G’day guys,

This is my first time posting so please go easy.

I have owned my 2006 350Z Touring MT with the Rev Up engine for a little over 4 years with 97,000KM (approx 60,000 miles) currently on the odometer.

The car is standard except for the following mods:
• Full header back exhaust with Outlaw 200 cell metal high flow cats
• Motordyne MREV2 lower plenum and 5/16” plenum spacer
• BC Racing BR coilovers
• Uprev dyno tuned (242whp)

Unfortunately, I’m facing what we believe to be spark knock when the car warms up after about 10-15 mins of driving. There is a significant drop in power like timing is being pulled but no CEL comes on. The car continues to be down on power for the rest of the drive, and even when it is restarted, unless I allow it a few hours to cool down. All through this the temperature gauge never climbs above halfway and there are no other symptoms.

The car is also only ever pumped with 98 RON (I think the US equivalent is 93 or 94) and I have tried a few different petrol sheds.

The issues began recently when I had the MREV2 and plenum spacer installed, and the car dyno tuned.

Suspecting a bad tune, and after getting the run around from the initial tuner, it has since been to a second tuner who confirmed that it was in fact pinging and advised that I should change my cats in case of a restriction.

However, after pulling off the old cats, the exhaust shop and I noticed that they seemed to be ok and that daylight could be seen through them. I also had a look at the fuel pump and filter before that and could see that it was quite clean as well as the fuel tank itself.

Since installing some new cats, the second tuner was able to retune the car on their dyno, apparently without it knocking, but advised that they were unable to put factory timing in it and as such compensated for it with more fuel.

Unfortunately, I have noticed a continuation in the severe drop in power after 10-15 mins of driving and am wondering if there could be any other causes for this. I’ve booked the car in to be checked over again by the second shop who are suspecting the new cats as a possible cause but I’m just a bit unsure.

It’s currently winter in Australia and I have noticed that the issue seems to be worse in warmer temperature than when the temperature outside is cold. I think it takes more like 30 mins for the issue to occur when it is cold.

I’m wondering if there are any other causes that could be behind this. Could the plenum not be installed correctly and causing this? Could there be carbon build up somewhere other than the cats that’s causing this? Could it be something completely different?

I’m racking my brain trying to get to the bottom of this and it’s frustrating not being able to drive my lovely Z at the moment.

Any help here would be greatly appreciated.
Thank you all in advance.

 

Its probably in the context of your post (and I missed it) but the car drives normally until you reach operating temp (~100c)?

Does the car drive normal (while warming up) through the entire rev-range?

Have you done any other work (maintenance / mods / repairs / etc) on the car since this problem has arisen?

Can you look at your coolant temp sensor?

can you do a full inspection of your engine bay harness?

 

Yes it does, the car drives great until it gets above 95 C and then at some point after that there is a sudden and significant drop in power.

Watching the coolant temperature on a scan tool, the readings seem to stay within normal operating parameters so we’re not suspecting a coolant temperature sensor at this point.

Since this first started, we have tried different OEM MAF and front O2 sensors (the rear ones are disabled with Uprev) to try and rule out possible causes, but the issue has persisted.

Apart from that the only other thing is that it has had its regular oil change.