Brake light switch and neutral safety switch problems

btwilson86 · 04-30-2010, 06:31 AM

Okay, I'm starting to suspect the BOV.

Stock turbo supras came with a bypass valve instead of a blow off valve. Biggest difference between the two is that the bypass valve will redirect excess boost pressure back into the intake pipe between the AFM and the turbo, meaning all of the air stays in the intake system and is accounted for by the AFM. Blow off valves vent the excess pressure to atmosphere. Our computers are programmed to "expect" that air to stay in the intake system, so if it is vented to atmosphere the engine will briefly run rich after shifting (which can cause it to chug and die) because it anticipates more air in the intake than what is actually there.

Basically, as far as the computer is concerned, each time you shift your BOV creates a giant boost leak. The only reason I can think it does it in the higher gears is because it takes longer for the RPMs to get there, allowing you to build more boost pressure thus loose more air/pressure when you shift.

jtown125 · 04-30-2010, 06:36 AM

One thing i do know...IT DOES RUN RICH!!! lol

So, lets go ahead and say its the blow off valve. Y would it not die after boosting in a single gear?

And to fix it?

btwilson86 · 04-30-2010, 06:43 AM

Well, the only thing I can think of is that the ecu has time to realize what happened and fix the fuel curve as the engine revvs down.

I was reading an earlier post of yours and you said that it doesn't die off after full boost, so I'm assuming during these times you reach a higher rpm which could help support my above statement.

Fixing the problem, AFAIK, would require either tuning in some way (piggyback ecu or something along those lines) or replacing the aftermarket BOV with a factory or an aftermarket bypass valve (they do make them). You usually don't get the same sound, but they provide better performance over an OEM one. If your donor car is a turbo and has the required parts, swap them in and go for a drive. If it still happens then that's not the problem, but I really think that will fix your problem.

FYI, when I had my 7MGTE I put an aftermarket high-flow cone filter and a AFM adapter on mine and it made the turbo spool and OEM BPV much more audible

jtown125 · 04-30-2010, 06:50 AM

I don't know how it can do it so fast though?? It is almost instintaniously.

Is there a way to reset the computer and maybe it will fix it in itself?

Since the BOV has been on for a while...y now?

I drove it home 600 miles from mississippi and not one problem.

And what was the cone shaped thing you were talking about?
how does that set up work?

BTW: The BOV is welded on to the intake.

btwilson86 · 04-30-2010, 06:59 AM

Resetting the computer is easy enough, just remove the 15 Amp EFI fuse from the fuse box under the hood. It's supposed to only take about 30 seconds to reset, but I always leave mine out for a few minutes.

I'm not sure how it could be reacting so quickly, but I do know that different supras react differently to aftermarket BOV's. Some will run just fine, some will not let you shift at all without it dying.

Wish I had more answers for you as far as why it's happening now

Since your bov is welded on, you'd have to replace the pipe if you changed the valve out. OEM pipes are plastic lol

Oh, and the cone air filter.... Basically it was a universal 3 inch air filter (like a K&N cone-shaped air filter). You remove the factory air box from the AFM and in it's place you can install an adapter that bolts up to the AFM on one side and allows you to clamp on an aftermarket air filter on the other side. As long as you use a decent quality air filter, you can safely allow the engine to quickly draw larger volumes of air into the intake, creating more power and better throttle response

jtown125 · 04-30-2010, 07:05 AM

well, I don't really want to change the whole thing, I'll go reset the ecu tomorrow when i wake up see what that does.

And i think the set up your talking about it already on there. It is a very popular aftermarket part cause a lot of the supra's i have seen are set up that way if what i think you saying is what im thinking of....lol

thanks for your help...ill post back tomorrow and let you know what happened.

cre · 05-01-2010, 03:54 PM

Check for and post codes FIRST.... then reset all you want. FYI, there's nothing but minor trim data recorded in the ECU, unless there's another significant problem elsewhere resetting it shouldn't make a noticeable difference.

I'm thinking it may be a bad IDL switch. (codes 51)

04-30-2010, 06:31 AM	#1
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	Okay, I'm starting to suspect the BOV. Stock turbo supras came with a bypass valve instead of a blow off valve. Biggest difference between the two is that the bypass valve will redirect excess boost pressure back into the intake pipe between the AFM and the turbo, meaning all of the air stays in the intake system and is accounted for by the AFM. Blow off valves vent the excess pressure to atmosphere. Our computers are programmed to "expect" that air to stay in the intake system, so if it is vented to atmosphere the engine will briefly run rich after shifting (which can cause it to chug and die) because it anticipates more air in the intake than what is actually there. Basically, as far as the computer is concerned, each time you shift your BOV creates a giant boost leak. The only reason I can think it does it in the higher gears is because it takes longer for the RPMs to get there, allowing you to build more boost pressure thus loose more air/pressure when you shift. __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

04-30-2010, 06:36 AM	#2
jtown125 Intake Join Date: Apr 2010 Location: Tennessee Posts: 40	One thing i do know...IT DOES RUN RICH!!! lol So, lets go ahead and say its the blow off valve. Y would it not die after boosting in a single gear? And to fix it? __________________ 89 mkIII turbo supra stick black w/ maroon interior!!!

04-30-2010, 06:43 AM	#3
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	Well, the only thing I can think of is that the ecu has time to realize what happened and fix the fuel curve as the engine revvs down. I was reading an earlier post of yours and you said that it doesn't die off after full boost, so I'm assuming during these times you reach a higher rpm which could help support my above statement. Fixing the problem, AFAIK, would require either tuning in some way (piggyback ecu or something along those lines) or replacing the aftermarket BOV with a factory or an aftermarket bypass valve (they do make them). You usually don't get the same sound, but they provide better performance over an OEM one. If your donor car is a turbo and has the required parts, swap them in and go for a drive. If it still happens then that's not the problem, but I really think that will fix your problem. FYI, when I had my 7MGTE I put an aftermarket high-flow cone filter and a AFM adapter on mine and it made the turbo spool and OEM BPV much more audible __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

04-30-2010, 06:50 AM	#4
jtown125 Intake Join Date: Apr 2010 Location: Tennessee Posts: 40	I don't know how it can do it so fast though?? It is almost instintaniously. Is there a way to reset the computer and maybe it will fix it in itself? Since the BOV has been on for a while...y now? I drove it home 600 miles from mississippi and not one problem. And what was the cone shaped thing you were talking about? how does that set up work? BTW: The BOV is welded on to the intake. __________________ 89 mkIII turbo supra stick black w/ maroon interior!!!

04-30-2010, 06:59 AM	#5
btwilson86 Super Moderator Join Date: May 2007 Location: Billings, Montana Posts: 1,034	Resetting the computer is easy enough, just remove the 15 Amp EFI fuse from the fuse box under the hood. It's supposed to only take about 30 seconds to reset, but I always leave mine out for a few minutes. I'm not sure how it could be reacting so quickly, but I do know that different supras react differently to aftermarket BOV's. Some will run just fine, some will not let you shift at all without it dying. Wish I had more answers for you as far as why it's happening now Since your bov is welded on, you'd have to replace the pipe if you changed the valve out. OEM pipes are plastic lol Oh, and the cone air filter.... Basically it was a universal 3 inch air filter (like a K&N cone-shaped air filter). You remove the factory air box from the AFM and in it's place you can install an adapter that bolts up to the AFM on one side and allows you to clamp on an aftermarket air filter on the other side. As long as you use a decent quality air filter, you can safely allow the engine to quickly draw larger volumes of air into the intake, creating more power and better throttle response __________________ 1989 7MGTE R154 Targa Top White Package w/Blue Interior Driftmotion 57trim CT26, Upgraded Intercooler, 2.25" Hard Pipes, 3" Turbo Back Exhaust with Test Pipe, HKS VPC w/GM 3 bar MAP sensor, APEXi S-AFC, Walbro 255lph fuel pump, ProSport EVO Series Boost / Fuel Pressure / AFR gauges, Lotek a Pillar Gauge Pod, HKS Type 0 Turbo Timer, Eibach Lowering Springs, Tokico Illumina II TEMS struts, custom powder coated Motegi Racing TrakLite wheels

04-30-2010, 07:05 AM	#6
jtown125 Intake Join Date: Apr 2010 Location: Tennessee Posts: 40	well, I don't really want to change the whole thing, I'll go reset the ecu tomorrow when i wake up see what that does. And i think the set up your talking about it already on there. It is a very popular aftermarket part cause a lot of the supra's i have seen are set up that way if what i think you saying is what im thinking of....lol thanks for your help...ill post back tomorrow and let you know what happened. __________________ 89 mkIII turbo supra stick black w/ maroon interior!!!

05-01-2010, 03:54 PM	#7
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Check for and post codes FIRST.... then reset all you want. FYI, there's nothing but minor trim data recorded in the ECU, unless there's another significant problem elsewhere resetting it shouldn't make a noticeable difference. I'm thinking it may be a bad IDL switch. (codes 51) __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar ---> Last edited by cre; 05-01-2010 at 03:56 PM.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
1985 Supra Alarm? or Neutral Safey Switch?	smitkis	MKII Supra	0	02-02-2010 09:17 PM