Cam and Crank Oscilloscope Pics

[krazy86t]

I've found a few threads talking about cam/crank timing and measuring signals with an oscilloscope. Unfortunately, most of these are so old that the picture links are dead and gone.

For instance this thread

Or several old posts on this thread in turbobuicks.com by GnJones231

http://www.turbobuicks.com/forums/129937-post10.html

Anyone else able to post pictures of cam/crank signals obtained on oscilloscope?

Thanks!

 

[krazy86t]

I'll load a couple pics. First is signal traces and it runs good. Delay from crank rising edge to cam signal falling edge is 36deg.

 

[krazy86t]

Next, is a trace when car was ok on start and idle but drove terrible. No power, backfire, surging

Crank rise to cam fall is 29 deg, too much CCW rotation on cam sensor

 

[87GN_70GS]

So the more advanced the cam sensor is the better it runs? Would be interesting to see the maximum amount of cam sense advance that can be tolerated

 

[krazy86t]

The gnttype.org web page on cam sensor set-up explains a lot of the details. Another page has instructions for setting crank-cam sensor timing with oscilloscope.

Crank signal is 60deg wide, so use this as reference to convert time display to degrees at any rpm. Assuming #1cyl on compression crank rising edge is 10deg btdc, cam signal falling edge should be 35deg later than this crank rising edge (35 +/- 5deg is spec). Obviously this corresponds to the well-known 25deg atdc absolute timing for cam sensor set-up.

So mine ran poorly when at 29deg, or cam signal advanced relative to spec. CCW rotation of cam sensor cap advanced the cam signal and probably messed up injector timing. +/- 5deg is pretty big window to hit, but I was slightly out at -6deg so car ran poorly. I would guess something similar would happen if +6deg (retarded atdc) with more CW turn of cap, but I didnt try it.

 

[TurboBob]

The gnttype.org web page on cam sensor set-up explains a lot of the details. Another page has instructions for setting crank-cam sensor timing with oscilloscope.

Crank signal is 60deg wide, so use this as reference to convert time display to degrees at any rpm. Assuming #1cyl on compression crank rising edge is 10deg btdc, cam signal falling edge should be 35deg later than this crank rising edge (35 +/- 5deg is spec). Obviously this corresponds to the well-known 25deg atdc absolute timing for cam sensor set-up.

So mine ran poorly when at 29deg, or cam signal advanced relative to spec. CCW rotation of cam sensor cap advanced the cam signal and probably messed up injector timing. +/- 5deg is pretty big window to hit, but I was slightly out at -6deg so car ran poorly. I would guess something similar would happen if +6deg (retarded atdc) with more CW turn of cap, but I didnt try it.

so, connect to one of the injector channels and measure it. as far as I have been able to find, the cam sensor timing does not affect the injector timing.



Bob