North American Turbocoupe Organization



Air/Fuel Ratio Gauge Question
tylerport Offline
Senior Member
#1
During normal driving, my A/F Ratio Gauge bounces back and forth between Rich and Lean, but rarely gets into the Rich (green lights). It always goes well into the Lean (red lights), usually going down to the first bar. Is this an indication that my engine is running lean? Should I adjust the fuel pressure up a bit?

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Jim Portteus
NATO Member
86 Turbo Coupe, LA3 w/ Intercooler and Larger VAM, Gillis Valve, 2 1/2" Downpipe to 2" Duals w/ 18" Glasspacks, 245/50R16's, 140MPH Speedo, A-pillar pod w/ Boost and A/F Ratio Gauges and Steeda Tri-Ax Shifter.
Jim Portteus
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Noname
Guest
#2
During cruising and moderate acceleration, the EEC using input from the o2 sensor to keep the a/f ratio as high (lean) as possible to minimize fuel consumption. Only during a cold startup and reasonable amounts of acceleration does the EEC purposely enrich the a/f mixture above stoich (and into, hopefully, the 12:1-13:1 ratio). Try cruising in 3rd gear around 2500rpm and lay into the throttle until you start building boost. The a/f gauge should start creeping into the yellow zone. If you go full-throttle, the a/f gauge should go even richer (due to the EEC's WOT fuel enrichment multiplier).
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Glenn 88TC Offline
Posting Freak
#3
My car almost always is in the stoich(yellow) area. The only time I see the red(lean) is when I lift off the throttle. My car goes to about 2 bars rich as I build boost. Don't put too much trust in that gauge. Under full boost the O2 sensor is ignored so I don't trust what it reads. I blew a head gasket while showing 2 bars green. A few more psi of pressure might be a good idea. When basically stock I ran around 43psi. Better safe than changing a head gasket.

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88TC
current mods: ported & polished big valve head(1.89/1.59), ranger roller, custom upper and ported lower intakes, t3/t4 turbo, powerstroke intercooler mounted full size, 60mm throttle body, R.C. Engineering 42lb. injectors, MSD 6al, MSD Launch Control, MSD 8.5mm wires, K&N filter, Walboro 255HP pump, Kirban adj. fuel reg., ATR header, full 3" exhaust with Dynomax Ultraflow muffler, Star stage III clutch, Hallman boost controller, Flex-a-lite adj. temp switch for stock fans, Weld Draglites with M/T ET Street 26x11.5/15

Coming very soon(ordered and on the way) SDS, 73pph injectors, custom roller cam
NO TC and NO headaches.
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tylerport Offline
Senior Member
#4
If I remember correctly, I set my fuel pressure to 39psi. That was last year, though, and I haven't checked it since.

At WOT the gauge shows two right away and then the third green light comes on at around 4000rpm.

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Jim Portteus
NATO Member
86 Turbo Coupe, LA3 w/ Intercooler and Larger VAM, Gillis Valve, 2 1/2" Downpipe to 2" Duals w/ 18" Glasspacks, 245/50R16's, 140MPH Speedo, A-pillar pod w/ Boost and A/F Ratio Gauges and Steeda Tri-Ax Shifter.

[This message has been edited by tylerport (edited 05-19-2003).]
Jim Portteus
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Jeff K Offline
Administrator
#5
Everything sounds perfectly normal to me. I dont think you need to mess with fuel pressure.

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Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 20 psi, forced air intercooler, water injection, bypass valve, Ranger roller cam, subframes, etc., etc.. // 86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP nitrous, ignition, gears, suspension, etc., etc.... // 91 Escort: Bone stock winter car // 02 Taurus Vulcan(wifes car)
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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