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Discussion Starter · #1 ·
OK, I'm not 'new' to this as such, just new to this forum. I'm a regular member of the UK GT4 owners club but I dont seem to be able to get an answer to this question from there so I thought I'd post it here in case you lot had an ECU genius amongst you. For the record - running a basically stock 185 on 12-14 psi with relief valve boost control and stock everything else.

From everything I've read online, the MAP sensor on the 2nd gen 3sgte (ST185, non RC or carlos) has nowt to do with fueling, it serves only to allow fuel cut and the work the pretty (useless) dash boost gauge. Unlike the ST205 which uses that instead of the flappy AFM.
I've been having some jerky acceleration and deceleration problems with my car, and not been able to track it down - plugs and leads are ok, dizzy and rotor seem fine etc etc. Checked all sensors like the AFT, temps, throttle position sensor etc - all within spec. So in a last ditch attempt I started pulling connectors off things of lesser importance to see if i had a fault on any of them. Dropped the boost to stock - no change. No codes present at any time.
So i whipped off the electrical connector to the turbo pressure sensor (left the hose on) and that instantly cured my 'stepped' acceleration and hiccuping deceleration. It also gives me better 'pull' in high gears.

This tells me that the Turbo PS either alters fueling, timing or some other vital parameter.

I dont want to leave it off - no fuel cut if the boost control goes badly wrong, so i'll have to get a new one, but the key issue is that everyone ive spoken too was under the impression it made no change to the anything unless you hit a threshold for fuel cut.

Thoughts?

James
 

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1990 Celica GTS
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MAP is the only thing that tell the ECU how much air is in the engine and how much fuel to use. Unless there is another sensor like MAF(AFM), ECU won't know how to run. You sure its the MAP you unplug? Cause most engine won't even run without it :eek: The MAP got 1 vaccum hose connect to the intake manifold and got 3 wires. Maybe a photo of the sensor you unplug will help.
 

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Discussion Starter · #3 · (Edited)
Yup, positive its the MAP, or to be precise on this one the turbo pressure sensor - since it does have a flapper type AFM although you probably cant tell that from my poor explanation :)

I think my main point was that considering it had an AFM everyone says it doesnt use the turbo pressure sensor for fueling changes. By unplugging it I fix some acceleration problems that arent fuel cut (no codes) so it must alter fueling?

J
 

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Ok I've check Toyota Electrical manual and yes its the Turbo Pressure Gauge sensor. I don't have the repair manual with me now so I can't say if it got anything to do with fuel. I'll say yes cause its connected to the ECU not just to the gauge. Maybe you can take the sensor out and clean it up with throttle body cleaner. Also check for leak if its connected with a hose.
 

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Discussion Starter · #5 ·
I'll be doing that tonight when i get in - it'd be nice if it was a simple fix like a leaky hose but i cant see a leak. It does go to the ECU but the general concensus is that it only servers to trigger fuel cut on overboost. As my mate, working on Ford engine controls, said "I doubt that but I've been proved wrong before" :)

Cheers

J
 

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Discussion Starter · #7 ·
Yeah, I've had a few people mention the plugs/leads/dizzy/rotor arm - seems a common fault. But i dont see why it would stop when i unplug the boost sensor if it had anything to do with them?
I've checked them out (car was new to me a few months ago) but they look pretty new, and resistance measurements show all the leads are well within spec from the manual. Like I say tho, its only been cured when i whipped off the pressure sensor, as if that is reading wrong or non-linear and affecting the fuelling.
It was never a misfire-type of jerk, more like the accelerator was being pressed unevenly, and on deceleration it would get to somewhere around 1800rpm then it would act as tho i'd dabbed the gas for a split second, then carry on as normal. All very strange, I hadnt considered they could be linked until i tried this.

J
 

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The turbo pressure sensor, yes all it does is read manifold pressure, tells the ECU when to put in a boost cut, also works the factory boost gauge on the cluster.

So your saying that you had some issues on a hard acceleration? Well, depending on your mods and what you've done, fuel cut is a possibility. Yes, one way to disable it is to pull the vacuum hose (i also teed my boost gauge here), but you'll have no safety device if you do overboost! I highly reccomend NOT disabling this device unless you have an aftermarket boost gauge. Then, just modulate your levels with your right foot :)

They're other ways to work around boost cut, but this is my preferred way because 1: its free and 2: Its easy. Just make sure you dont unplug the electrical connection to the TPS, its still needed on there.

Yes other things that come to mind with a stuttering type situation is ignition componets, and knock/ pinging/ predetonation.
 

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A boost controller doesnt correct the TPS boost cut. Electronic devices such as FCD's can be built by yourself for 5 dollars.

The blow off valve/ bypass valve, is a device that vents the pressure that your turbo created, back into the atmosphere. Its inserted in the loop of the intake tract, and under vacuum following high boost pressure will open, and vent to atmosphere. If this pressurized air were to stay in the sytem, it could damage the compressor wheel in the turbo itself, caushing thousands of metal shrouds to be sent through your engine. Which is not good :thumbdown
 
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