graham_mitchell

I googled this one, I'm sure you can find more: http://www.autotest.org.uk/ (under 'engine diagnostics')

GabiOsz

Thanks again for the advice, my car is booked in tomorrow to have the O2 sensor changed by a porsche trained independant mechanic, I'll have a chat with him and get him to investigate the problem.

Graham, thank you I did find autotest a week or two ago after my post about it, I may have to give them a call once I have have the mechanic look into it.

Interestingly, if I rev the engine a little (to 1,500 rpm) and turn it off as the revs are falling I never get this problem, I hope this dosen't harm the engine.

ASH.PALIN

Hi Gabi

Had an awful time with deiseling/detonating after a 24k service at JZ machtechs, they tried their hardest to sort it out but were unable to do so, ie they could find no faults, The car felt as if it was being choked under load or on aggressive or mild acceleration. anyhow, on this site was a posting about an inlet y branch on the varioram system which collapses with age and once I cleared this the detonating seems to have stopped and the car accelerates far better...................back to her old self.
Also, just for your info JZ machtechs do an injector overhaul using an ASNU system which I had done on my old 964 (£130-150+)
I dont know if your car is a varioram but my detonating seemed to be an induction rather than an ignition problem..........seems to be fine now
good luck

Ash

GabiOsz

Ash,

My car dosen't have a vario ram, but it is possible that there may be a vacum leak or some problem with the inlet system. I was having detonation under acceleration with the performance chip installed, Steve W. suggested changing the O2 sensor, which is being done tomorrow in Hampstead, I wonder if its all related? A little more food for thought anyway.

Where exactly is JZ Machtech in relation to London, is it near Reading or something? I may take them up on the injecter overhaul if this problem contiues.

I wonder if the fact that I am using a cone filter would cause any of these problems?

ASH.PALIN

Hi Gabi

Machtechs are in kings langley M1 junction 6 / west bound m25 (1 junction A41 turnoff)
follow signs for kings langley swing a right at the roundabout and then a left at T junction about a mile after Machtechs are on an estate(left turn) just before the railway bridge.
07000 100911
They have a sort of informal diagnosis day on saturday where you can just tip up and chat about your old bus and get free advice........they're always helpful Chris Boys is the workshop manager and very Knowledgable Steve and Jonas are not usually there on sat
Hampstead??
I found that Mario wasn't great for me (964), and he ripped me off!

Just my opinion

all the best

Ash

maurice97C2S

Gabi, have you had your engine wiring loom checked / replaced for the recall ?

cheers, Maurice

GabiOsz

Maurice,

The car went in to the OPC west London for the recall shortly after i bought it, I am fairly sure that they replaced it....... No change.

ASH.PALIN

Gabi,

Have sent you a PM

Ash

GabiOsz

Well, a new oxy sensor seems to have cured the problem with shut off. However I replaced my chip and there is still a clattering noise at 2000rpm - 3500rpm, and when I put my foot down last night there was a large cloud of smoke that came out of the exhaust, what causes this?

Steve Weiner-Rennsport Systems

Gabi:

Put the stock chip back in until you get to the bottom of this. These cars do not detonate with the street-gas chip that I have unless there are other things going on here.

Have the A/F checked on a rolling road to make sure that its not horribly lean from a vacuum leak. Sometimes the rubber boots at the bottoms of the intake manifold and the head flanges will leak air.

Running the engine and spraying a bit of carb cleaner at those junctions should show whether or not its admitting false air.

GabiOsz

I think I had better .

Where exactly are the junctions that I should be checking with the carb cleaner? The vacuum system is something I had not realized was there let alone important to the fuel system.

I'll try and find a dyno near me, thanks for the advice, I like the chip very much it's just a shame the car sounds like a tractor from time to time with it in there, the car hasn't quite run right since i bought it, it has nothing to do with the chip i'm sure.

ASH.PALIN

Hi Gaby

Still in trouble i see.............i know that detonating is a real pain in the ****!!
As I said to you before, once I'd sorted my vacuum hoses etc (as Steve has outlined) it has stopped completely it's just not an issue anymore And it treally was one, it was cured via this website.............Mario should sort this out for you!!.........it's not a to big deal to sort out the vacuum advance on a non varioram model

good luck!

GabiOsz

Is this something I can check myself? I just need a little more detail. If not then it will be a trip to Mario.

Steve Weiner-Rennsport Systems

OK,.....

Looking at the engine, you'll see rubber sleeves and clamps at the bottom of the 6 branches of the intake manifold. These are prone to leak over time as well as the flanges that attach the intake manifold to the heads.

Using a can of carb cleaner, spray a tiny bit at each junction and listen carefully for a change in idle speed. If the idle jumps up a bit, you've found a vacuum leak that allows extra air to get into the cylinder and lean it out. Tighten the hose clamps and flange and test it again. Do this for all 6.

After that, you need a pro.

GabiOsz

The mechanic checked for vacum leaks and there is no false air being admitted, but he cleaned the air mass meter and things seem to be running very well now