why use lexus LS400 AFM

[rodgill]

Having found that the Lexus AFM aint cheap, i decided to experiment with an
AFM bypass tube.
I found that a 1 3/4" pipe with an adjustable restrictor does the same job, as
it can by-pass the AFM by the 27% required by the bigger injectors(550cc>).
I've set this up on my 1990 7M-GTE to lambder of .98 and it go's like stonk! :)
The Co% at idle is adjustable from .6% to 2.5 (no cat) and stay's around
the 1.2 to 2.8% at 1200 to 5000rpm (no load).
I have also fitted a Bosch 16LTR/min Fuel pump designed for BMW 850. :yes:
Up to now everthing seems to be ok.If there are any big bang's i will let you
know. :crybaby:

[Bondango]

Having found that the Lexus AFM aint cheap, i decided to experiment with an
AFM bypass tube.
I found that a 1 3/4" pipe with an adjustable restrictor does the same job, as
it can by-pass the AFM by the 27% required by the bigger injectors(550cc>).
I've set this up on my 1990 7M-GTE to lambder of .98 and it go's like stonk! :)
The Co% at idle is adjustable from .6% to 2.5 (no cat) and stay's around
the 1.2 to 2.8% at 1200 to 5000rpm (no load).
I have also fitted a Bosch 16LTR/min Fuel pump designed for BMW 850. :yes:
Up to now everthing seems to be ok.If there are any big bang's i will let you
know. :crybaby:


But when you stock Karman signal gets to its limit you will get fuel cut. even if you are by passing it by 25%. The LEX AFM will not hit fuel cut until 25% above the stocks limit. So using the bypass valve u wull also need an FCD defender :bigeyes:

[Anh]

By passing 25% air from the AFM doesnt mean 25% extra boost. It's actually 25% extra PSI of total manifold pressure @ x air temp. So if fuel cut kicks in at 12 psi, it would mean a total PSI of 26.5 psi in the manifold. A 25% raise by a bypass would mean manifold pressure may increase upto 33.1 psi - which is 18.6 psi of boost untill fuel cut @ x air temp.

Anyway, the toyota ECU reports a too lean condition if you exceed 30% so any form of bypass within that tolerance is possible.

[Lofty]

I think people go the Lexus route because it is tried and tested. Leaking air past the AFM is OK but the effect may not always be linear. It is possible to leak air using the PCV hole in the accordion hose for example, but there is no way of knowing whether it is leaking too much air at lower RPM and too little at higher RPM. With a larger AFM the effect will be linear, if possibly restrictive. Part of the reason the Lexus works is because it has a proportionately larger air bypass than the stock AFM.

rodgill Any pics of your bypass?

Also it is unlikely that you can "adjust" fueling at anything other than idle and WOT as the ECU will eventually compensate.

[rodgill]

I think people go the Lexus route because it is tried and tested. Leaking air past the AFM is OK but the effect may not always be linear. It is possible to leak air using the PCV hole in the accordion hose for example, but there is no way of knowing whether it is leaking too much air at lower RPM and too little at higher RPM. With a larger AFM the effect will be linear, if possibly restrictive. Part of the reason the Lexus works is because it has a proportionately larger air bypass than the stock AFM.

rodgill Any pics of your bypass?

Also it is unlikely that you can "adjust" fueling at anything other than idle and WOT as the ECU will eventually compensate.
Yeah, i can see that it may not be linear,so i am going to put a resitor divider
network on the AFM Signal OutPut lead instead of a Bypass Tube.
That way it will be a linear Reduced Signal to the ECU.
It aslo seem's that the ecu can only handle an ign retard 10 degs BTDC,
therfore i am going to try a programmable retarder so as to increase boost
without Knocking. :)
The fueling can be adjusted by modifying the lambda sig & TPS with either
a resister network or a programmable PIC circuit. :flush:

[Stuart B]

Yeah, i can see that it may not be linear,so i am going to put a resitor divider
network on the AFM Signal OutPut lead instead of a Bypass Tube.
That way it will be a linear Reduced Signal to the ECU.
It aslo seem's that the ecu can only handle an ign retard 10 degs BTDC,
therfore i am going to try a programmable retarder so as to increase boost
without Knocking. :)
The fueling can be adjusted by modifying the lambda sig & TPS with either
a resister network or a programmable PIC circuit. :flush:

a resistor will not work on the supra as it is a frequency output...the frequency is the key item not its voltage....resistors will not change the signals frequency!!!

I MUST STRESS THAT MESING WITH THE AFM IS VERY DANGEROUS FOR YOUR ENGINE...AT WIDE OPEN THROTTLE IT DOES NOT USE THE LAMDA, ONLY THE AFM...THIS MEANS IF YOU HAVE TRICKED THE ECU THAT LESS AIR IS COMING IN (WHICH IS WHATY U ARE DOING), IT WILL AD LESS FUEL....MENING THE ENGINE RUNS LEAN AND POSSIBLE MELTS. :banghead:

When the lex afm is used 550 injectors ARE required at the same time as they supply more fuel, or as in this case the same amount of fuel for the new shorter duty cycle that the ecu feeds them than they would have got on std inj/afm.



Stu