6.0 to 4.8 Swap - Still super lean after fixing intake leaks

[marmstrong]

Hey all. First off, this is me eating my humble pie. I've done a lot of fun and crazy things with cars over the years without ever making a forum post. Lots of searching and reading and winging it has gotten me where I needed to go. But this whole tuning thing... It's got a steep learning curve on it.

Background:

I bought an '02 Silverado 6.0/4l80e 2wd a few years back. It was abused but I brought it back around. It ran great! I stole that drivetrain for my 1990 Suburban and the truck got what I had laying around, a good (better shape than the 6.0) 4.8 from a 2005 silverado. At the same time, I converted the truck to 4wd and put it on 38" Boggers with no lift, but that's another story, probably for another forum.

When I did the engine swap, I basically changed over just the long block so there was no rewiring of plugs or sensors. I have tried several different stock 4.8 tunes from the repository and one that I know to be 100% factory from a different forum. Even trying a 6.0 tune resulted in lean fuel trims.

While logging, I was getting STFT+LTFT in the ballpark of 40% lean. Pulling a sparkplug showed that it looked a little lean, so I knew it wasn't an O2 sensor issue (I had changed one out due to stripped threads). Also, both banks had the same trims, so I'm really confident it wasn't O2's.

Around Thanksgiving I changed the intake manifold gaskets because they were reused. This helped some with the lean issue, but not a lot.

2022.11.24 - First drive after radiator swap, new working tune - 2022.11.24.hpl

Around New Year's I blocked off the EGR due to a suspected leak. Sure enough, the flex hose from the solenoid to the intake was cracked. I just took another log tonight and it looks like my leak is completely gone at low RPM (slightly negative fuel trims now). However, I'm still 10-20% lean with a bone stock 4.8 tune.

2023.01.11 - Test Drive 1.hpl

I've included my most recent log and tune. I bought GRG's layout package but half of the channels wouldn't read so most of my tables wouldn't populate. Kinda pissed about that, but I'll fix that later. I just used the autopopulated SAE channels to get fuel trim logs.

I'm running out of ideas on what to address. I need some smart people to point out the silly thing I'm missing so I can keep learning.

tl;dr
What on earth is causing my stock 4.8 tune to be so lean on a stock 4.8 engine?

[Ben Charles]

Simple, have you checked fuel pressure

[marmstrong]

Thanks for the reply, Ben.

I checked fuel pressure back in July when I first had the engine running in this truck. I was seeing about 40-45psi at idle and 55-60pis under WOT. The gauge was duct taped to the windshield, so there may be a little error in my readings.

I've always had a concern about the fuel pump in the truck, but it's never given me any overt issues. I suppose it could be getting weaker, but considering the consistency of fuel trim issue, I'm less inclined to believe it.

[marmstrong]

It was going to nag at me if I didn't check again because you're right, it looks exactly like a fuel pressure issue.

Idle fuel pressure is 47-48psi. Wot @ ~5000rpm is 57-58psi. Unfortunately that checks out just fine by my understand g of the vacuum referenced FPR.

[blindsquirrel]

Fail the MAF and see if it's better in SD. Easy way to rule in/out a MAF issue.

You don't have any open breathers on the valve cover or anything, right? Any air that can enter the engine without first going through the MAF will royally screw things up. Block off the brake booster hose, you'd be surprised how often that gets overlooked.

[marmstrong]

I swapped the MAF with one from another truck back when I first got the new engine running to see if the trims changed. I can't remember if that's the MAF that's still in it though. I'll give it a try tomorrow.

The truck has hydroboost and I've quadruple checked that the plug is in the back of the intake.

I did replace one cracked breather hose a while back as well. I can do another check.


So, what I'm getting from these replies is that the experts don't believe it is a tune issue? It's likely a mechanical or electronics issue?

[blindsquirrel]

Well, if you've already added, what, around 15% to the 6.0's VE table, and it's now a 4.8, and it's still lean... sure, you could keep diddling the tune and get the right numbers to come out, but the tune isn't the root cause.

I would still be failing that MAF just to see how it responds.

[blindsquirrel]

Your file still has EGR (& AIR pump) enabled, is that intentional?

[marmstrong]

Damn, I managed to remove my post.

To be clear, I haven't intentionally changed fuel or timing at all. I performed segment swaps for the engine and transmission (basically a 4.8/4l80e tune). I changed some ancillary things like rear O2's and gearing.

By my figuring, this should be a stock engine running a stock tune. I can't figure out why that combination would lean out at higher rpm.

Are you seeing added fuel compared to what a stock 4.8 should have? I'm still learning what I don't know, so I may have done something super simple and not even realized it.

As far as the EGR, the intake is plugged, solenoid is unhooked. I turned off the DTC's and wrote the tune. Perhaps I didn't fully turn the EGR though. Either way. It's not letting air into the intake anymore.

Being a 2500hd, it didn't have an air pump.

[kevin87turbot]

Damn, I managed to remove my post.

To be clear, I haven't intentionally changed fuel or timing at all. I performed segment swaps for the engine and transmission (basically a 4.8/4l80e tune). I changed some ancillary things like rear O2's and gearing.

By my figuring, this should be a stock engine running a stock tune. I can't figure out why that combination would lean out at higher rpm.

Are you seeing added fuel compared to what a stock 4.8 should have? I'm still learning what I don't know, so I may have done something super simple and not even realized it.

As far as the EGR, the intake is plugged, solenoid is unhooked. I turned off the DTC's and wrote the tune. Perhaps I didn't fully turn the EGR though. Either way. It's not letting air into the intake anymore.

Being a 2500hd, it didn't have an air pump.

90% of the time, a lean issue like yours is either a fuel pressure issue or faulty MAF or a vacuum leak. I would disable the MAF like Blindsquirrel indicated.

[marmstrong]

Fuel pressure is officially ruled out.

A vacuum leak should affect high vacuum, low flow situations more heavily, right?

I will fail the MAF tomorrow and see how it does. That's a step I wouldn't have thought to take yet. I appreciate it you guys. I will report back.

[marmstrong]

Blindsquirrel I checked the primary VE table and see all that extra fuel you're talking about. 124 percent at 4800rpm, 105kpa. That makes zero sense. Checking it against the tunes I pulled data from doesn't check out either. Way too much fuel. Obviously something happened. I'll start over on the baseline so my tables actually match a stock 4.8. Then I'll disable the MAF.

[blindsquirrel]

Are you seeing added fuel compared to what a stock 4.8 should have? I'm still learning what I don't know, so I may have done something super simple and not even realized it.

Your VE on top, a stock 2002 LQ4 'U' 2500HD on bottom. Bigger numbars = moar fuel. You posted a 6.0 file, I can only see the ones you post, I don't know what's in the other multiple files you've been shotgunning at it.

screenshot.11-01-2023 21.54.44.png

As far as the EGR, the intake is plugged, solenoid is unhooked. I turned off the DTC's and wrote the tune. Perhaps I didn't fully turn the EGR though. Either way. It's not letting air into the intake anymore.

Being a 2500hd, it didn't have an air pump.

Engine > General > AIR Pump: [ECM] 2020 - Air Pump Disable Coolant Temp: Below this engine coolant temperature, the air-pump is disabled. (high temp to disable)
Engine > Exhaust > EGR General: [ECM] 210 - EGR Enable: Master enable/disable for EGR.

[blindsquirrel]

If it's lean now with the inflated VE, it will be even leaner with a stock VE, even if it's the stock 6.0 VE. 4.8 VE will be even worse. This is not a tune issue since it's already being given gobs of fuel and still lean.

[blindsquirrel]

I have seen trucks from that era with some kind of scum/coating that comes loose inside the tank and/or lines and ends up making it all the way into the injector inlet screens. Symptom is usually misfires and lack of power though, not overall lean everywhere (misfires on cylinders closest to the rail inlet and the crossover pipe from bank-to-bank since they get the crud first).

[marmstrong]

Shotgunning is probably the best word for it. Plus I only work on it in fits and starts so the info isn't fresh in my mind. I'll pull together a 4.8 tune (much closer to the 6.0 tune you posted than my current tune is, obviously). But, like you said, it's going to be much more lean after that. I'll baby it while I get a SD log.

Thats interesting about the injectors getting plugged up. I agree that it would be a more sporadic issue though. I have some other fuel rails and injectors I could throw at it (maybe one bank to see if it makes a difference?), but their quality is highly questionable.

I will say, the 4.8 is a dog compared to the 6.0, even on 31's. I'm hoping that fixing the tune will resolve some of that. I'd at least expect it to break the rear end loose on wet pavement, which it will not do currently. If it doesn't perk up, it's going to need a doubler for out on the trails.

[marmstrong]

Alright guys.

I reviewed my tune and the ONLY difference compared to the stock 4.8 tunes I have was the VE table. No idea when or how it happened, but whatever. I copied the 4.8 VE table over and turned off the AIR pump and EGR properly this time (thanks blindsquirrel).

I failed the MAF (got the P0103 DTC), copied the high octane table over to the low octane table, and disabled DFCO. I did NOT touch PE because I was afraid of going way lean. I took a log after resetting LTFT.

Considering I essentially lowered the VE table by 20% across the board, I'm surprised by how close to nominal the trims are. My interpretation is that my MAF is FUBAR and I potentially still have a vacuum leak

Please let me know your thoughts on the new log. I've also included a spreadsheet I made to visualize the differences between the tunes more easily. Don't know if it will help you out, but it's helping me for now. What is your preference: LTFT on or off during VE tuning? I can see the merits of both (accuracy vs speed).

Attachment 127360
2022.01.12 - Tune From Scratch.hpt
Attachment 127361

P.S. It's raining and cold in Ohio right now. Colder and wetter than yesterday's log.

[kevin87turbot]

Good deal! It was the MAF.

The logs don't appear to work on your post. It just shows invalid attachment when you click on them.

[marmstrong]

Hmm that's frustrating. I'll repost them tonight.

While I agree that the MAF was probably 90 percent of the issue, I'm still getting LTFTs over 10 percent in the limited rev range I was logging in (expecting it to be worse up high). My exhaust is the only thing that isn't 100% stock in the drivetrain, but that's still a stock 4.8 y-pipe with cats and a stock muffler with no exhaust after the muffler. I can't see that making the engine any more efficient.

I got to thinking about the vacuum leaks again. A leak after the TB would lead to lean fuel trims at high vacuum, low load. A leak between the MAF and TB would grow more apparent as pressure dropped in the intake tube (high load, high rpm). So that's another thing to check.

Can old injectors (230k miles) start to lean out? In the old school diesel world you usually run more rich and less efficient due to dribble and poor pattern.

[Ben Charles]

10% probably about right with exhaust work and I’m sure the tune is still targeting 14.68 as stoich as well