[Mk2] [Turbo] Faulty Knock Sensor

[gavaroo]

Just a quick question...

Could a faulty knock sensor give you a massive flat spot at about 1800-2000rpm followed by a huge back fire!

Cheers, Gav.

[screech205]

A faulty knock sensor will make the ECU fault light come up on the dash and the car will go into safe mode.

You'd know about it if the knock sensor went down, trust me!!

Did you ever get the fuelling checked mate?

Steve

[bri0905]

How would you know if the knock sensor was down?
Where is it?

[gavaroo]

Hey Steve,

Yes it's been checked and it was apparently fine but the garage said I had a faulty AFM and this was causing the problem. This has since been replaced and the problem seems to have gone but been replaced with a huge flat spot and then after about 10mins or so a huge backfire and the car cuts out!

This is a list of the stuff that I have now replaced is the past few months.
plugs, leads, dizzy cap and rotor arm, air filter, fuel filter, coolant sensor and AFM. The car has also been in 3 different garages now in the past 2 weeks! Oh, and every one says the car is going like a rocket, then I get in and guess what... it ain't!

The garage that the car is in now says that the knock sensor is showing a fault but I was wondering if this was cause or effect of the flat spot?

What do you recon?

Cheers, Gav.

[gavaroo]

The knock sensor is under the inlet manifold and a diagnostic check should indicate whether it is faulty or not.

Cheers, Gav.

[screech205]

Hmmm the big flat spot and backfire could well be the knock sensor picking up a big knock and going into safe mode. Do a code check for yourself and you should get code 52 coming up every time.

Standard Toyota knock sensors can be damaged by a backfire daft as it sounds but that coupled with the problems you've had seems to suggest something else. If indeed you have code 52 then get yourself a GM knock sensor from Twosrus and see how you go from there.

I'd seriously get it on the rollers mate and get it set up properly, ie fuelling and timing. it'll cost a bit but it'll be cheaper than replacing a melted piston if you are getting detonation!

Steve

[gavaroo]

Cheers Steve,

The new GM knock sensor is getting fitted today and the garage was picking up a knock sensor fault. I had read before that a back-fire could kill the toyota one. Just wondering which came first... the problems with the flat spot or the faulty knock sensor? I suppose I'll know when I get the car tonight.

Your totally right about getting it tested on the rollers. I'm discovering there's no point in trying to do things on the cheap with these cars as it does indeed seem to end up costing more aswell as being extremely frustrating!

Thanks again, Gav.

[screech205]

Yep i'm learning that lesson too but the hard way

I bet you had the flatspot problem first which then created the backfire that killed the sensor!

keep us posted mate as you may well be able to help me with my problem too if you sort it!

Cheers

Steve

[gavaroo]

This is becoming a joke now. My car is still in the garage and has been there since Saturday and they still don't know what is wrong with it.

They have changed the knock sensor but are apparently still getting a knock sensor fault detected and I think the flat spot is still there too!

Has anyone heard of Dixons of Dunblane before? They apparently specialize in imports but I'm beginning to wonder. Perhaps they just specialize in importing cars rather than actually fixing them. We shall see I suppose!

Anyway, good luck with yours too Steve. I suppose a problem shared is a problem halved eh?

[screech205]

Tell em to check the wire from the ECU to knock sensor, been a couple of problems on here caused by that.

Can't say i've heard of that garage before mate, good luck with it!

Steve

[gavaroo]

The wiring has apparently been checked already and is ok. The guy was actually suggesting that there may be a fault in the ECU? Is this at all likely?

[screech205]

Very much doubt it mate but if you know someone near you with another tubby or perhaps put a post up to see if someone will lend you one for a bit just to test it.

I went down the ECU route and it made no difference whatsoever.

Do you know what knock sensor they put on? If it's a generic one then that's probably what's causing the problem. I'm always weary of garages fixing my car or telling me they've done something so i do most of the work myself. The only person i trust with my car is Pete at sBits and lucky for me he's just down the road!

If i were you i'd get the car back, get em to put your old sensor back on and check yourself that there's continuity in the wire from the ECU to the knock sensor. I've got a wiring diagram of the ECU pinouts somewhere so we can sort that out. If the wire's ok then it can only be the knock sensor that's causing the problem. It is code 52 you're getting?

Get yourself a GM sensor from Twosrus and we'll take it from there.

Keep the faith!

Steve

[BenF]

What error codes are you getting? With a dead knock sensor the car will start OK, but as soon as you're moving the check engine light will come on, and the car will bog down really badly when you accelerate, and then take off when there's enough boost.

As for ECU - if you can find someone in the same area as yourself with the same year / revision '2, you could try swapping the ECUs between cars in return for some beer tokens ?

I know of someone here who killed his ECU by doing some arc welding on his chassis.

[gavaroo]

Cheers guys,

It's a GM one from gtschris that they have just fitted. Not sure what the error codes are as I put it in the garage before checking as I thought it was a timing thing. However, they have told me that it is just coming up with a knock fault on their diagnostic machine.

I also don't like putting it into garages I don't know and to be honest I'm beginning to wonder how much time they are actually putting in to try and fix it?

Gav.

[Spittinflames]

Just had a quick read through your problem, I've had plenty of problems with knock sensors there a right pain in the ass.

Can i just ask, You say that they installed the new knock sensor but the error code 52 is still showing........ They did clear the codes after fitting the sensor didnt they as im pretty sure it will still show?

Also make sure the knock sensor is in tight enough, mine came loose which caused the check light to come back on and showed the 52 code.

[gavaroo]

Cheers dude.

They did definately clear the old codes, apparently there were a few stored, and the knock code has since shown up again. When I call them up again today to hassle them I'll pass on that the sensor needs to be pretty tight or it will show a fault.

Thanks again, Gav.

[Spittinflames]

Cheers dude.

They did definately clear the old codes, apparently there were a few stored, and the knock code has since shown up again. When I call them up again today to hassle them I'll pass on that the sensor needs to be pretty tight or it will show a fault.

Thanks again, Gav.

I wouldnt over tighten but obvioulsy loose is no good, when i say my light came back on because the sensor was loose i mean that i could turn it by hand

The problem i see with them is you can tighten the nut bit up with a spanner but when you put the sensor in its just round so can only be tightened by hand.

I cant see why it would show up 52 code with a new sensor in straight away.... Make sure they've clamped the 2 wire togeather properly.

When they installed it did they say the light came on straight away or was it after taking it for a run

[gavaroo]

That sounds like a rather stupid design. I think they said that the fault showed up again after they took it for a run but I'll check that too when I call them.

Cheers, Gav.

[BenF]

The knock sensor is very delicate - if you tightened it up 'FT' it'd break straight away.

ISTR that the Toyota sensor would need something like a deep 27mm socket to get it off/on - or use a monkey wrench carefully.

You will have to clear the ECU codes - but after replacing it you shouldn't see the same error code again assuming the car is just idling.

You checked the timing etc is all OK and there isn't actually massive amounts of detonation happening under load?

[gavaroo]

The timing has been checked and is apparently ok. They are getting the following error codes after giving the car a run:

knock sensor
turbo pressure
intake temp
air flow

They have done bu88er all to fix it since wednesday so I'm going to get it tonight and I'll see if there is any kind person near glasgow that would let me try parts from their car to see if i can solve this.

Cheers, Gav.