Because you can get needed information that isn't available any other way.

Here is one we talked about in the last Group Therapy session that really illustrates this.

'98 Dodge Intrepid with a 2.7 would not start with the cam sensor plugged in.  Vehicle history unknown.

The capture tells all but does take a little study.

Thanks Keith... ;)

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I just got done w/ a 1990 MB that I needed the scope to set the fuel ratio and check 02 switching.  I also used it to see if a switch was working when loaded up. Never could have done it w/o a scope

mikem wrote on Nov 8^th, 2009 at 11:38am:

I just got done w/ a 1990 MB that I needed the scope to set the fuel ratio and check 02 switching.  I also used it to see if a switch was working when loaded up. Never could have done it w/o a scope

Hi Mike

Are you talking about the pressure differential sensor that one measures a low current?

Did you save any waves?

Mick

Tom if that thing is really a 98 don't you have the wrong sprocket on it? The ckp pattern looks right for a 98.
That cmp pattern looks like it belongs with an ngc controller and the one that belongs with that should have grouping of 1,3,2,1,2,3

Rick,

You have my vote for being the next president.  ;)  

Mick wrote on Nov 8^th, 2009 at 12:59pm:

mikem wrote on Nov 8th, 2009 at 11:38am: I just got done w/ a 1990 MB that I needed the scope to set the fuel ratio and check 02 switching.  I also used it to see if a switch was working when loaded up. Never could have done it w/o a scope Hi Mike Are you talking about the pressure differential sensor that one measures a low current? Did you save any waves? Mick

Hi Mick,

No I scoped the 02.  when I first got to the car it had a very low voltage output (20mv if that).  The only way I could get it to move was by pressing on the MAF plate.  I ended up disconnecting the sensor from the PCM and setting the fuel injection with the little allen wrench.  Once the 02 voltage output was reasonable, I was able to fix the real problem with the car which was a bad idle switch.  It was pretty simple but the scope let me see the 02 start swinging the voltage once it was adjusted properly.  I do have pics but they are boring!

Quote:

don't you have the wrong sprocket on it?

Right, Rick.   8-)

Should be more like the picture below.  Good luck finding this one without a scope.   ;)  

You would not need Pico power for this example but when you need a scope, you need a scope.

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I haven't personally seen it Tom but I got involved in a conversation about the problem once. Strangly enough there were two cases on the tdf forum the same day one was ngc with the older sprocket and the other was like this example. The two fellows just needed to trade cam sprockets and their problems would have been cured.  

  Mike I don't know which way the idle switch failed on that mb but either way it shouldn't have bothered it at idle. If it went bad as in always closed then it would try and move the hydraulic actuator towards no fuel at engine speeds higher than 900 rpm at normal operating temp and higher speeds at colder temps but it should have idled fine. If it went bad always open then it shouldn't have botherd anything. Did you check the duty cycle on the blue and white wire at the diagnostic plug?

Hi Rick
           Funnily enough I had a similar problem on a VW with an idle switch. That would never had been solved without the scope. The switch would close with the throttle but very momentarily and breifly open although often. Caused a rough idle, rich mixture and gave it a slight backfire during over-run. Other workhops had replaced the plugs, leads, cap, ect ect chasing the problem. Viva la scope!!!