LQ4 - Pedal 155%, Inj. 122%, Drivability

[NTENSIONAL]

First Post - LQ4 - Pedal 155%, Inj. 122%, Drivability

I bought a 1986 Suburban C20 Silverado recently and it came with an LS swap already installed. I don't have any reputable tuners within a 2 hour drive, so I've decided to tackle this myself for now. There are a few maintenance issues (outlined below) that need to be addressed, but I am concerned that there are also some strange driveability and hardware issues that are unrelated. Of course, the steering box dumped the pitman seal last night, so I have to swap the box this weekend as well before I can log the truck again, hopefully the pump didn't burn up. (I did, swapped as well)

If anyone feels like giving me a hand that would be great, but I'll be ok either way. Just wanted to document sorting this out for myself and others. Mostly just looking for pointers if any of this existing stuff seems way out to lunch. If fixed, built, tunes many things over the years, I'm a good troubleshooter, but this is my first LS and my first time with HPT. This is a big wall of information...

The truck is running and driving somewhat normally. My understanding is that it has been running this tune for a few years.

Issues

Very limited torque off the line, putting the pedal to the floor results in a leisurely roll up to speed. I've driven lots of 4.8, 5.3, 6.0 trucks of this era, I have a pretty good idea what they should feel like. Tune shows abuse settings are largely disabled or otherwise set higher than stock. I thought I got a log of WOT from stopped, but apparently the logging takes quite a few seconds (~15) to start in standalone mode. Most of my logs missed the thing I was trying to document lol. Should I be stripping down my Channels or adjusting sample rates on anything in particular?

The throttle position reads 100% at approx. 50% pedal travel. (155% at the floor, log 14 shows this pretty well). I have looked through the TAC/Pedal P/Ns from a bunch of swap sources, my hardware seems like it should be compatible.
Does flashing different years of software have any effect on compatibility?

The truck has uneven throttle response. Some of this might be the knock sensors taking out some timing (4deg) but i have logs that don't show any knock reduction. The pedal going over 100% seems to be having an effect. If I am at 3/4 pedal and back off slowly, it suddenly pulls hard, like 25-50% harder. I would think the computer only looks at TPS not Accel Pedal, and TPS cycles through 99.6%

The transmission shifts very solidly. It yanks the truck hard through the shift at moderate throttle positions. The shift speed tables are a bit strange in the tune, once everything else is sorted I might take them back to stock and reevaluate shift points. I also wonder if this is also because the transmission thinks the pedal position is higher than it is?

It sporadically requires two attempts to start, but always starts on the second attempt and idles very well. Multiple prime cycles of the key has no effect on if it will start. (this is probably Cam Pos. Sensor)

Minor surging/flutter at 50MPH/full OD lockup only.

I believe there is also a small exhaust leak on the driver's side, hopefully it will be nice this weekend and I can take a look at that too.

Reviewing the logs, I see the PCM voltage is low, as low as 11.5V and not exceeding 12.9V. I will confirm voltage with a meter, but that seems much too low.

Tune

Reviewing the tune that came on it I see a couple things:

900RPM Idle accross the board. I did a manual override to 600 and it idled fine for a few minutes, maybe tuned for a monster cam?

PE EQ Ratios are 2+ and the PE engagement is reduced. Ramp 4.0 (maybe that's why my injector DC is over 100%>)

Base spark/airmass table looks to be bumped 2.5-3deg, smoothed/extended - Minimum Spark Retard limit is 0, Max Knock retard is ~4

Torque management has a bunch of changes, eliminating the limits

Shift points have been moved higher 1>2 and 2>3 shift pressures are up about 30% in the normal table, Shift Timing is -25%, Minimum TCC DC is 96% for the whole table. TCC Apply is loced out to 412kph in 2nd and 3rd

Final Drive setting is correct.


DTCs

P0200 - NOID lights and see if I can find a harness issue. Cyl 7 has at times shown a misfire, but it is not consistent. At idle cylinders 4 and 7 have the least effect on RPM.

P0332 - Will replace knock sensors and do the cam sensor while the intake is off, anything else I should address under there?
(OEM GM vs Carquest Knock sensors? The GM ones are about 3x the price)

P0101 - MAF looks like it is reading OK, I will wait until other issues are sorted to address this

Plan of attack & Questions

Verify voltage at battery > check grounds and power leads/test alternator
NOID light > determine if there is an injector harness issue
Fix the Exhaust Leak
Steering Box Replacement
Order a Fuel Pressure adapter/sender > install
GPS Calibrate VSS > Calibrate Speedometer Output
Replace Knock Sensors and Camshaft Position Sensor

If anyone can shed some light on this pedal thing, or things to check with that (best resources?), please let me know. If it's not causing a problem, I won't mess with it, but my foot says that it is.

Should I just flash a stock Tune onto it and go from scratch? 2003? 2005? Does it matter? How can I tell which stock to use, or the year of my engine?


Hardware

*As far as I know* there are no modifications to the engine, it was supposedly a stock junkyard pull. It was retuned by a shop after this motor went in.

Transmission - 4L80E Case - 24208421 - MJP

Engine - LQ4?? (can't see any identifying marks)

Cylinder head - 317

PCM - SERV. NO. 12589463 HDW NO. 12589162 - 2005 C/K-TRUCK/MPV, LM7, LQ4 2006 C-PICKUP, LM7

Tac Module - TMD1-160E1 - 12588923
Pedal Module - 9 Pin - 2003-2005 Gen III Truck/SUV/VAN drive by wire Pedal

Oil Pan - 12577396

Tune and Log Files

Tune - As Received - 2025.07.15 - As Recieved.hpt

XML Channels - 1986 Suburban Channels.Channels.xml

Log 15 - Shows the end of a "WOT" (155%) pull - Log-0015-1GTHC29U35E214874.hpl

Log 14 - Shows some variable throttle - Log-0014-1GTHC29U35E214874.hpl

Before

before.JPG

After

burb.JPG

[Alvin]

The tune is honestly a mess.

You are commanding like a 7 : 1 AFR at WOT in PE likely to compensate for the MAF only reading around 120g/s at WOT.

I would check fuel pressure at WOT cause likely whoever tried to tune this didn't understand he couldn't get the fueling where he wanted to be because of weak fuel pressure or a bad MAF. These engines do come with barely adequate injectors.

It's OK that Pedal % is so high. That is how this year range truck looks when you scan them.

[NTENSIONAL]

Thanks Alvin,

I had a suspicion that Fuel Pressure would be one of my diagnostic steps here, I need to drop the tank anyways to fix the vent (luckily the tank is new). I will check out the pump situation when I am back there, but there is a gold colored pump-looking unit in front of the tank that I thought looked suspect for an LS.

I won't flash a stock tune until I get all my parameters monitored, in case this richness is protecting the engine at this point. Probably going to have to get a WB in the mix too.

[Alvin]

The only way to check the fuel pump is with a fuel pressure gauge tested at max load.

That PE isn't safe. It's far too rich.. but like I said the entire thing is a mess and it looks like it got into that mess over a couple mechanical issues (maf, maybe fuel pressure)

[bk2life]

[B][U]First Post - LQ4 -

you have lots of data there for us.
Is the engine stock?
no cam?
what number is on the injectors?
what maf is on it?
what map?

If it is a stock engine, id load up a stock tune for the motor and trans and start over.
A stock tune will get you almost where you need to be for a stock engine, and then you can tune it in about 45 mins.

[gtstorey]

Consensus on here is GM only for knock sensors. And most other sensors. But especially the ones that are hard to get to.

[Fast4.7]

Consensus on here is GM only for knock sensors. And most other sensors. But especially the ones that are hard to get to.

GM or NTK is all I will use for knock or 02 sensors.

[NTENSIONAL]

Thanks Everyone,

Is the engine stock?

I see no indication that anything was modified, 25317628 injectors, Delphi MAF, stock TB. Didn't pull the bracket to look at the MAP, but I would expect nothing radical there either.

I found 03/04/05 tunes for the LQ4/4L80E. The 05 tune I found looks very close in the areas it hasn't been modified, but there is a difference in the injector offset between the 05 and 03 tune. I'll have to dig into that and see what makes more sense. Searching the repository is a bit of a shit show tbh. Keyword searching is weak. Would love to find an exact match Stock 2WD/DBW Tune.


This PE table is wild. I did some thinking and it's definitely making sense with my symptoms. The combination of the incorrect pedal ratio and the 2x PE Ratio means:

at 3/4 pedal and back off slowly, it suddenly pulls hard, like 25-50% harder.

The truck is coming out of PE at TPS drops below 100% and that's why it pulls harder. I don't know who thought this was a good idea.

Hopefully the steering box comes in early this weekend and I get a chance to dig into this further. I'll let you know what I find.

[NTENSIONAL]

Minor Update - Got my steering box and pump replaced - so progress may continue.

I spoke with the original builder of the truck and he sent me some tune files to use as a base tune. I compared them with a stock 05 6.0 file and they are pretty much stock, with the exception of regular swap stuf + abuse/torque management/shift points & lowering when PE kicks in.

MAF only reading around 120g/s at WOT.

I pulled the intake to swap the MAF and found the K&N pipe crushed out of shape, leaking air at the Throttle Body, heated and returned to round. Ran a quick log and MAF is up 66% at idle, so I think it's probably just time to put the new (stockish) tune in it and test drive it. I'm still going to try to do the NOIDs on it.

I also checked Battery Voltage, I am getting 14.3 @ idle on the meter and my control module voltage is up to 13.3 on the log, from 11.5-12.9, the battery just went through like 20 restarts bleeding the power steering, so I will hold judgement until it's run 100miles and is up to temp. Still makes me think I should get in and clean all the power and ground connections.

Finally, my idle log shows a 190 Misfire history on Cyl #7, but still 0 for current misfires. How long do they stay current? I don't think I've ever logged a misfire in realtime.

Thoughts?

IMG20250722162027.jpg
IMG20250722163129.jpg

Log
Log-0016-1GTHC29U35E214874.hpl

[NTENSIONAL]

Well, I will keep picking away at it, but I flashed a new tune and that is a world of difference. Drives like a normal truck should, I'll get into the logs a little more later and pick away at the outstanding issues, but this is much improved, I've even got open loop. It still runs a little rough, but we'll take it one day at a time. The spark plugs are probably mostly charcoal.
No change to the throttle issue, I'll just put in a mechanical stop if it still bothers me.

Thanks for the help everyone.

Log-0018-1GTHC29U35E214874.hpl
6.0l 4l80e 12592618 os 2025.07.22 - Hybrid Stock and Original w swap deletes_shifting_abuse.hpt