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The mkiv Supra Owners Club

Turbocharger boost on auto


Alex_GT

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Hi guys, I have never driven an auto before, and I seem to be having trouble with the car accelerating.

 

When should the turbo boost on an auto? Is it controlled by throttle pressure? In that if you only press the throttle slightly, the turbo will never boost regardless of RPM? I drove the car on a short journey this afternoon and the boost gauge never moved from the bottom of the dial, should the gauge read at 0 in the centre when idling/no boost?

 

The autobox also seems to shift into top gear really quickly, I get to about 35/40 and when I try to accelerate it's really slow at picking up speed. Any ideas?

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It seemed ok when I got the car a few days ago, the turbo would boost at low revs slightly, not sure about the second one though the autobox shifts up really quickly so I've not been able to get to 4000 RPM, but on the journey today there was nothing, the needle just stayed dead at the bottom of the dial and I couldn't hear the turbo. When I first got the car the needle would stay at the bottom then when I could hear the turbocharger it would go up slightly above the bottom line, is this normal anyway? I'm not sure if I'm even reading the boost gauge correctly, if the needle is sitting at the bottom of the dial when idling is there already a boost problem or is the gauge faulty?

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I went out again yesterday, it seemed to be ok. I don't think I was pressing the throttle hard enough before, but I've not been able to see if the second turbo is working as I'm already going 60mph before I get to 3500/4000 RPM, and I don't like giving the car full throttle in 1st/2nd.

 

When should you lock the car into 1st or 2nd? Can this only be done when the car is stationary?

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When should you lock the car into 1st or 2nd? Can this only be done when the car is stationary?

 

Nah, just on a normal drive when you are doing 30-40mph pull the shifter into the 2 position, then you can play with accelerating up and down, I think '2' maxes out under the national speed limit. Be careful with full throttle if it's damp, but if you are worried only do it on a straight road and leave the traction control on (it's a old/poor system but will do the job on a straight bit of road)

 

in all honesty I'd try and get a longer term owner to have a go in it to see if they think all is normal :)

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A decent lump of throttle won't do any damage to the gears/drivetrain in 1st or 2nd if it's stock or BPU, the only thing it's bad for is fuel economy :D. You should feel 'something' happening by about 3k rpm, you should really feel something happening by about 5k (changeover to both turbo's is about 4-4.5k rpm).

 

The factory boost gauge will pick up if you give it death (hit the kickdown button on accelerator pedal, it's fun) from about 15mph to 70, it won't show much if you're driving below 70 at steady speed, the turbo isn't pushing much boost then anyway.

 

I'd recommend reading this thread for more about the auto box, it can do a lot if you want to: http://www.mkivsupra.net/vbb/showthread.php?86128-The-Autobox-Modes-of-Operation

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