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RPM reading wrong

Posted: Mon May 13, 2013 12:25 am
by jacmifish
Hi,

I'm running the megajolt lite jr. and had started to tune the system when I noticed the RPM readout on the gauge cluster tach and the megajolt digital readout were different, e.g. the computer would say 2500rpm and the tach on the gauge cluster would say 1700rpm. I know the gauge cluster readout was defiantly more correct.

Since the rpm reading on the megajolt system would read a much higher rpm it would engage the wrong columns on the ignition map.

What I find strange is that I'm sending the output tach signal from the megajolt to the tachometer and my Powerjection III system, so why would that be correct and not the other?

By the way I do have it set to read out the correct number of cylinders. =P

Car is a Plymouth Duster with a Slant six

Any help would be awesome thanks! =)

Posted: Wed May 15, 2013 6:23 pm
by jacmifish
Anybody?

Posted: Sat May 18, 2013 6:56 am
by brentp
Hello,

You will need to double check the number of cylinders set in Megajolt. Note, this is a separate process from reading the ignition map.

1. connect megajolt to the computer
2. read the engine configuration
3. make sure 6 cylinders is selected
4. write it back to the unit
5. power cycle the megajolt and read it back again to make sure it says 6 cylinders.

Posted: Sat May 18, 2013 2:13 pm
by jacmifish
I have previously followed those steps and it confirmed that it was configured with 6 cylinders. I have made it "re read" the controller after flashing the config and it is still the same.

Posted: Tue May 21, 2013 1:19 am
by brentp
Out of curiosity, what kind of RPM readings do you see in the megajolt software if you change the engine cylinder count to 4, 6 or 8 cylinders?

Posted: Thu May 23, 2013 12:23 am
by jacmifish
Hey Brent. I will give that a shot near this weekend, thanks.

Posted: Sat May 25, 2013 7:47 pm
by jacmifish
Hello again.
Before changing around the cylinder settings I decided to test a few things in the system. One things I thought about first was maybe that I wired up the tach output incorrectly on the megajolt because I have it running to my fuel ecu and my tachometer. I removed the tachometer feed and the RPM seems to be normal now will cranking (I think). Something I'm not sure about is that when I cranking the motor and watching the megajolt rpm readout it dosen't register until the motor fires, is that normal?
Testing resistance for the coil pack on the connector getting .9ohms on each coil, then between the coil towers on the same coil the resistance were as follows: coilA 13.88Kohm, coilB 13.69Kohm, coilC 13.83Kohm. I'm not to familiar with that but it seems normal from what I have read. A couple of the plug wires seem to have pretty high resistance with the highest being 6Kohm/ft. I plan to buy some wires soon and see for a difference.

Posted: Mon May 27, 2013 3:46 pm
by jacmifish
Okay so I resolved the issue. The problem was I was following an incorrect diagram of the coil block order :( so two of the pairs were switched :oops: Everything seems to function now and the only odd things is when it is at idle the rpms seem to flutter a bit but they die away.

Also I checked with using my tachometer and ecu unit at the same time from the megajolt and its seems to work fine =)

Here is my video of it on start up
http://www.youtube.com/watch?v=mHFyjEBI ... e=youtu.be

Posted: Tue May 28, 2013 5:35 pm
by brentp
Hi! glad you got things sorted out!