Battery voltage 0.10????

[Nick1224]

My Jeep Grand Wagoneer has been running on MS1 v2.2 fuel only for almost three years now. My HEI4 pin module died so I decided to build a MS2 v3 (code 2.89 I think...whatever one is posted in the megamanual) and use a 7 pin so I could control timing.

I had to decrease my fuel A LOT and then it hit me that the battery voltage low might be contributing to this. Actual running voltage is 14.4ish but on the realtime display it reads 0.10v???

Has anyone experienced this before or have any ideas? Seems to run fine but want to get this fixed before tuning it too much further.

Thanks

[Matt Cramer]

Check R3 and R6, and make sure the boot header on the main board is not shorted out.

[Nick1224]

H1 is not jumpered. R3 and R6 read ~8k ohms each and appear to be soldered in OK.

I did notice the strip (copper strip embedded in the PCB) that passes from the power input 12v+ on the DB37 and goes on the outside corner on the bottom of the main board toward the FETs appears to have shorted at some time.

[Matt Cramer]

H1 is not jumpered. R3 and R6 read ~8k ohms each and appear to be soldered in OK.

Not good when R3 is supposed to be 50K and R6 is supposed to be 10K.

I did notice the strip (copper strip embedded in the PCB) that passes from the power input 12v+ on the DB37 and goes on the outside corner on the bottom of the main board toward the FETs appears to have shorted at some time.

You'll need to jumper around it then. This is what supplies power to the battery voltage measuring circuit.

[Nick1224]

Thank you for your help! I'm going to be a little dense here.....looking at the v3 diagrams.....do I need to jumper from the 12v DB37 pin to R3? I tried just jumpering from 12v DB37 to the lead of the fet it looks like it's going to and it started to smell like electrical burning so I shut it off and removed it.

Thanks again and sorry for my lack of comprehension....been out of the MS world for a long time.

[Nick1224]

I checked voltage at R3 and there is almost nothing there.....0.10v. So Can I just get 12v to R3 or will I fry something?

[Matt Cramer]

You'll need to figure out what's burning. Do Q9 and Q12 have the mica insulators under them? Make sure they're not shorted to the heat sink.

[Nick1224]

Q9 was grounded! Thanks!

Got battery voltage and got everything retuned now that it isn't compensating for "12v" of battery difference.

It will idle forever, but now U5 heats up after driving for 5 min and everything shuts down....boo. I'll have to look through to see what that could be.

[Nick1224]

I replaced U5 and it still gets crazy hot. There was infinite resistance between the U5 holes when I replaced it. When U5 gets really hot the car stalls or MS shuts down. Any ideas?

[Matt Cramer]

There's a short somewhere on the 5 volt side of the MS that is causing the U5 to draw more current than it should.

[Nick1224]

D19 conducted both ways....so I replaced it. They didn't have the 6.2v so I used the 12v until I could get one. Car ran great drove for 40 min on the highway. So we decided to use the Jeep for our camping trip. Ran great until it just lost power. Ms had no flashing lights and megatune was disconnected. Coasted off the road and found c16 c17 and vregilator to be red hot. Cooled them down and she fired right up. So we checked their temp as we drove. We checked and they were cool and then it shut off again. Then they were red hot. D19 was not appreciably hot. After that I kept Rome under 2750 and we went 90 miles without a glitch. ????????

[Nick1224]

The lead between c16 and the negative foot of voltage regulator was toast. Must have had intermittent connection. Jeep runs better now....but my laptop has a corrupt windows system file. Can't tune any more and ill just have to make it home on that tune. If it ain't one thing it's another. Merry Christmas

[Nick1224]

So Ms shut down a couple more times at random rpms. Switched c16 to 470 if and ran 50 miles and then c17 heated up about every mile. No way to go across alligator alley. Replaced c17 at a rest stop with another 470 if and ran the 100 miles home without a glitch. What harm can come from such a large cap at these sites?

Glad I made it home. Glad I brought the soldiering iron and power inverter.

[Matt Cramer]

Replaced c17 at a rest stop with another 470 if and ran the 100 miles home without a glitch. What harm can come from such a large cap at these sites?

Glad I made it home. Glad I brought the soldiering iron and power inverter.

No such thing as too much filtering your power supply. 470 uF should be fine.