CX500 Turbo RPM wrong

[eestrine]

Al and Experiewnced Squirter

Thanks for the diode pix, installed diodes but didn't help. Ran the tachref program today. First I hooked the crank sensor to VR1, got good pulses. Then the Cam sensor to VR1, good pulses. Removed signals from VR1 AND hooked the Crank sensor to VR2, NOTHING-no pulses. Opened uSquirt box and checked the connections, everything good. We have two uSquirt boxes, both did the same thing, no pulses on VR2. Could it be that both are bad in the same way??? I doubt it.

Looked carefully at the circuit board, I may be wrong but it looks to me that there is no trace from pin 4 of the big connector to anything else on the board. Hard to check circuit because of unclear markings on board.

Tomorrow will put the scope on pin 3 of the CPU and see if there is a signal there.

Elliott, MSEE, MSCS

[24c]

Elliot, are you using the cam lobe to trigger your cam sensor? I read earlier you have one tooth, just checking because cam lobes give a lower voltage than a sharp edged tooth profile. You have tried reducing the clearance to improve the volts generated, so an easy thing to try and boost the VR2+ sensitivity is to mod the offset voltage...by altering R48 or R55.

[eestrine]

24c, please do not respond to this message. I need to hear from Grippo. Thanks


I looked at pin 4 of the big connector and get a good 4 volt peaK to peak signal. At pin 3 of the CPU, there is no changing signal, just a constant 5 volts. I do ot have the facilities to be messing around changing the resistor values. Grippo, is 4 volts p-p enough to trigger the computer??????

Elliott

[grippo]

The VR2 signal does not trigger the ECU directly, it is what comes out of the Tach2 circuit and you are saying that is a flat 5V, so that is why the ECU is not being triggered. I hope you didn't try scoping pin 3 at the processor - that is extremely easy to fry. It should only be checked at R58. The transistor Q7 at B (base)is what is not being triggered, because if it was current would flow from C to E and the output end of R58 would change from 5V to 0V and the ECU would be triggered.

I believe that 4 V should be enough to trigger Q7, but I will ask Bruce to take a look at this thread.

[Bruce Bowling]

I looked at pin 4 of the big connector and get a good 4 volt peaK to peak signal. At pin 3 of the CPU, there is no changing signal, just a constant 5 volts. I do ot have the facilities to be messing around changing the resistor values. Grippo, is 4 volts p-p enough to trigger the computer??????

Elliott

OK - lets check the VR2 input circuit to make sure it is correct:

1) Disconnect the second VR sensor from the VR2in+ input.
2) while looking at the voltage on pin 3 of the processor (or either side of R58) touch the VR2in+ wire (going to the ampseal pin 4) to ground - what is the voltage?
3) Do the same thing, this time touch the CR2in+ wire to ground - what is the voltage?

You can do this test on the second VR channel because the trip threshold is roughly 1.7 volts - the 0 volt and 5V (vref) swing past this threshold and you should see the transition on the output.

Report back here.

BTW - 24C is on the right track with the diodes, lets make sure the circuit is working as it should, this test will give us that answer.

- Bruce