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Discussion Starter #1 (Edited)
Well maybe i'm being to picky....Or I want my cake and eat it too......but its bothering me nonetheless
Car runs really good tho, drives perfect and has great power.
I was hoping my 5.3 would get better fuel mileage. sucks just like the ls1. Taking it easy, not much traffic, mostly highway driving and I average in the 15-16 range. I'm not happy with that. Cruising, the dash says between 19.9-22.3 usually....but my overall is lower. even with very short idle periods. so let me highlight some things..

5.3, 9.5:1 compression
222/233 cam, 115 lobe sep
dorman Ls2 intake
ngk tr7 plugs gapped at .025
3600 power adder yank
lighter than stock (10lbs or so) wheels

what i've tried:
tuning, tuning and tuning. I've turned off the LTFT, relies on Short term fuel trims. No MAF. I turned on lean cruise. It will add 1-2mpg but for some reason it was randomly going rich at cruise to 12.xx-13.xx....never could figure that out so I turned it off. I'm locking up the converter early and gear changes early under light throttle. I've experimented with timing and optimized that. I use dfco but it cuts off at 1500 rpm, can get it to go lower without causing transition issues (because of kpa of coast down and light throttle overlap too much). I've just about ran out of ideas short of changing camshafts and/or possibly intake manifolds.

any ideas of what I can do to help it? I'd like to drive the car more but its hard to justify when i have a 2019 silverado 5.3 that gets 20-22mpg even with traffic. If I drove the truck like i do the car, its gets 25mpg. Yea, A big ass 4dr truck. I know theres lots of technology there but i should be about to get 20mpg if I baby it.
 

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Well, tune 4 cylinders off like the truck does and bam, mpgs!

I can’t really offer any useful advice aside from going with a taller gear set and/or M6 swap
 

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@Kfxguy My GTO's mpg is not that great either. At this point, I am just driving the car for enjoyment more than necessity. On the highway an M6 will always get better mileage hands down. I've just learned to accept that.
 

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Discussion Starter #5
The high-stall converter is killing the mileage around town.
I don’t think so. It barely got better when it was stock. I lock the convertor up down low so there’s not much slippage. And make the trans up shift at low speeds.
 

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You've done all the tricks I can think of. My '87 Camaro had DFCO and lean cruise in the programming, but it was disabled, just like the speed and rev limiters. I enabled them when I started messing with the programming, so I was surprised to find the GTO has DFCO when I first got it. I was able to get 24-25 mpg on the highway with a mild 383, hogged-out aftermarket TPI intake, A4, and 3.42 gears. My GTO gets 22-24 highway but it's also about 400 lbs heavier and not as aerodynamic as the Camaro. I average 17-18 overall with a good amount of around-town driving and cold start-ups.
 

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I can get close to 30 with my 04, maybe right at it with slightly more agressive lean crusie settings and 87 octane gas.

I have the factory holden settings in now, can get around 28-29 if i drive like an old man.

All the same, with the cam and turbo, i think it's safe to say you've changed the BSFC of your engine, especially the efficiency at cruising speeds.

You could pop a stock cam back in and see what happens.
 

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Discussion Starter #9
I can get close to 30 with my 04, maybe right at it with slightly more agressive lean crusie settings and 87 octane gas.

I have the factory holden settings in now, can get around 28-29 if i drive like an old man.

All the same, with the cam and turbo, i think it's safe to say you've changed the BSFC of your engine, especially the efficiency at cruising speeds.

You could pop a stock cam back in and see what happens.
I did consider doing a factory cam that’s bigger than my stock cam.

do you ever have a rich condition with your lean cruise? Man I got an issue that’s been stumping me. It will go into lean cruise and if I give it a little gas it’ll dip to 12.xx -13.xx afr and stay there until I go below the disengagement mph for lean cruise. I tried messing with power enrichment and see if that’s the issue but it doesn’t seem to make a difference. I think I might disable power enrichment and see what happens.
 

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I'll have to pay attention next time i drive it, but the only time i usually see that happen is when the ECM is doing the o2 test
 

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I've gotten as high as 26/gal 70-75 on interstate. Surface roads are another story, 17-19 is the norm
 

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GT2-3 cam may help. It's shorter intake duration along with wide LSA works great for me.
It is basically a Z06 cam with more.
It is supposed to work well with FA.

However the auto trans were never known to get the mpg as the manual.
 

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Discussion Starter #13
I drove to work today, redoing some things on the tune. seemed to do maybe 1-2mpg better this morning but i'm going to finish out what i started and do the fill updrive, fill up test. Last I checked my mpg calculator in the car was off by almost 2mpg.
 

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Discussion Starter #14
I'll have to pay attention next time i drive it, but the only time i usually see that happen is when the ECM is doing the o2 test
yo, I enabled the lean cruise with all stock settings from a holden. What do you have yours set at for mph engage, disengage and how many seconds on the delay? I used stock settings but never saw it come in (barely) until I was on the interstate for a while.
Also used the settings for the DFCO from the holden...they work better than the 04 gto settings. I did have to play with the kpa that it comes in tho because of my cam.

changing cams is still on my mind. I guess so what it I have to run 18psi vs the 14-15 i'm running now.

On a side note, I saw a 5.0 on the interstate and he had some big drag radials on the back. I figured he'd try to mess with me, but he didnt bite. he passed right on by me ( I was doing the speed limit) and then after thinking about it, I caught up to him real quick. He didnt seem interested. Probably a good thing, I need to stay out of trouble lol.
 

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I did consider doing a factory cam that’s bigger than my stock cam.

do you ever have a rich condition with your lean cruise? Man I got an issue that’s been stumping me. It will go into lean cruise and if I give it a little gas it’ll dip to 12.xx -13.xx afr and stay there until I go below the disengagement mph for lean cruise. I tried messing with power enrichment and see if that’s the issue but it doesn’t seem to make a difference. I think I might disable power enrichment and see what happens.
Do you have cat over temp disabled? The lean cruise could be causing the temps to be interpreted as high therefore the computer would be adding fuel to cool it down. I would probably not disable it as it could possibly affect other areas of the tune (for example in a G8 disabling it will cause DOD to not work) but I would set the enrichment value to 1.0.
 

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Discussion Starter #16
Do you have cat over temp disabled? The lean cruise could be causing the temps to be interpreted as high therefore the computer would be adding fuel to cool it down. I would probably not disable it as it could possibly affect other areas of the tune (for example in a G8 disabling it will cause DOD to not work) but I would set the enrichment value to 1.0.

yes i have it disable. I'll try that, good idea!
 

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Discussion Starter #17
Ok. My average in the car said 12.9mpg. Said I used 8.3 gallons. I actually used 6.8 gallons and mpg was 14.9 with a good bit of wot passed and tuning. So lemme do this again. Just filled up. I’ll drive it normal. I’ll try anyways. Lol.
 

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I used to get up to 30mpg with the stock cam and the LPE GT2-3 cam. Could only get 25-26mpg with the FTI 220/224 cam and GMPP heads.

Lean cruise will go rich every so often, it is hard coded to do that. But it should go right back to your settings. I found that the Holden settings were too aggressive. Been since '04 when I tried the Holden settings so I could be wrong, I want to say they were 16.5 or so. I usually shot for 15.5-15.7 ratio.

I'm assuming your converter is locked up while cruising? You can try to crank in more timing at cruise also. SD and MAF has to be pretty spot on also.
 

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Discussion Starter #19
I used to get up to 30mpg with the stock cam and the LPE GT2-3 cam. Could only get 25-26mpg with the FTI 220/224 cam and GMPP heads.

Lean cruise will go rich every so often, it is hard coded to do that. But it should go right back to your settings. I found that the Holden settings were too aggressive. Been since '04 when I tried the Holden settings so I could be wrong, I want to say they were 16.5 or so. I usually shot for 15.5-15.7 ratio.

I'm assuming your converter is locked up while cruising? You can try to crank in more timing at cruise also. SD and MAF has to be pretty spot on also.
Yea the convertor is locked. It would really get horrible mileage if it weren’t lol. I have it set to lock as low as possible while lightly accelerating to the point where it’s just at the point it doesn’t surge and doesn’t bog the engine.

the highest the timing will go is 40 degrees. I can set it higher but it won’t go any higher.

so much for checking my mileage. Last night I went out and did a bunch of wot tuning. Found I have an issue somewhere. After making I dunno, 6-10 pulls, it starts running lean. I must be losing pressure or something. It does not matter how much fuel I set to dump, it will lean out past 5500.
 
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