You can reprogram for the change in voltage, but it's still necessary to change the resistor because the resistance curve of the stock air temperature sensor is so different from the GM one.

Basically you have to both reprogram using easytherm, AND change the bias resistor.

 

Gotcha, i'll do that today while i'm wiring the pullup resistors.

 

I had a question about that. Does it have to be metal film resistor like the one your replacing or would a carbon film one work just as well?

 

It needs to be a 1% resistor, and I think all 1% resistors are metal film...

However, I've never done this but you might be able to get away with measuring the actual measured resistance of a 5% resistor, and then inputting that into easytherm.

I'd recommend just using the metal film resistor.

 

The 5% resistors I've measured all fall well within the 1% tolerance anyways, so I'd not worry much about it. As muy says, just measure the resistance, and if it varies from its rated value, use the actual value when generating the thermistor tables in EasyTherm.

 

yeah, I guess if you don't have an ohm meter, I'd use the metal film (I was recommending that assuming you don't have an ohm meter), but if you have a way of measuring the resistance, then do what renns said and measure it, and use the measured resistance.

 

Parastie...please tell us you own a multimeter. If you don't own one, go out now and buy one, even a $10 unit, and then tell us you own one. No one should be attempting to build/install an ecu without the basic tools required to do the job...

 

haha, the only reason I don't assume that is because I've had people ask me questions, and I assumed they had one, and they didn't. I've had people doing installs like this using basic continuity testers to test their wiring... Sorry if I seemed a bit boneheaded.

 

Parasstie, Next time you place a order to digikey do yourself a favor and order a extra ZTX688 and LM1815 chip thier fairly cheap and no one carries them at local electronic shops. During the build and getting it working your bound to make a mistake or two everyone does and those parts come in very handy. I just personally hate waiting on ordered parts. I had to order a second ZTX688 and paid almost 10.00 total for a 1.20 or so part. Just a suggestion. Also not a bad idea to put the Lm1815 chip in a socket so if you have trouble later it can be changed easily and help with troubleshooting. Theres a lot of information on using this with a 7 and it gets comfusing..least it did to me. Take your time building it. I found it helpful to insert the components and bend the leads holding them in place and NOT soldering them. Then go back and see what you need to swap out for RX7 specific parts. Also a good idea to print off the megamanual. Read it first front to back. Then go through page by page and assemble and test each ckt as you go like it says. Then when your done you can be 100% sure you have a working unit. This procedure also helps you understand what parts are accosiated with what ckt in the unit. Just trying to help you avoid the mistakes I made. Once its built re read the posts on here with the MS in front of you and a printed schematic and double check things. I bugged renns and muy a lot lately so you may benifit from reading through some of the posts. Good luck.

 

Interesting, I guess digi-key had enough demand for the lm1815 to start selling them in single-part quantities... I had to order like 30 of them the last time I ordered because they said they're going to stop carrying them in single-part quantities.

Also, as soon as I test the idle circuit with the ztx689, I'm going to start using those. I've had no problem with the 688, but the 689 is rated for a higher voltage, so I will probably switch. If you've got a 688 though, there's no reason to switch really.

 

Ohh... I thought from your earlier comment that he'd said he doesn't have one. I was in shock at the thought. We're not installed a pair of 6x9 speakers here!

Glad to see there's finally some running installs popping up given you've put lots of support hours into this. Once a critical mass of a dozen or so experienced users is created, the this area of the forum should become self-sufficient. It'd be nice to see more posts related to tuning, dyno testing, custom installs, etc, instead of just soldering issues!

 

LoL
I suppose i should reply.
I actually ordered 2 lm1815 and 2 ztx688 just incase i burned one, so i'm covered there.
Also, i do have a digital ohm meter that i've been using for all my resistor testing! Thanks for the concern renns!

 

Glad to hear it! I just recently acquired a DMM with capacitor measurement capability. That's a real plus, as smaller caps often have illegible codings. Popping them into the DMM verfies capacitance quickly without a magnifying glass and decoding chart.

 

I also ordered my kit from Glen's Garage, every resistor was in a package said where it went on the board. It's a nice kit, though i have a few extra parts....

 

I've got a couple of PMs about this, so here's the full corrected list for the v3.0 board. Muy, if you see anything that i'm missing, please edit!
1. Megasquirt v3.0 kit from Glen's Garage.

2. (VR Circuit)3. 3-4.7Kohm resistors

To use the BAC for idle control, these are the instructions I followed:
1) First, remove Q20 and R39. Replace Just jumper R39 instead.
2) Replace R19 with a 510 ohm resistor.
3) Replace Q4 with a ztx688 (orient it with the flatter side the same direction as the flat spot on the silk screen) Leave a little bit of space under the ztx688 when you solder it.
4) remove D8
5) Using a 1N4001 Diode, jumper pin 3 of the ztx688 to a +12v source. The banded end of the diode goes to the +12v source.

Which means you need:
4. Idle Control (BAC) The last piece is the manifold temp sensor.
5. 47K Ohm resistor

So, once again:
1. Megasquirt v3.0 kit from Glen's Garage.

2. (VR Circuit)3. 3-4.7Kohm resistors

4. Idle Control (BAC) 5. 47K Ohm resistor

Always order extra parts! Just incase.