Step 55 weird tps readings

[akeboshi]

I'm on step 55 of the ms2 v30 pcb installation and all the sensors are reading off the stim nicely except for the tps sensor. I try to calibrate it in megatune but it doesn't work. The two references are the same even if I turn the pot nothing happens. I tested the voltage of the tps pot and and it varies with resistance smoothly, resistance readings are ok with the pot and resistors r4 and r7 are reading 2.42k ohms as well. What is wrong?

[msiddalingaiah]

Can you trace the TPS signal all the way to the processor? Check C8, C9, and R9. You might have left out R9 or shorted a connection to ground.

[akeboshi]

i just checked what you suggested, c8 was 1.084 c9 was 0.103 BUT when i have the leads off the board it says .094 on the fluke. r9 was 1k. everything looks ok except that if one would subrtact what the multimeter was reading with open leads from the actual reading with the capacitors it would be .887 for c9 is that an ok reading?

[msiddalingaiah]

i just checked what you suggested, c8 was 1.084 c9 was 0.103 BUT when i have the leads off the board it says .094 on the fluke. r9 was 1k. everything looks ok except that if one would subrtact what the multimeter was reading with open leads from the actual reading with the capacitors it would be .887 for c9 is that an ok reading?

I'm not exactly sure what you are measuring there. What is the voltage along the signal path from the stim back towards the processor?

[akeboshi]

c8 and c9 are capacitors so i checked the farads, and r9 is resistor so i checked resistance. ill follow the voltage from the stim to the megasquirt board as you said as soon as i get another chance. thanks so much for the help!

[akeboshi]

i went ahead and finished all the steps and i hooked it up to the computer and laid the unit (inside the case) on the hood of my car. i turned all the knobs and low and behold the tps worked as well or so i thought.... it seemed to work correctly for 20 or so seconds and then did what it usually did-picked a random number and slowy increased. i checked r9 like it said in the troubleshooting section but its exactly the opposite of what it says in the megamanual.


You can measure the resistance of R9 directly on the board (it should be about 1K Ohm ± 50 ohms). R9 is above the "&" in the copyright notice. You can also check the resistance from the CPU pin #26 (near the H1 boot header) to R9 - on the side of R9 nearest the DB37 you should have less than 1.0 ohm (0.1 is better), - on the side of R9 nearest the DB9 you should have ~1K Ohm.
i have 1k of resistance on r9 itself (good)
i have 1k on the side nearest the db37 (NOT good)
i have 0.3 ohms on the side nearest to db9 (also not good)
what did i install wrong to make it do this?

[msiddalingaiah]

If you are measuring resistance from from CPU pin 26 to R9, and both side of R9 read 1K, there is a bad connection from pin 26 to R9. Take a look at the board itself and follow the trace from pin 26 to R9 (or from R9 back to pin 26). Pull the CPU and measure the resistance from the socket. Check CPU seating and solder joints.

[akeboshi]

GOT IT!!!!! i did what matt told me and measured volts on pin 26 to the grounds and they faded so i checked the joints to the db37 and i found a janky looking one. resoldered it and npo it works adc is 8 and 1080- perfect. thanks for helping me fix this problem!!!! megasquirt is kickass!!!!