made base idle at 750 and smoothed over to mostly just under 900 cold
Raised for cam but this cam is mild enough to not need too much idle RPM, also keeping low for stock converter?

Idle Immediate Prop - took back to stock
keeping stock gives it a little more lope by constantly trying to make small quick adjustments for the slight deviation the cam is giving?

Idle Predicted Prop - took back to stock

Idle Speed Control Reserve - took back to stock

Idle torque limit offset - bumped up 25 or 30%
gives a larger window to adjust in?

Idle External Load - bumped up about 20% over stock

VVE table - shifted to match cam torque curv and air flow profile. Looks really nice.

Virtual Torque - shifted torque values up in the RPM. Looks very nice also.

Electronic Throttle Pressure Ratio Limit - bumped up from .9 to 1.0

VVT position vs baro pres - cut down to max of what limiter allows. kept extra retard in cruising speeds.

VVT position WOT - retard in mid range RPMS but back to advance in high RPM
The cam card is showing to retard more as RPM rases to rev limiter. Cam card is for L83 though, so I imagine it is not optimal for L86?

VVT ramp rates - mostly cut down but looked tuned out nicely

VVT enable/disable RPM - raised a little

Main spark vs Airmass - bumped up timing in idle areas

VCP spark - zeroed out

minimum spark table - bumped up common areas

AC Torque - scaled Y axis to cut down values

Drive demand - dropped down low speed and low throttle areas
Better transition between idle tables and this table?

Fuel Pressure propositional gain - bumped up some

Minimum fuel pump duty cycle - lowered slightly

base fuel pump duty cycle - lowered slightly

HPFP leading edge angle - raised some, lowered others. Not they typical Y axis scale for fuel lobe

HPFP Peak duration - close to double values

HPFP noise disable RPM - lowered

HPFP pulse - disabled

[GHuggins]

Well, you took that apart with a fine tooth comb Don't know if it'll work for you or not. It's straight out of another tune I did for a 6.2 that had nearly an identical cam with fuel upgrades, but that build also had a whipple and ported heads... You might be better off with the lower idle torque tables at idle, but I imagine the rest will work better for you. It does give you an idea to what all's required on the gen5's for decent cams that cause you to lose your low rpm pumping efficiencies though.

The only thing I didn't change for you was the DI fueling. This should also be lowered in your idle areas at the minimum about 5 or 10 points. You can even try raising it a little as that will sometimes help to smooth out idle. Lowering will make the fuel burn more efficiently while raising will make it more "lazy" which as stated can sometimes help smooth things out.

Don't know if it'll fix your problem as the builds aren't 100% identical and the engine it came from did have more drag. Just something for you to try.

[Dominatorstang]

The changes helped me/it out greatly. I really liked how the VT and VVE looked a lot like the torque profile of the cam. I think those two especially are great improvements for me to start and not all to far off in many ways. I will check out the other tips you gave me too. My idle is very stable too with the changes, only need some slight tweaking. No surges that I have had so far at all.

I took it down the road and back for a log on SD mode and overall it is doing great compared to how it acted before. No surging and even the fuel pressure looks to stay on track more in most ways. Currently I am trying to verify if the below things from the log are normal or a problem I am trying to tune around.

-HPFP looks to be more stable now, but still the actual spikes up over the commanded and sometimes hangs out high or low for a moment before it pulls inline. I am not sure this is normal.
-shows cruising is average of 10 or 12% rich. Lower RPM's average 25% rich. To correct these I am going to be cutting my VVE table to a pretty low value again.

[Dominatorstang]

Oops, forgot to attach the log.

drive with ghuggins tune vve.hpl

[GHuggins]

Before you change the VVE, try playing with DI fueling first. I looked at the one I had done, I raised it 5 in the upper left 4 cells and then lowered it 5 or so around there. Then I changed the rest a lot, but it was boosted.