Here's an odd question.

Since the car was tuned last fall for the blower (A&A P1sc w/ 3.8" pulley) I have noticed that the mpg has suffered quite a bit. Since I am not driving around at high rpm or with my foot in it (meth not done yet, I stored the car all winter) I feel the only tangible change was the tune.

Since the sc runs in vacuum while driving unless I get on the pedal, I don't see why MPG with the same setup and factory tune could average 22mpg and make highway numbers in 38 to 44... but now with the tune it averaged 15mpg and is pulling high 20s to mid 30s mpg when on highway in the same cruise control state.

I'm not crying about the gas, but it seems an unlikely outcome and I don't know if I should be concerned at all. I do have EFI Live and can take a look at the file.

 

Your DIC may report incorrect mileage because of bigger injectors.

Or then your tune has way too low ignition advance.

 

Excellent thought on the injectors affecting DIC programming.

I will get some data based on miles per tank and compare again later.

 

I've also seen a lot of tunes that are too aggressive with entering power enrichment mode as well as commanding way too much fuel at lower boost levels. Those 2 issues will certainly wreck your mileage.

 

I have a few projects on the car first, then need to figure out why the Alky kit (used, with new pump and tubing) works on test but not under boost. I had even wired it straight to the map on the intake.

Once I get to that, I'll look deeper into the tune when I make sure the meth a/f is safe.

 

Are you SD tuned? How much boost? Wired light green wire from the MAP to the green wire on the PAC? Measured the voltage of the green wire with the key on, at the PAC? for future reading: 2-bar sensor should read ~2.46V and 3-bar, 1.28v with the key on.
If so, I would take the cover off the controller, expose the 2 ***** and put them both at their mid point to start with. PM me if I can help.

 

If I get the chance, I'll take a look at it over the weekend. Lots of "family" time taking away from my "garage / armory" time.

 

While out breaking in my clutch (stop and go for 500 miles) My DIC said I was getting 10.4 mpg. I did the math at the pump and I was actually getting 15.96 mpg.

I have a cammed A&A TI with 131 pound injectors.

 

Like the guys that put the whole EQ Ratio table the same and set the PE throttle table to 0 or 20.

 

Filled it today. 15.6 gallons in for 206 miles traveled since last fill. I reset Trip A for every tank of gas and Trip B for every oil change.

That gives me a real average of 13.33 mpg.

Most of my miles are highway where I use 6th gear and cruise between 70 and 80. Around town I will hold onto gears a little longer if I'm in stop and go, but I'm not rolling around at 3000.

The tank had 26 miles used when parked for the winter. The rest was in the past week. No WOT runs because I have no methanol yet and I was told it is tuned "very tight" to the edge of lean. (Could it evaporate out of the car while parked for 4 months?)

Combo is:
Base 99 LS1 w/ 70k miles
Straub bushings
BTR springs and pushrods
Fast 92
LS7 tb
60# siemens
SD tune
A&A P1sc w/ 3.85" pulley and the older piping / fmic where the lines go LEFT and around into the IC and up instead of past the horn.
KB BAP
LPE (walbro) 255lph pump pulling steady 69psi
SW headers / x-pipe and borla stingers
MAP is about an inch off the back of the intake on a thick vaccuum line and is new as of about July of last year.
IAT is in the top dead center behind tb on the intake. Located there to read the temp change from methanol injection approximately 8" in front of it. I believe it is a model from a GTO.

Like I said, I'm curious about this fuel consumption since the driving being done is passive. It still has the winter storage Z wheels with ten year old cracking Firestone Wide Ovals on it - so you know I'm not speeding or beating on them and risking the car, just ferrying it back and forth for a week while I had my daily's wheels refinished.

It makes me curious. The tune may be fine. There could well be other issues at play. But to go from a prior overall average of 22.7 mpg on prior tune (tuned for the injectors and blower, but not above 4k since I identified that the prior Racetronix fuel pump was not delivering sufficient fuel past that point). So I cruised it for a few weeks with the new pump (higher psi at 69 vs 45psi) before going back for a re-tune to the current one and managed a consistent 22.7mpg per tank.

The current tune was intended to be final with the fuel system working and with what I believed was a fully functioning used Alky kit. It fired on 'test' but I had never checked for map signal function and made the error of presuming it worked. Then when we got to the dyno we discovered that was not the case. I tried piggybacking the signal straight off the intake MAP instead of the vacuum line map for the alky kit while I was there, but still no luck. So it was tuned with the expectation that the methanol would be added soon after. I will remedy it within the next week to two. And to be honest, I am going to rip the entire wire harness for it out and start from scratch. Wiring it was the one thing I asked a friend to do while I installed a DD column and boost / afr / fp gauges. When I later checked the work, the connections were ridiculously loose and I redid them, but I trusted the wiring done by the head of IT for one of the largest insurance companies in the world. Programming servers does NOT, apparently, equal wiring proficiency. So I'll gut it and start from scratch to be sure it is exactly as it should be. I will also test the system for MAP signal function and full PSI before hard mounting the wiring this time.

 

Hadn't thought about this for a while. Did check it today at the pump.

15.555 gallons filled for 198.2 miles traveled. 12.74mpg

The vast majority of that time was on the highway in 6th. No wot because I have not resolved the REP issue above 80% throttle yet (other family stuff going on.) And no hot rodding it because I'm still on my rotten winter tires which are not what I would call safe.

Before the blower and injector change, the car would average 27mpg in such driving conditions. 22 if driving around town. High teens if I was screwing around. The blower was added along with 60# injectors. Air temps here have been high. But oil hasn't topped 210 and coolant hasn't gone above 198, even with the AC on.

Does it seem reasonable for the car to be drinking that heavily just spinning a blower at under 1.8k engine rpm?

 

Do you have a wideband hooked up? I would interested to see your afr at cruise and idle.

 

Yeah. Idle sees about 14.2. Cruising varies 14.2 to 14.6.

 

Post your high octane timing table.

Also, if this tune is "work in process" that may explain something.

 

I'll bring the laptop down tomorrow and see what I can figure out. I haven't touched the software since September or so.

 

Tusc---For what it's worth, my 2000 supercharged Corvette with Procharger P1 SC1 (7.2 lbs. of boost, no alky meth. autowith 3.42 gearing installed) gets 17 - 18 m.p.g. in mixed driving (mostly highway but some city). On long highway trips it will do 19.5 - 20 m.p.g. So I think you should be getting better gas mileage than what you recently reported.

 

If you're using HP Tuners, Send me your tune and I'll look it over. It's possible your injector offsets are high and DFCO is turned off. That's just another thing that will add to your consumption.

 

Thanks for the offer. This tune was done on EFI Live, though. My efforts are going on hold for a while, as I start a new position on Monday. I would have covered more ground, but I also spent the last two days dealing with a septic tank backflow and ensuing cleanup. I'm pooped!

I did note at the last refill that it pulled 305.8 miles and filled 16.207 gallons, so 18.87 mpg. All driving under the same general conditions. The only difference being new TB and I realized that the prior tank with lower mpg had a bottle of Techron in it.

With the new job, I'll be in a tailwind for a while as I get a hold of the operation so postings and time in the garage will be cut down briefly.

 

Now that Im not breaking in the clutch and shifting at 2k, Im getting 12 mpg on E85 lol. That includes Mexico runs as well. The right foot dictates the mpgs far more than anything as Im sure you know.