Newbie needs help. allowing PE does not increase performance.

[55Belair]

I've been playing around with and reading everything I could find on tuning since purchasing my own copy of the software last fall. Now that the good weather is here and the car is out of storage, I've started trying to get a little more performance out of it. The motor is a 2000 LQ4 out of a Silverado 2500 still mated to the original 4L80E. The 873 cast iron heads have been swapped for 853's mostly as a weight saving measure, exhaust is 2 1/2 inch with straight through mufflers, no cats. The entire package is swapped into a '55 Belair - no that it makes a difference. My original tune was done by a local guy (delete VATS, EGR, Evap) regular swap stuff but no performance enhancements.

As a first step, I thought I would make changes to PE to allow it to come in earlier so I changed Delay RPM to 1400, and zeroed out the time delay. I then changed both the hot and cold throttle tables to 25% across the board. When I tried a scan with this new setup, the car didn't seem to make any more power than it did with PE disabled. I note that the AFR does go down to ~12.5 under WOT but that I also get a KR of 8*. I put the old tune back in. Since I'm brand new at this, I thought I'd post a scan of both tunes so that hopefully someone can set me on the right path. I'm guessing I have lots more reading ahead of me. I also posted the original tune if that can shed light on things. Thanks
With PE.hpl
Without PE.hpl
2019-05-13 (tow Mode enable).hpt

[5FDP]

Do you have a wideband hooked up to read the real time air fuel ratio?

I ask because when you do go full throttle your o2 sensors take a nose dive and to me that says it's way leaner than what you wanted to be running at. Also your fuel trims are maxed out at +25% showing you have a major issue there as well. Be it a exhaust leak, fuel pressure issue, vacuum leak. I suggest that you stop flooring it until that is fixed.

I wouldn't exactly call PE a power adder, it can just make the vehicle react faster to the changes in the throttle and come into the proper fueling much quicker. The idea of power enrichment is command the correct air fuel ratio that would make the most horsepower and torque. Once that ratio is achieved, one could alter the timing to gain power from the engine.



Do you know your fuel pressure? Is it staying at 58psi all the time and not dropping??

Add your injector pulse width avg for both banks to your logs too, you want to be watching that.



As far as the knock goes, look for any trouble codes with the VCM scanner. If you have any knock sensor related code that is present or pending, that will cause the knock sensors to pull the maximum allowed timing that is set in the tune. In your case the max allowed is 8 degrees of timing. You can look at the maximum knock retard tables and both show 8 degrees if you want to verify for yourself.


Figure out your fueling issue/Vacuum/exhaust leak stuff first, then start working things over again. The way you had your PE setup before is okay but try doing it this way instead.

Hot/Cold 50% throttle.

1,400rpm delay is fine.

0 second time delay.

50% enable torque.

80-85 on the MAP kpa instead of 55kpa.

[55Belair]

Unfortunately, I haven't had a chance to look into a wideband yet. Will be looking at recommendations and how to include it with the scanner.

I installed a new external fuel pump on the frame rail when I did the swap, I haven't put a gauge to it - I will. I'll double check for a vacuum leak - nothing is apparent under the hood. Is there any common place for vacuum leaks on these LS's?

I'm a little confused about the exhaust leak. I'm running the stock truck manifolds to 2 1/2" dual pipes. The mufflers are glasspacks so very little back pressure - would a leak really make a difference - or do I not have enough back pressure?

Thanks for your help. I'll keep posting my progress and will post what helps and what hurts this condition as I get it dialed in.

[5FDP]

Just the intake and intake piping for vacuum leaks.

If you can do a smoke test, that is the fastest way to see if anything is leaking. Old intake gaskets are a common leak at the cylinder head.

An exhaust leak prior to the o2 sensor be it from the exhaust manifold flange or the flange at the collector are common leaks. Those can throw the fuel trims for a loop. Not often to people find exhaust leaks after the o2 sensor, only if they are close to the sensor or if the exhaust was dumped right after the sensor would it pull in air with the exhaust pulses and skew the readings.


For sure check your fuel pressure. Low fuel pressure in swapped vehicles is something I see often. The calibration was built around having ~58psi of fuel pressure from the factory.

[55Belair]

Thanks for all your help, can you elaborate on "50% enable torque." Where do I find that?

[5FDP]

Ahh, never mind of that one. That is seen on the 2001+ calibrations and this is a 2000.

It was just stuff I had in my head for things I always change but this computer is a tad older than many I've done.

[55Belair]

Had a closer look at the car today -specifically with regards to exhaust and vacuum leaks. Nothing. Also no pending or active KS related DTC's. I will wait until the rain stops to take it to a friend's shop and get a loan of his fuel pressure gauge.

I've been doing some reading on widebands and am more confused than ever. If I take out the O2 sensor and insert a wideband, then where does the ECM get it's signal for that bank? I only have one O2 sensor per side. I've read the sticky on incorporating the wideband signal to MPVI2 - may as well be written in a foreign language, it's way above my technical ability at this stage of the game. If I can't log the data, not much sense in having a gauge. When I'm WOT I'm kinda busy with other stuff, can't be looking down at the gauge. LOL

Or am I missing something?

[5FDP]

Many people do this and it's not uncommon, they remove the o2 sensors completely and run open loop only and use a wideband o2 sensor to correct the fueling based on special graphs/chart they create.

If you were to remove a o2 sensor to use a wideband, you'd be doing the same thing then re-installing the o2 sensor when you are done. The computer doesn't need o2 sensors run but it needs them to function if you are trying to use closed loop fuel control that the computer offers.

Ideally you need to weld in a separate o2 sensor bung so the wideband can be installed all the time. That is, if you want to have a wideband gauge in the car. If not you'd be doing the method above and removing it when you are done tuning.


Wideband tuning requires that the computer be put into open loop and that all fuel trims and closed loop functions be disabled, so that nothing can alter the commanded air fuel ratio. Each half of the airflow model has to be done separate from one another as well. The MAF can be done first or the VE tables.


Wiring the wideband into HP Tuners using the standard MPVI or MPVI2 is really simple when you break it down. The wideband will have a 5v input and output wire, power and ground. These computers also use 5v circuits for various sensors. The most common used is the EGR circuit because it's a 5v sensor/part. You'd wire the correct 5v wire from the wideband to the 5v pin on the computer. Should be like pin 55 for the EGR, then create the channel to log the wideband with the scanner.

There are tons of threads and even youtube video's that break the whole thing down, can't really get it wrong if you follow them.






I think for now, just figure out if you have a fuel pressure issue. Something is cause the fuel trims to go haywire. And honestly, being that the engine is stock it shouldn't really require a extensive tuning with a wideband. If thinks like intake manifold, camshaft, headers were installed, then yes it would need a lot of work to fix it.

[55Belair]

Thanks for your reply again, I'm learning a ton of stuff here by researching this. Your explanation of wiring a wideband into the MPVI2 is very clear, I can manage that for sure. I did my own wiring harness for the swap so adding a new input where the EGR used to be is straight forward.

Wideband tuning requires that the computer be put into open loop and that all fuel trims and closed loop functions be disabled, so that nothing can alter the commanded air fuel ratio. Each half of the airflow model has to be done separate from one another as well. The MAF can be done first or the VE tables.

The fact that I know how to do only about 10% of this and that I really don't want another gauge in the car tells me that I should skip all this wideband stuff. If I can get this LQ4 to deliver factory rated power and PE to come on when I hit the skinny pedal without pulling a bunch of timing, I'll be a happy camper. Thanks for your input, I'm sure with your help I can sort this out. I'll post again when I get the fuel pressure readings, meanwhile I have a bunch of more reading to do.

[cobaltssoverbooster]

it should be said that you dont need to mount the gauge, you just temporarily wire it up for tuning. remove the oem pre-cat o2 sensor and install your wideband in its place. the trims have to be disabled so temporarily tuning with the o2 sensors fully disabled isnt an issue. it is highly recommended to use the wideband since the oem sensors do not provide accurate exhaust analysis during power enrichment. they do have the added benefit of being accurate through the entire operating range so that means if you tune the whole thing with the wideband then when your done you can enable the trim system and let it run.
the aem wideband instructions are free to download and read. they offer a great example as to why the oem narrowband sensors are inferior to the wideband units in case you want to add that to your reading material.

there are some long posts in here and ill admit i didnt read them 100% through. if it hasnt been mentioned yet, the oem o2 sensors run the trim system which is disabled during pe enrichment states due to their design as explained in the aem wideband instructions. unfortunately re-enabling the trim system in pe is not possible. this means you cant copy and paste tune pe events when using the oem sensors.

[55Belair]

Just finished reading he aem wideband instructions - interesting for sure. I'll definitely look into getting one and installing it, question is: which model go I get? Is there a thread somewhere that will help me make that choice. But before I go down this road, I'm going to try and get it running better than it is before chasing this.

The other question that comes to mind is: how do you "disable the o2" sensors to tune with the wideband?

[55Belair]

Life sort of got in the way of "Fun with Cars" but I finally got back at this. I followed up on the suggestions:

Checked the exhaust, all is good front to back. Put a vacuum gauge on it - 20 inches at idle, dead steady, double checked all the hoses and connections, no leaks. Tonight, I finally got my buddies fuel pressure gauge and hooked it up. It has 48 PSI at idle and immediately jumps up and holds 58 psi when I hit the throttle.

Is there anything else I can do to get this engine to produce anywhere near advertised power? I'm a bit lost right now as to what the next logical step might be. Can someone chime in?

[5FDP]

Put it on a dyno, then you'd know how much power it makes at the tire.

Then you could do changes while on the dyno to see where the best gains are. Could gain power and torque going richer on the air fuel ratio under WOT or it could take away power. Timing here and there could help with mid range and top end but again the dyno is needed to see where you are actually at.

Street tuning only gets you so far, it's great for making sure fueling is there and everything is safe but the street can't tell you horsepower/torque at the wheels.

In the end you are still dealing with a stock 6.0, they make good power for what they are but it's nothing to really brag about.

[kevin87turbot]

I suspect that either your fuel pressure is dropping at WOT. You need way more fuel at WOT.
You will max out the stock injectors pretty quickly with your combo. You might try a more aggressive fuel table until you can add larger injectors and/or verify fuel pressure at WOT. See the sample below...
Be careful about running it lean. It won't tolerate it for very long.

2019-05-13 kw mod1.hpt

[55Belair]

I was trying to avoid the cost of putting it on the dyno by buying the software and playing around with the tune. I realize the limits of a stock 6.0L set up, I just want to squeeze as much out of it as I can. Presently, it pulls 8* of timing at WOT, if I can stop it doing that I figure I'll be well on my way to that. Trouble is I don't know enough about the cause/effect of things to get me going in the right direction.

I'll try adding fuel like you suggest Kevin, just not sure how you do that - is there a thread or reading material that explains this?

[cobaltssoverbooster]

the ls motors are fairly fuel sensitive. once you lock the wot fueling down to the 12.3-12.5 afr range the wot kr should come down. its should not exist at all if you run a bone stock 6.0 ignition map. from here you can toss a few degrees in until the knock sensor shows activity.
my 6.0 denali pulled hardest around 12.3 afr but every motor is different.

if you have all of the trq management shut down and the engine runs around 12.3-12.5 with max ignition around 12-20* at wot high rpm then your probably close to all shes going to put down with stock heads cam.

[55Belair]

Thanks for the reply. The thing that has me puzzled is that as far as I know, this IS a bone stock ignition map so the KR has got me stumped.

This all started when I played with the PE, to make it come in sooner and didn't really notice any change in the before and after. I logged a few pulls and noticed the KR. If I could get it to run as you describe, I'd be more than happy and it would be perfect for my style of driving in this old cruiser. So how do I go about getting the fueling at WOT down? I'm starting to think I should maybe hunt down a stock tune from the repository and build from that, in case the guy who originally deleted the VATS on this made other changes that are causing my problems.

[cobaltssoverbooster]

tune the ve using a wideband. the pe enrichment ratio values are target values (stoich/pe eq ratio=afr target)
set them to the desired afr target ~12.4 and leave it be.
try a map threshold around 70 kpa and a tps threshold around 65%
if you have a trq threshold set it to around 50%

trying to make pe come on sooner can load up the cylinder if the engine doesnt like it coming in that soon and cause kr to show up.

[kevin87turbot]

I was trying to avoid the cost of putting it on the dyno by buying the software and playing around with the tune. I realize the limits of a stock 6.0L set up, I just want to squeeze as much out of it as I can. Presently, it pulls 8* of timing at WOT, if I can stop it doing that I figure I'll be well on my way to that. Trouble is I don't know enough about the cause/effect of things to get me going in the right direction.

I'll try adding fuel like you suggest Kevin, just not sure how you do that - is there a thread or reading material that explains this?

Just load the tune that I posted... I just modified your tune.

[kevin87turbot]

The KR is because of the lean condition. Once you get it to run the proper AF ratio, the KR will go away.