Boost 'struggle'??
 

I had a quick look to see if this has been asked before...and before i ask,

93 TT, 105,000km, 6spd, only mods worth mentioning that i know of.. is exhaust.

My question is: When i put the foot down in 2nd gear, i get a nice pull from the turbo from about 3800k upwards, but when i change to 3rd, it pulls a little, then makes a noise like its struggling? Instead of the nice boost that you'd expect, it just feels like shit to be honest. feels like its trying to boost but just can't.. It might boost for 1 sec or so, and then the power just turns off until i change gear...

I guess my question is, are you meant to get the same boost feeling in 3rd/4th gear as you do in 2nd? It does not feel or sound healthy. Drives perfect apart from this problem. Diagnostic is all clear. Cheers for any ideas!!

http://img40.imageshack.us/img40/9348/2222wt.jpg
By phuzion123 at 2011-09-01

http://img204.imageshack.us/img204/469/1111vb.jpg
By phuzion123 at 2011-09-01

http://img13.imageshack.us/img13/4732/021pzc.jpg
By phuzion123 at 2011-09-01

Through all gears you should still get a good pull as the turbos spool and as you move through your power band. As with any set up, as you move up through the gears it may be a little less. But from second to third as far as how hard it pulls shouldnt be that big of a difference that you would be concerned about. What kind of noise are you hearing and where does it sound like its coming from?

There's more load on the engine in higher gears, which means you're asking the turbos to work harder. 105K km is very low for a '93...are you sure that's the correct mileage on the engine and especially the turbos?

Also, maybe a dumb question but by any chance does the rpm needle go up without speed increasing?

If you could post a youtube vid with sound, that would be great. Hopefully it doesn't sound like this:
http://www.mkiv.com/techarticles/dea...eath_whine.wav

You know what, i think when this happens the RPM needle might keep going up without speed increasing, or very little speed increase. Is that bad??, ill check that out. Nah it doesnt sound like that one... The best word to describe the noise is kind of a stutter? maybe sounds a tiny bit like that clip but it's not a loud noise. Yeah 105,000 km is correct as far as i know. Car was imported from Japan 4 years ago at 81,000. I have the paperwork to prove that, and it's had 1 owner here in South Australia since then. ODO says 105 too. Owned by a female uni student so wasn't driven a lot.

Ill go for a quick spin tonight and check it out. The supra is off road at the moment because one of the rear wheel bearings has gone so im trying not to drive it too much till next week when it's fixed.

One other thing that may be of interest, It only seems to do it if i put the foot down in 2nd, keep foot down till 6.5k revs or higher then change to 3rd and put foot back flat. If i gun it in 2nd, change at about 5.5k then flat in 3rd it seems to pull nicely. Is it possible for the turbos to not be able to spool fast enough with the gear change and just fail?

Ill try to set my iPhone to record and then go through the gears, It doesnt do it every time, just sometimes.

Thanks for ur help.

Please let us know how the test run goes. If your rpm climbs without the speed increasing, it could be a slipping clutch. This problem gets worse in higher gears - try a high-boost acceleration in high gear on the highway.

Thanks for the info. Supra is off the road at the moment while i get this wheel bearing sorted. I'll do a test run as soon as its done.

How much PSI does a stock 94' run? I have no idea if the previous owner of my car changed it at all, but when i go flat out my boost gauge shows about 12 i think.. If i did run higher psi, what's the highest that you'd want to go?

11.5psi is the oem boost spec.

If you raise your boost, it depends on the octane of fuel that you run. With an otherwise-bone-stock* 2jz-gte, running 93 octane gasoline (calculated via (R+M)/2) you should never exceed 16psi. If you do so, your engine will be damaged in direct proportion to the amount you exceed this limit. For example, at 17-19psi, your 2jz-gte may survive for several years, but your compression numbers (and horsepower) will decrease gradually. Regularly hitting 20psi and above on 93 octane fuel, your 2jz-gte will likely die within months or even weeks. Keep it at 14 or 15 psi and your 2jz-gte should last just fine. When you want to 'play hard', fill the tank (don't mix) with 100+ motor octane unleaded race fuel, and feel free to boost to about 21 psi safely (ideally you'd monitor the oem knock sensors to find the exact limit).
Disclaimer1: all this assumes proper maintenance (eg. keeping your fuel filter changed, your cooling system regularly flushed, regular synthetic oil changes, etc., etc.).
Disclaimer2: Temperature and atmospheric density are also factors. High boost on very hot days is more likely to produce detonation. Near sea level the atmosphere is more dense, so cylinder pressures may be higher...which may be more likely to promote detonation, everything else being equal.

*When I say otherwise-bone-stock, I'm primarily referring to the timing and fuel curves in the oem ecu. In general, I mean no modifications other than those specified by "BPU" (with as many plusses "+" as you want that do not affect the oem fuel and timing curves). Anything that affects these curves (eg. a 'piggyback' ecu (eg. PHR MAP ECU II) or 'standalone' ecu (eg. AEM)), your max boost with any specific octane of fuel will depend on the (extensive) tuning required to properly configure these devices.

Oh nice... I run it on 98 octane every tank. So basically what your saying is, i could run my supra at 14 or 15 psi, (on 98 octane) and it should be fine?

How do i change the PSI? Boost controller install? (real newbie)

EDIT: My boost gauge looks like this
http://img40.imageshack.us/img40/1986/001cbc.jpg
By phuzion123 at 2011-09-06

- Am i right to say that if when i gun it, and the boost gauge shoots upto 1.0 that i am running around 14 psi?

Thanks

Is that 98 *motor* octane, or 98 *research* octane?

To raise boost, install a boost controller OR do one of the simple mods on mkiv.com
http://www.mkiv.com/techarticles/clamp_mod/_clamp.jpg

1 bar is about 14.503773800721814 PSI

just 98 Octane BP unleaded

You need to find out the motor octane of that fuel from BP. I'm quite sure it is not 98.

Oh, when you raise the boost, you'll hit fuel cut. You need to install a GReddy BCC to avoid this.
http://www.mkiv.com/techarticles/bcc.../bcc_intro.htm
http://www.mkiv.com/techarticles/bcc...GReddy_BCC.htm

Thanks mate.

If my boost gauge is correct, then i am already running around 14 PSI. So if this is true i should have a greddy BCC installed already? I'll have a look.. What happens when the fuel cut kicks in? Maybe this is my problem?

Fuel cut is very distinctive... it feels almost like you drove your car into a wall, and only right at 14.5 psi (never below that). You may be right - 2nd gear may go by too fast to hit the fuel cut boost level.

Try this as a test :
http://www.mkiv.com/techarticles/ffcd/freefcd.htm
Don't use it long-term or the longevity of your turbos can suffer.

Okay, Supra is back on the road ($700 later)... Now that i've paid more attention, the boost gauge hits about 0.7 bar, So i reckon I'm running the stock boost still. It hasn't played up so far either, nice smooth boost apart from 1 time, in 3rd gear, it boosted nicely, then stopped for 1/2 second then kept going even though my foot stayed flat. It seems the 2 week rest in the garage has fixed some of these problems.. weird.

Another question i have is, From cold start the idle is perfect, sitting at about 1k rpm. When i drive a short distance (4km or so), stop the engine and start it about 15 mins later - The rpm at idle is down at around 400 - 500 and jumps up and down. It might go down to 350 or 400 and almost stall, then jump to 500 - 600 then back down again. Any ideas what might be causing this?

Just curious - what was the $700 for?

The idle issue is likely an IAC problem or a vacuum leak. Is the ecu throwing any codes?

$700 for a new wheel bearing and the labour involved. $210 for the bearing, the rest was labour.

Nah the ECU is all clear..

After doing some reading and searching on google for 'boost leak' I reckon that this is exactly what's wrong with my car. When the boost kicks in it just feels weak and sluggish, maybe overboost?

I'm an absolute noob at this stuff, has anybody posted a how-to?

Extra: Just realised i've never looked at the boost gauge when i floor it. It's all over the place! jumps to 0.5 bar, then down to 0.1.. back up...

Does that scream anything?

You need to pressurize your intake system with an air compressor (up to 15psi should be fine) ... all the way from the air filter/maf back...and listen for leaks. You'll have to rig up an adapter from your intake/maf to the air compressor.

It turned out to be fuel cut!

Awesome - glad you got it figured out, and even more glad that your Mkiv Supra TT is behaving exactly as Toyota built it to.

What I'd be a bit critical of is *anyone* trying to raise boost without doing *all* of the BPU mods. The "BPU" spec was written for a reason - so no one would have to worry about stuff like fuel cut when modding their Mkiv Supra TT! Sigh.

Yeah... I bought this car from a young girl who obviously did not care for it and had no idea how to. Her idiot boyfriend probably raised the boost and didnt know what to do about the fuel cut!

Thanks for your help