3SGTE 4gen - Power limitation issue - No fault codes

[ST-Ryu]

Hi forum,

I've been running this issue last months and I can't find the reason.

I run the car and when I reach about 3,000 rpm and I press full gas, then a power limitation appears, like a ignition limitation, and no boost power (but boost sounds and reach full pressure). And it is like 100hp of power feeling. When I reach this rpm range I feel a constant poor sound change.

Last weeks I cleared all fault codes I had: like Oxygen Lambda sensor replacement, and MAT sensor which it didn't have 5V. I replaced the fuel pump too, installing a 255LPH walbro pump.

I don't know what can be the reason of this kind of power limitation. Maybe I have been thinking about replacing the knock sensor for possible false readings to ECU, but no fault codes on ECU right now.

Engine is a 3SGTE 4gen A/T ECU engine running stock.

Thanks very much in advance.

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[jondee86]

I think that you need to check the timing. First, make sure the ignition timing is correct (easy), and then check the cam timing (not so easy). You also need to check that the VVT solenoid is working.

Cheers... jondee86

[ST-Ryu]

I think that you need to check the timing. First, make sure the ignition timing is correct (easy), and then check the cam timing (not so easy). You also need to check that the VVT solenoid is working.

Cheers... jondee86

Thanks for your response I will try to check timing with an oscilloscope.

But I think this turbo engine hasn't VVT system.

However I will buy a spare knock sensor and I will try I there are any changes.

Any idea is welcome!!

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[jondee86]

But I think this turbo engine hasn't VVT system.

Yes, you are correct. I was thinking of the N/A BEAMs engine. But now the checking of the cam timing will be easier

The reason I say check the cam timing is because you say you have spark, fuel and boost pressure, only there is no power increase after 3000rpm. This suggests that airflow through the engine is being restricted in some way, or that the spark occurs too late. Does your exhaust get really hot ?

Cheers... jondee86

[ST-Ryu]

Yes, you are correct. I was thinking of the N/A BEAMs engine. But now the checking of the cam timing will be easier

The reason I say check the cam timing is because you say you have spark, fuel and boost pressure, only there is no power increase after 3000rpm. This suggests that airflow through the engine is being restricted in some way, or that the spark occurs too late. Does your exhaust get really hot ?

Cheers... jondee86

Today I have no enough time to check timing. But I checked the knock pin and earth with voltmeter and no signal! 0V. Repairing guide says that it must be 5V and some down pulses when detonations or 'knocks'.

I have disconnected plug from sensor and nothing changes.

According to the electrical diagram, that pin grounds via ECU, but the other side outer ECU grounds too. I'm confused, where voltage comes from?

I attach the diagram scheme. The knock pin is labeled as KNK.

Thanks very much.

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[jondee86]

I don't know much about the electronics involved, but as I understand it your diagram shows the knock sensor pin internally connected to ground via a resistor. I think that this is called a "pull down" resistor and its purpose is to make sure the pin is normally at ground potential (zero). So I don't see why the manual would say that there should be 5V present ?

If the sensor is a standard single wire Toyota item the signal voltage is generated by the piezoelectric crystal when it is subjected to vibration at the "tuned" frequency. So there will only be an output signal when the engine is generating vibrations at the knock frequency. Then, depending on the level of knock, the ECU will retard the ignition timing.

In general, you could expect the ignition to retard immediately and noticeably if you suddenly go to WOT after gradually increasing the engine speed to 3000rpm AND there is a tuning, fuel or ignition problem that makes the engine prone to knocking. The ECU will gradually restore timing when engine load (and knock) is reduced, but the timing will remain retarded for as long as the knock level remains high. As far as I know the ECU does not latch a code just because the engine has experienced episodes of knocking.

If the lack of performance you are experiencing is due to the ECU retarding timing, then it indicates that you either have a engine timing problem or you have bad fuel with a very low octane rating. By the way, the knock sensor must be tightened to the factory specification. A loose sensor can cause false knock, as can certain other mechanical that generate noise/vibration in the knock sensor frequency range.

Cheers... jondee86

[ST-Ryu]

I don't know much about the electronics involved, but as I understand it your diagram shows the knock sensor pin internally connected to ground via a resistor. I think that this is called a "pull down" resistor and its purpose is to make sure the pin is normally at ground potential (zero). So I don't see why the manual would say that there should be 5V present ?

If the sensor is a standard single wire Toyota item the signal voltage is generated by the piezoelectric crystal when it is subjected to vibration at the "tuned" frequency. So there will only be an output signal when the engine is generating vibrations at the knock frequency. Then, depending on the level of knock, the ECU will retard the ignition timing.

In general, you could expect the ignition to retard immediately and noticeably if you suddenly go to WOT after gradually increasing the engine speed to 3000rpm AND there is a tuning, fuel or ignition problem that makes the engine prone to knocking. The ECU will gradually restore timing when engine load (and knock) is reduced, but the timing will remain retarded for as long as the knock level remains high. As far as I know the ECU does not latch a code just because the engine has experienced episodes of knocking.

If the lack of performance you are experiencing is due to the ECU retarding timing, then it indicates that you either have a engine timing problem or you have bad fuel with a very low octane rating. By the way, the knock sensor must be tightened to the factory specification. A loose sensor can cause false knock, as can certain other mechanical that generate noise/vibration in the knock sensor frequency range.

Cheers... jondee86

Yes! You are right about knock sensor. I was in a mistake. Sorry.

My theory was that maybe the sensor could be dead, or giving false readings.

Yesterday I disconnected the plug and ECU doesn't throw any error (so maybe ECU doesn't know if sensor is connected).

Then, with sensor connected and car RUNNING idle, I checked volts on sensor and no volts. No signal. Nothing. Maybe there should be small pulses on normal idling? In my case no pulses.

This is why I suposse I have a problem on sensor/wiring.

I will check resistance on the wire and i will check the knock sensor doing knocks or taps.

I don't know how to measure if my fuel is bad or not, or if there is an ignition problem. Right now the fuel is 98 octane.

Thanks very much.

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[jondee86]

I believe that the ECU should latch a Code 52 fault if the knock sensor has a short circuit or open circuit condition in the wiring. So I would expect that unplugging the sensor would show a fault. But I don't have enough information to know for sure if it would latch it straight away or only after driving for a while.

Regardless, if the knock sensor is causing the loss of power by retarding the ignition, it must be working. If it was not working and the engine was knocking, then you would certainly hear some "rattling" when you stamp on the gas !!!

Bad gas is a remote possibility if you fill up from a high turnover gas station. So better to look at the other possibilities that might cause a lean fuel condition or retarded ignition timing. That is why I suggest checking cam and ignition timing to eliminate one possible cause. Another thing to check is the small hose that connects to the fuel pressure regulator. If that is not connected the engine will (possibly) run rich when out of boost and lean when in boost.

Cheers... jondee86

[ST-Ryu]

I believe that the ECU should latch a Code 52 fault if the knock sensor has a short circuit or open circuit condition in the wiring. So I would expect that unplugging the sensor would show a fault. But I don't have enough information to know for sure if it would latch it straight away or only after driving for a while.

Regardless, if the knock sensor is causing the loss of power by retarding the ignition, it must be working. If it was not working and the engine was knocking, then you would certainly hear some "rattling" when you stamp on the gas !!!

Bad gas is a remote possibility if you fill up from a high turnover gas station. So better to look at the other possibilities that might cause a lean fuel condition or retarded ignition timing. That is why I suggest checking cam and ignition timing to eliminate one possible cause. Another thing to check is the small hose that connects to the fuel pressure regulator. If that is not connected the engine will (possibly) run rich when out of boost and lean when in boost.

Cheers... jondee86

Thanks very much for all of your answers and ideas. I will check all of them and I will return here to tell the results.

Have a nice day @jondee86

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