fuel cut at 16psi with a lex afm?!?! wtf?!?!

[b005t3d]

okay, im kinda pissed here. i didnt spend the time, money, and effort to find a perfect lex afm and hit fuel cut at 16 psi. could it be the fact that i have 550's with a stock fuel pump? sorry if this is a repost but im to mad to search for now. thanks for any help in advance.
boost

 

[jdub]

okay, im kinda pissed here. i didnt spend the time, money, and effort to find a perfect lex afm and hit fuel cut at 16 psi. could it be the fact that i have 550's with a stock fuel pump? sorry if this is a repost but im to mad to search for now. thanks for any help in advance.
boost

Dude...that's about the psi (16-18) any car will hit FC with a Lex AFM.

 

[supra90mkiii]

i hit 18 psi once accidentally, all that happened was my i/c piping popped off. no fuel cut.

 

[tonysupra]

16 psi sounds about right but i have seen people boosting more and some boosting less. I'd recommend getting a fpr and walbro though.

 

[b005t3d]

cool thanks

 

[87_7MGTE]

check your fuel pressure. do you still have the j-tube, or did you bypass it or drill it out? you shouldnt be hitting fc at 16 psi, should be around 21 psi or so. the fuel pump could be making trouble but i would check those things first.

 

[jdub]

The fuel injectors or the fuel pump or the fuel line volume ("J" tube) has nothing to do with fuel cut. It's the volume of intake air sensed by the AFM...period.

Fuel cut is there as a protection against an over boost...the ECU cuts fuel to prevent it and causing damage to the motor due to a lean condition. Fuel cut on a stock AFM will occur at 10-12 psi of boost...the Lex mod works (raises fuel cut) due to the larger amont of air that is "un-metered"...i.e the part that bypasses the sensor through the section with the adjustment screw. That and the larger diameter of the AFM itself. Fuel pressure and larger injectors are there as a supporting mod to prevent your motor from running lean and burning itself up.

It completely depends on your ECU and the signal the AFM electronics send to the ECU. Some will hit it at 16 psi, some at 18 psi, some might even make it to 21 psi. Mine (with the Lex mod) hits cut at 18 psi...it's perfectly normal.

 

[87_7MGTE]

i know how it works, i used to have it before i went standalone. trust me, it makes a difference. at least it did in my case.

 

[GrimJack]

The only thing that is likely to cause FC early is a boost leak post turbo.

 

[b005t3d]

The fuel injectors or the fuel pump or the fuel line volume ("J" tube) has nothing to do with fuel cut. It's the volume of intake air sensed by the AFM...period.

Fuel cut is there as a protection against an over boost...the ECU cuts fuel to prevent it and causing damage to the motor due to a lean condition. Fuel cut on a stock AFM will occur at 10-12 psi of boost...the Lex mod works (raises fuel cut) due to the larger amont of air that is "un-metered"...i.e the part that bypasses the sensor through the section with the adjustment screw. That and the larger diameter of the AFM itself. Fuel pressure and larger injectors are there as a supporting mod to prevent your motor from running lean and burning itself up.

It completely depends on your ECU and the signal the AFM electronics send to the ECU. Some will hit it at 16 psi, some at 18 psi, some might even make it to 21 psi. Mine (with the Lex mod) hits cut at 18 psi...it's perfectly normal.

by the way, fuel cut is really spark retarding in our cars. you can look it up on Mitchell on demand or alldata. thanks guys. im just kinda dissapointed then i guess. i had heard the rumors of 21 psi but i guess my lame ass piece wont make it there. time to go map or something.

 

[bigal0043]

idk know alot about the lexus afm but i read that you need a adjustment screw.. does yours have one? or do those screws just adjust for idle?

 

[The Reaper]

i didn't adjust anything. with the stock CT and 550's and a lex i hit fuel cut around 21+.

now with my bigger turbo on lex and 550's and stock fuel pump my WG is sticking and i hit 16-17 psi and it hits FC HARD!!!!

 

[jdub]

I have a modified screw...it does help with idle at first, but I'm a believer that it's really the ECU that learns the new set up and controls the motor parameters accordingly. IMO, the $$$ you pay for the modified screw is better spent on supporting mods.

If you install a Lex AFM, you can run the stock fuel and injectors, but be warned you can cause a lean condition under the higher boost...that will kill your motor. 550 injectors is what you want to run...the Lex is about 25% larger; 550 injectors are 25% larger...they balance each other out. A Walbro pump provides the flow to support the injectors...an adjustable FPR provides some very basic "tuning" ability to match fuel flow to the injectors.

Edit: Something else to understand. Each turbo is different in the volume of air it moves...for example, a CT26 moves "X" volume of at at 14 psi a SP-61GT turbo moves "Y" volume of air at 14 psi. "Y" in this case is significantly larger than "X"...since the AFM is sensing air volume, you may hit fuel cut at a lower psi than you did on the CT26 with a MBC or shim mod. The ECU is smart in this case; it knows more air is being forced into the cylinders and cuts to protect the motor.

 

[antman]

i personally don't believe fuel cut comes only from the afm. jdub states alot of relavent facts, but if that was the only factor. then it seems to me that we would all experiance fuel cut at around the same psi. with the exception of density of air, altitude, ect.. a bone stock supra will see fuel cut at 11 or 12 psi. upgrade the fuel system and you'll see 14 psi. i think the tccs takes more into acount than just the intake volume. if the computer see's a lean condition and cannot correct it. than its time to shut it down before the driver destroys the engine. just my opinion. never seen it on paper.

 

[WeDgE]

I am running the Lex/550s as well and hit fuel cut @ 15-16psi on the T78...but only when it's cold outside.

You'll be fine w/o the adjustment screw.

 

[jdub]

i personally don't believe fuel cut comes only from the afm. jdub states alot of relavent facts, but if that was the only factor. then it seems to me that we would all experiance fuel cut at around the same psi. with the exception of density of air, altitude, ect.. a bone stock supra will see fuel cut at 11 or 12 psi. upgrade the fuel system and you'll see 14 psi. i think the tccs takes more into acount than just the intake volume. if the computer see's a lean condition and cannot correct it. than its time to shut it down before the driver destroys the engine. just my opinion. never seen it on paper.

Fuel cut as we started discussing does come from the AFM and where you hit it depends on the turbo you are using and depends if it's a stock AFM or with the Lex mod. The AFM sensor (used on both) senses volume...where that volume goes after that is not sensed by the ECU...that's why a small boost leak can make you hit fuel cut at a lower psi.

The motor will retard timing also as a protective measure. The knock sensors is a good example...at high boost on pump gas if you get "ping" or detonation, the ECU will retard timing in an attempt to stop it. It may look like fuel cut, but is done for an entirely different reason. If you are running 91-93 octane gas at 21 psi, you are begging to detonate your motor and no head gasket can take that!

 

[TealMetallicDream]

boost leak?

 

[jdub]

boost leak?

Boost leak in the piping from the compressor to the IC to the throttle body. The AFM senses the air volume drawn in, but some of it escapes prior to reaching the intake manifold...makes fuel cut happen at a lower percieved psi on the gauge. The AFM is sensing the same volume as usual.

 

[antman]

thanks jdub!, but no need to repeat yourself.

 

[jdub]

thanks jdub!, but no need to repeat yourself.

Hey...I know, but sometimes saying it a different way will help him understand