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The mkiv Supra Owners Club

De-cat - help!


richardharmon

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I fitted my front de-cat pipe at the weekend, as I haven’t got my restrictor ring fitted yet I’ve put the baffle in the exhaust to help keep the boost down. I also fitted a TRL VFCC which seems to be working fine. My problem is that when the car hits about 1.1 to 1.15 bar of boost the engine stutters like there is some sort of fuel cut in place. The red light or the check engine light never come on. To test if it was the fuel cut I set the over boost protection on the VFCC to maximum, the problem still occurs at the *same* boost levels. I have eliminated the RLTC by simply switching it off. I have not up-rated the fuel pump or changed the plugs yet.

 

So, anyone had this problem or know what is causing it, I suspect the pump isn’t up tp the job but would have thought the effect would be more gradual, this really feels like the over-boost fuel cut, or RLTC hard cut but without the warning lights and the RLTC switched off!?

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Yep I've had the same problem since taking the front cat off (my car already had the 2nd cat out when I got it)

I've had the colder running plugs fitted by Dude and a TRL FCD but the problem persists. Also the Intercooler piping keeps blowing apart, so be aware of that too, mine did it again tonight for the 3rd time.

 

I guess it's the fuel pump, on mine at least.

I think I'll just go back to having the one cat in, it's too much hassle, seeing as I'm not thrilled about the reduced turbo life expectancy at 1.2 bar either.

 

YMMV

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Originally posted by richardharmon

I have not up-rated the fuel pump or changed the plugs yet

 

Richard, certainly dont discount changing the plugs. i was advised to do this when i decatted and had the exhaust fitted. I know of two owners who didnt and had the problem you have described. One is a local guy not on the BBS and the other Justin. Chris Wilson warned me of this potential problem so it may be worth contacting him.

 

I probably should know what my plugs are but i do not have the exact description. I know they are NGK Laser Platinum sold by CW.

 

HTH

 

Chris

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Originally posted by richardharmon

Thanks guys.

 

Chris, so have you replaced your fuel pump then?

 

No, i have CW Full Decat, Apexi N1 exhaust system, TRL Fuel Cut Defencer and the colder rated NGK Laser Platinum Plugs, oh yeah and the slag of all mods, the restrictor ring.

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I thought the likes of spark plugs not being up to the job was more of a soft cut in characteristics and the harder cut was down to fuel cut.

 

My engine light comes on on cold days and I have both cats in and running stock apart from zorst & airfilter - people reckon its still fuel cut though - just waiting to plumb my boost gauge in so I can see what is going on with theboost before I get a vfcc - stock fuel cut kicks in at 1.5 - is that right ?

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Stock fuel cut comes in at 1.0 bar and not 1.5 bar.

 

Mine's topped out at 1.4bar with 2 de-cat pipes, Nur Spec R, HKS Racing Suction intake, SBC-ID, Walbro Pump and FSE. The next thing is to fit the restrictor ring to get me down to a safe'ish 1.15-1.2 bar stock, then use the SBC-ID to up it slightly.

 

As I am only running standard Jap ceramics!! :eek: :eek:

 

Ben..

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Originally posted by far

stock fuel cut kicks in at 1.5 - is that right ?

 

I think you are getting your 15psi and your 1.5bar mixed up mate ;) Like soonto said, FC is around 1.0bar/15psi.

 

In RichardH's case, surely it is the plugs - I had colder plugs fitted as a matter of course when it was de-catted.

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Thanks dudes :thumbs: I think you are right outa' I is getting confused :stupid:

 

Anyway so we reckon you can still hit stock fuel cut on a cold day with both cats in and running just an after market zorst & filter ? :thumbs:

 

Thanks in advance

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Yeah, i think you might be hitting FC with the cats still in. Maybe only on cold days, but i'm sure its possible.

 

TBH, you need an idea of what boost you are running anyway. If you aren't hitting FC, then at least you can eliminate it as the problem.

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yep got a boost gauge which im gonna plumb in this weekend - TBH it seems to have only started when its been cold weather (last 6 weeks) and ony really happens when its at night and very cold/dense air - cheers outa' as usual some spot on info there :thumbs:

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This sounds exactly like my problem which was the coil packs. Try some IK24 plugs first though, as it did improve the miss considerably, just not completely.

If you do need coil packs, I got some from Curt Aigner at Elmhurst Toyota in the states for 270 shipped for the 6. They are over 500 in the UK.

I am led to believe that swap testing was the only way to test but I am not sure.

BTW My car has done 100k and the coils are known to get tired.

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Another one to Richard ;)

 

I had the same mate. My car came over decatted, but stock fuel cut in place so it kept hard cutting. Fitted the VFCC and it was sorted but then started to miss on the high boost. Fitted a set of Denso IK24's and problem solved - its not returned either :D

 

I also have a restrictor, no fuel pump. Varies in boost from 1.05 lowest to 1.1 normal and 1.15 on colder days. This morning with the cold damp lightly foggy air it was a fraction under 1.2 - feck the car was flying!!!!! :eek: :D (note to self, install a fog generator for front of car!!!! ;))

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