Hey guys,

 

I have tried everything I can think of to cure my detonation problem and nothing has helped. So far I've tried running on Optimax exclusively (well over 2000 miles by now), changed to a JWT chip, changed to NGKxx-11b spark plugs from Courtesy, cleaned every sensor/connector I could get my hands on, even installed a JWT pop-charger and corrected the timing to 15degrees BTDC. Still the same rattling noise between 2k and 3k revs under light load.

Under Jeff's thread Phil_m mentioned clogged up injectors and the lambda sensor. How do you clean the injectors and how do you check that the lambda sensor is functioning properly?

If there is anyone else out there who could run off a list of possible causes of detonation then please clue me in ... I'm getting desparate now.

 

Thanks for you help guys!

 

Danny

 

[This message has been edited by Danny (edited 17-12-2001).]

Interesting that it's under light load Danny... Tres interesting..

 

On cleaning the injectors - run some injector cleaner through with a tank of fuel - make sure it's safe for cars with CAT's (Redline make one that the US boys swear by, any Redline stockist should have it, failing that Demon Tweeks do sell it)

If you get really desperate you could get them flowtested, but that's expensive - plus I'd expect the detonation to manifest itself under more conditions if the problem was injectors..

 

To check the O2 sensor, you can put the ECU into it's O2 sensor check mode, and the ECU LED and engine check light will flash as the sensor cycles between rich & lean conditions (which it should do regularily). If I could remember it all off the top of my head I would, but if you have a look at this link;

http://www.ttzd.com/tech/diagnostictech.html

 

That should explain it all far better than I could The diag POT & light on our cars (RHD) is on the left of the ECU - the side that is facing the open car door.. You have to look hard, it's a bit cramped in there

 

Danny,

 

Since i have a small amount of time on my hands allow me try to shed some light on what is going on. Might also help out my old mate Jeff and all.

 

The ECU on the TT like a lot of modern cars these days is what i call a Feedback loop system. Bascially the ECU knows a lot of things about the engine fomr the 10 billion sensors in there - With regards to your problem you will be mainly interested in :

 

The Crank Angle sensor.

The Throttle Position Sensor.

The Mass Airflow Sensor

The O2 / Exhuast gas sensor / Lambda Sensor.

 

Firstly you say you have checked and setup correct the CAS in which case you can scrub that.

 

Without going into it in super detail The ECU will use the Reading it gets from the Amount of Air Going into the Engine (MAS) and the gases going out of the exhuast EGS / o2 to decide how much fuel to deliver and when ... basically.

 

You have a JWT , Intake and Exhaust so we assume that you have the correct Air Fuel Maps in the ECU. i.e The ECU is delivering trying to deliver the amount of fuel that it thinks you should have.

 

Therefore one of a several things could be causing a problem.

 

The MAS is providing a incorrect reading for the amount of air going into the engine. The O2 sensors are giving a incorrect reading for what is coming out the engine.

 

In both cases i believe that the ECU will give and Error (most of the time) if it is not gettin a value from either of the mentioned sensors OR it is gettin a error that is out of range.

 

First step is to do a ECU Diagnostic and see if you have any error code.

 

It is unlikely that the above would cause detonation and not cause rought idle / hesitation also however.

 

Do you have a accurate Boost guage and Do you know how much you are running - Could be that you are running too much boost for the engine to cope with , either by poor tuning or failure in the waste gate system

 

You are correct in that it could be a sticky injector - unfortuantly other than running some injector cleaner thru them ('spit') you have to remove them - have them bench / flow rate tested and then repaired accordingly - there is a specialist here in nottingham that does the work queit competitvely however you might want to take them out yourself .... ( they aren't the easiest things to get to mind you ! )

 

Hope that helps and hope you get your Detonation cured ASAP.

 

 

 

------------------

Z ya

 

Nico91TT

 

Nico,

I think I've kind of contradicted you on the other thread re feedback not operating at high revs (above 3,000 I think).

I guess we should have an argument now !!!

D

Isn't it just the knock sensor that stops working at that point?

Hey Hairy guy - Outside now

rant - swear - curse - call name - pull hair - scrath with nails etc...

 

hehe

 

Yeah just read that mate - I have no idea - altho it does make sence, As you said the change in mixture does take a reasonable time to feed thru to the ECU.

 

I presumed that the Closed loop system operated on all Z's altho the fueling maps are just AFR's basically. I thought the Feedback from the O2's was a basic offset to alter the base line fuel delivery judgin by how rich / lean we were on the last pulse. Not sure how much the ECU is permited to change the curve by, common sence would dictate no euff to cause damage - but hey were talking Nissan here !

 

Besides our friend Danny is having problems under 3k ... so HA !

 

Good to have some nice Tech arguments on here for a change other than if my Gear nob is better than yours etc.

 

Anyway while mulling this over we could be talking other fuel delivery problems here also - Check for Hissing noise at startup and Fuel smells when cold - Could be you have a failing Pump or diphram somewhere in the system that is unable to supply enuff fuel at low RPM - You can check the Resistance across the pump terminals to check the Pump - at certain RPM and check the Reading with the manual.

 

 

 

 

------------------

Z ya

 

Nico91TT

 

Uh oh the handbags are coming out

 

My understanding was that most (if not all) ECU's ignored the O2 sensors above a set RPM limit, as Dave said. I wasn't aware that there was a difference between the UK & Jap ECU's in this respect though - you learn something every day as they say

 

My money is still on O2's, as Nico said it's under 3000rpm, and light throttle (if it was WOT then I believe the O2's are again ignored)..

 

Come on Danny, do an ECU diag..

 

BTW - I have read many times on TTnet of failing O2 sensors being sluggish enough to cause problems, and yet not flag the engine check light on..

Then again.. Hmm.. surely hesitation would manifest, but maybe not I guess..

 

If I'm not careful, I'll fall off this fence I'm on

As I swiftly duck to avoid the blow of Nico's best Gucci handbag ...

 

I'm not sure how the closed loop actually works but the maps look REALLY weird below 3,000 (or whatever the threshold is). They're fairly flat but it looks as though the fuelling is really high (almost at full airflow/max revs level). I guess it reads the map in a different way.

 

If you're ever down at SE ask Pete for a look at the maps for a Jap & UK model and you'll see what I mean. Not sure if he has any theories on why the two differ - presumably one has better emissions than the other but that results in worse power.

 

Now, having got that out of the way, you'd better watch out or I'll throw my lipstick at you in the girly 'crap throwing' way.

 

Dave

 

P.S. Apologies to Ajay, Mrs Timmy and all other Z related females - I'm sure you can all throw properly !

Personally that would imply to me that the ECU is totally ignoring the fuel maps below 3000RPM on that ECU, and using the O2 readings - correction, it's using the fuel maps as a base, and if the O2 dies, it can go into super-rich-prevents-damage-limp-home-mode (can I get any more -'s in there?)..

 

Interesting though - I suspect you're right and it's an emissions thing.. Dont forget, we only emissions test at idle & fast idle (or is that only if it fails at idle? I forget)... I bet the Japanese tests are far more stringent..

 

Careful with that lipstick, its a big drop off this fence and I dont wanna fall

 

[This message has been edited by aaronjb (edited 17-12-2001).]

It may be worth having someone else check if it is actually detonation!

 

Faulty O2's will not cause detonation. The O2 sensors are only used on "open-loop", generally low to low-medium acceleration. When accelerating medium to hard it goes into "closed-loop", the O2's are ignored and a pre-defined fuel/air/timing mapping from the ecu is used instead.

 

Danny, did you have this problem before the upgrade?

 

If not then you need to eliminate each upgrade one by one. I would start first with the pop charger, borrow a standard ECU.

 

Keep us updated

 

Andy

Originally posted by Anders UK:

Faulty O2's will not cause detonation. The O2 sensors are only used on "open-loop", generally low to low-medium acceleration. When accelerating medium to hard it goes into "closed-loop", the O2's are ignored and a pre-defined fuel/air/timing mapping from the ecu is used instead.

 

That's the thing.. Danny said it was only under light load.. (which I'd read to be light acceleration)..

Of course, it probably depends on your definition of light and medium

I've been in Danny's car when this happened and I can confirm it was under gentle acceleration (any more and the box changes down) and this was with no mods at all. To be honest the noise was really quiet and I wasn't totally convinced that it was pinking. My suspicion was that it could have been something vibrating, because the noise seemed to be too high a frequency for the speed of the engine.

Thanks fellas for all your interesting feedback. I suppose I should add the following to my original post:

 

I have only had the JWT chip since late last week. Prior to that the car was bog standard with the exception of the Pop-charger (which I installed two weeks ago). I haven't as yet installed the boost jets cos I need to buy some more rubber tubing and jubilee clips (I'm not intending on going over 1bar boost though). Other than the JWT ECU and Pop-charger, my car is a completely standard '90 Jap spec TT. Prior to the JWT upgrade the detonation manifested itself quite clearly but only when the engine was warm and I was accellerating lightly (eg., travelling at 50mph and slowly increasing speed to 60mph). There is no change in this scenario after the JWT upgrade. Prior to the upgrade I performed an ECU diagnostic and code 34 showed up (det sensor). After the JWT upgrades, the ECU still shows code 34. Idle is perfectly smooth and there is no hesitation to speak of. I do get the occasional fuel leak in the morning but that's always a case of retightening the clips.

 

What I will do tomorrow is buy some injector cleaner and put that in with a tank full of Optimax. Also will have a look at the O2 sensor diagnostic procedure.

 

Thanks again for all your feedback. If anyone thinks of any thing else, please let me know.

 

Cheers fellas

 

Danny

I second that the O2 sensors won't cause detonation... I would get a pressure check done on the fuel system and make sure the pressure regulator is doing its job properly. The problem with doing an O2 diagnostic is that if there is a fuelling problem then the O2 sensor will read as faulty even if its not

 

Interesting problem though....

 

CheerZ,

 

Andy

Check all your heat shields ! - If it is one of them vibrating that is causing the problem then you are gonna be pissed !

 

If you know someone with a Techtom try and get them to hook it up and go for a drive - As posted somewhere in all this the Knock Sensor will detect detonation under 3K and this will be reported on the Techtom if you have it configured properly - That should tell you if you are definatly gettin detonation or not !

 

 

 

------------------

Z ya

 

Nico91TT

 

Danny,

We can give this a go sometime if you're passing. As you know I have a Techtom. To my knowledge it doesn't tell you definitively that the knock sensor has detected a knock, but youn can deduce it because the BCSV's will remain OFF when the water temp is above 59 deg C

Originally posted by Nico:

As posted somewhere in all this the Knock Sensor will detect detonation under 3K and this will be reported on the Techtom if you have it configured properly

 

Only it wont in Danny's case - he said he's getting a code 34 on the ECU diag...

Don't have my book with me - what's a code 34 ?

Code 34 - Detonation Sensor

 

Danny

I'm not yet convinced its detonation.

 

Try this:

 

Drive along at around 30 mph, with O/D on and the hold button ON!...then floor it. The hold button will stop any kickdown thus retaining high gear. Now record at what revs the "noise" starts and finishes. Let us know.

 

Ideally, I would like to hear it to a) determine whether it is detonation and b) determine how many cylinders are invloved. 1 cylinder would suggest something like a faulty injecter that starved a cylinder and then smoothed out as it increased flow or a faulty spark plug. All cylinders affected would suggest a wide number of different causes.

 

It may also be an idea to check the condition of each spark plug. Look for over heating, white or very light grey.

 

I think you will find that the open/closed loop principle does not work just on revs but a combination of revs and throttle postion - it depends how hard you are accelerating. Its definitely all pre-mapped at WOT despite the revs.

 

Where are you based?

 

Andy

 

 

Right, done a bit more looking into this. Checking in the service manual there seems to be an indication that the fault could be the EGR valve or associated bits.

Looking at these it boils down to either an air leak, faulty egr, or oil getting into the bores.

 

Hope this helps,

 

CheerZ,

 

Andy

Az,

Just realised what you meant. The 'normal' state of the BCSV seems to be OFF. They are only enabled when the throttle is open and once the temp goes above 59 deg C, thereby allowing them to raise the boost above the 7psi standard. Puzzled me at first, but this seems to be the only sensible explanation for what the Techtom displays.

Yep that was my understanding too.. However it was also my understanding that if the ECU was reading a code 34, you'd be permenantly stuck in safety boost, detonation or no.. So the BCSV's would always read OFF no matter what..

Yup. That's exactly what I meant by you could deduce that knock had been detected because the BCSV would stay off. It would be an interesting test ...

Yeah but if he's getting a code 34, the ECU can never detect the detonation anyway.. and if it's stuck in safety boost (because it's getting a code 34) then the BCSV's will only ever be off, and he'll never get full boost..

 

Hmm would be interesting to see if he's actually in safety boost..

Ho hum .... I thought that the ECU reset the 'knock' status each time it was turned off, but the memory of the condition was retained for 50 on/off's - that can be recalled only through a Consult.