Tach issue, and VAF elimination question.

[josh95mx]

So I have gone through the forum quite a bit so see if I could answer this myself but I still have a couple of questions I was hoping someone could help me out with.

I have a MAZDA MX-3 that I am running my MAPECU1 on. I just got it all wired up and was working great (all set in auto tune). Well I went on a short light drive as the manual suggests, and got back and realized that the tach is only now registering intermittently (after further testing it seems the tach works fine at startup when cold, but after like 5 minutes it starts working intermittently). At idle it is saying 0RPMs and when I rev it it registers proper rpm for a split second then back to 0. I know when I did my HEI conversion recently that there is an issue with the OE cluster tach recognizing the signal and have to run a resistor, I am wondering if this might be the same thing, or just a glitch with my PC. Any thoughts?


Also I got this unit to eliminate my VAF. As of right now I have it hooked up in "AFM comparison configuration", as the wiring diagrams show I should. After I have proper full set of maps, do I then wire it in an air temp sensor, then rewire it as shown for "Normal operation mode" so I can remove the VAF?

I am unsure, any help is greatly appreciated.

Josh

[MAP-ECU Man]

It sounds like the White RPM MAPECU wire might be loading the tach signal too much. You could connect it to the ignition signal going to the ignition coil rather than the cluster tach signal, if you know which pin that is.

The data you get from learn mode will need to be "massaged" to fill in the gaps before you can run with it. Alternatively, you can use the data to find an existing base table that is close to your requirements which you can then tune. You are correct, once you are happy with the fuel table you wire in the IAT and rewire to MAF Eliminate.

[josh95mx]

Yeah, that is a good idea, I will try that.

Thank you for the information.

[josh95mx]

So I checked my wires and I do have the white wire from the mapecu hooked up to the proper ignition signal wire. I should probably clarify that the rpm or tach that I am having issues with the one in the mapcon v2.3. It works fine when the car is cold but after about five minutes it gets glitch.

Do you think I should run a resistor in line?

Thank you

[MAP-ECU Man]

OK. I cannot see how the temperature of the engine will affect the MAPECU RPM signal, unless the Ground of +12V signal is changing. I have never heard of that before and have never had to install a resistor, etc. Otherwise, is the communication link between MAPCAL and the MAPECU failing? What does the Status box say when the rev counter stops?

[josh95mx]

Well I know that most aftermarket tachs are not compatible with the signal that comes from the ignition signal wire, most run an MSD tach signal resistor. I know I needed to run a 1ohm resistor for my HEI mod when I switched from internal coil to external, otherwise the signal could burn up the factory tach. Perhaps that is what is conflicting it (my resistor that is inline at the dizzy)?.. My first thought was that it was a communication error, as I went through a couple of Serial to USB cables until I found one that had drivers for Windows 7. It could be a communication issues, as when I first hook up the ECU to the PC it works fine. Rpm's are spot on, but after about 5 minutes of being on or linked the tach in MAPCAL reads 0rpms at idle, but if I rev it the rpms will read for a split second at the peak rpm that I reved it out to, then back to 0. Now in order to get it back I have to unlink, turn the car off and wait about 10 minutes. Then it reads proper again. At first I thought it was a loose wire with my connection. So I have verified with my multi meter that I have a perfect signal coming from it. The car is running perfect, so my thought is that the MAP ECU is functioning just fine. Perhaps I should try to uninstall and reinstall the MAPCON again..

The box in the lower corner will say "reading" , but no error comes up.

Thank you again!

[MAP-ECU Man]

Hmmm, it is a strange one. Perhaps it is the resistor? Mind you 1 ohm is virtually nothing so it is not going to do much. Which side of the resistor did you connect the MAPECU white too? The MAPECU input can tolerate high voltages from an ignition coil but the input needs to ground properly to read a signal. In other words, high voltages are OK but it must be seen to switch close to ground to work properly. Not sure if that helps or confuses the matter future.

The communications sounds stable and OK.

[josh95mx]

Sorry I meant 1K OHM resistor. That ended up being the issue with the tach reading for the MAP ECU. I ended up running a separate wire off of the HEI module before the resistor and it works great.

Though now I seem to not be able to remove my VAF. I have installed a gm IAT sensor and rewired as "normal mode" and it will not seem to run. It will start right up and idle though as soon as I give any throttle it starts to die. Do I need to change some settings within MAPCON to make it function properly? I tested the Ohms from the VAF tem and it reads something like 2.86 the GM IAT sensor I bought reads like 3.14. I would think that they are close enough but it will not stay running. I do have another IAT that reads 4.65 ohm. Any help is appreciated.

[MAP-ECU Man]

The GM IAT will not be accurate but as you say, it should be close enough to work. It sounds like your OEM ECU does not like the VAF signal from the MAPECU for some reason. Have you filled all the zones of your fuel table? Do you want to upload it to the forum so we can take a look?

[josh95mx]

I filled in the zones as instructed. It would start up and idle then I could give it fuel and it would reve out a little bit (it was rough), then when I let off it would die. I can upload the map I have this evening. Thank you again for the help!