Erratic RPM reading with Sincotech 922 digital display Any other rpm signal locations

[Oktobr]

Car is a 1989 240 stock b230F

Hooking the control module and the display directly to pos and neg of batt both power up and sync. The sincotech has one signal wire to the module for RPM signal. I've tried directly from the neg terminal of coil and also from the white with red wire behind dash. Both exhibit same behavior. RPM is erratic and jumpy both in numbers and the graph displayed. With what seems to be a lot of noise. I can make out that it is reading the signal somewhat accurately behind the noise. Any assistance would be appreciated. I've read some meters require a 10K ohm .5 watt resistor added in line to the rpm signal from the coil will reduce the noise. Wanted to ask around before I did anything. Thank you ahead of time. Is there a signal from injectors I could tap into?

 

[bobxyz]

I couldn't find an online installation manual for the 922 - what does it say about hooking up the RPM wire?

I did notice that they offer a $20 RPM adapter to fix the problem:

DO914 Sinco Tech Rpm Adapter

It is suitable for SINCOTECH SENSOR KIT RACING CAR DASHBOARD,such DO904/907/908/909/912S/916S/922/926. when you gets REVs from Ignition coils and find the RPM band is alwasy flashing , it means the RPM signals are disturbed, you can install the RPM adapter to resolve the problem .

sincotech.store

Alternately, you could try tapping into the EZK-to-ECU RPM wire. It's EZK pin 17 to ECU pin 1 (for LH2.4). The mitchel's wiring diagram says the wire is YEL-GRY at the EZK but BRN at the ECU. I'm sure the pin numbers are correct, but don't trust those wire colors.

 

[Oktobr]

Partner, If I could buy you one I would. Please have the next one on me. Thank you very much. I reached out to Sincotech and they were actually at a loss. So imma try that part they have after my tapping attempt. The only pictures they have in the manual are very lacking. It shows going straight to coil neg.

 

[Oktobr]

Adding a 10K ohm .5 watt resistor inline with the signal didn't work. Guess that's for magneto ignitions.
Next step, is to try and tap at the EZK. Last but probably what I should do is add that RPM adapter. But that's gonna be a wait for it to come in. Shows 20$

 

[dl242gt]

It's probably set up to work with a digital rpm signal. If there is enough signal strength to drive the sinco tech unit the digital rpm signal from the EZK to the ignition amp should work.

 

[Oktobr]

It's probably set up to work with a digital rpm signal. If there is enough signal strength to drive the sinco tech unit the digital rpm signal from the EZK to the ignition amp should work.

Where is best place to find that? https://ozvolvo.org/d/9733-9733

 

[dl242gt]

Where is best place to find that? https://ozvolvo.org/d/9733-9733

Rather than mess with the EZK I would try pin 4 of the ignition amp. That is the trigger signal from the EZK.

 

[Oktobr]

.

 

[Oktobr]

gonna try blue wire on powerstage pin #4

 

[dl242gt]

gonna try blue wire on powerstage pin #4

I'm sorry, I think I made a mistake. It looks like the shielded signal is pin 5. Try pin 5..

 

[Oktobr]

I'm sorry, I think I made a mistake. It looks like the shielded signal is pin 5. Try pin 5..

Yeah blue didn’t work. On my 89 240 I have small black, larger black, white/red, and blue wire from the powerstage. The larger one would be the shielded one right? And I don't think a regular wire tap would work there huh.