3sgte hesitation

[solitaire]

Im very concerned about my 90' sw20.

Everything is stock apart from a K&N and a manual boost controller which stays on 10psi.

Yesterday after work i was sat at the lights in albany (long flat 80k stretch). I had been on the motorway for about 20 minutes, no traffic, heaps of air flowing over the intercooler. I had been sitting for about 30seconds at the lights.

I generally let it bog ever so slightly if im not in a rush from the lights, once the clutch took hold i planted my boot. (i like that stretch of road)

What would usually happen is that boost would build and the power would be fairly constant untill i changed gear. It felt a bit underpowered and as i changed gear i felt a little bit of vibration through the gear stick. I planted my boot in 2nd and it pulled for a moment and then hesitated, the boost gauge read 10psi but it felt like there was no boost at all... almost as if it was running incredibly rich.

interesting point. The only other time this has happened was about 2 months ago at the same set of lights... After about 3 minutes of highway driving it returned to normal - same as last time.

I have not checked the diagnostic pin outs yet... i plan to tonight if i get home before dark. I was hoping someone might of experienced this.

I dynod it fairly recently at Torque performance and they said it knocked a couple of times on the run but as i was running 98 there was nothing to worry about... it ran 143kw's and the af was around 12ish... which the guys at tp said was fine.

any opinions or suggestions apreciated

[pureadrenalin]

143kw is very good for 10psi.
12ish afr is a little lean for my liking, and VERY lean for a stock ecu running 10psi.

My old BOV would let go at about 13psi and power wise the car would fall flat on its face and run VERY rich (you could see black clouds in the rear view mirror) and still show 10psi on the boost gauge.

My old MR2 (before I got a boost gauge installed) would drop into it's safty mode (VSV valve open) and drop to 6-7psi (wastegate spring) which felt like a huge drop in power

[solitaire]

143kw is very good for 10psi.
12ish afr is a little lean for my liking, and VERY lean for a stock ecu running 10psi.

Yeah i get mixed opinons of that... but i tend to aggree with you, a friend recomended that i got my injectors cleaned, which to be honest i have been too slack to do...

Someone else mentioned a Oxy sensor but Warwicks gut feeling was that it was a costly replacement if i do not know the oxy sensor to be stuffed.

Is there anything else you would recomend to stop it leaning out? I have only had this car for 6 months and previous to me it had been neglected from what i can tell...

My old BOV would let go at about 13psi and power wise the car would fall flat on its face and run VERY rich (you could see black clouds in the rear view mirror) and still show 10psi on the boost gauge.

Aaahhhhh!, that sounds interesting... ill turn the boost down to 8 and see how that goes.

[pureadrenalin]

I thought if the oxy sensor was stuffed it ran richer.
On a dyno at 10psi, I woud expect your afr to drop off the scale rich (lower that 10:1), so thinking about it, 12:1 is a little concerning.
Change your fuel filter?

You've got an actual boost gauge right? not the stock one?

side note: you can't turn your boost lower that 6-7psi, thats what the wastegate spring is.

[solitaire]

I thought if the oxy sensor was stuffed it ran richer.
On a dyno at 10psi, I woud expect your afr to drop off the scale rich (lower that 10:1), so thinking about it, 12:1 is a little concerning.
Change your fuel filter?

You've got an actual boost gauge right? not the stock one?

side note: you can't turn your boost lower that 6-7psi, thats what the wastegate spring is.

I wouldnt know about the oxy sensor... it probably does just to be safe, it was a passing comment from someone

I should give you a little more background. First time i dynod it the afr averaged 12.5 and peaked at 13 while on full boost (9psi).

I replaced the fuel filter and dynod again... no change

i replaced the afm (the original was well out of limits of resistance according to bgb.

Dynod again... peaked at just under 12 (average 11.5ish)

I have an actual boost gauge although i cant gurantee its brand.... it did seem to match the dyno plot boost reading though...

and here we are...

[vvega]

sounds liek your stock ecu is picking up know and pulling all ya timming
ask al all about it
wildcard had it too
could just be a faulty knock sensor


v

[solitaire]

sounds liek your stock ecu is picking up know and pulling all ya timming
ask al all about it
wildcard had it too
could just be a faulty knock sensor

Cheers mate, is it likely that the diagnostics would show this or is it possible to have a faulty sensor without diag showing it up?

[flygt4]

mr2sik had a good case of knock too

[Caveman]

sounds liek your stock ecu is picking up know and pulling all ya timming
ask al all about it
wildcard had it too
could just be a faulty knock sensor


v

yep thats what happened on the dyno that time, remember

knock sensor was cutting in and pulling the timing killing all the power.

I unscrewed the knock sensor out of the block and it pulled hard to redline (without detonating to death for about 4 months of racing too)

basically I came to the conclusion the factory knock sensors get damaged easily or are over sensitive.

[IH8TEC]

dylan you had 4agze computer aye? did it show up check light when you had knock sensor out? or did you still have it plugged in, just not screwed into block?

[Caveman]

dylan you had 4agze computer aye? did it show up check light when you had knock sensor out? or did you still have it plugged in, just not screwed into block?

yep brendon I have late ae101 gze computer. I just earthed the sensor by taping a thread in a piece of steel plate and earthing that plate. Stupid thing came loose sometimes and engine light would go on and ecu goes to limp home mode.

Not the best idea because if your engine does decide to detonate you'll be in shite however you can run knock link or some other after market knock management.

[solitaire]

Right... ran diagnostics

24 - Intake air temp. Sensor Signal
31 - Airflow Meter Signal this pisses me off because i just replaced it
42 - Vehicle Speed Sensor Signal
43 - Starter Signal

I will go through the bgb and troubleshoot these but i thought i would update with what i found in the diagnostics.

Any thoughts apreciated in the meantime - but im guessing its number 24 that is causing the hesitation...

[Alex B]

Reset the computer and see if the codes are still there. AFM code might still be up from last time.

[sergei]

that amount of fault codes are either because some one was playing with sensors and disconnecting them or there is something more fundamental at fault as in faulty wiring, loose ground, faulty ECU...

[solitaire]

Thanks Sergei. I reset it last night (had to pull the battery as the efi fuse didnt wipe it after 20mins).

Tried again this morning, i'm fairly sure its the temp sensor causing the hesitation because it is easily reproduceable at low speeds on these hot summer days.

Having said that, I am more interested in resolving those faults than just making the hesitation go away - bgb here we come

Loose ground anywhere specific?

[RunningRich]

Done the basics, cap and rotor?

My ST165 had an occasional huge retardation of the ignition when it was *really* wet, damn thing wouldn't pull. I put it down to the knock sensor playing up. Also test drove a ST185 like that once.

Mk 3 Supra owners are into rewiring the knock sensor wire with new shielded cable. I suspect the 3S-GTE models also suffer similar faults but I've never seen much talk about rewiring them.

You could unplug the knock sensor and see how it goes as a test?

[solitaire]

Ok Not a bad idea... Ill give that a go, any problem in accessing it?

Ive done the cap and rotor and while i have only had the car for 10,000k's the recomended service get done every 5k. So far cap, rotor, plugs, oil twice, tranny once etc.

The bgb says only change the tranny fluid every 2 years... thats not right is it?

[Caveman]

Dont unplug the knock sensor the car will go into limp home mode.

You need to take the knock sensor out of the block, IIRC it takes a 27mm socket. You then need to earth the sensor housing somewhere else (usually it earths from the thread to the block)

[solitaire]

Dont unplug the knock sensor the car will go into limp home mode.

Ah ok... given that the boys at tp says is was knocking a little bit is it likely to be safe to run without it? or do most cars knock every now and again?

[Caveman]

Dont unplug the knock sensor the car will go into limp home mode.

Ah ok... given that the boys at tp says is was knocking a little bit is it likely to be safe to run without it? or do most cars knock every now and again?

Hmm its a little unprofessional for them to say that...

If the ecu cant see a knock sensor it'll think 'oh crap must protect engine' and kill all power to the engine, only providing enough to 'limp home' really slowly.

The way to get around this is unbolt the sensor from the block and earth it manually while having it plugged into the ECU. The ECU can still see the knock sensor it because its plugged in but it will never detect knock because it is not in the block

The flip side is if you get a bad tank of gas on a really hot day, bad things could happen