hey guys,

im in the process of trying to start my car with my ms3x. i have it all wiring and installed. the problem im having is getting a tach signal at cranking speed. i have a working sync'd signal if i spin the cps at higher speeds, but not at 250rpm. im guessing i need to play with the pots a little more which i am trying to do. any ideas or tips and getting a slow speed tach signal. i have the pots all zero'd out my spinning 6 turns anti-clockwise right now.

thanks,
Matt

 

sounds like a good guess!

 

Check your CAS wiring. The cable needs to be shielded and the foil shield grounded at one end of the cable (I have mine grounded at the common ground for all the sensors and ECU). Make sure the corresponding wires for the CAS are connected to the correct pins on the MS3x. The ground wires (not the braided shield) for the CAS can be connected to any ground on the MS3x harness.

 

yeah i have it wired through shielded wires. i made a bench test rig to spin the cps and i can generate a tach signal from 450rpm and up but it cant get it when im cranking the car. im charging up the car battery now so i should be able to mess with it more tonight. does anyone know what settings on the pots worked for them?

im going to ask my boss i can use his oscilloscope to help tune it in. if so that should make it easier.

 

Like you, I had the adjustments on the pots all the way to zero and no problems with a tach signal. Bear in mind, there are two sets of pots on the MS3: one set on the main board and one set on the MS3x. The ones on the MS3x are obviously the ones you want to adjust.

Do you have a JimStim with JimStimX? That will generate a tach signal at that speed and could help determine if the issue is with the CAS or MS3x.

And to be clear, the CAS cable metal shield is grounded on one end, right?

 

yes the shielded cable is grounded. i thought the pots on the main board were for the primary ignition trigger (main vr) and the ms3x pots were for the sync trigger (2nd VR)? no stims here, could be nice, but i should be able to do fine without.

 

Whoops, you're right, both main and MS3x boards are used for the CAS. Referring to this page, How to MegaSquirt your FC RX-7 under ECU modifications for MS3, is the jumper for JP7 off?

There are other jumper settings related to the CAS there as well. Quoting from DIYAutotune: "Set up the ECU up to trigger from the VR Input. Jumper TachSelect to VRIN and TSEL to VROUT for a V3.0. For a V3.57, set the JP1 jumper on the main board to the 1-2 position, and set J1 to the 3-4 position."

 

yes my jumpers are set up as per instructions on aarons website and diyautotune. i have a tach signal once the cps gets spinning faster, and the signal stays sync'd too. but when im cranking the car i cant get signal.

 

Good luck getting it figured out Matt. I'm going to be running the shielded cable for my 2nd VR circuit tonight and then I'm set to try mine...

I know one wire goes to the the cam input on the MS3X, but does the other get grounded to the common sensor ground on the main harness (the black w/white tracer wire)? And does the shielding get grounded to the same wires that ground to the engine? I'm not sure why I have such a mental block about this, but I always get confused when reading about the grounds etc...

 

i connected it to one of the ground pins on the ms3x db37. i have an older thread in this section where aaron answers the same question of mine.

 

When I was trying to get a better signal from mine, I adjusted the gap between the magnets and the rotor in the cas closer and i was able to read somewhat slower rpms

 

i will try this too, thanks

 

Yeah I saw that thread a few times, still have a mental block with it.... lol. Can the shield ground, and the G- wire go to the same ground?

 

i used separate grounds. i read somewhere that using the shield as a ground could cause interference.

 

So I got my CAS hooked up tonight and decided to turn it over to see what would happen. I had the same result as you, nothing on cranking, but if I spun the cas by hand it would read. I adjusted the pots on the MS3X card and voila! It reads (and syncs) on cranking now. I still have to put my UIM on and wire up the fuel pump, but I'm happy I got this far.
If you haven't messed with those pots (I just turned them counter clockwise a bunch of times) try that and see what happens.

 

thanks man. worked great! time to start this beast up. i hadnt got to messing with those yet because i didnt think the main was working.

 

It was a shot in the dark on my part, but seemed like a logical enough place to start lol. Glad it worked for you as well, looks like we're neck and neck for first start at this point... I'll be putting the uim back on tonight as well as the alternator etc and probably do a little wrapping on the wiring so it doesn't get dirty/damaged. As Aaron's writeup suggests though I won't fully wrap it all up until I know it'll run...

 

so whats the best way to set base timing on an MS3. i change it to fixed timing and set it and cranking timing to "0". then if i stab the cps in on the first mark it will fire L1 around 40 degrees after the mark. why is my timing not what i tell it? is the notch on the stock wheel not aligned with the first trigger?

 

I could be wrong, but I don't think you can set the base timing just while cranking. It needs to be idling, and you change it from "use table" to "fixed timing" and set the fixed timing value (not the cranking advance) to "-5" then line up the leading mark on the pulley.... That's how I understand it at least.

 

yeah, ive set the cranking timing and fixed timing to the same, it should be able to be verified during cranking according to the megamanual.

 

The megamanual does not apply to the ms3 or ms2/extra firmware.

The procedure is:

Set the tooth #1 angle to 5 degrees.

Get the engine running.

Set Fixed timing to -5.

Line up the -5 mark on the pulley with the indicator on the engine.

Turn off fixed timing and use the table instead.

Ken

 

Thanks ken, i will give that a try.

 

well that worked great, as well as changing one of my ignition settings. she now starts up and idles very easily. thanks again ken.

 

What setting did you change?

 

in the ignition settings i had the cps set as crank wheel speed, not cam wheel speed. idk if thats what made the difference, or if it was just finally having my timing set right.