i think i've got a bad bypass valve...or something....

S

stan

New Member
May 21, 2006
123
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0
south orange county
www.stansanders.com
I'm hitting 4psi boost, holding, adn then slowing dropping down to 3-3.5 after 5500-5800rpms. i'm new to the supra, but i know this is less than i should be hitting. got into the engine compartment and don't hear any obvious boost leak sounds, so i'm thinking that means either

a)my bypass valve is shot and leaking, but still semi functional

b)my boost gauge is off


its a completely stock / original '88 turbo, save a headgasket replacement and various minor repairs over the years. anyone know how i can figure out what's causing this problem?
 
tropical 87t

tropical 87t

New Member
Dec 18, 2005
68
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0
Lake City, FL
I have a similar problem that just started a few days ago.

(87t, manual, only intake and exhaust mods)

It seems I'm hitting fuel cut at around 4psi boost, a little black smoke out of the exhaust, and I'm hearing what sounds like a deep, hollow, exhaust leak sound near the back of the engine near the turbo elbow area. The noise is louder when I accelerate.

I just replaced the plugs and wires thinking I was running less than 6 cylinders but that didn't help.

The engine would hesitate every other time I floored the engine by hand with the throttle linkage under the hood.

I get no error codes off the super monitor and maintenance has been regular as far as fluids go. No over heating or coolant level changes or abnormalities.

Any ideas?
 
S

stan

New Member
May 21, 2006
123
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0
south orange county
www.stansanders.com
i just got the car last night so i havent had a chance to fire it up, and i dont know if any noises i'm hearing are out of the ordinary since this is my first supra, and first turbo car. i'm going to see about downloading the service manual today and try blowing through the bypass valve to see if its shot. if i can blow through it in both directions with my mouth, that means it needs to be replaced, right? i'm sitting on the beach right now (wireless - gotta love it) but when i get home i'll fire it up and see if i have smoke.

2.5psi seems like a decent leak that you would hear if it was in the piping. i'm thinking that bypass would make sense since its leaking but its dumping it back in so it doesn't make much noise.

assuming the bypass is dead, if i get an aftermarktet BOV will i be able to use that to replace the old oem bypass valve? i was looking at using something like an HKS SSQV.
 
antman

antman

Supramania Contributor
Apr 6, 2005
632
0
16
TN
With the car in its stock form. I'd just get an oem replacement. Until you get a full hard pipe kit or an upper pipe. Once you start modding the car the hks is a great BOV, but i recommend startin with a intake and exhaust.

Good luck with the new car and welcome to the supra community.
 
trydrew

trydrew

Suprafied
Nov 4, 2005
1,038
0
36
Earth
antman said:
With the car in its stock form. I'd just get an oem replacement. Until you get a full hard pipe kit or an upper pipe. Once you start modding the car the hks is a great BOV, but i recommend startin with a intake and exhaust.

Good luck with the new car and welcome to the supra community.
Click to expand...

A good, simple replacement that doesnt require welding or anything to install is the Bosch 110 Bypass valve. Do a search for more info.
 
trydrew

trydrew

Suprafied
Nov 4, 2005
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Earth
stan said:
had a friend drive behind me while i did pulls from various gears. he didnt see any smoke. what do you guys suggest as a next step?
Click to expand...
Go ahead and check your bpv, and check your turbo while your at it. Report back.
 
S

stan

New Member
May 21, 2006
123
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0
south orange county
www.stansanders.com
found the problem! the bypass valve was not closing fully, and so leaking out a majority of the boost. luckily for me jose at drift motion was going into the shop. drove up and got a greddy type-s BOV and upper hard pipes. score!
 
tropical 87t

tropical 87t

New Member
Dec 18, 2005
68
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0
Lake City, FL
johnathan1 said:
Is the car doing any other weird things? Black smoke maybe? Did it just start doing this all of the sudden?
Click to expand...


Yes, it just started doing this all of the sudden. There is a little black smoke out the tailpipe. I also hear a sound like a rusted out muffler sound near the rear of the engine when I'm driving. I can't find anything leaking....still searching.
 
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