1jz 1/4 throttle same as full throttle?

[naten]

something odd happened first post below

[naten]

hey guys,

Just a quick question for anyone who might know, is it normal for 1/4 throttle to yeild the same acceleration/boost as full throttle? I havent checked the numbers on ye old gtech but it feels almost identical. Its so close that i took a mate for a drive and he couldnt notice the difference either.....

Am i being paranoid or is something askew?

Car is a MA61 with a 1jz, everything stock except fmic and 3" zorst from the dumps back. Car runs pretty good other wise just a slight hesitaion before full boost (approx 3-4k).

Nath

[Vios-GT_07]

my 4A-G does exactly the same thing.. i drive with barely 10% throttle most of the time.. and going from 1/4 to full throttle is only induction noise and the engine works slightly harder.. and i got that hesistation just before 3000 rpms, though i've narrowed it down to either the fuel pump being worn, the muffler being an S-flow with a valve to make it straight through under load, and the distributor needing a service.

[oldcorollas]

at lower rpm, the amoutn of air going into engine is less... so you might be able to hit full boost at half throttle...

what does boost gauge tell you when you are at 1/4 or full throttle?

at higher revs, is it the same? ie, 6000 or 7000rpm?

[naten]

vios: Thats practically the same sumptons i have tho there are a few difference in the cars (4a vs 1j) i dont think the zorst would cause it tho. I guess maybe the fuel pump could

oldcorollas: There is literally no viewable difference in a 0-100 run at a 1/4 throttle and a 0-100 run at full throttle. Boost is the same (peak and when it comes on) and speed feels the same. It also pulls the same through to 7k. The hesitation feels almost the same but it isnt as pronounced with 1/4 throttle.

which is confusing me.

Things im thinking it could be. TPS or maybe fuel pump?

I would of thought the fuel pump would cause a lack of performance though rather then something like this.

Thats odd can any else see my reply as the first post and dated some time in 2002?

[oldcorollas]

if it is fuel pump then it will do catastrophic things at higher rpm.

perhaps the pump cannot maintain the pressure required for the boost level, but if it runs out of flow, you will go lean, and it will either ping or cut when you run it to 7K.

first thing you need to do is get it on a dyno, or borrow a wideband oxygen sensor to check the AFR's. if the AFR's are ok, then it is not fuel.
if on the dyno it is making the same power at 1/4 throttle and full throttle, then either the throttle is too big, or you have a massive restriction in the system.
if the power is what you would expect, then it is just the throttle being too big for the rev range you are using
basically, chuck it on the dyno and see if there is actually anything wrong before chasing things.

vios, that is normal to use small throttle.
full throttle is meant to be "too much" at max rpm WOT... so you usually need to use very little, and at say, 3000rpm, you need much less air than at 8000rpm

[naten]

hmmm will wander down in the next few days and see if i can get her dynoed

Yea that makes me think the fuel pump is ok. Agreed best way to know is a dyno test and suss things out from there.

I checked over the TPS as per these specs:
http://mkiv.supras.org.nz/articles/engine_2_41.htm

And it was all within spec with the exception of the idle switch. I had to wind the idle screw completely out for it to register 0v at idle. Now the problem is the throttle isnt cracked open at all so the idle is only around 500 and stalls when coming to a stop.

Would you suggest i adjust the tps slighting so idle is at 0v ? Ive been told the tps is very fiddly and not to mess with it. I did take it off but i didnt adjust it, i removed it via the housing that it sits on.

If i dont adjust the tps i can just wind the idle screw back out but it means the tps wont drop to 0v and indicate idle to the ECU.

[chris davey]

silly question but, have you checked how much 1/4 throttle is actually opening the TB? Ie, it could actually be more than that.

Sometimes it is the simplest things

[thepeter]

agreed with chris davey - check the throttle cable tension, it's not too tight/loose?

[naten]

checked the cable and how it opens etc and its normal

so flat in the car is full on the TB quater is a quater etc etc

Getting the TPS to go to 0v at idle fixed my idle rpm variations (would hunt 200 rpm) but its idling a little low. Ive backed the idle screws all the way out so the TB is 100% closed, would it matter if i crack the throttle a bit to keep a decent rpm?

What im assuming is that its ok to do this as long as the IDL pin on the TPS is still at 0v at throttle shut.

Im meant to be getting the car dynoed tommorrow morning so ill have a better idea whats doing then (as long as i dont whimp out, $95 a run seems a bit steep)

[wilbo666]

The procedure for setting up the TPS has a few steps if I recall,

The first step is to adjust the throttle stop if I recall,

Then adjust the TPS.

When adjusting the TPS it isn't about getting the output to 0V as such, it is a range.

Also you need to set it up so that the IDL contacts are closed at idle, and then break at the specified clearance...



http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=101

Cheers
Wilbo

[naten]

ok im playing around with it now. +rep for ur help

Its within specs listed.

The only thing i cannot figure out is where to set the idle stop screw to start with. As in how much it should be opened to before adjusting and taking measurements etc

any ideas?

[naten]

unless thats whats written on the page and i cant read it

[Kyosho]

naten: As has been said, it is often quite sensible to not fully require 100% throttle to feel like you're at full noise

In alot of cars, 80% of your power is made with 25 - 30% of the throttle, the last 20% isn't exactly noticeable in seat of your pants.

The last part is, are you sure you're using 25% throttle? I'd be thinking you're using alot more.
I used to beleive I was only using 10-15% throttle when accelerating normally, when I did a datalog from my ECU, I'm actually using 25% throttle, but it feels MINIMAL!
I'm betting your "25%" is really alot more then 25% and more like 50%

Also, at around 50%-60% throttle, my car "feels" the same, as at 100% throttle, but if I watch the boost guage, I'm actually held back by a psi or two, and flattening it fully yields full boost, and there IS more power, but not HUGELY noticeable. (But it's there... )

[naten]

positive about throttle position have been playing with it for ages now.

hit a brike wall.

I havent adjusted the tps yet as im unsure where the throttle stop screw should be to start the hole process.

Where im at: the car now idles awesome when first started once its fully warm and i have hit some boost idle is around 500rpm and it will stall most times coming to a stop.

I can up the idle screw to make the idle higher but it then mean that the TPS will have to be adjusted back to give me the 0v at idle thing.

sound right?