3.5, strange acceleration issue at 100mph+

[Rooney1000]

Hi all

Was out tonight in my 2018 3.5 Atom and have an issue that hoping someone might be able to help with.

Whilst driving the car accelerates quickly through 2nd and 3rd but then 4th, as it starts to get towards 85mph upwards starts to slow down, almost like despite pressing the throttle down hard it is like I am not ! Then, when up to 95mph and then into 5th the car will get to 103 / 104 mph but wont go any faster. It sounds like it is, supercharger screaming, but the car doesnt go any faster ! I felt it a couple of times early in the drive when in 4th, felt like a lot of noise but no real go and those speeds and then on some 'testing' on the drive back it really didnt want to go any faster.

Anyone experienced this before ? As above 2nd and 3rd feel quick, as quick as they should be I dont know, but real issues at the 95mph + area.

Nothing changed on car, had to put £10 of normal unleaded in the car the other day but back on super unleaded tonight so cant believe that could cause this (and as above, 2nd and 3rd feel quick). Will phone factory tomorrow as well, just hope nothing they need the car for as 4 hours away

Thanks
Chris

[John Scherrer]

Doesn't seem like engine issues, more like brakes binding or hub bearing seizing?

Can you do a test drive and dip the clutch - Does it seem to free wheel ok or slow down. After the drive, check that there's no excessive heat on the brakes and that there's no evidence of oil seeping out of the wheel bearings.

Jack the car up and check each wheel seems to spin freely ?

Nothing stuck in the air intake area?

Strange one.

[Rooney1000]

Thanks for your reply. Checked this morning, nothing in the intake area and when driving and dipping the clutch the car just coasts as I would expect, no slowing down unless on a gradient etc. Can't see any oil seeping out either.

I think the car is slower all round, used app to record acceleration and where-as normally would hit 60 in around 3.5 secs this morning it took 5 ! Sounds fast and feels fast but obviously isn't (felt like a boy racer).

[K20A2]

Did you perhaps check the oil level?
If the oil level is too low, VTEC will not be activated.

[Rooney1000]

Yes checked the oil level, both cold and a few mins and it is sitting in the middle of the two notches so assume fine. I also added some oil the other day so not sure it is that?

[wasp]

Could it be supercharger belt slipping? When was it last replaced?
I have seen it have a similar effect previously.

Cheers,
Stu

[Rooney1000]

Never replaced, only had the car a few months, private buy but serviced at factory before i got it. Its only done 4,000 miles and is a 2018 car so be surprised if it needs replacing ?

Spoke to the factory, they thought it could be that the cat has broken up and got some parts lodged in the exhaust, just taken that off but all looks fine (i think).

Hate it when things go wrong !

[wasp]

If parts were lodged in the exhaust then it would probably do the same at the top of the rev band in all gears I'd have thought?
Phone Rookie back at the Factory and ask him if it's possible.
They are amazing techs there but wouldn't change something like the belt if it didn't look worn.

Hope you find the solution, 3.5 s/c cars are fantastic cars and usually bulletproof.

Cheers,
Stu

[Rooney1000]

So Ariel think this is the cat. The honeycomb part of the cat inside it is loose and moves around, not broken up yet but on the way and probably restricting gas flow. Hopefully that's the case. £600 + Vat though..arrgh. Cat bypass only £120 but no MOT pass.

Hmmm !!

[John Scherrer]

Get (or borrow) the Cat Bypass pipe and retest. If it makes no difference, it’s not the Cat itself.

[Rooney1000]

Is it illegal to run a cat bypass? You need to tell your insurance company don't you?

[Atlarge]

It’s probably not strictly street legal without the cat but I think you’d probably have more trouble explaining away 100+ mph if stopped by the old bill!

[John Scherrer]

You only need to run it down the road for a mile or two, then take it off.

[Rooney1000]

Yes but Cat is bust regardless, the catalyst / honeycomb part is loose which it isnt supposed to be so I would need to replace (even if that doesn't fix the original problem - would still need a new cat unless I go the bypass route).

[K20A2]

If you are a club member you could perhaps borrow the club catalyst for testing if this option still exists. (?)