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Location:
Rocklea qld
Registered:
February 2003
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megasquirt wiring question
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Wed, 31 August 2005 12:43
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ive recently hooked up a laptop to try to start roughly tuning my megasquirt and found my throttle is way out. when rthe car is stopped it says 100% throttle. and when u rev is it comes back to about 80%. ive tried moving the wires around and cannot get it to make much difference. last time i had the engine running ( previous car) there was no issues with it at all...any got any suggestions on how i can tell what each wire on the tps is actually for or how i should go about this.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: megasquirt wiring question
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Wed, 31 August 2005 13:31
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umm. there are site around to tell you how to test the TPS, but a toyota manual (if it is tyota part) will help..
for mine, i just used 5V from a computer power supply, put one of the wires to ground, and then checked voltage on the third wire, to se it went form 0 at no throttle, to 5V at full throttle.. or thereabouts..
should be able to find a site telling you how easily (iirc that tyota 101 site had it there..)
or use a multimeter to test resistances, and use logic to tell which is which 
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Location:
brisbane
Registered:
December 2004
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Location:
Tasmania
Registered:
May 2002
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Re: megasquirt wiring question
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Thu, 01 September 2005 07:31
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The most crude TPS is just a switch saying when the throttle is closed, which then puts the computer into idle mode. I guess everything will work without a TPS, but the computer would be running off the load maps the whole time, and never see the idel maps. It would be hard to get a good low and quite idle like this, and overall fuel ecconomy wouldn't be as good if left to idle for a time.
All EFI thottle bodys have a switch of some sort, so why not use it.
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Location:
Brisbane
Registered:
February 2003
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Re: megasquirt wiring question
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Thu, 01 September 2005 10:11
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megasquirt requires a variable resistance TPS, not switched TPS.
easiest way to work out how to wire up the TPS...
Mount the TPS on the throttle but disconnect the wiring from the relay board, and use a digital multi-meter and switch it to measure resistance.
The resistance between two of the connections will stay the same when the throttle is moved.
Find those two - one will be the +5 Vref and the other a ground.
The third is the sense wire to MegaSquirt.
To figure out which wire is the +5 Vref and which is the ground, connect your meter to one of those two connections and the other to the TPS sense connection.
If you read a high resistance which gets lower as you open the throttle, then disconnected wire is the one which goes to ground, the other one which had the continuous resistance goes to the +5 Vref from the MegaSquirt, and the remaining wire is the TPS sense wire.
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Location:
brisbane
Registered:
December 2004
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Re: megasquirt wiring question
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Thu, 01 September 2005 10:48
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if your idleing for that long of a time that it causes you bad fuel economy haha theres something wrong , yes why not use it im just saying i chose not to it doesnt give me any disadvantage besides an idle map.. which really doesnt matter. i was just stating that if its giving him that much drama it doesnt need to be used to get the car up and running even fully tuned it doesnt need it.
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Location:
Brisbane
Registered:
February 2003
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Re: megasquirt wiring question
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Thu, 01 September 2005 11:18
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Berad: MS needs a functioning TPS, otherwise it thinks the throttle is shut or WoT.
So ben needs correctly wired-up TPS to get the thing running - no old-style switched TPS is going to help (as noted in the previous post 'megasquirt requires a variable resistance TPS, not switched TPS.)'.
cheers,
Charles.
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Location:
Perth
Registered:
April 2005
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Re: megasquirt wiring question
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Fri, 02 September 2005 00:49
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Hi,
I have been doing some reading about mega squirt and i am keen to have a go. I was hoping you could help me with a few questions.
How much did it cost to your door?
Do you think i could make it use my existing loom so i can plug in and out between ECU's while i am getting started?
People on the MS forum offer their programs, is it that easy to down load and implement into my own MS (have to tune a little i know)?
Sorry for all the questions but i have to be sure i want one espicially when you can find second hand ECU's like micro and ems for $400 to 700.
Thanks,
Ty
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Location:
Hobart
Registered:
June 2002
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Re: megasquirt wiring question
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Fri, 02 September 2005 03:22
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actually MS doesn't NEED a TPS.
It is only used for acceleration enrichment. You can use MAP based enrich if you like. Most people find TPS based accel enrich better though.
I ran my car for a few weeks without the TPS it is not critical. You just wire it so that the computer see that the throttle is completly shut. If you wire it at WOT it wont start because it will go into flood clear mode.
A switch tps is no good though. It wont do anything useful. Megsquirt doesn't look at the position of the throttle, only the rate of change, to detect when you stamp on the throttle to add extra fuel.
For the original post... if the megasquirts think you have 100% throttle when you go to start it, it shoudn't start, it should be in flood clear mode.
Follow the charles instructions for wiring up the TPS. Then remember in megatune you have calibrate it, this is only for the display though. It won't affect the running of the engine.
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Location:
brisbane
Registered:
December 2004
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Re: megasquirt wiring question
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Fri, 02 September 2005 04:40
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thank you... lol im not good at explaining
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Location:
Rocklea qld
Registered:
February 2003
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Re: megasquirt wiring question
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Sat, 03 September 2005 03:21
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ive tried completely disconnecting it so it reads o% and that made no differenec. ive tried calibrating it and it always comes up at 248. originally it ran before i did anything but after about 20 seconds everything was black from ecsessive fuel everywhere. ill try a few of the other ideas and see how i go.
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Location:
Brisbane
Registered:
February 2003
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Re: megasquirt wiring question
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Sat, 03 September 2005 03:56
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try:
-connecting the TPS input direct to an earth to simulate throttle shut (e.g. idle)
-leaving the TPS VRef disconnected
then see if the TPS position reads closed in megatune
that will confirm that the wiring from Relay board to ECU is correct (and from my test bench it was working if you connected stuff up as per the text on the board base).
it will also let take the TPS out of the equation so you can get the idle fueling right
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Location:
Rocklea qld
Registered:
February 2003
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Re: megasquirt wiring question
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Sun, 04 September 2005 10:27
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input being which wire??? i tried testing for resistence and couldnt get any reading at all and when i had the car just sitting there with ignition on and laptop hooked up i could see the throttle creeping up 1% at a time as if theres power leaking into it...
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Location:
Brisbane
Registered:
February 2003
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Re: megasquirt wiring question
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Sun, 04 September 2005 11:21
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i was trying to get you to disconnect your TPS at the relay board, then run a short jumper wire from connection marked TPS to any of the earths.
That should force it to think that the throttle is shut.
To test the resistance of the TPS to identify the three pins, you have to disconnect it from the relay board - you can't do it live or connected to the ECU... then follow the instructions:
(Note: set the multimeter to a low resistance range (e.g. 0 to 2K ohms)
Mount the TPS on the throttle
Disconnect the wiring from the relay board
set your digital multi-meter to measure resistance.
start measuring resistance across pins as you move the throttle
The resistance between two of the connections will stay the same when the throttle is moved.
Find those two - one will be the +5 Vref and the other a ground.
The third (the one not being tested at the time) is the sense wire to MegaSquirt.
To figure out which wire is the +5 Vref and which is the ground, connect your meter to one of those two connections and the other to the TPS sense connection.
If you read a high resistance which gets lower as you open the throttle, then the disconnected wire is the one which goes to ground, the other one which had the continuous resistance goes to the +5 Vref from the MegaSquirt.
The remaining wire is the TPS sense wire you identified earlier.
cheers,
Charles.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: megasquirt wiring question
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Mon, 05 September 2005 01:15
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| people100 wrote on Sun, 04 September 2005 20:27 |
input being which wire??? i tried testing for resistence and couldnt get any reading at all and when i had the car just sitting there with ignition on and laptop hooked up i could see the throttle creeping up 1% at a time as if theres power leaking into it...
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if its creeping up, it is not connected, and the input is "floating", ie that input wire is not connected to anything
maybe you should check for continuity within the loom...
and check the TPS resistances.
and if they are both fine, reflash the MS code using easytherm and try again.
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Location:
Hobart
Registered:
June 2002
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Location:
Rocklea qld
Registered:
February 2003
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Re: megasquirt wiring question
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Mon, 05 September 2005 11:53
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i had the engine running fine in the previous car. after removing it qand going turbo and transplanting it into the new celica something has gone terribly wrong. ive already been onto alot of electricians and dyno tuners to see who is gonna be the best but id like to sort out most of the stuff myself. ive been the manual alot of times but wiring just isnt my strong suit.
ive tried the tps resistence but i couldnt get a reading at all anywhere. its going to a electrician for them to do a test on it as soon as i fix my fuel pump which just stopped.
as for seeing the engine on the street, i want the exact same thing. but its just not happening for me atm. BTW what tps are u guys running and how hard where they to sort out. mine is a vl one and has to plugs so maybe its stuffed and i will use a different one.
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Location:
Hobart
Registered:
June 2002
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Re: megasquirt wiring question
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Mon, 05 September 2005 12:17
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ah fair enough. Didn't realise you had it going.
I'm running the TPS that Haltech sell with their computer. Only because a mate had one spare. Once you work out which wire is which it is not hard at all.
Keep trying to get the wires sorted on your TPS, i'm sure you'll get it. There's only so many combinations 
Make sure the megasquirt is ok by using the stim and playing with the TPS knob.
Cheers
Chris
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Location:
Brisbane
Registered:
February 2003
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Re: megasquirt wiring question
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Mon, 05 September 2005 12:21
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ben, i have to drop my ute around to motorama on wednesday nite for a service - i'll try to swing past your place on the way there. will bring MMeter with me.
cheers,
Charles.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: megasquirt wiring question
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Mon, 05 September 2005 13:13
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i'm running the stock 7KE TPS, but there is a TPS from farnell (that ppl got in a group buy on the OZ and NZ section of MSEFI a while ago) that costs about $50 and is basically the same as what is supplied by haltech and Wolf afaik.. the part number is in the msefi thread..
i vote wiring.. or dodgy wiring has cooked something perhaps???
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Location:
Vancouver
Registered:
June 2004
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Re: megasquirt wiring question
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Tue, 06 September 2005 07:22
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what version of MS do you have? Is it an MS1 or an MS2? Have you tried flashing the processor with the latest firmware? I seem to recall the V1.0 MS2 boards had an issue with early software doing funny things with the throttle position sensor, and that was addressed with updated firmware (V1.0 and later)...
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Location:
Adelaide, SA
Registered:
May 2002
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Re: megasquirt wiring question
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Tue, 06 September 2005 09:05
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I almost bought a MSII kit the other day, the only thing that stopped me was probably that they had none in stock.
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Location:
Rocklea qld
Registered:
February 2003
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Re: megasquirt wiring question
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Tue, 06 September 2005 10:46
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good news tonight. finally got it going. didnt check tps stuff but atleast it goes again. im thinking ive broke a wire somewhere but im not real good at that part so ill wait for you on wednesday charles. any idea what time so i can be home.
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Location:
Brisbane
Registered:
February 2003
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Re: megasquirt wiring question
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Tue, 06 September 2005 13:24
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ben, slight change of plans - will be thursday nite not wednesday - when i pick car up from motorama... too many things on wednesday nite to do. will be around 8:30pm or later.
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Location:
Rocklea qld
Registered:
February 2003
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Re: megasquirt wiring question
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Wed, 07 September 2005 10:27
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sounds good
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