liquidforce917

So i have been playing with a bunch of different things on my own (and with my tuner) to get my mileage up to something more reasonable.

My main question: Is this kind of MPG acceptable for my setup? or could there be something I have missed (vacuum leak, MAF issues, ....)?

Car Specs:

Full Vararam Intake
Stock MAF
LS2 TB
Ported FAST 90
42LB injectors
Hand Ported+Milled 243 Heads
2.02 Intake valves
235/238 112+4 INT: .620 EXT: .586
(Cam has 13* of overlap)
LT Headers
Full Exhaust
OEM C6 Z06 wheels/tires

My tuner says my O2's are functioning properly

Anyways, I do a good bit of city driving and idling at lights, this kind of driving normally nets me an average of 10.4 MPG.
On highway runs in 6th gear between 50-70 MPH I get an instant MPG reading which never goes over 20 MPG (with cruise control on). On my last 150mile cursing trip (80% interstate) my average was 17 MPG.

An interesting Fact: Whenever I calculate my MILES/Gallons after each tank I always get a value about 2 MPG higher than what the DIC says. I think that may be caused the the 18/19 wheel size. Any ideas?

Since then I have: removed my FAST and checked it for leaks/resealed it, replaced the hoses in my catch can, resealed my valve cover to intake hose (LS2 does not have the fitting the LS6 does), and moved my MAF in front of the air bridge.
The reason I moved my MAF farther away from TB is because I was thinking that the cam overlap causes it to have low vacuum and could cause the air to pulse back through the MAF since it was located right in front of the TB.

As of right now I am waiting to retune the car with my changes, but as is the car has made no change in MPG.

After reading many H/C MPG threads I am pretty sure I am not paranoid and the majority of people are getting higher MPG than I am.

Any Ideas/ Thoughts are appreciated!

If it will help I can add pics of the intake setup.

Dcollins3208

You might post a log in the scan and tune section and maybe someone can decipher it for you. In the mean time, how are your plugs/wires? Also, an exhaust leak pre - o2 or near the o2 sensor can affect gas mileage

Rx7Rob

I don't think the DIC mileage is correct after a fuel injector change.

My gas mileage is also in the toilet after a cam (228r)/headers/intake/injectors and SD dyno and street tune. Went from a solid 32 on the highway to about 22. I haven't checked it around town.

My calculated mileage is less than the DIC (stock size tires).

RonSSNova

I believe the mileage calculation should be correct after an injector change. The PCM for sure knows the injector pulse width.

As for tire size change, you can input that into the speedo section, the whole system recalculates.

A cam with that much overlap pushes a lot of I burnt fuel out the exhaust. Pretty simple. Has a much bigger effect at idle and city driving.

Just believing the DIC, my C5 shows as low as 12 mpg to and from work (26 mile round trip) when the traffic really sucks. When traffic is light, it will manage 17. Idle time crawling of course is next to 0 mpg. Even though my commute was 70% freeway, many times it was a total crawl.

On the highway I've seen 26. And although mine is an 11.0 car, my cam has no overlap.

Ron

liquidforce917

I will do that.
As for the plugs and wires: the wires are new and have protectors on them, and the plugs have 5K miles on them and I just had them out to check the gap on each one. They look fine and are all the same gap.

I do have very small leaks right at the header and head. I am using a felpro gasket (http://www.summitracing.com/parts/fe...Fa47OgodIRoAjA).
Do you think going to a MLS gasket could fix this? Other than this the exhaust side is tight before the cats.

Dcollins3208

Oem gaskets are the best man

liquidforce917

Thanks Ron,
You are correct it does throw fuel out the back and before the tuning it was so dense that it would start to burn your eyes if you were behind the car lol

Anyways I do need to have the system recalculated for this size tire (may help the DIC), is there any way that there could have been something overlooked in the tune?

After the first street tuning I came back expelling my problems with the fuel consumption and we retuned and he said it is calling for more fuel! All of this had led me to believe vacuum leak somewhere, but I have checked everything I know!

Are there any places the FAST intake is known for leaking (besides if the bottom on cracked, mine is not)?

Bill Curlee

A couple of things to look at.

What are your LTFT doing at cruise and at idle

How did you tune your Volumetric Efficiency Table (VE Table)? Did you do an AUTO VE (that’s what its called in EFI Live)

If your VE table is well tuned, efficiency will go up. If the LTFTs are high, that will also cause efficiency to suffer.

My heads cam 42/lb/hr injector 450 RWHP ZO6 will get 25-27 highway 16-17 city highway. Mileage Sucks creeping /crawling. Your car is set up really close to what I did to mine

There is a table in the PCM that you can adjust to get your calculated fuel mileage back in spec. Don’t ask me what table it is. My buddy fixed mine when it went out of whack.

If you moved your MAF, it needs a MAF retune If the MAF table is not correct that too can contribute poor fuel efficiency.

Bill

RonSSNova

I agree with Bill.

This is why I bought HP Tuners and learned (still learning ) how to tune. The drive around stuff is what takes 90% of the effort for sure.

Ron

Rx7Rob

Of course the pulse width is known, the amount of fuel injected / pulse is not.

Evidently there is a table (mentioned earlier in the thread) that needs to be modified.

RonSSNova

The injector flow rate is also known. You have to change it if you change injectors.

I'm not seeing a table in HPT that relates to the mileage calculation......

Does anyone know exactly where this calculation takes place?
Perhaps the BCM?

Rx7Rob

Are you talking about the bulk injection rate? Not quite the same as the injector output vs duty cycle. Its not exactly linear. Years ago I built a rig to fire an injector at various duty cycles while measuring the lb/hr output. I mapped the output for the various injectors I was running in the Rx7. The "turn down" ratio was an issue because I needed a lot of flow under boost and minimal flow when not. I was trying to do it without staged injection.

I'd have to do some deep digging but I may be able to put my hands on photos of the injector at various points of flow after triggering it on. Not so sure I can find the injection / duty cycle plots.

Bill Curlee

Ron

Its not in the BCM. BCM is only programable using the TECH 2 and that only changes the RPO codes that pretains to the build.

I have EFI Live and I will ask my budy how he did it.

Bill

RonSSNova

Thanks Bill. I'm really just curious.
There is a chance that hp tuners doesn't let you at it. I searched the site and no one had even asked about the calculation.

Rob. I meant the bulk injection rate divided by the specific gravity of the fuel times PI cubed.......
As you can tell, I have no clue what the DIC uses for the info to come up with an estimate of the MPG.
Whatever it is, it must be spit out the serial buss.

I guess bottom line, forget the DIC and use a cell phone app.
:-)

None of this helps the op get better gas
Mileage.

Ron

Billdog350

Hey guys, jumping in here at Bill's request. The fuel economy DIC reading is a result of your injector pulsewidth and a calculation that is run based on that. Essentially it just adds up how long your injectors are open, based on their flow rate, and it knows how much fuel is burned. Why my 2012 Chevy Cruze is off by over 3mpg every fillup is beyond me...some trickery going on at GM but I digress.

If you tune your car by setting your injectors for the ACTUAL flow rate (keep in mind advertised flow rates vs pressure, a ford SVO 30 flows MORE fuel in a GM due to the higher rail pressure). Once your injector chart is properly sized, then you should be going in and adjusting your MAF, and MAP tables (VE) based on wideband feedback.

I was able to tune my 420rwhp LS1 H-C-LT car to get over 32 REAL WORLD mpg using this method.

If your DIC readings are off, injector table is where to start (keeping in mind it will throw your entire tune off and you will have to scale everything accordingly). There might be another DIC scalar for the MPG if I recall, I'll have to find my old PC and boot up EFI Live and see if I can tell you which # it is.

Rx7Rob

So, just changing injectors will result in the DIC not being correct unless changes in the computer are made. Thats what I was saying "I don't think the DIC mileage is correct after a fuel injector change."

Ron, I know you can compute the injection amount. What I measured was that at short pulse widths it does not follow the calculate rates.

I guess the big question is, do any of the tuners tune for mileage? The majority of time for my tune was on the road and finished with dyno pulls. I'd have to guess the street tuning concentrated on driveability and not mileage.

From what you explained I don't want to touch the injector map since it would skew the whole tune. I'll leave it as is and ignore the DIC. Then just tweak the MAP tables since I'm SD.

Looks like it finally time for me to get EFILive.

OP, about a year or so ago there was a thread in Scan and Tune where someone was on a quest for mileage. Might be worth searching for that thread.

BillDog, how long did it take you to get the tune where you like it? Or has it turned into never ending tuning?

Billdog350

Rx7Rob, It took me about 6months of playing around to learn how to tune for fuel efficiency. I'm a bit of a nut. I wanted my 228/232 LS6 intake, LG longtubed, ported 243 head car to run and idle well enough to drive in traffic, and still get good mpg on the highway. If your STOCK car can get 25-28mpg highway, why can't a car that's MORE efficient get more mpg? I proved it. Ask Bill Curlee, I had his z06 getting 26mpg if I recall.

Now that I have a knack down, I could do it in an afternoon I would suspect. You need to start with your stock tune, adjust your injector table for the REAL injectors you have, and then do your MAF and VE tunes using a wideband 02 and scale accordingly. I do not profess to be "better" than any of the professionals out there, I just know I have tuned 3 ls1's and one ls2 (in my 1997) and all of them get at least 25mpg and make well over 420rwhp on a dyno.

One of the big key's is making sure you have NEW 02's ready to install AFTER we get a base tune going with the wideband (which also must have a fresh 02 in it). 02's get fouled VERY quickly with fuel and your readings will be junk after that. Also I tune and keep the front 02's active which is a huge component for fuel economy. One the 02's stop responding, your idle will go to crap and your economy will suffer.

Remember, you're adding 50-100rwhp and those longtubes do NOT keep the heat into the 02's to keep them oscillating like they should. If I buy another C5 or C6, and build it, I'll use the Z06 headers instead of longtubes to prevent the 02 burn out issues. I could always tell when the 02's started going, bad idle, bag mpg, etc. If you checked using EFI Live or HP tuners, you would see that instead of large jagged swings, they're about half the oscillation and are more rounded off. Once they're "lazy" there is no way to recover without replacing them.

All_Motor_C5LS6

Great info on the 02s

RonSSNova

Continues to be a good discussion.
I really didn't think there was a magic table that computes fuel consumption.

There are more tables than just accurate flow rate for the injectors. The data is very detailed. If you have factory GM injectors, this data is easy to come by. Not always the same story with aftermarket.

The injector data are constants. You don't "tune" with those numbers.

I've not tuned my car for mpg. But at 25+ for a A4 car with 3.42 gears and a best of 10.99 at the digs, no complaints.
City is of course a different story because of the cam.

Tuning is really about calibrating the maf and VE in open loop with a good wideband in open loop so that when you put it back in closed loop, the PCM doesn't have to do wild corrections.
Tuning for power is about setting the timing an mixture for best power and torque. It's really the easiest part. Well, unless you do it at the track like we did.

Rob, I hope you got it that I was teasing you a bit there. You really should get tuning software and play.

I currently my new project which is a 5.3 LS with a turbo on E85. Mileage is not a concern! Ha

Finally, I need to give my tuning mentor CTD a shoutout for teaching and helping me with my C5. The 5.3 in my Nova is on me. So far it's running very well.

Ron

Billdog350

Ron, on your point about tuning, you're dead on and I agree 100%. Calibrating MAF and VE is basically all there is to it, minus the factor of timing which can throw off your fueling again....

As far as your comment about injectors, there are a few schools of thought by tuners on that one. If your ENTIRE tune is off and running rich for instance, logic would stay to go to ONE table (your injector table) and scale it accordingly rather than go to your MAF and multiple VE tables to accomplish the same thing. If there are spikes or low spots at various points in your tune, the VE and MAF tables will solve that. When I first started tuning I set the injector table for what my injectors "should" have been putting out and it caused a lot of work on the VE and MAF tables, and my DIC wasn't accurate. Later I noticed some tuners suggested correcting your injector table. Once I started there THEN tuned the MAF and VE, both my DIC was correct as well as the MPG improved. I'm not saying there is only one way, I'm just stating what worked well for me and what made logical sense to adjust.