CX500 Turbo RPM wrong

[eestrine]

I am working on a Honda CX500 Turbo. Using dual tach mode. Two VR sensors 80 degrees apart, one 1 inch long piece of metal on the crankshaft that triggers sensors. The engine finally runs but the RPM in the data log is wrong. ON the electric tach connected to the coil the RPM is steady at 4000, but the RPM in the data log is changing between 6000 and 10,000. Also, the advance is changing between 27.5 and 15.7, when the table is filled with 26.0. (27.5 is the base timing setting). I tried connecting 1k resistors from the VR+ to VR ground on both sensors as Matt suggested. Made it better than with no resistors, but still very noisy. Also tried 2k resistors, not much difference than 1k.

Elliott

ps. my email has changed to etmagic@indie-promos.com

[24c]

Looks like you are reading double, as 6-10K is 8000 give or take 2K revs. You don't have the MAP connected or anything that is causing the advance to fluctuate, IAT temp or retard settings etc in some other area of the MicroSquirt software?

[grippo]

Are you maintaining synch - or does the rpm keep jumping to 0 ? Does the trigger+/ count up or down in the datalog ?

Also make sure the second output offset (Odd-fire angle) is set to 0. This is NOT to be used in dual tach mode because the odd-fire is taken care of by the location of the sensors.

[eestrine]

Attached are the data logs from the runs with the 1k and 2k resistors. It appears that we are staying in sync. As you can see, the trigger+/- counts down and then stays at a fixed negative value. The second output offset is 0.0. The MAP is connected.

Elliott

[grippo]

If you plot the deltaT column you will see that the values alternate between 5000 and 15000 microsecs - or 5 and 15 ms. That is what the ECU is seeing as tach input pulses. It is really seeing this because all it does is time the pulses and this is what it is seeing. From those numbers it calculates the rpms. It is too consistent to be noise, unless it is crosstalk between the inputs, so both sensors are coming in on the same channel. I don't see how the engine is running like this. You could try disconnected the one of the VRs and see what that looks like, then do the other. When you do this, disconnect the injectors so you don't screw up your engine. A scope would make it easier.

At 4000 rpm the pulse from a single tooth wheel will arrive every 15 ms, so those are the correct ones, the 5 ms may be coming from the crosstalk or whatever it is.

[eestrine]

Well I found the problem with the changing advance. The RPM limiter was set at 10250 rpm to retard 12 degrees. The incorrect RPM was now and then exceeding 10,250 and that was causeing the retard. This did not change the RPM problem. Will try single cylinder tests on Monday. Should these be done in single or dual mode??

Elliott

[grippo]

If you have a scope, I would run the dual mode and scope each VR input. The time between the falling edges should be the same on both channels, but they will be out of phase by the angle by which the sensors are offset. Another option is to use the tachref program to capture both VR inputs. In this case the tachref program replaces the normal code and there is no mode.

If you just run the program and use it to get the deltaTs, run Dual mode but make 2 runs, the first with VR2 disconnected, the second with VR1 disconnected.

[eestrine]

We have decided to abort using two crank sensors. Instead we will use the CX650 flywheel which has 9 (nine) trigger tabs soldered to the flywheel. We will use 1 crank VR sensor and 1 camshaft VR sensor. NOt clear which mode I use to get the engine running in this configuration. Would appreciate help with settings. The crank sensor is connected to VR1 input and the Cam to VR2 input. One coil on output 1 and one on Output 2.

Thanks
Elliott

[24c]

eestrine I don't know if 9 teeth will work

[grippo]

In the configuration you are talking about, you have 2 cylinder sequential Use the option for "M-0 Wheel w/ Falling Cam Sync with Tach or Wheel" or Rising whatever worked before. Skip teeth would be 9 and 1 cylinder would fire every 360 deg. This should be a much better setup than the dual tach which gives poor timing resolution during accel/decel.