12 MPG????
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TECH Apprentice
Joined: Jun 2002
Posts: 319
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From: NH
12 MPG???? I am going on my 3rd tank of gas since the conversion was completed. I am getting 12 mpg. I have 4:56 gears out back. My car and I weigh in around 3200 lbs. What the f$%k 
My 427 fuel injected big block got 11 if I went a little easy. Heck the LS1 is even seeing a fair amount of hwy miles per tank. In 5th gear I avg around 2000 rpm and in 6th it is normally around 1500 rpm. Car stills smells of gas around the new tank. No leaks. VSS is not working. I need to fix that. Those of you getting much better mileage, what is your secret? Anything I can compare with you high milers? O2 readings?
My 427 fuel injected big block got 11 if I went a little easy. Heck the LS1 is even seeing a fair amount of hwy miles per tank. In 5th gear I avg around 2000 rpm and in 6th it is normally around 1500 rpm. Car stills smells of gas around the new tank. No leaks. VSS is not working. I need to fix that. Those of you getting much better mileage, what is your secret? Anything I can compare with you high milers? O2 readings? Thread Starter
TECH Apprentice
Joined: Jun 2002
Posts: 319
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From: NH
Re: 12 MPG???? First of all, I will need to know what LTFT's are? Second, I am still getting started with my EASE scanner. Problem is that it will not stay connected while driving. I assume this is because I used the chassis ground and not the PCM ground when I spliced my ALDL connector in. When I fix that I will let you know. Assuming that it is, why would it be running like that? It is a stock PCM I assume. No codes that I wouldn't expect. I have no rear 02's but my understanding is that they do not effect the air/fuel control by the PCM.
TECH Enthusiast
Joined: Nov 2001
Posts: 554
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From: Ontario Calif.
Re: 12 MPG???? VSS not working will not help mileage at all. It helps the ECM determine alot as far as engine management. Not being familiar with your setup: are you running front O2 sensors?
Thread Starter
TECH Apprentice
Joined: Jun 2002
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From: NH
Re: 12 MPG???? Yes, I am running front O2's. My VSS may be working. I am having trouble with my EASE scanner. It keeps disconnecting. I thought it was my wiring of the DLC but it is not. I hooked the scanner to my Silverado and it does the same thing. And also there was no VSS signal there. I know it works on my truck.
Thread Starter
TECH Apprentice
Joined: Jun 2002
Posts: 319
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From: NH
Re: 12 MPG???? I took some data on the way to work this morning. Long term fuel trims range from -5.5 up to -14.8. They seem to average on the lower side when I have 1/2 to 3/4 throttle. When I am cruising with very little part throttle on the highway the numbers stay on the high side. In general when I am in 5th and 6th gear at part throttle the numbers are big negative (-10 to -15). So, as suspected it is running rich. Why? And what can I do to adjust it without LS1 edit? You should know that I have no gaskets between the exhaust manifolds and the exhaust system. I will be getting some this week. Also, I have learned how to take custom data, so on the way home I will take more readings, like rpm, maf, intake air temp, etc. Let me know what you think please. 
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Joined: Nov 2001
Posts: 1,707
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From: Anderson, Indiana
Re: 12 MPG???? ANY air leaks upstream of the O2 sensors can easily cause poor fuel mileage, bad running, etc. That air flows over the sensors, the sensors read it as a lean mixture, and then add fuel to get the mixture correct, when the mixture was probably fine to start with.
The worse the air leak is, the worse the fuel mileage will be.
Correct all of the little problems so that the engine can run as designed, and you'll not only see improved gas mileage, but the performance will increase as well!
The worse the air leak is, the worse the fuel mileage will be.
Correct all of the little problems so that the engine can run as designed, and you'll not only see improved gas mileage, but the performance will increase as well!
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91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
91 Z28 LS2 408CI, LS9 Supercharger, LPE GT7 cam, Yank3000, 3450 raceweight.
Latest numbers: 9.71 ET, 141.42 MPH, 1.40 60' , 610 RWHP Mustang Dyno
www.speartech.com
Thread Starter
TECH Apprentice
Joined: Jun 2002
Posts: 319
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From: NH
Re: 12 MPG???? I have now replaced the exhaust manifold collector gaskets. Not much help. I have logged LTFT's for my 17 mile trip to work. The averages are -10% on both sides. Again, still goes very high (-15%) when cruising in 5th and 6th gears with little or no throttle. Some wot's bring it to 0 or even slightly positive (2.3%). So, to bring down my average I would have to run ***** out all the time 
Not so bad but definitely will not help the gas mileage. Does anyone know if the PCM uses the VSS signal in determining LTFT's? My signal works now but is very inaccurate becaue of my 4:56 gears. PCM still thinks they are stock.
Those MAF translaters are like $300!!!
I'd rather go for LS1 edit. What else can I try/monitor to help me out?
Not so bad but definitely will not help the gas mileage. Does anyone know if the PCM uses the VSS signal in determining LTFT's? My signal works now but is very inaccurate becaue of my 4:56 gears. PCM still thinks they are stock. Those MAF translaters are like $300!!!
I'd rather go for LS1 edit. What else can I try/monitor to help me out? TECH Enthusiast
Joined: Nov 2001
Posts: 554
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From: Ontario Calif.
Re: 12 MPG???? The minus reading means you're running rich. The ECM will move the L-trims to lean when you go to WOT. If you were positive in your L-trims the ECM will move you rich.
The ECM does not use the VSS for LTFT (that I'm aware). This information comes from the front O2s. If you're sure that there are no air leaks and your O2 sensors are good and the MAF is working correctly, then it sounds like you need a MAFT or LS1edit. At least from the info you've given.
The ECM does not use the VSS for LTFT (that I'm aware). This information comes from the front O2s. If you're sure that there are no air leaks and your O2 sensors are good and the MAF is working correctly, then it sounds like you need a MAFT or LS1edit. At least from the info you've given.
