Bad Gas Mileage
Thread Starter
Senior Member
Joined: Mar 2000
Posts: 669
Likes: 0
From: Red Bud, Illinois
Car: 1989 IROC-Z
Engine: 383
Transmission: Pro-Built 700R4 2400 ACT Stall
Axle/Gears: 2.77 Borg Warner 9-Bolt
Bad Gas Mileage
Okay, normally i wouldn't complain but something is fishy here. The last mod i did was port my Plenum and match the runners. I haven't touched the intake. Shortly after that my Fuel Pump went out (a whole 19 PSI at 1500 RPMS) Now it's replaced and i'm at 46 PSI w/vacuum disconnected. How did my mileage go from 210 - 215 to 100 - 116 (sometimes not even touching 100). I have a 180 degree thermo and the rest of my Mod's are listed. The 100 - 116 is on 87, 89 octane (no knock present) and on the highway. Am i just that badly in need of a tuneup. Just last week i changed my O2 (it was blacker than ****). Any idea's or idea's are welcome. Oh yea, and my car idles at 1000 - 900 rpms, no matter how the IAC and TPS are adjusted (spent an hour playing around with them).
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89 IROC-Z 350 TPI
-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
[This message has been edited by branz28 (edited March 19, 2001).]
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89 IROC-Z 350 TPI
-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
[This message has been edited by branz28 (edited March 19, 2001).]
Joined: Jul 1999
Posts: 10,950
Likes: 26
From: Orange, SoCal
Car: 1990 Pontiac Trans Am
Engine: 355 TPI siamesed runners
Transmission: Tremec T56
Axle/Gears: 12-Bolt 3.73
Sounds like you have a leaky injector, or a leak in your fuel lines or gas tank. Since you say the O2 sensor is really black, I'd vote for a leaky injector (or even a bad spark plug) on the driver's side. Have you looked at your spark plugs?
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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-
------------------
West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-
Thread Starter
Senior Member
Joined: Mar 2000
Posts: 669
Likes: 0
From: Red Bud, Illinois
Car: 1989 IROC-Z
Engine: 383
Transmission: Pro-Built 700R4 2400 ACT Stall
Axle/Gears: 2.77 Borg Warner 9-Bolt
My injectors were pretty good, they held pressure for over an hour with very little movement. Bad spark plugs could be possible but i'll have to wait till this weekend to see how they look because i have no tools at the house right now 
------------------
89 IROC-Z 350 TPI
-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
------------------
89 IROC-Z 350 TPI
-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
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