vb921 problem

1seymour · Post by **1seymour** » Wed Jul 12, 2006 9:08 pm

when i set my dwell to > 3.5, after running for about 5 minutes, if i rev the car, the spark cuts. if i lower it to around 2.0, i can run for more time before it happens. does anyone know what might cause this and what i can do to fix it?

v3 board, v29q2 code

some logs and my msq at:

http://www.msefi.com/viewtopic.php?t=20106

davezed · Post by **davezed** » Thu Jul 13, 2006 1:19 am

Hi 1seymour
First up the usual array of "suck egg" questions:
1) Is the transistor getting hot (Q16)?
2) Did you build the MS or buy it?
3) From above, there is a pull down resistor allocated on the PCB (R57) to the base of the VB921, the manual advises not to install this (http://www.megasquirt.info/ms2/ the select V3 Main Board and search for Q16 and/or R57), can you confirm R57 is not installed?

Cheers
DaveZZ

davezed · Post by **davezed** » Thu Jul 13, 2006 1:37 am

Next time I'll follow your link/MS version before commenting,
First up, are you using Q16? If not then the output driver (Q6) to the D14 (the one you have selected to give spark out) will not handle what you are trying to drive. You have dwell control selected so I assume you are driving a coil directly. If so then either ensure Q16 is linked in to drive the coil or some other driver circuit.

Cheers
DaveZZ

Post by **jsmcortina** » Thu Jul 13, 2006 1:53 am

If you can run fine at 2.0ms dwell then use that setting. Excessive dwell causes overheated coils and ignitors.

James

1seymour · Post by **1seymour** » Sun Jul 16, 2006 6:58 pm

just double checked, everything looks good.

prebuilt unit. i have a stim and it appears to work fine on it.

jumpered igbtout to ign.

r57 is not installed.

330ohm resistor between igbtin and "top of r26".

i have the resistor in r43. since it didn't say i had to remove it, i didn't. "most users replace with a jumper"

i'll check to see if q16 gets hot shortly.

1seymour · Post by **1seymour** » Sun Aug 06, 2006 11:44 am

it doesn't get hot. not sure what else to check.. any ideas?

corsa_A · Post by **corsa_A** » Sun Aug 06, 2006 10:09 pm

1seymour wrote:when i set my dwell to > 3.5, after running for about 5 minutes, if i rev the car, the spark cuts. if i lower it to around 2.0, i can run for more time before it happens. does anyone know what might cause this and what i can do to fix it?

v3 board, v29q2 code

some logs and my msq at:

http://www.msefi.com/viewtopic.php?t=20106

I have set dwell to 1.6 on vw vr6 engine rising to 2.0 coused ignition cuts at 3500 rpm, so try to lower that value. My vb921 isn`t getting hot with that values.

1seymour · Post by **1seymour** » Mon Aug 07, 2006 6:59 pm

2.0 is as low as i can go to get it idling. above 2.1 doesn't seem to make a difference at idle.

1seymour · Post by **1seymour** » Mon Aug 07, 2006 7:10 pm

i had the car idling for a while tonight without any spark cut, though. i wasn't doing a whole lot of revving, though, just tuning my idle. i'll try revving it up now to see if i can get it to act up. i thought it was fixed once before like this but only to get about a block down the street before turning around and limping it home.

im at 4.0 cranking, 2.3 running and 0.1 min. discharge right now.

1seymour · Post by **1seymour** » Mon Aug 07, 2006 7:18 pm

i can't get it to cut out now.. i'll take it for a spin in a little bit and see what happens.

1seymour · Post by **1seymour** » Mon Aug 07, 2006 8:22 pm

the problem seems to be gone for now at least at lower rpms. i'm going to keep tuning and see what happens.

1seymour · Post by **1seymour** » Wed Aug 09, 2006 10:11 pm

im using 2.3 running and 4 cranking with a 0.1 min discharge now. i was able to go around the block so i think the issue is solved. anyone know why this would happen?

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