Pinking (Pre-Ignition) 2002 Avensis 1.8Vvt

[Andy Gibbons]

Hi, hope you can help or point me in the direction of a previous post.

The car is a 2002 Avensis 1.8vvti estate just coming up to 100,000 miles. Once warm the engine is prone to pinking under moderate accelerator settings, any gear.

The following parts have been fitted in the 2 years I've owned the car:

All three Lambda sensors (All new Denso)

Catalytic converter (Pattern part)

Airflow sensor (Denso original)

Vehicle is regularly serviced, air/oil filters plugs & fuel filter recently.

Is it worth resetting the ECU (by Battery disconnection or ECU fuse removal)? The assumption here is that the ECU modifies and stores revised parameters based on specific driving style etc. of the owner. It's also an assumption that disconnecting the power will cause this data to be erased or overwritten by a default setting. Does anyone actually know?

Other than that I love it. Probably the best car I've had, regardless of age and price.

Kind regards

Andy

[waqar_lionheart]

I feel like I have finally found my long lost brother. Welcome to the pinking club my man.

Please read my extensive posts about this.

My only thing left to investigate is injectors which have now got a messed up spray pattern. I am saying this because my car normally is running slightly rich, but under slight load and a gentle press on accelerator causes it to pink but when i press the pedal slightly further the pinking disappears as if i press the pedal further more fuel is injected into the chamber and lean condition is cured. If you have any other thoughts about this pinking issue i ll be very happy if you could share them. Like you I love my car too.

Regards,

Waqar

[Andy Gibbons]

So, the best way to solve a problem is to understand it first. I researched 'pinking'. This is what I discovered:

There are two way that the petrol/air mixture can be ignited other than by the spark plug itself:

1) Mixture it ignited by excess compression, or by residual deposits of carbon/hot spots in the cylinder, sometimes BEFORE the spark at the plug! This can destroy the engine very quickly.

2) Mixture is ignited in small pockets BEFORE the main combustion reaches it. This is the 'pinking' that we're interested it here. Why does it happen?

Firstly, despite fuel injection and other advances, when the cylinder is charged with mixture during the induction stroke it's petrol/air ratio is not evenly distributed. There are pockets within the charge where the fuel/air ratio is perfect and others where it's not. These 'perfect' pockets will ignite more easily than other areas where the ratio is not ideal.

Secondly, we need to understand how the mixture burns when the plug ignites it. Two things happen. The mixture begins to combust around the plug and the burn spreads out into the surrounding charge. At the same time a shock wave is also generated, which travels much faster through the mixture than the combustion. This shock wave races ahead of the burning mixture and can be strong enough to ignite the pockets of ideal petrol/air BEFORE they are ignited by the combustion process itself. This effect is known as 'detonation' and is common to most explosive systems. This is the cause of pinking. The sharp crackle as some parts of the mixture ignite prematurely. These 'detonations' cause premature burning of some of the mixture, before the piston reaches the ideal position in it's stroke. In effect they try to slow the rotation of the crankshaft, robbing the engine of power and stressing it's moving parts excessively. They also cause localised hotspots within the combustion chamber which can cause burning and holing of the piston crown for example.

What affects the chance of pinking?

Temperature. The hotter the mixture the easier is will ignite. A warm engine is more prone than a cold one. On hot summer days the incoming air temperature is higher. Pinking is usually worse when the engine has warmed up, and on warm days.

Ignition timing.The spark plug is timed to fire just before the piston reaches the top of it's stroke, allowing the explosion of the charge to build up to full intensity at the correct point as top dead centre is passed. This timing advance is necessary to obtain the full power from each charge. The amount of advance required depends on a number of factors, such as engine speed and throttle opening. In modern cars the ignition timing is controlled by the ECU, which takes data from the various sensors (crankshaft sensor, Camshaft sensor, airflow sensor etc) and computes the advance required. To prevent over advancement of the timing a 'knock' sensor is fitted to the engine block and the ECU uses it to detect 'detonation' noises within the engine. When knocking is detected the ECU retards the ignition timing to prevent it.

Fuel grade. Fuel is graded using a R.O.N. number. This 'Research Octane Number' is an indication of how prone the fuel is to detonation. The higher the number the less detonation.

I'm running my Avensis on 95 RON at the moment. When the tank is empty I will use 'Super' unleaded which is usually 97 RON to see if there's a difference.

It is possible to test the knock sensor by tapping the block near (but not on!) the sensor. Apparently one can hear the idle speed change if the sensor is working. It's in a **** of a place under the inlet manifold on mine so I might just replace it!

The problem could also be down to carbon (coke) build up within the combustion chamber. These engines do like using a bit of oil so it may be that there's sufficient build up @ 100000 (my engine) miles to cause it. We used to use Redex, tipped neat down the carburettor (having removed the air filter housing first!) fo try and remove coke, but someone nearby usually called the fire brigade on account of the sheer exhaust smoke generated as the Redex did it's stuff.

Hop I've got most of the facts right about 'pinking'. Now to try and cure it!

All the best

Andy

[Konrad C]

Andy,

You and Waqar are in area (county, pinking issue, etc).

Read his posts on this if you have not already.

What about additives like BG44K, and similar other chemicals that you put in the fuel tank?

You are right about carbon build up, as this can cause the problem you mentioned - higher compression, temperature. Using these chemicals may help reduce this carbon and clean the injectors, without the need of dismantling and de-coke.

BG44K is supposed to the best of it's kind. Then there is this new Terraclean system.

Great post.

[waqar_lionheart]

A while back I had a quote form Terraclean I cant remember where they were based (crawley/redhill area). But if i remember correctly, the quote was for around £120. Lots to think about now coz it will get rid of the sludge and crap thats sitting in the engine but will it also open some of the holes which are blocking more oil getting into the chamber????? thoughts, I am finally conceding that my car is burning oil as opposed to leaking it, there might be some hope yet depending on when I and Konrad can get back together.:). Anyways I ll try BG44K in the very near futures.

Regards,

Waqar

[Andy Gibbons]

Hi again Waqar and Conrad.

Pinking occurs on light throtttle settings. Agree with earlier comments regarding lean mixture at these throttle settings. Engine runs sweetly otherwise. Just bought some BK44 and added it to the fuel to see if that makes a difference. Next step to try 97 RON premium when the tank is emptied of 95. Contemplating a strip down and clean of the intake system.

I will get to the bottom of this, eventually!

Cheers

Andy

(Box Hill eh? only a few miles from me!)

[waqar_lionheart]

Hi Andy,

I am about a mile from box hill. I dont mind meeting up to discuss. I and Konrad met up around box hill quite sometime ago. I have tried the 97RON before and it does make a difference but trust me, with the difference in fuel prices in some areas for 95/97, I wouldnt be happy putting 97 in when it should run perfectly fine on 95. Anyways, like you I must also get to the bottom of this. I would be very interested in the strip down and clean of intake myself. PM me please if you would like to discuss a meet.

cc Konrad.

Regards,

Waqar

[Andy Gibbons]

Update!

Last Friday, stripped and cleaned the throttle body (again) and the airbox, just to be sure there was nothing amiss there.

Saturday took the 'Yota out for a long run, mixed motorway, A road and town, about 80 miles in all. Running well but still pinking. Arranged to meet my mate the worlds best mechanic at 2 pm.

We checked the induction system for leaks using a smoke detection system. None found. All good. Plugged the car in (OBDC). No DTC's stored. Checked the operation of the idle control valve. Fine. Then Fred (world;s best mechanic, remember?) says " Take the camshaft sensor out and clean it up, especially the connector." Did this. Nothing drastic found in the way of corrode terminels etc, but........

....THE PINKING IS CURED! GONE!

Even though it was not generating an error code from the ECU it was the cause of the problem. The ECU can only see if the sensor presents a resistance (it's an inductive coil sensor) and therefore assumes it must be okay. I can only assume that the terminals had begun to increase in resistance so that the signal generated by the sensor had become weak to the point where the ECU was unable to accurately determine the camshaft position (and therefore the correct timing).

Having shelled out a bit recently I will have to wait until I can afford a new sensor but I will replace it as soon as possible. Meantime the car runs like a dream. The power comes on smoothly at every throttle setting in a variety of air temperatures, regardless of whether the engine is cold or warm and independent of gear selected or RPM.

Cheers Fred - The world's best mechanic!

[waqar_lionheart]

Hi Andy,

This is very good news indeed. I was doing a few oil leak checks last week and told Konrad that my camshaft pos sensor is covered in oil muck. When i did that I thought to myself what if this is not sending right data to ecu because it is absolutely covered in oil but then i thought there is no error code hence I am okay but clearly from your post a strong contender for investigation. Thanks to Fred and you I am gonna invest in it when the money comes in.

Regards,
Waqar

[Konrad C]

Andy,

That is a great fix. Sounds like Fred is a great mechanic. Can I add that if you have fixed a bad connection, the sensor is fine and you should save your money.

Waqar,

Andy's findings may be the answer to your problem and when the oil leaks are fixed, the engine is running fine again. It will be a lot cheaper than an engine strip and treatments. If you can, given the sensor a clean and see if it works for now.

Konrad

[waqar_lionheart]

Hi,

I dont think i ll be stripping it to be honest. I will however take off the connecting socket and degrease it and see how it does. Like Andy, may be my sensor is good too but the connection is bad. Hopefully. I am keeping my hopes up.

Regards,

Waqar