PCM delivering wrong fuel mixture?

[Matthew Jeschke]

@Mudsport96 it's been so long since I tuned the injectors. Yeah, could be other way around for pressure. I looked at swapping all the L59 fuel system over but was way too much work. The guy coaching me on tuning just said how to adjust what I needed in the parameters. Worked like a champ.

I need to learn more about spark. I've probably studied it for a good 40 or 50 hours of YouTube university haha... Tuning forums are DANGEROUS though. So many people just there to chat and don't know what they are talking about. Honest to God, this is the BEST forum I've found EVER for mechanic stuff! The little you've all shared with me is more than I've heard from tuning forums. Problem is you don't know good from bad on those.

Anyways, I'm running the LM7 spark map on the LQ9 build. It works down low but I think it's a bit much timing up high. That said, its far less timing than what I see on the Corvette or other LS1 or LS2 builds factor settings, so thinking its safe. Down low I don't see any knock at all... Up high I can get it but I never really go WOT so I've not done much time playing with any of that yet. Timing actually scares me to death haha... On my high priority todo list is to start transferring LQ9 baseline spark settings into my current tune. I just don't know how one thing will affect another, tuning is quite complicated.

@Marky Dissod could be... idk? I am using a wideband so it's quite reliable either way. I tried with narrow bands but can only do so much, and no PE with those. When tuning PE I made PE PIG rich, then slowly leaned it out. The computer doesn't have any feedback for PE (narrow band O2 sensors only really work for cruise and idle from what I understand). So I read the wideband with each run I leaned it out to get closer to 12.6:1. I said good enough when it got between 12:0 and 11:0 to 1. I don't really do any WOT stuff with the truck. I may revisit PE in future but spark is really my next thing to tackle.

The truck tune was kicking PE on at 90% throttle and don't recall what cylinder pressure... but really high. It only really goes to PE when the engine is REALLY REALLY under load. I think they may have baked the extra fuel into the VE table was my guess.

With the aftermarket cam, I had to redo all that stuff. PE is really kind of stupid. Best if the VE table is all dailed in, in my opinion (blend from 14.7:1 light cruise & idle to 12.6:1 WOT stuff). However, I'm using PE as that's how it was explained to me to tune it.

What I'd REALLY love is if the controller had a pin that would go high (for a switch) when PE is enabled. Then you could have the computer run an injector at the throttle body to put in water or methane. Then just run 1 lambda all the time with the main injectors. In my opinion that's the route to go with direct injection to clean the intake runners but manufacturers are too cheap to do it. They could even just pump gas through the throttle body injector.

 

[Mudsport96]

Yeah, with the aftermarket cam designed for towing or a heavy vehicle, cylinder pressure will be way different than a typical performance cam. So knock may show up in unexpected places. Have you watched GoatRope Garage on YouTube? He has a few good beginner videos for tuning the P01 computers. Not excessive detail, but good enough to get a fella going a good direction.

 

[Matthew Jeschke]

@Mudsport96 I think I watched all the P01 & P59 Gen III tutorials he made. They were helpful enough to acquaint me with tuning. However, had TONS of little questions along the way. Was going to hire him, but ended up making friends with a good guy off another forum who is SUPER sharp with the stuff. He builds Turbo LS setups and all kinds of cool stuff. He has been coaching me over the phone. Really really thankful. He also coached me through my 4L60E build, as well as build some stuff via mail for me. He shared an AWESOME 4L60E build recipe, that requires a little bit of tuning but non of the gimmicky shift kit stuff.

There's multiple ways to go about tuning. He has coached me a bit differently than the Goat Rope guy.

Specifically, on fuel. I notice everybody makes their fuel curve REALLY REALLY rough. They just copy over the histogram they make from doing logging runs and multiply it in but don't do enough smoothing. I started out doing that, and the fuel just got worse and worse for me. Then my friend said I should really be smoothing more. So I smooth the graph manually (by hand each cell). The engine runs REALLY good that way, and fueling is very close... Also there's quite a bit of hype on getting fuel to within +/-1%. That's nearly impossible. You start overshooting one way or the other. My buddy said within +/-5%... I noticed, you can get tighter when engine is pumping more but down around idle is VERY tricky... Once you turn on closed loop (after tuning) it tightens up, but +/-1% or even 2% is DARN hard around idle or light cruise w/ open loop.

There is also VERY VERY little idle tuning advice. Idle is SUPER important in my opinion. People like the romance of WOT tuning but in my opinion why bother if your vehicle idles poorly. I don't recall when I finished my engine build, it's been a few years now? I've been studying tuning ever since then... Honestly, for spark, I'd love if I had the money to just hire a speed shop w/ dyno to do that but I'm always strapped for $$$$

Another challenge is the knock sensors. You don't want to desensitize them too much, but you need to turn them down a bit. Knowing exactly how much is the trick. It's REALLY hard to know. I'd LOVE if I had more time to design a harness that goes between the sensors and the computer. I'd put in a small chip and it would give you a more accurate knock reading. You could calibrate it by turning down advance, then doing some test pulls, then putting back your old spark map. It would also connect via bluetooth to a headset to listen. Plus it would allow you to keep the stock PCM. I used to design stuff like this, I got my masters in engineering to design embedded systems (custom electronics w/ software). I just have NO time at all with my day job.

 

[Marky Dissod]

... quite a bit of hype on getting fuel to within +/-1%. That's nearly impossible. You start overshooting one way or the other.
My buddy said within +/-5% ... I noticed, you can get tighter when engine is pumping more but down around idle is VERY tricky.
Once you turn on closed loop (after tuning) it tightens up, but +/-1% or even 2% is DARN hard around idle or light cruise w/ open loop.

When you say +or-5%, 122 / 5% rich tends to be better than 134 / 5% lean.
Then add timing a scoshe at a time in a given regime, check the trims, and adjust - idle, comically gentle acceleration, gentle acceleration, noticeable acceleration, etc - until you reach a point of diminishing returns.

By the way, believe in tuning normal driving regimes with 87 octane and while carrying extra weight.

 

[Matthew Jeschke]

@Marky Dissod I hadn't thought about extra weight! Great idea, I kept trying to find roads with a slope on them but is difficult to find one long enough. I could literally just throw a bunch of weight in back... hrm! Great idea!

You have great points with the rich versus lean. I gave that lots of thought... The narrow bands will pull it in to around 14.7:1... However, I tuned with this in mind... I wanted idle / cruise to be more towards lean side... so if it was adding say 5% fuel I felt was fine (worst case). However, as the graph got higher RPM and pressure, I blended in closer to rich side.

I honestly, don't know how knock resistant the engine is at low RPM & pressure. Maybe I should have err'd on the rich side?

There's SOOOOO much thinking goes into tuning it's CRAZY. If I had a TON of time, I'd just tune the VE table for all open loop (no narrow bands or PE). If I had even more time, I'd design an adapter so I could use wide band sensors and keep the stock PCM.

 

[Marky Dissod]

... hadn't thought about extra weight!
Great idea. I kept trying to find roads with a slope on them but is difficult to find one long enough.
I could literally just throw a bunch of weight in back! Great idea!

If you put too much weight too far in back, the bottom of the rear bumper starts to act like a tiny parachute.
Obviously uphills are great for real world tuning, but they're not always easy to find or in close range.
Narrow bands do NOT pull to 14.7:1 - they pull CLOSE, but they NEVER ACTUALLY hit it on the nose.
(Imagine an expert sharpshooter who can't ever hit anyone in their 3rd eye, but consistently blows away eyeballs.)
That's why 128 ALMOST NEVER HAPPENS, and never happens predictably or consistently.

We all want idle & cruise to be on the lean side ... but don't get overeager.
122-128, adjust the spark, adjust the fuel, 122-128, adjust the spark, adjust the fuel, bit by lil bit ...
Eventually you'll know when adjusting spark hits diminishing returns.
THEN you can adjust the cruise to get a bit closer to 128.
I can't recommend adjusting idle any lil bit lean. Ask anyone who used to tune engines with screwdrivers.
Engines like to idle a wee lil bit rich. If you get the spark just right, 122-125.

As for cruising a lil bit lean, I went about it differently, maeyt.
Again, 122-125, then it does its thing. If you want to talk about it, private conversation, please.

 

[Matthew Jeschke]

I'm till working hard to try and figure this out. Not much progress so far... It's still down to 12.5 MPG from 14.5 MPG.

I'm currently going over data I collected in HP tuners from previous iterations of my tune where I got better mileage. Injector duty cycle doesn't look much if any different really. Wondering if I lost some pumping efficiency though / change in vacuum versus engine speed? What metrics would you guys look at in a data log?

Other considerations:

Air Intake: I installed a Banks Cold Air Intake (after issue came about). Didn't seem to affect much. I may throw factory intake back in just to see if changes anything. Want to log data though... I need to get a good set of PIDs for airflow, vacuum, etc so I can make a comparison of the two intakes.

Evap System: my evap canister fell apart. I really had felt this was the culprit. I dropped the tank, and rebuilt the lines with some new quick connects. I also replaced the nipple that snapped off on the canister. Is there a way to pressure test the evap though? Maybe I have a major leak yet?

Spark Advance: my baseline advance was from an LM7 5.3L that was originally in my truck. I copied the spark settings from a LQ9 into my tune. This is where all the efficiency troubles seemed to surface. I saw a drop in MPG so I switched back to the old LM7 baseline but for some reason this didn't fix my issue?

Trans cooler: I installed a TruCool trans cooler that had been sitting on my shelf for years. The trans runs SUPER cold.... Way TOO cold (another post). I'm certain it's adversely affecting mileage but 2MPG??? That seems a bit much no? I have a oil thermostat & parts on order to fix this issue.

 

[strutaeng]

A few of my $0.02:

Air intake: I was reading a book by Werner about rebuilding engines and mentioned that removing the MAF sensor screen causes lean condition. My 06 Suburban LQ4 actually has that screen removed from the PO, and it does run a bit lean. Not sure if that's really an issue or not. Easy enough to change the OEM intake tube, I guess.

EVAP: do you have any codes on this? If not, it's probably okay. You could smoke test the system to see if there's a leak, in conjunction with operation the vent valve via bi-directional scanner and monitoring fuel tank pressure voltage.

In the rare case where the purge solenoid diaphragm tears and the intake is constantly sucking fuel tank vapors, the system will tend to run rich. So I don't think this is your problem.

Spark and Tune: you didn't do a segment swap when you swapped to the 6.0? I'm guessing some folks are good enough with tuning and can just take any tune and make adjustments to a different engine, but most will do a segment swap and make adjustments from there. You know much more than me about tuning, so I really don't know on this honestly.

Transmission cooler: did you happen to bypass the radiator cooler? I guess it's technically a fluid "warmer" for the colder times of the year. What temperatures are you seeing there? And at what ambient temperatures?

 

[Marky Dissod]

Regarding ATF cooling (and motor oil cooling, for that matter):
the radiator sidetanks people refer to as coolers, are not exactly coolers.

1. Immediately after a cold start, the radiator coolant warms up more quickly than the motor oil and ATF,
UNLESS motor oil and ATF get to warm up more quickly by being in proximal contact with the radiator.
In COLD start scenarios, the radiator sidetanks are NOT coolers - they are WARMERS.
(So, yeah, if you live in a state with warm enough winters or no winters, they are USELESS to you.)

2. When the engine is operating properly as expected, it is nearly impossible for the fluid(s) in the sidetank(s) to be colder than the coolant.
Unless the engine thermostat is cooler than OE, and/or the engine fans are programmed to run at cooler temps than commanded by GM,
the sidetank(s) are temperature regulators at best, if not warmers.

3. If the engine and or the transmission are working / playing hard, it should be evident that even if the engine coolant is doing a good job of shedding heat, the motor oil and ATF are warming the coolant.
Again, the motor oil and the ATF will NEVER be cooler than the antifreeze / coolant.

4. In the event that the antifreeze / coolant flow is compromised for ANY reason, the antifreeze / coolant will get hotter and hotter,
and the motor oil / ATF will follow suit.
THIS is why if the engine overheats, the motor oil AND the ATF should also be replaced.

EXTERNAL COOLERS are coolers in the truest sense of the word. Radiator sidetanks are not coolers.

 

[Matthew Jeschke]

A few of my $0.02:

Air intake: I was reading a book by Werner about rebuilding engines and mentioned that removing the MAF sensor screen causes lean condition. My 06 Suburban LQ4 actually has that screen removed from the PO, and it does run a bit lean. Not sure if that's really an issue or not. Easy enough to change the OEM intake tube, I guess.

EVAP: do you have any codes on this? If not, it's probably okay. You could smoke test the system to see if there's a leak, in conjunction with operation the vent valve via bi-directional scanner and monitoring fuel tank pressure voltage.

In the rare case where the purge solenoid diaphragm tears and the intake is constantly sucking fuel tank vapors, the system will tend to run rich. So I don't think this is your problem.

Spark and Tune: you didn't do a segment swap when you swapped to the 6.0? I'm guessing some folks are good enough with tuning and can just take any tune and make adjustments to a different engine, but most will do a segment swap and make adjustments from there. You know much more than me about tuning, so I really don't know on this honestly.

Transmission cooler: did you happen to bypass the radiator cooler? I guess it's technically a fluid "warmer" for the colder times of the year. What temperatures are you seeing there? And at what ambient temperatures?

GREAT Help... I dove deeper into the evap system. The solenoid is broken / stuck open, and command signal is stuck high as well.

EVAP SYSTEM: Purge solenoid is broken / stuck open

Command signal (harness side) always 1.5Ohms to ground green / white wire. However, I assume the pink (or orange?) wire is the control signal. Its stuck at battery positive voltage. I cannot get the control signal to switch regardless if I command the PCM to otherwise. Tests done w/ ignition on start but engine not running.

Solenoid I cannot get it to switch opened or closed on the bench w/ 12v command signal. It's froze open. Perhaps from being held open for too long (command side)? I assume it's normally closed (when not powered).

Maybe this is my issue...? I need to get fixed, but just blocked the purge solenoid for now to test theory so it's always closed.

SPARK AND TUNE: I originally re-baselined from a LQ9. Then got a guy to help me do tune, I don't know exactly why, but he said to go back to the tune from the LM7 I replaced. I used the LQ9 from that point forward as guidance to do my tune. He said he really doesn't like to do a complete rebasline from another vehicle as the PCM has stuff specific to the chassis as well I think was his reasoning.

TRANSMISSION COOLER: Ambient temp 45F trans temp < 100F. Ambient temp 75F trans temp around 120F.

Regarding ATF cooling (and motor oil cooling, for that matter):
the radiator sidetanks people refer to as coolers, are not exactly coolers.

1. Immediately after a cold start, the radiator coolant warms up more quickly than the motor oil and ATF,
UNLESS motor oil and ATF get to warm up more quickly by being in proximal contact with the radiator.
In COLD start scenarios, the radiator sidetanks are NOT coolers - they are WARMERS.
(So, yeah, if you live in a state with warm enough winters or no winters, they are USELESS to you.)

2. When the engine is operating properly as expected, it is nearly impossible for the fluid(s) in the sidetank(s) to be colder than the coolant.
Unless the engine thermostat is cooler than OE, and/or the engine fans are programmed to run at cooler temps than commanded by GM,
the sidetank(s) are temperature regulators at best, if not warmers.

3. If the engine and or the transmission are working / playing hard, it should be evident that even if the engine coolant is doing a good job of shedding heat, the motor oil and ATF are warming the coolant.
Again, the motor oil and the ATF will NEVER be cooler than the antifreeze / coolant.

4. In the event that the antifreeze / coolant flow is compromised for ANY reason, the antifreeze / coolant will get hotter and hotter,
and the motor oil / ATF will follow suit.
THIS is why if the engine overheats, the motor oil AND the ATF should also be replaced.

EXTERNAL COOLERS are coolers in the truest sense of the word. Radiator sidetanks are not coolers.

Interesting, I had kind of thought that liquid to liquid / radiator cooler whatever you want to call it, would help heat the transmission up. The oil cooler / cooler gets feedback from the radiator & engine coolant if it's plumbed through there. Makes since.

From what you are telling me, the trans cooler must be after the radiator in the plumbing?

Trans output -> Radiator -> cooler -> trans input?

Or is it

Trans output -> cooler -> radiator -> trans input?

My thought was to install oil thermostat as follows...

Trans output -> radiator -> thermostat (too hot) -> trans cooler - Trans input
bypass (too cold) -> trans input