Can anyone tell me in resonably plain English what a detonation sensor does and why we have one on our Zeds, and why Nissan put it in the most f*****g annoying place possible!!

 

Many thanks

 

Andrew

The detonation sensor is, basically, a microphone that listens to engine noise (all engine noise, that is directly transmitted through the block).

 

Now, more specifically, it's a piezo transducer that is bolted to, and in direct contact with the bottom end. It picks up a lot of noise, most of which is normal engine noise and total garbage, it's the ECU's job to listen to this noise and filter out the crap, and listen for the tell tale noise of detonation (the colliding flame fronts, basically, that make a high pitched metallic knock).

 

When the ECU detects knock, it shuts off the BCSV's (Boost Control Solenoid Valves) to drop the boost to it's natural regulated level of 7psi (instead of ~9psi), and also retards the timing (I forget the amount of retardation, but it is considerable) to try and prevent further detonation occurring.

 

The car continues to run in this state until the ignition is next switched off and on, at which point it resets and runs normally (unless it hears det. again).

 

However, it is important to note two things;

 

a) The ECU only listens below 3500rpm - above that, engine noise drowns out any knock that the ECU can distinguish.

b) The level of retardation and boost reduction might not be enough to stop bad detonation at high RPM.

c) If you've got an aftermarket boost controller fitted, it won't be able to lower the boost anyway.

 

A code 34 (detonation sensor open circuit or out of tolerance) will also cause the same symptoms - 7psi of boost and retarded ignition timing - but will not reset after ignition off, unless the condition clears (in the case of a faulty connection, say).

 

The sensor is where it is for a good reason - it's in the best position on the block that Nissan could find, in order to pick up the specific noises and specific frequency that it's listening for.

 

So there you go.. Anything else? :)

You the Man!!!

 

Cheers. That answers all my questions. I now know what it does and why.

Interesting.

 

My TT is showing a fault with this knock sensor. I've been told a 1 meg ohm resistor to bypass this sensor will make the ECU think all is well and will therefore stop the boost decrease. Whats is everyones opinion on the risks involved in doing this ???????

 

 

Thanks

 

andyZ

Yeh, that's one of the main reasons I asked about it.

 

My TT showed ecu codes 13 (coolant sensor) and 34 (dreaded detonation sensor). I've got no boost under 4000rpm and 0-60 runs at approx 8 seconds. I have had this since I bought it so the end result is I reckon we are running in safety boost.

 

Weird thing is ECU now shows 55 code and all I might have done is wiggle a few of the connections. I have even tried resetting the ecu and still it says 55.

 

HMMMMMMMMMMMM!!!!!!!!

 

Sat in front of me now is a new coolant sensor and harness from Courtesy- job for Sunday.

 

Checked resistance last week from connector that leads to detonation sensor (not ECU-that was fine) and although it reached the necessary resistance amount, the level rose slowly. I tried various earths but it still took a couple of minutes to climb.

 

Now I thought either something has a resistance or it doesn't, not it starts off with a little and gradually rises.

 

So I too am thinking how dodgy the bypass method or relocating the sensor to the top of the engine is. (should I have to go down this road). My thoughts are its dodgy to bypass anything that was put there for a reason and we would run the risk of a detted engine. Not pleasant, however the cost of replacing the original item can't be too pretty!!

 

:confused:

Andy & Andy;

 

You're right (Andrew) that if it was put there for a reason - it ought to be there.. So, it ought to be fixed properly, rather than bodged..

 

But..

 

It *is* a major PITA to fix - you have the choice of removing the upper and lower plenums (I'd guess 4-6hrs work to remove the upper, an hr to remove the lower, if you've never done it before - plus about $200 worth of gaskets & hoses to put them back on again!) to get at it, or if you drop the gearbox off and get the car on a lift, you can just about get to it from the bottom & back of the engine (if you have long arms!).

 

Personally, I'd do it from the top - remove the plenums. For a start, you can replace the myriad of little water hoses under there that all perish and burst with age, and you can replace the PCV's too, plus having the upper plenum off makes changing the O2 sensors a piece of cake.

 

Having said all of that, I'll let you in on a secret. My car has no det sensor - it has a 1MOhm resistor. Now, I don't plan on it running like that forever - when the engine gets pulled and rebuilt for the new car, the det sensor will get properly replaced.

 

But! I wouldn't recommend that you all go out putting a 1MOhm resistor on your cars. Yes the det sensor is inactive over 3500rpm (and that's where you're most likely to get badly destructive det), but, you can also get terribly destructive low RPM det from things that you just wouldn't expect - that's what it's there to stop, mainly (like to stop a sh*tty tank of fuel from blowing a hole in a piston!).

 

Bottom line is - yes a 1MOhm resistor will work, but KNOW the risks - you now have no protection at all from detonation. And lets face it, any protection is better than none! (Not strictly true, some people can hear det, but you need to know what you're listening for, and it goes without saying that you can't hear it when the stereo is on :D).

 

As for relocating the det sensor - that's another option, and yes, it should work, but it almost certainly won't be as sensitive. Again, you are reducing the already flimsy level of protection it affords.

 

Now - Andrew (Warren) - your symptoms don't exactly sound like safety boost on it's own.. Your turbo's ought to still spool relatively quickly - certainly a lot sooner than 4000rpm, even with the BCSV's closed. Your temp sensor won't be helping though if the ECU is missing that, I believe it will switch to the so called 'low octane' maps - again, running more conservative fuel and ignition mapping (unless you have a JWT chip - their low and high octane maps are identical. I don't know what SE do, but I would bet that they map identically for both sets - on a tuned motor, you are already admitting you're not so worried about extra levels of protection from such things). That along with running with extra retarded ignition and lower boost, will reduce your power quite considerably. The 1MOhm resistor is a very good way to test if your problems are the det sensor, however. So by all means, fix that temp sensor, wire in the resistor and try it out - but listen for detonation carefully while you're doing it. If everything is hunkydory - fix that det sensor properly.. :)

 

Oh and one last thing - testing the resistance on the det sensor is odd, not like a normal component - because of it's very nature as a piezo transducer.

 

Disclaimer: If you fit a 1MOhm resistor, and detonation destroys your engine, I am NOT responsible! Just in case anyone thinks of trying that one out...

If you are using a boost controller is there any point in having it?

The ECU can't reduce boost and just retards the ignition so why not disable the sensor and listen out for detonation at low revs?

Mainly for the very reason you state - it still retards the ignition.. And you never know, that might (though it is doubtful) be enough to stop whatever detonation was occurring..

 

Plus, if you leave it there, you can hook a warning light up to the BCSV line - Maciej has a circuit on his site - that will let you know if the ECU has detected detonation.. Afterall, do you want to drive around with the stereo off all the time? :)

if the sensor is fine and no errors but engine is detonating will the ecu pick this up as a code 34 or is it souly for the circuit?

Originally posted by Devil

if the sensor is fine and no errors but engine is detonating will the ecu pick this up as a code 34 or is it souly for the circuit?

 

no - code 34 means a fault in the sensor circuit

well how do you know if you have detonation then if you running a boost controller?

well how do you know if you have detonation then if you running a boost controller?

 

 

I think Aaron already mentioned it, you can make up a small circuit board that will light an led when the car is in safety boost -http://home.swipnet.se/e-solutions/SB-ind.html

 

I got one made up and it works (tells you you're in safety boost).

 

Vijay

Thanks for the advice.

 

I've just swapped engines over. Is it possible that I might have a loose connection. It seems plugged in alright. I don't suppose theres a separate earth wire for it. Thought I'd better check the obvious first.

 

Thanks again

 

Andy

think how much money you could make if you could train a small furry rodent to get in and change the kock sensor!! - he would need very strong paws though. And a special spanner.

Originally posted by senna

think how much money you could make if you could train a small furry rodent to get in and change the kock sensor!! - he would need very strong paws though. And a special spanner.

 

A very special spanner indeed to change your KOCK sensor, some spanners would have to be larger than others obviously!! :D

See what I've started!!

 

I only wanted to know how a detonation sensor works.

 

We're now talking ferretts and KOCK's.

 

Luvly!!!!!!!!!!!

:D

Originally posted by AndyZ

I've just swapped engines over. Is it possible that I might have a loose connection. It seems plugged in alright. I don't suppose theres a separate earth wire for it. Thought I'd better check the obvious first.

 

It earths through the block, I believe, and so needs a good electrical connection to that through it's base, but;

 

The connection you can see is actually the connection from the main loom to a small sub loom - very often the connector at the end of the sub loom corrodes and dies due to the heat, along with the sensor itself - and getting to that is the hard part (you can't get to it without doing one of the two things I mentioned earlier).

 

So unfortunately, unless the fault is obviously in the bit you can see - it's most likely underneath the lower intake..