[1jzgte-MA70] I keep hitting the FC on cold days(night)

[shipkiller]

basic mod:
jza70 engine and ecu
3" stainless y-pipe with 3" downpipe and 3" muffler (stock cat on the line).
2.5" intercooler piping with 3" big driftmotion intercooler.
safc II
that's about the end of relevant mods.

I hooked up my boost controller and put it on the lowest setting. Now, on a hot day I can boost all fine to 11~12 psi no problem, but as soon as the temperature get, let's say, below 18~C. I hit more than 13psi and hit FC.

What can I do now, my MBC is on the lowest setting (and I tried with direct pressure to the wastegates like stock, still the FC when cold) and I don't think a FCD would be the anwser.

 

[Supra NA-T]

well a fuel cut defender would elimiate the fuel cut, hense the name

 

[te72]

Try removing the boost controller. No reason with those mods that you wouldn't be able to hit 11-12psi all day long anyway.

Threads like this are making me wonder if I don't have a tuned/modified ECU. Far as I can tell, the only reason I ever hit fuel cut was because of dirty plugs.

 

[hvyman]

Iirc stock fc limit on a 1j is right around 14psi. Will be sooner when it's cold out.

Bcc or fcd with a wide band and safc and 2jz 440 can boost up to 17psi with stock twins. Tho the twins might not last long then.

 

[shipkiller]

already have wideband and SAFC II.

so yeah, I think It will be the best for me to find a set of 440cc and tune down the map signal a bit to compensate, allowing for boosting a minimum without FC (something I cannot do actually)

 

[525gte]

If you still running stocki injectors you will still hit fuel cut at about 14 15. Psi.. you need larger injectors to take advatage of the the sfac. Buy tuning out fuel your changing the voltage the ecu sees from the map allowing you to run more boost .. I am at 22 psi in3rd and 4th.. but I still get fuel cut in 5th at about 17psi. I think its cuz of load on the engine

 

[te72]

Iirc stock fc limit on a 1j is right around 14psi. Will be sooner when it's cold out.

Bcc or fcd with a wide band and safc and 2jz 440 can boost up to 17psi with stock twins. Tho the twins might not last long then.

Odd... I'm almost certain I have the stock 370cc injectors, and I run upwards of 17psi, although my AFR is approaching lean conditions by then.

 

[hvyman]

i can hit 7psi on my 6262 before fc. Im still on stock gauge tho. But from memory its usually around 14psi.

It will vary from car to car and location as well. I hit 10-11 psi on my 57trim 7m with no fc

 

[te72]

If I understand fuel cut correctly, it is about how much air is flowing through the head, not a specific pressure... if that is the case, I wonder if I have a leak somewhere, and it takes 17psi of pressure to flow enough air to hit fuel cut? Like I said, already running into a minor lean condition at that level, I certainly don't want to crank up the boost any more and melt something just to satiate curiosity...

 

[destrux]

Fuel cut on a 1JZ is based on pressure. Fuel cut on a 7M is based on mass flow.

Did you really try taking the MBC off or did you just back the knob off completely? There is a bleed hole in a ball and spring MBC that will leak and cause the boost to go up 2 or 3 psi even with the MBC set completely loose.

 

[shipkiller]

I will try taking it off. but it will be a PITA since the rear wastegate is almost untouchable (close to the firewall)

 

[hvyman]

Just tee the lines together. Took me 2 min to remove a mbc off my car.

 

[shipkiller]

wouldn't the "long" vacuum line contribute to a bit of spike/overboost as opposed to stock (direct to WG from the compressors?)

 

[hvyman]

Naw. I never had that problem. Makes it easy to reinstall the mbc or ebc as well.

 

[te72]

Fuel cut on a 1JZ is based on pressure. Fuel cut on a 7M is based on mass flow.

Did you really try taking the MBC off or did you just back the knob off completely? There is a bleed hole in a ball and spring MBC that will leak and cause the boost to go up 2 or 3 psi even with the MBC set completely loose.

Thanks for clearing that up. My ecu might be tuned then... interesting, it doesn't have any indication of being tinkered with, no stickers or anything like that. No boost cut (that I'm willing to find anyway), no speed cut... hmm.

As for mine, I'm running a Turbosmart mbc. Had a ball and spring setup (what they call their 'gate system'), but taking out the ball/spring alleviates a bit of a spiking issue I had with their MBC. No worries though, this is what the instructions say to do if the boost comes on too soon/hard. I actually fixed what I thought was boost cut by replacing my plugs. 2.5 years later, as it turns out, they had a bit of oil on a couple of them (bad rings or pcv proximity from what I understand), and after replacement, runs smooth as it can.

Just tee the lines together. Took me 2 min to remove a mbc off my car.

Same here, I just teed into the existing 4-way tee on the stock turbo setup... Not even sure HOW you would get to the nipple for the rear wastegate.

 

[hvyman]

Think you could do it from the bottom but it's not worth it.

 

[shipkiller]

Update on the situation, The car has just recently been pulled out of storage.
The lines T-ed together limit the boost to a solid 12psi but between 6700~8000rpm it creeps to 14-15psi and hit fuel cut hard. I guess there is nothing I can do since the stock wastegates port are too small.
It pulls nicely at 12psi anyway.