[BryanPendleton]

Alright, bear with me. I am not a Supra owner, but a good friend of mine just picked up a 89 Turbo Supra from Florida and drove it back to Texas. He is not to familar with the car nor am I, but I consider myself knowledged in general turbo systems, engine managment, combustion engines, etc. With that said, the car supposedly has a j-spec turbo motor swaped into it. It is also equipped with an aresenal of bolt-ons, including a Greddy Profec B boost controller. With the EBC off, the boost pressure peaks at ~5psi. With the EBC turned on, and as we begin to increase the boost, the ECU appears to be cutting fuel or ignition at ~6psiTurbo, as we "hit a wall" as soon as boost begin to exceed ~5-6psi. I am not 100% sure the "wall" is boost dependent, but from our experiementing it certainly seess so. What is manifold pressure regulated at on a stock 89 turbo? J-spec turbo motor? I am not aware of any piggyback electronics, but I will be checking things out soon. Just looking for some ideas on possible areas to look.

 

[Woooossshhh]

he is hitting fuel cut... what other supporting mods does this car have? exhaust? he might have a boost leak.. give us somemore info on the car... also is it a 7mgte or 1jzgte?

 

[SuprAng]

boost leak... sucks, but try and find what in the induction system is causing htis...

 

[Ricer]

Ill go with a boost leak also. Check all intake related piping. HTH

Jake

 

[BryanPendleton]

he is hitting fuel cut... what other supporting mods does this car have? exhaust? he might have a boost leak.. give us somemore info on the car... also is it a 7mgte or 1jzgte?

Motor is 7mgte. What I do know at this point from my brief observation at night, is the car is running a 3in exhaust, HKS SSQV BOV, Greddy Profec B, Greddy Turbo Timer.

 

[Woooossshhh]

yeah check for a boost leak... those 11+ year old rubber pipes tend to crack.. especially under higher boost

 

[BryanPendleton]

If there is a boost leak, why would the ECU be cutting fuel? Does the 7MGTE ECU use MAP's or MAF sensors, or both. Looks as though it uses a MAF sensor?

If there was a leak in boost, I would think that the boost pressures would simply be limited, do see why ECU would cut fuel, or how it would know there is a boost leak.

 

[BryanPendleton]

yeah check for a boost leak... those 11+ year old rubber pipes tend to crack.. especially under higher boost

Certainly worth checking through, but this car appears to have some custom plumping and is using mostly silicone hose connectors.

 

[werkkrew]

It uses a Karman style AFM...

No map sensor

The ECM cuts spark if the air flow frequency exceeds 1500hz...if you arent leaking boost, and youre getting enough fuel then its usually around 12psi.

Check all the hoses for tightness, check your FPR, and check the fuel filter

The FPR hose is on the front of the valve cover on the side with the battery, its a little thing on the end of the fuel rail.

 

[BryanPendleton]

It uses a Karman style AFM...
The ECM cuts spark if the air flow frequency exceeds 1500hz...if you arent leaking boost, and youre getting enough fuel then its usually around 12psi.

Good info. I am not familar with the Karman AFM. Does it use hot-wire filaments to measure the mass air flow rate? Or what?

Also, "air flow frequency". I am confused on that one. Air flow frequency is not a parameter of fluid dynamics I am familar with. Are you perhaps refering to the measured resistance of the AFM sensor itself? If so, then 1500hz must correspond to some calibrated mass air flow rate or volumetric flow rate, but again, I am not familar with the Karman AFM.

 

[BryanPendleton]

Alright, did a google search and quickly turned up info on the Karman AFM.

The Karman AFM use a wire or "strut" to generate turbulent vortices which a sensor then counts the frequency of the vortices. The frequency of the vortices are proportional to volumetric flow rate. So 1500hz appartently corresponses to a specfic volumetric flow rate. Which makes sense. The ECU generates a fuel cut at a "threshold" volumetric flow rate.

 

[werkkrew]

The Karman AFM montors the air passing through it VIA a sensor in the center (im not sure EXACTLY what the sensor is composed of) then it sends a square wave signal to the ecu which is the volume of air. The faster the wave, the more air. When the frequency of that wave reaches 1500hz, the ecu cuts spark. This volume of air, on a stock turbo is USUALLY equivialent to ~12psi. Depending on a number of variables including weather, but you should be at least seeing 8-9psi on a totally stock turbo with no boost control.

When you turn the boost control on, you should see 10-12 before fuel cut off.

There are a number of ways around this fuel cut off but I think you should get it working properly before you explore those options.

The reason everyone thinks you have a boost leak is becasue the AFM is seeing that volume of air, but the intake manifold isnt. So obviously somewhere in between theres a problem.

 

[BryanPendleton]

hmmm. . . so if we only have ~5psi of manifold pressure at rpm's on the order of 3-4k, I could not imagine that we have exceeded this AFM threshold and we haven't exceeded 6psi, so I still don't understand why the ECU would be cutting fuel.

 

[werkkrew]

well...check your fuel supply, check fuel pressure.

Still. What im saying is, youre seeing 6psi, the afm might be seeing a much larger volume because in between the afm and the manifold air that the AFM tells the ecu is there, isnt actually there because its leaking out of the piping some place

 

[BryanPendleton]

The reason everyone thinks you have a boost leak is becasue the AFM is seeing that volume of air, but the intake manifold isnt. So obviously somewhere in between theres a problem.

Duh. . . your abosolutely right. the 7mgte is a draw-through setup up, so the AFM is metering atmospheric air (ie. pre-turbo) and if there is a leak, then . . . yadda yadda yadda. . .

I'm used to MAP sensor turbo cars. . .

Thanks guys. . . I knew you guys could help.