tach only reading half RPM'S???? - Performance Forum

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tach only reading half RPM'S????
Wednesday, March 22, 2006 7:20 PM
so I bought an msd tahc adapter and I think I might have gotten the wrong one I got 8920 or something like that. it said tach adapter but whatever.

so anyway, I hooked it up fired the megasquirt and sure enough half rpms. so does anyone know of a fix. thanks gentalmen.


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Re: tach only reading half RPM'S????
Wednesday, March 22, 2006 7:24 PM
What kind of tach do you have? Did you cut the wire on the back of it for a 4 6 or 8 cly engine? That is your problem... I think you have it cut wrong....







Re: tach only reading half RPM'S????
Wednesday, March 22, 2006 7:31 PM
Even with the wiring diagram and the diode I sent him to get a clean signal it's not working. I can't understand that one.

you have 2 coil, one wire on each coil negative, one ground and one tach signal. It has to work but it's not. I really don't know anymore. I'd like to see a picture of the install.


Gilles
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Re: tach only reading half RPM'S????
Wednesday, March 22, 2006 7:41 PM
I honestly think with your set up mfk it was me. at least Im hoping.

karo I didnt see any wires on the back just some tape. msd makes two tach adapters a tach driver and a tach adapter. I have the later. isnt there some kidd of resistor I can use to just double the rpms?


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Re: tach only reading half RPM'S????
Wednesday, March 22, 2006 7:47 PM
Dude, no offense, but I'm amazed you haven't destroyed your car yet with not knowing what your doing with the Megasquirt.

The tach adapter I'm assuming you have is only hooked up to one of the two PCM to ICM signals. This will only show half of the cylinders firing.

However, if you had actually read the Megasquirt documentation, you would know that you can scale the tach signal to read correctly by setting the MS to read a 2 cylinder signal.....

Is the same trick you do with an SAFC and other systems that require a tach signal.

Change the "Number of Cylinders" on this screen in MT:






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Re: tach only reading half RPM'S????
Wednesday, March 22, 2006 8:34 PM
hey man Im kinda hurt on that one. I have yet to hook up my injectors and wont be doing spark so the ms is nothing more then a diagnostics tool right now. theres is almost know way I could hurt my engine. unless there was a wiring problem. why the attack?

I do feel like a moron for not going back. as soon as I saw your pic with out reading your post I knew what to do. I have just been so foucsed on geeting it to read a tach signal at all that im I litlery blocked out the ms in my head.

belive me when I say I have gone over my constants a million times. I am using 2.4 fuel maps and have been trying to get in touch with as many as possiable. owners as I can.

in fact if my ways are not to inferior I would like to talk to you abut a few things


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Re: tach only reading half RPM'S????
Thursday, March 23, 2006 5:16 AM
I thought about doing it in megasquirt, and was going to mention it, but i had a concern. If you set megasquirt to 4 cylinders, isn't it going to use that constant somewhere else, like in the injection, or if he did spark, and that is going to mess something up, if the computer things there are only 2 cylinders...?? or is it not an issue. Has someone run it like that and had no problems?



Re: tach only reading half RPM'S????
Thursday, March 23, 2006 6:57 AM
megasquirt is a batch-fire ecu, so all the injectors fire at the same time whether its 4, 6, 7, 12 cylinders whatever.... And the ecotec is a waste spark ignition already where two coils fire at the same time, one on a cylinder thats on the combustion stroke, the other that's on exhaust i think... so basically, the MS set to two cylinders isn't doing anything that the eco ecu wasn't already.




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Re: tach only reading half RPM'S????
Thursday, March 23, 2006 8:38 AM
Jcavi wrote:hey man Im kinda hurt on that one. I have yet to hook up my injectors and wont be doing spark so the ms is nothing more then a diagnostics tool right now. theres is almost know way I could hurt my engine. unless there was a wiring problem. why the attack?

I do feel like a moron for not going back. as soon as I saw your pic with out reading your post I knew what to do. I have just been so foucsed on geeting it to read a tach signal at all that im I litlery blocked out the ms in my head.

belive me when I say I have gone over my constants a million times. I am using 2.4 fuel maps and have been trying to get in touch with as many as possiable. owners as I can.

in fact if my ways are not to inferior I would like to talk to you abut a few things


I'm not attacking. I'm just trying to push the point through that diving into this system head first without TOTAL knowledge of what you're doing has the potential to cause a ton of damage. Reading absolutely everything you can on www.megasquirt.info to fully comprehend every single little setting and detail the MS offers is your one and only advantage to getting everything installed properly and running without any guesswork. The MS literally has control over absolutely ANYTHING regarding engine control. That's a really scary thing considering one slip up on the smallest setting could possibly lead to a rod thrown through your block.

If you want to talk to me about the MS, feel free to pm/im/email whatever you want. I'd be more than happy to answer questions. Again, no offense was meant from my statements. I'm just trying to make a point.




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Re: tach only reading half RPM'S????
Thursday, March 23, 2006 10:03 AM
thanks man point takin


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