MSefi.com read only forum (Jan.15,2018)

Hi Guys,
I have a MSII with a V3 main board that I have been running for a few years with no issues. Started having problems this spring with it going lean under acceleration. Now it does this plus does not want to start and run intermittently. When it does run the problem gets real bad after the warm up enrichment kicks off. On top off this I am having issues with the serial connection working. I purchased a new cable with the same results. The two problems seem to be related.
The stim is working like it should and I can see all the parameters on tuner studio. I can get the serial connection to fail on the stim after the mega squirt has been up and running for a while. Cycling power to the stim will allow it to reconnect sometime. Or I just have to wait for it to cool down.
This is a list of things I have done and checked.
Loading latest 2.92 code and it did not help. Was running the 2.90 code.
Cleaned the board with IPA and a tooth brush.
Checked the clock count up and did the loop back test.
Checked U5 found the left side at 11.44 Volts, Good Ground in middle, and 5.04 on the right.
S12=12.16V S12C=11.43V Proto Board =5.04V Boot Jumper =1.95V On the 40 pin board, pin 19-20=5.04, pins 1-2=5.03, pins 31-32=5.03
Checked RS232 for volts and ground and found. Pin 1=4.92V Pin 2= Negative 6.86V Pin 3=4.33K Ohms Pin 4=Open to Ground Pin 5=3.2Ohms Pin 6=Open to Ground Pin 7=4.34 K Ohms Pin 8= Negative 6.88V Pin 9= 4.92V
Performed the connection troubleshooting guide with no issues found.
Checked Q12 and Q9 resistance to ground between the heat sink and the tab. Both are about 60K ohm.
Replaced the fuel pump and filter. Swapped F.P Relay. Removed and cleaned the injectors. Did the injector test mode. No issues found. Checked plug wires and changed the plugs with no change.
Confirmed the IAC , TPS, Coolant, and IAT are working normally.
I attached a data log from a few weeks back. Any suggestions on other things to check would be appreciated.
Thank you for your help.

Do you still have 5V on VREF when the communication shuts down on the Stim?

Matt Cramer wrote:Do you still have 5V on VREF when the communication shuts down on the Stim?

Sorry for the slow reply.

I believe I still had 5 volts even with the communication loss. Not sure where to check for the 5 volts on the stim? I did check for 5 volts at the TPS VREF and it was there with comunication loose.

I've done a few thing since my last post. I changed U6, C22, and D19 with no change. Then I pulled the relay board and found that I could make the injector terminal block go open by wiggling it. So I took the relay board out and wired everything up direct. At this point I thought I had the problem fixed. The jeep started and ran good and I was able to communicate with the laptop. However after driving for about 7 miles it quit and smoke came out of the computer. C16 and R20 are toast. Plus one of the TBI injector fuses blew. But I believe the fuse blew when I tried to restart on the side of the road. Both of the fuel injectors have ohmed out good when I have checked them.

So, did something on the jeep side cause the issue with the computer? Or is the problem with the computer?

Right now I am planning on changing C16, C17, R20, and possible U6 again. Any other components I should consider ordering? I attached a photo of the board showing C16.


Thank you for you help.

Have you checked your fuel pressure using a gauge?

I've seen voltage spikes pop C16 before. We up-rated C16 from 25 to 35 volts a few years ago to improve durability.

Matt Cramer wrote:I've seen voltage spikes pop C16 before. We up-rated C16 from 25 to 35 volts a few years ago to improve durability.

Thank you Matt. I will be placing an order.

Due to frustration I took a break from try to fix this computer. I was back at it today and replaced all the items that were smoked including R20. Now as soon as I put power to the Stim R20 starts to smoke again. Does anyone know what will cause this?

A resistor smokes because something that it's feeding is drawing too much current. Most likely in this case, Q5 or Q15 has failed short circuit.

trakkies wrote:A resistor smokes because something that it's feeding is drawing too much current. Most likely in this case, Q5 or Q15 has failed short circuit.

Do I check Q15 like a normal transistor? Can I check them both without pulling them out of the board? Thank you for your help.

Ok gentlemen I have the short to ground issue fixed. I replaced Q5 and Q15. That took care of my smoking R20.

Now I have two other issues that are plaguing me.

First when the computer is hooked to the vehicle I can not see EGO voltage. However if I briefly touch pin 16 power to pin 15 ground on U6 the EGO voltage comes to life on Tuner Studio. Then if I try starting the vehicle it goes away soon after start. I have confirmed correct EGO voltage on pin 28 of the CPU when it is not showing up on Tuner Studio.

My second issue is that Tuner Studio does not want to come on line or dies soon after engine start. Its is working at this time and I was able to do a data log that I attached.
If you look at the data log you will see the EGO working and then quits soon after start. Then a pause and then me grounding pin 16 with the EGO coming back on line.

Everything seems to work ok on the Mega Stim.

During the repairs I did load the latest MSII code.

Any ideas? Could I have a bad CPU? Thank you for your help.

Tune File:

Can you replicate either problem on the Stim, or do both the EGO readings and your communications work normally there?

Matt Cramer wrote:Can you replicate either problem on the Stim, or do both the EGO readings and your communications work normally there?

The EGO readings and communication are normal on the Stim.

Are you using non-resistor spark plugs by any chance?

Where is the MS grounded?

Matt Cramer wrote:Are you using non-resistor spark plugs by any chance?

Where is the MS grounded?

Using an Auto Lite resistor plug. The ground is run to the engine block and the negative lead from the battery is hooked to it.

Matt Cramer wrote:Are you using non-resistor spark plugs by any chance?

Where is the MS grounded?

I moved the grounds directly to the battery with no change.

Basically I am back to my original problems:

1st It starts and runs on warm up enrichment. As the enrichment kicks off it runs worse.
2nd the laptop does not like to connect. If I connect the USB cable when the engine is running it kills the engine.
3rd when tuner stuido is up there is no O2 voltage.

Everything works normal on the Stim.