No o2 and RPM signal

[MadMax78]

Hi

I'm at step 55 of the assembly and testing the inputs with megatune. My CLT, IAT, TPS and mapdaddy are working. However my o2 and rpm gauges are not.

For the o2 I checked the voltage output on pin 28 of the cpu socket, it receives a voltage there and when I change to o2 pot the voltage changes. So the correct voltage reaches the cpu pin. How could it happen I can't read this value in megatune? I loaded the AFR table for the LC-1.

As far as the rpm goes, I can't get it to do anything. I don't know how I should error check this circuit. Also in the manual a couple of things are not so clear to me. I want to use a VR sensor trigger wheel on crank assembly to let the MS control my coil and let the dizzy only route the spark, nothing more. So I installed everything as per step 50B but skipped 50B7 and 50B8, maybe that is why it is not working. Can someone tell me if I can install these capacitators with the setup I have in mind? I was a bit confused since the manual explicitly stated they should only be installed if you did not want to control ignition timing.

I followed step 51 all the way and at step 52 I jumpered VRIN to TACHSELECT and TESEL to VROUT.

Also how should the pots R52 and R56 be adjusted to get a RPM reading? I tried rotating them CCW untill they started to make a clicking sound? Is this normal?

[MadMax78]

Strange, I can't edit my posts for only a couple minutes after posting. Anyway, I did some more searching on the site and found that the o2 reading does not refresh if there is no rpm signal. I did a test by plugging in the MS, reading the AFR value, unplugging the power, changing the o2 pot and plugging it back it. o2 seems to work fine, so that's one "problem" solved.

So it's just rpm that's not working. I searched and read numerous topics but couldn't find any information on how to effectively troubleshoot this. I checked out the page on adjustment of R52 and R56 and tried rotating R56 CW from fully CCW, but to no avail. At least now I know the click sound isn't because I destroyed them

I'm calling it a day for now...

[MadMax78]

Ok, did some more testing,

I did the LED test, and it flashes when I connect it to ground and VRIN/TACHSELECT, so summarizing:

- Stim is adapter powered, MS has 9.8 volts on U5 and 4.99 on the regulated side.
- D1 and D2 are installed, D2 is installed in reverse and jumpered
- VRIN is jumpered to TACHSELECT
- TSEL is jumpered to VROUT
- I tried the recommended adjustments on R52 and R56
- I have a flashing LED when I connect to the VRIN/TACHSELECT and ground

[MadMax78]

Sorry for having a bit of a single sides topic here

It's really annoying I can't edit my previous posts...

It's quite hard to do searches because I can't search for 3 char terms like rpm or Q23. I just started looking through older topics and some similar problems occurred, some people had problems with transistors Q22 and Q23. I checked the resistance on these and I noticed that on Q23 the two pins nearest to the DB9 side of the board i.e. the left two (looking at the top of the board) are connected to each other, 0 resistance. This is different on Q22 and some other transistors I checked. Is this normal or does it mean the two pins are soldered together?

I tried to remove some solder with my wick, but the terminals are so tiny, I can't get it out. So before I go any further it would be nice if someone could confirm that this is likely to be the problem.

[Matt Cramer]

Q23 can appear shorted depending on how you have adjusted R56.

Also, make sure the wheel decoder is off (trigger wheel teeth set to 0).

[MadMax78]

It indeed was the R56 adjustment that caused the "short". So that shouldn't be the culprit then. I verified the wheel decoder is set to 0 in megatune.

[Matt Cramer]

Will it work if you jumper it for Hall/Optical?

[MadMax78]

Ok, so I swapped the VR jumpers to hall jumpers and added the xg1 xg2 jumper. It now does get a tach signal .

So errr... what does this mean for the VR circuit?

[Matt Cramer]

You'll need to follow the signal through the VR circuit with your LED tester. Where do you lose the signal?

[MadMax78]

I found the problem, U7 was still in a pink bag. And errr, I couldn´t find U4... So... I installed U4 in the place of U7. Do you think this may have busted a component? Or should I be good if I just desolder it and put in U7?

Can't believe I actually made such a dumb mistake

[Matt Cramer]

Should be safe to just swap them out; it's not likely anything is damaged.

[MadMax78]

Awesome, it's working!

For the record, I got R56 all the way CCW and R52 two rotations CW, gives me stable rpm from 0 to 7k rpm.