7mgte + bleed valve + boost gauge = 5psi?

[Danners]

The thread has been open since August, so don't expect anything to happen quickly! i'm not relying on it. I have my local Toyota guy checking on a proce for me and will let you know if i get answers quicker than you do.

How many wires does the 7M one have? The 1J is a 3 wire o2 sensor.

[Kedderz]

its a 3 wire unit, with the bottom wire on mine previously been disconnected. thats truely puzzling me at the moment, why would have such a smooth idle and decent fuel economy ($50 98RON gets 350kms with a decent amount of go pedal)

Ill post what I find from repco/sprint etc tonight in the soarer thread.

[thechuckster]

they probably disconnected the heater wire - so it just took the sensor a little longer to warm up to operating temps.

Any toyota sensor should suit. An old 1-wire unit would even do the job once you worked out what the pins outs of the plugs are.

The sensors should be around the $50-80 mark (being old narrow-band units) - go to the wreckers if the parts store tries to stiff you.

[Kedderz]

would the heater wire being disconnected throw 02 sensor codes?

[BeRad]

dunno how the 7m boost control works but with the 3s there was 2 wastegate lines and the other had to be blocked off for the valve to work.... just a suggestion.

[Toml]

dunno how the 7m boost control works but with the 3s there was 2 wastegate lines and the other had to be blocked off for the valve to work.... just a suggestion.

There is just the one line, so how Kedderz' car was hooked up should've worked. Either the bleed valve was hooked up backwards or it just plain doesn't work..

they probably disconnected the heater wire - so it just took the sensor a little longer to warm up to operating temps.

Any toyota sensor should suit. An old 1-wire unit would even do the job once you worked out what the pins outs of the plugs are.

The sensors should be around the $50-80 mark (being old narrow-band units) - go to the wreckers if the parts store tries to stiff you.

There's no point replacing an old (possibly inaccurate) sensor with another old, possibly inaccurate sensor. Get a brand new one.

Don't get a 1 wire sensor; the stock sensor is three wires and has a heater for a reason. You should also be able to get away with a 4 wire sensor as long as you ground the signal ground correctly, but don't quote me on this.

As for aftermarket sensors, I haven't been able to source a replacement 3 wire sensor from anyone but Toyota (who charge an arm and leg for it). I bought a 4 wire bosch sensor from Repco for around $100 but haven't had a chance to wire it up as yet.

Denso makes the OEM ox sensor for the 7M. In the USA, Denso also sells an aftermarket sensor which can be had for about US$30. Kedderz if you're interested we could purchase a few of these and have them shipped together? Shouldn't cost much more than $50 each and you'll get a stock sensor with stock flange, but you'll still need to find a stock connector.

[Kedderz]

the wiring and connectors im either going to have to resplice correctly or replace from a wreck for the stock connectors.

ive got no quams splitting postage with you tom, ill prolly get 2 just in case ;-)

[Toml]

Yeah I was thinking of grabbing a couple too. I'll send the guy an email and see if he's got any available at the moment.

I'd suggest looking around on here or supraforums.com.au for someone with a second hand oxygen sensor just to steal the connector.

[PlacentaJuan]

this is the bleed valve i am buying (technically not a bleed valve)

thanks to bigworm for this one, he uses it on his 1j and comparing it to another 1j cressida it works better:

http://cgi.ebay.com.au/Turbotech-man...QQcmdZViewItem

[Bored?]

I recently put a bleed valve on my mz20, (then promptly blew the head gasket again, but that's another story...)

A bleed valve installed between the turbo compressor housing and the waste-gate actuator should be fine.

When I did mine, I noticed that a number of the rubber hoses between the turbo and throttle body had cracks in them due to age and heat, so I replaced them. You might like to check your car for similar problems, since a big boost leak could also stop you making much boost.

The flexible pipe that attaches to the throttle body was the worst. Replace any problems with silicone hose.

[Kedderz]

yeah im going to rip out the stock air box and have re run alot of the boost/vaccum lines and make them more acessible cause right now they are a PITA

[Shifty]

Be careful with some of these suggestions about cranking the bleed valve, disconnecting the wastegate, etc. The people making these suggestions aren't the ones who have to replace the motor when it goes bang. Sure there's a boost cut but you can easily cause engine damage before the ECU senses the problem and cuts in.

Now, 4.5-5.5psi is about right for a standard 7M. I've driven two essentially standard MA71s (one was mine, the other was one I test drove while making my purchase decision) and they both read about that much.

Just stick with the bleed valve and turn it a quarter turn at a time, of a half turn if you must. As you bring it on boost apply the throttle gently and watch the boost gauge carefull to see that it doesn't spie up too suddenly. In my experience bleed valves do very little and then all of a sudden a half turn doubles your boost... you need to approach that point carefully! It may seem tedious but it will get you there in the end, and you won't risk cracking a piston in the process.

Another option for upping boost incrementally is to lose the bleed valve, and instead space the wastegate actuator out with a washer under each bolt. Add more washers step by step until you reach the desired boost level and it cost you 25c for washers instead of however much for a bleed valve.

[BeRad]

if you read what some have said is, "be careful boost will rise quickly so when you see it lift over 5 come off the gas", if you cant come off the gas by 10psi theres something wrong and if the engine goes boom from 1 spike of boost to 10psi for a matter of milliseconds it was a hunk of shit anyway.

id be disapointed if my engine couldnt take one quick stint of 20psi.

a bit of common sense goes a long way.

[Kedderz]

thanks shifty, nice post. I have played around with it alot recently and since changing which pipes attach where on the valve i have gotten it to boost to around 7-8 with spikes to 9. Obviously this isnt the best situation and as ive said above i want to replace the vaccum lines to eliminate boost leaks that may occur and also relocate the valve from its current position.

you are definately correct about how 1/2 a turn makes alot of difference with a bleed valve, before today i wouldnt of believed you, but yes 1/2 a turn for me means 6-7 psi at WOT to boost cut.

currently I have the valve set to the minimum setting which returns stock boost.

and yes as berad has said I only disconnected the wastegate to see that tehre wasnt a boost leak, even then it wasnt at WOT and common sense was used.

[BeRad]

You wont get rid of those spikes completely. bleed valves just wernt cut out for accurate boost control, some will do it better than others but theres still that risk, if you want to eliminate it fully space the gate, change the spring in the gate, or buy an ebc....