Voltage Issue Help

[mvega801]

Hello all, this is first time posting about an issue on this forum just want to say thanks as I've found lots of information on trouble shooting threw out the years while visiting the forum. I have been searching the web and forums and have not found any of the symptoms similar to one's I have encountered in the last few months.

the car is a Toyota ae86 with a hi-comp 4age on 8psi of boost
silver top block with stock st pistons and 16v head from large port blue top.
440cc supra injectors.
gm. IAT sensor
stock dizzy.
t/3 turbo.
ms1 3.0 running latest firmware 029y4a

The issue occurred after a boost leak test. while assembling the vehicle the battery was being install and the wire that goes to the starter was put on the ground of the battery a mistake on my part do to all my cabling being the same color. I went to start the car and just heard the solenoid engage, so I quickly swapped the wires back and started the car it ran a bit rough at first but then ran fine after it warmed up I thought the roughness was in part to do with the air leaks in the throttle body (which are fixed now). so I took the car for a test drive and got a hesitation around 3500-4000 rpm right around when the turbo kicks in after 4000 rpm it kind of just works past it and power comes back. I have been logging all my runs and have noticed the mat signal is different than before.
So I started to check voltage coming out of the sensor wiring and I am getting 2volts disconnected, CLT sensor is the same also. I pulled MS apart checked r4 and r7 I have 5volts going in on both R7&R4 and 2.19 volts after on both R7&R4. I did not build the unit it came preassembled and I am just wondering if I should be seeing 5volt at the IAT&CLT sensors. TPS has 5volt, Map has 5volts also, Map and IAT sensors where replaced with new ones in an attempt to figure the problem out.

2014-11-07_11.33.15.msl

2014-12-05_16.59.58.msl

msq as of now.zip

Thank you I hope you can help as I am all out of ideas

[john.p.clegg]

In the dim and distant dark recesses of my mind I seem to recall changing the resistors R4 and R7 to calibrate the air/coolant sensors rather than do it with firmwear...maybe 27Kohm.

John

[mvega801]

john thanks for the info I will try and see what happens, I will post my results thanks again.

[mvega801]

Update, after replacing the r7 resistor with 2.2k recommend for Toyota sensors (I left r4 resistor in place as it is used for GM IAT sensor) I am still experiencing the same issue with the car.
There does seem to be a lose of power and it is a bit sluggish while cruising before hitting boost where it bucks and hesitates, range is around 3500rpm.
There is also no change in the logs, my MAT and CLT are not really registering any changes or doing any thing in megalogviewer, they are minimal not consistent like in previous logs.
Just to try to rule out any ground wire issues or shorts in the harness I ran the sensors straight to the MS unit with no luck.

voltage filters for MAT are r5,c5,and c6 and CLT are r8, c8 and c7 these do not appear to be damaged
Is there a chip or processor that is dedicated to providing direction to these sensors like chip 4n25 on MS board is it possible that I burnt this chip up when the wires were crossed on the battery, sending some type of voltage spike?

Any help or ideas are welcomed, and thanks again guys

[mvega801]

Well it seem there is more to problem then I described in my original post the voltage issue is internal I have been searching the forums and have came across the test procedure for sorts in the board, the only thing that is out of circuit is d19, I am stuck on what I should pull out next to diagnose, any help would be appreciate thanks.

Test with cpu in place 12.52v from power source. with d19 out of circuit.

u5 left leg 11.82v

q9 center leg 10.24v

s12c 11.76v

s12 10.24v

q12 10.28v

d9 banded end 11.57v


test without cpu in place. with d19 out of circuit

u5 left leg 12.23v

q9 center leg 12.27v

s12c 12.19v

s12 10.23v

q12 10.25v

d9 banded end 12.23v


5volt rail cpu in place, d19 out of circuit

s5 4.93v

proto area 4.93v

d9non banded end 4.96

u5 right leg 4.96

d19 banded end 4.93


5volt rail without cpu in place d19 out of circuit.

s5 4.95v

proto area 4.95v

d9 non banded end 4.96v

u5 right leg 4.96v

d19 banded end 4.95v

cpu pins 1, 20, 31, all have 4.93v

[Matt Cramer]

There is a partial short from 12V to 5V, but (oddly enough) not enough current flowing through it to fry D19. Try cleaning solder flux and residue off the board to see if that's shorting it together.

[mvega801]

I'll get it cleaned up and redo voltage tests, thanks Matt.

[mvega801]

My results after cleaning the board, I am lost cause the voltage has switched around now. where I was not seeing 12v I am now seeing it, and where I had 12v previous the voltage has dropped. I cleaned the board as stated in the manual, cleaned a few times to verify what I was seeing. What is the minimum voltage for12v and 5v rail? Should it be higher than 12v or 4.98v? Thanks again for the help, I feel like I am getting closer to figuring this issue out.

Test with cpu in place 12.30v from power source. with d19 in circuit.

u5 left leg 11.53v

q9 center leg 12.31v

s12c 11.55v

s12 12.31v

q12 12.31v

d9 banded end 11.55v


test without cpu in place. with d19 in circuit

u5 left leg 11.59v

q9 center leg 12.32v

s12c 11.59v

s12 12.31v

q12 12.31v

d9 banded end 11.59v


5volt rail cpu in place, d19 in circuit

s5 4.93v

proto area 4.93v

d9 non banded end 4.96

u5 right leg 4.96

d19 banded end 4.93


5volt rail without cpu in place d19 in circuit.

s5 4.95v

proto area 4.95v

d9 non banded end 4.96v

u5 right leg 4.96v

d19 banded end 4.95v

cpu pins 1, 20, 31, all have 4.93v

[jsmcortina]

Quick answer. 4.8-4.9V is fine. 11.5V is ok with a 12V PSU also. I didn't check the detail any more than that.

James

[mvega801]

Thanks james, would this explain why the sensors, mat & clt have been reading slow or barely logging information back to the megalogviewer? The car ran great for years, before this issue. Thanks for the help.

[mvega801]

What would be the next thing to check on the 5v rail? With the voltage just being shy of 5v I'm not to sure where to go from here, I don't want to cause any damage to the board. Thanks.

[slow_hemi6]

Having had a read of your problem and what caused it I would have actually tried to reload the firmware to the processor first. If that gave no positive result then given your voltages seem ok, I would have had some fears for the processors adc channels and tried a new processor. I have 2 spare MS1 processors though, so fairly easy for me to do that.

[mvega801]

Thanks luke. I upgraded to the latest firmware available when the issue occurred, but I will give that a try n report back. Thanks have great weekend.

[mvega801]

After reloading the firmware, I gave her a start she was rich at first, I turned down the fuel a bit and she idled fine. Voltage has remained the same, I then used the wife's laptop that is running windows XP( mine was w7) I was a able to get a good log with the CLT reading close to MAT. I'm not sure that w7 might have been making the program read off, Ill check that tomorrow, but the power that came back to the board after cleaning it made a difference. the hesitation is still there but it is very short compared to be for. I recently upgrade the manifold and I am not running TPS any more as my setup has no room for it, I am sure that may be playing a part in slight hesitation, but I will post up my log today and tomorrow when I have a bit more time to mess with it, thanks guys I am happy

[mvega801]

Sorry for taking so long to get back to forums, been working. But I had time to log with w7 and xp and found no difference, the car is running great, thank you all for all the support guys.