Wiring TPS into megasquirt? - Tuning Forum

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Wiring TPS into megasquirt?
Thursday, August 11, 2005 9:18 AM
I finished up my Megasquirt a couple weeks ago, and I've been installing it. Now what I did for all of the other required sensors, Coolant Temp, O2, yadda yadda was doubled up the sensors (2 CLT's etc). Like Excidium I want to maintain factory wiring to a certain extent. You can't do this with the TPS though, what wires to you take signal from and can you leave it going to the factory PCM or do you have to just disconnect it and run it to the Megasquirt completely?

Also, on a quick side note. Do you need extra wires and jumpers on the board to run MSnS? I'm not overly familar with the operation of it. I was thinking of just waiting until I can get the MSII Chip and jumpers put in. That way I could control spark, fuel, and an IAC Stepper Motor. Thanks!


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Re: Wiring TPS into megasquirt?
Thursday, August 11, 2005 10:08 AM
like I said in the Megasquirt thread I just updated, why are you guys doing this? It's wasted money.

The system works fine with the stock sensors. Big deal if you have to tap into the stock wiring. It doesn't make any difference at all.

To tap into the TPS, run the TPS signal line from the MS to the dark blue line on the TPS sensor's connector.

I don't know anything about the MSnS because I'm working with a Megasquirt-II platform.



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Re: Wiring TPS into megasquirt?
Thursday, August 11, 2005 10:44 AM
Mostly because I had the stock sensors available to me and connectors, so hey why not have a separate connector for each. There are two wires that come from the megasquirt to the TPS. If you tap into factory wiring, is the 5V Reference already provided? So you simply wire TPS signal wire back to the megasquirt? Also, will it cause voltage loss if you wire the TPS signal to the PCM and the megasquirt?


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"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Thursday, August 11, 2005 11:29 AM
If you are still keeping the stock ECU in the car (which I'm assuming you are), wiring up the MS sensor input only works just fine (I've confirmed this on my own car). You do not need to supply the TPS with an additional 5 volts since theres already 5 volts there from the stock ecu.

There is no voltage drop.



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Re: Wiring TPS into megasquirt?
Thursday, August 11, 2005 11:51 AM
Here's a little tidbit from the MegaManual that supports my reasoning for using multiple sensors.

" I am planning an MegaSquirt install soon. Can I keep my existing intake air temperature and engine coolant temperature sensors functioning with my stock ECU for timing, while also splicing MegaSquirt into them at the same time for fuel?

Next, you need to determine the stock computer's bias resistor. This can be tricky because some ECUs (GM for example) have 2 bias resistors and swap them in at different temperatures to gain accuracy. Example, -40F to +40F and +40F to 230F. If your ECU does this, you can't easily hookup the MegaSquirt in parallel.......You then need to use EasyTherm to create a new table which uses the correct bias value"

Now I'm not sure if this pertains to the LD9 but I just found it easier to use the extra sensors that I had lying around. Let me know if this dossn't apply to our motors. I know that the TPS will be fine, just wasn't sure about the CLT and IAT


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"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Thursday, August 11, 2005 1:04 PM
^ Exactly. If you don't figure out exactly what the bias values are and if/when they are switched to different values, your values will never be perfect, and I could never live with that.

You can use the bais value that the gm computer uses when the car is warmed up, but then during warmup you'd have to except whatever conditions this caused. Again, not the best solution in my opinion.

The GM computer does this bias switching to gain better accuracy as far as I can see, so obviously there is at least some motivation in having the correct values. I don't think anyone has done significant enough research to figure out just how inaccurate the above situation could become.

If anyone has, it's slowolej..



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Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 6:14 AM
Hey excidium
How hard was it to get MSnS working on your 2.4? Do you think it would be more worth it to go with the MSII daughterboard and run spark from there? Thanks


<IMG SRC="http://j-body.org/registry/paul7878/amsoillogo_iso1.gif">

"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 6:14 AM
Hey excidium
How hard was it to get MSnS working on your 2.4? Do you think it would be more worth it to go with the MSII daughterboard and run spark from there? Thanks


<IMG SRC="http://j-body.org/registry/paul7878/amsoillogo_iso1.gif">

"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 6:14 AM
Crappy double post


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"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 6:14 AM
Crappy double post


<IMG SRC="http://j-body.org/registry/paul7878/amsoillogo_iso1.gif">

"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 6:14 AM
Crappy double post


<IMG SRC="http://j-body.org/registry/paul7878/amsoillogo_iso1.gif">

"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~

Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 8:54 AM
Jesus White_Z. hehe

CORRECTION: There IS a voltage drop on the sensors if you have both the stock ecu and MS hooked up at once. My bad guys. I didn't test enough to see a difference until last night.

Excidium, are you absolutely sure that there's two bias resistors in the stock ecu??? I can't seem to find this information anywhere in my technical manuals or GM technet.

I'll try doing the suggestions for figuring out the bias resistor values on the MS main page and see if I come up with two different values depending on the temperature range.

The MS site suggests if you absolutely need to do this, use the hotter of the two resistor values. The lower end of the temp scale doesn't matter nearly as much as the upper end during regular operation.

Quite frankly, I don't have the option to use a separate IAT sensor for the MS. The GM s/c has one hole in the charge side for the IAT sensor. If I wanted, I could drill out another hole but I definitely don't want to screw with that. Putting a tube or something in place of the IAT and then extending it to adapt to two IAT sensors would be pointless since they wouldn't be in direct contact with the air to determine it's temperature.

Sorry if this is off topic from your TPS question White_Z. With the MS hooked up, I'll check tonight to see if there's a voltage drop on the TPS by checking the TPS values with an OBD scanner. The stock ecu already knows that 0v is 0% and 4.47 volts (I think) is 100% throttle position. If I see anything different for values coming from the stock ecu, there's a voltage drop.

I'll check it out.


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Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 10:25 AM
Sweet, I'm at work and I don't know what the deal is with this thing double and triple posting. If it happens again, I'm waitin till I get home to mess with the forum stuff.


<IMG SRC="http://j-body.org/registry/paul7878/amsoillogo_iso1.gif">

"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Friday, August 12, 2005 10:25 AM
Sweet, I'm at work and I don't know what the deal is with this thing double and triple posting. If it happens again, I'm waitin till I get home to mess with the forum stuff.


<IMG SRC="http://j-body.org/registry/paul7878/amsoillogo_iso1.gif">

"Ribbed for her pleasure, but I turned them inside out".
~Dick Solomon 3rd rock from the sun~
Re: Wiring TPS into megasquirt?
Saturday, August 13, 2005 9:49 AM
Mr. Pute:

I remember a long time ago I did the tests to see if the bias resistor was changing value and it was as the engine temp increased. You can do this test yourself on your own car.

Here's an excerpt from msefi.com about figuring out bias resistors (you may have already seen this)..

Bias Resistor Stuff

This was actually one of my original questions to the megasquirt forums way back before I had even purchased it... Perry Harrington is one smart cookie..



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