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 Really bad gas mileage 
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Post Really bad gas mileage
I have a 96 Z28-SS automatic and it has the worst mileage I have ever seen in any car. I had a 96-Z28 automatic back in 96 that I put 200k on it before I sold it and it was not even close to this bad. Both cars have 3.23's.

This car had many owners before me so I have no clue what's been done to the car. However, I bought it because it didn't seem to be modified in any way. Just about every other 96-Z28 I saw for sale was far from stock.

I'm not interested in boosting HP. There's always someone willing to spend more money to go faster. I just want to fix an incredibly bad mileage problem.

Can someone please tell me where to even start looking?

Thank you kindly in advance,
Ken


Sat May 31, 2014 10:52 am
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Post Re: Really bad gas mileage
First thing i would do is get a scantool on it and and see how the sensors are working. Could be a number of different things from old plugs, wires, lazy o2 sensors, dirty maf, clogged filter, dirty throttle body, etc.

If you plan on changing plugs better have a case of cold ones beside you. Its booked as a 8hr job!

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Sat May 31, 2014 11:09 am
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Post Re: Really bad gas mileage
Vetty wrote:
If you plan on changing plugs better have a case of cold ones beside you. Its booked as a 8hr job!


Only 6 hours the 1st time, but with a hoist ;) lmfao, leave most of them pita shields off, will speed up future tune ups ;)

Basically give it a good overhaul/tune-up, as Matt suggested it could be many little things adding up or just one large bad thing, in the LT1's I have always had the best luck with Delco plugs.

No exhaust leaks? Especially a header gasket leak? In our old 96 we blew out a header gasket and the fuel mileage I swear dropped in half, lol

Another funny thing, ours was an M6, we pulled the stock 3:42's and put in 4:10's and gained fuel mileage, figure that out :mrgreen:

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Sat May 31, 2014 11:43 am
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Post Re: Really bad gas mileage
What is it getting? My 96 gets 11.5-12 litres per hundred km mostly highway

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Sat May 31, 2014 5:58 pm
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Post Re: Really bad gas mileage
It took $46.00 to go 276 km. All highway. What's that work out to?

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Previously - 1996 Z-28, 1989 Pontiac GTA, 1985 5.7 IROC Z-28, 1976 Camaro LT, 1974 Trans Am 455HO, 1974 Z-28, 1967 Firebird Sprint,
1967 Camaro 230 cu-in 140-hp "Blue Flame" straight six with a 2-speed powerglide.


Sat May 31, 2014 7:13 pm
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Post Re: Really bad gas mileage
Depends on the price per liter I used $1.34 and came up with 12.5 L/100km

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Sun Jun 01, 2014 7:12 am
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Post Re: Really bad gas mileage
Kensredzed wrote:

Can someone please tell me where to even start looking?

Thank you kindly in advance,
Ken



How well does it run? Is it blowing black smoke or any other noticeable signs of trouble? Sluggish etc?

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12.1 @ 112 mph 1.69 60'

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Sun Jun 01, 2014 11:34 am
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Post Re: Really bad gas mileage
If it didn't run like a charm, I would at least know where to start looking.

Has lots of power. Very clean exhaust. Passed an emissions test with flying colours.

When you let go of the brake and the car idles forward, it barely has a slight lurching (or miss) on one cylinder. Never happens while it's stopped or while driving. I've had a bad wire/plug before and know the difference. Just touch the throttle and the car wears the shoes right off.

Thank you for everyone's input. I will have to start with the basics like a tune-up. I need to check the car for a chip.

About the exhaust leak... All SS's have an exhaust leak straight out the tail-pipe. Nice, loud sound when you step on it. Restraint seems to be the only way to get any kind of good mileage.

The automatic shift points are also higher than my stock Z-28.

I have lots of areas to look at thanks to everyone's suggestions.

Thanks for everyone's help,
Ken

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1996 Z-28/SS

Previously - 1996 Z-28, 1989 Pontiac GTA, 1985 5.7 IROC Z-28, 1976 Camaro LT, 1974 Trans Am 455HO, 1974 Z-28, 1967 Firebird Sprint,
1967 Camaro 230 cu-in 140-hp "Blue Flame" straight six with a 2-speed powerglide.


Sun Jun 01, 2014 7:04 pm
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Post Re: Really bad gas mileage
After a complete tune-up it did not improve.

After more searching we found 7 separate code failures in the EMC. The engine light never came on and the car seemed to run fine with the exception of the mileage.

In the end it was a defective ambient air tempurature sensor suggesting it was at minus 88-degrees. It called for a super rich fuel mixture that threw the other sensors off.

What a lesson that was...

Thanks,
Ken

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1996 Z-28/SS

Previously - 1996 Z-28, 1989 Pontiac GTA, 1985 5.7 IROC Z-28, 1976 Camaro LT, 1974 Trans Am 455HO, 1974 Z-28, 1967 Firebird Sprint,
1967 Camaro 230 cu-in 140-hp "Blue Flame" straight six with a 2-speed powerglide.


Mon Jul 28, 2014 12:40 pm
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