MK1 G10T Plug and Play Fuel Cut Solution

Only for the die hard, committed G10T MK1 aficionado's still left out there.
Old news, old parts. But, new hands on update.
So I like to make big power with old technology, using mechanical mods
to manipulate factory electronics and make the most HP utilizing the
stock electronics. The fuel cut has always been an issue and though I
was referred to a swap solution years ago, it has sat gathering
dust until recently.
It appears the Toyota MR2 VAF swap is quite effective.
It uses the same connector, appears to maintain an
adequate A/F ratio, and requires little modification.

After modifying and adjusting the OE VAF, and struggling with
it to have a device cooperate and provide acceptable results
for a daily driver, the Toyota VAF is surprising.
I purchased an off the shelf air filter flange, and a suitable K&N
cone filter that would allow enough room for mounting after
analyzing almost every filter K&N had to offer. Also sourced the
correct sized silicone elbow for mounting/fitting on my application.

So far so good. I need to make a mount for the VAF to eliminate
vibrating noises, but everything fits in my application.
I had modified the OE VAF airflow bypass valve, and spring tension
to suit my specific needs and was happy with the results, though
periodic adjustment was needed due to frequency of driving,
ambient temps/time of year in SoCal. For the most part the results
were good, as long as I drove it frequently. It seems as if the car
sat for weeks at a time, I would have to loosen up the VAF flap
spring to get it to idle ok, whereas if I drove it weekly or more
the car was more cooperative. Quicker to start & stable idle.

I was getting decent results, though a bit rich on WOT, and the
occasional fuel cut due to excessive airflow. But since I hadn't
serviced my air filter in at least a year, the fuel cut was only
occasional under high load/airflow or during those misty, cold
dense air days/nights due to the extremely dirty/clogged filter.
Finally swapped the MR2 VAF and K&N filter combo and things
seem to be good.

Instead of running a 10:1 A/F ratio @ WOT, now I'm getting at max
11:1. This should help unnecessary fuel consumption, as a recent
oil change indicated the oil was soaking up the rich condition
evident by the pungent odor of the crankcase oil, while still
providing enough fuel at WOT to eliminate detonation.

So the big bonus here, is that the Toyota VAF doesn't contain the
means to initiate fuel cut. Further testing will confirm this.
Of course you will need to get the earlier model unit, as the later
model unit reverses the voltage output, but it can be a super easy
swap with only a few mods needed to adapt the ID/OD couplings
for your setup, and a creative mounting solution.
i wonder if this would work with the mk2 t3...same vaf / fuel cut issues....
need to find me an mr2 for a donor...

excellent write-up!
According to [usermention=55]@suprf1y[/usermention] there is no fuel cut.
I have this great cam and cant use the 1500 rpm where it works best.
[usermention=85]@blueturbofly[/usermention] For the MKII the trick was to get one of the Toyota air meters and swap in the electronics of the MKII meter
Fuel cut is initiated when the vane in the airflow meter (VAF) reaches the
near end of travel. This indicates a large amount of airflow which the
ECM interprets as abnormally high supercharger pressure, and momentarily
cuts the injectors off and activates the check engine light and stores a code 31.

This can be caused by a number of factors such as, modified air box, modified
air filter, larger diameter air intake tubing, weak airflow spring, modified exhaust,
modified head, larger valves, manifold porting, modified turbo, increase in
boost pressure via boost controller, cold/dense/high humidity ambient air
and perhaps a few other factors.

You cannot (should not) restrict the travel of the vane in the airflow meter
to prevent extreme travel as this will eliminate supplemental fueling and
you can go lean real quick under load. You can increase spring tension in
the airflow meter to prevent/delay extreme travel which will trigger the fuel cut.
However this can cause other issues that need to be compensated for, such
as adjusting the factory sealed bypass airflow to allow more bypass air
to maintain a stable idle. Adjusting spring tension will also skew the info
the ECM perceives as actual airflow, so you need to monitor A/F ratio with
an accurate on-board real time monitor and ensure your fuel ratio is adequate
by means such as proper injector size selection, modified fuel pressure or
modified fuel pump or a combination of above variables/components.

Fuel cut is referred to several times in factory literature, however there
is some translation and understanding required as the literature states
that the ECM monitors for abnormally high boost pressure, which in fact
is not exactly true. There is no actual measurement of boost pressure, other
than the dual diaphragm distributor that when under boost, will retard
timing due to the nature of the twin diaphragm one of which advances
timing and one of which retards timing under boost, while at the same time
signaling the ECM via the ignitor to illuminate the green 'TURBO' lamp on
the instrument panel tachometer, a feature unique and special to the
MK1 T3 Turbo Sprint and variants. So the literature states it monitors
boost pressure to initiate fuel cut, when in fact it is really the extreme
travel of the airflow meter valve. Switching to an alternate model VAF
which has the same voltage output scale seems effective and the mod
airflow meter does not contain the electronic features that will trigger
the ECM to cut the fuel injectors.



they didnt actually go into such detail in the book, they kept it it wouldnt be as confusing to the ''tech'' fixing it....just replace the vaf, instead of opening it up and fixing it....

i am happy with the 10 psi i get out of my modified t3...
None of the reference data even refers to the airflow meter as the root
of fuel cut. They infer the system to be more sophisticated than it is.
If you have a working knowledge of these systems, and an understanding
of general auto mechanics and principles, you can pretty much figure it

It's great having these forums and discussions available through the
years, I've actually learned a lot. It's also a huge bonus to have not
only the FSM, but also all the supplements and technical data I
could find. I refer to these often to remember what I've forgotten.

But honestly, it's really the want and need to know. Having owned
one since the day I bought new from the Chevy Dealer, I've logged
over 1,000,000 miles on my daily driver and handfull of of other
T3's I'm attempting to maintain.

That describes over-boost. My system stock will not go over 6500rpm.

fireflyse, I think you're missing the mark here.

I've just explained and documented the relationship between high boost
pressures and fuel cut for the MK1 T3.
If you are having this issue,
briefly cuts the injectors off and activates the check engine light
the trigger and cures are above.

If not, then perhaps you have a different issue.
Interesting. Yeah I'm not well versed in MKll stuff.
Some things overlap, seems like the fuel cut/overboost code might
carry over, but I'm guessing.
I do know 6500 is the Redline on the tach, also know the aggressive
cam I got from Mike has a powerband that would cut off around
that RPM.
If the fuel cut is triggered by the flapper travel, don't know why
things would change for MKll, but sorry, I got nothin for you.
I'm specialized up to '89, nothing later.
That would have been a question for T3 Ragtop.
I have over boosted the engine and set the code so I agree with all that you wrote about it, that carries over to the MKII. However I have added a vane stopper and adjusted the return spring on the air meter with stock boost and cannot overcome the 6500rpm fuel cut. No one I have encountered has been able to so far. My 3Tech cam would still be making power to 8000rpm if I could get past the fuel cut. Richards Blue vert was a stand alone so he could programme his own rev limiter.
Toyota MR2 1985-1986

(I believe I have this info with pics posted somewhere in another post)

Thank you to Rolajoint (Teamswift) who originally shared this mod with me
years ago on the TS site via PM. It's a shame we lost all our PM's when Jard
let the site laps before Ivan acquired it, I never thought to back them up.

So a side note, this mod worked perfect. I had bought the MR2 used maf on Ebay,
and it sat for many years before I installed it. It worked fine for several months
then one day my AF gauge told me zero fuel at cruise speed.
I nursed her on the journey, and completed my trip and return trip home
by 'snapping' the throttle when fueling failed, and fueling resumed, failed,
and repeated procedure. I purchased the above replacement MAF, which still
sits in the box, yet to replace the used ebay purchase which I assume failed
while in service. I need a CA smog cert to get tags, I've not been motivated to
to put er back in service due to this and all the issues in the last 3 years due
to Covid. Any side help would be appreciated ;)

Caution though on Rock Auto purchases, I bought a rebuilt distributor
for a MK1 T3 on Rock Auto, just because they had one, and it didn't work.
I'm just sayin if you buy a rebuilt MAF, make sure you get a warrantee,
might be better off with a used OE, it's a 50/50 chance I suppose.
I don't know anything about MK1 stuff, but fuel cut sucks. Is the VAF just sending a signal to the ECU when it is open all the way? I remember on my mx6/probe GTs that people would do a VAF hack to trick the ECU in thinking it wasn't open all the way. I don't recommend even with a functional wideband o2 sensor. Was there never a chip made that removed fuel cut? I would contact the guy from Redline who made chips to see if he ever made anything for the MK1 ECU. I'll see if I can find his contact.
This has been covered, again and again.
But, basically when the VAF reaches the far end of travel, it initiates the fuel cut.
It triggers the code that says excess boost pressure, which is not true.
There's nothing that measures the over boost, but the way the system is designed,
they figure if that much air is traveling through the VAF, then the boost must be
too high, so it triggers the fuel cut. If you do modifications to increase the intake
air flow, this will also peg the vane under boost and trigger fuel cut,
as well as driving on cold, foggy mornings under load, the dense air mixture will
also be more likely to peg the vane and trigger the fuel cut.
As far as I know, there is no RPM activated fuel cut. I've missed plenty of shifts
and pegged the tach, I've never experienced fuel cut due to that.
If you tighten the spring in the VAF, you can sort of trick or delay fuel cut and it
will allow you to run higher boost, but too tight will lead to idle issues as there
is not enough airflow at idle to overcome the spring tension, and your car won't idle
because the vane isn't moving and and there's not enough airflow to sustain a good
idle, so you have to remove the plug for the air bypass valve and adjust it for more
airflow to sustain an idle, but if the spring is too tight the vane won't move and
tell the ECM to provide fuel so it will idle lean because there is no fueling.
Basically you need to find the middle ground and find the setting that works
best to sustain an idle with enough fuel and and support high boost without
activating the fuel cut. This would be on applications where the the boost
is well above the stock 5 psi, more like 15 psi. There's no way to know if the your
fueling is an issue unless you have a good A/F gauge, otherwise your just guessing and
there's no way to find the happy medium.
If you block the vane from traveling, then you won't get the fuel cut, but you won't get fueling either under load, under boost. So you will run lean and blow a piston.
You would never know, unless you have a good A/F gauge which will tell you that
you are running extremely lean under boost, whether it's stock or modified,
if you block the vane, you're asking for trouble. You need an onboard A/F gauge
to make sure your fueling correctly, if you actually have one then you know exactly
what I'm talking about, if you don't then I just can't explain enough what a valuable
tool it is to tune your ride. Install one, and learn how to read it and understand
the concept, it's eye opening, it will tell you exactly how your fueling works under
all driving conditions, start, warm up, WOT, open loop, closed loop. You will learn
exactly how the systems work, you won't learn this from the FSM.

If you want to avoid fuel cut without all the mods, tweaks, adjusting and headaches,
then install the MR2 VAF, make sure you have a good A/F gauge to make sure
everythings fueling just how you want.
I prefer the analog style one with the needle, I think it's easier to read than
the digital one, unfortunately it looks like the AEM uego one is no longer available,
but there are other similar ones on the market.
You can do what you want, and yes I have a wideband o2 sensor in my car that needs it. On my Probe GT turbo chip which runs a VAF and has fuel cut in the same way they just changed the code on the stock OBDI chip. What I'm saying is there are still a few guys out there that have the hard ware to flash those chips. I'm just not sure if anyone did it for the MK1 chips. They open the data set and take the voltage input (or signal) from the VAF and change the programmed output. If the MR2 VAF works and you have one it is a done deal unless you want more control which a standalone would be a better choice.

I missed the entire first page of this thread. I thought it was a weird post. It makes more sense about already going over.