Hi Gang,

You are all probably aware that sometimes a particular piece of equipment will affect or has an affect on the way a vehicle behaves when it is connected to the said vehicle.

Today I had a 2000 Mitsubishi Elentra L4 DOHC 2.0L come in with a complaint of ' won't start after sitting for half an hour after the engine had been run '

I checked for stored DTC's and none were found. The RPM in the data stream registered when I cranked the engine and other parameters were correct while the vehicle was behaving itself.

I then hooked up the PicoScope to the crank sensor to see if the waveform was okay. To short cut, I connected the negative probe to battery -ve and the positve probe to the sensor output wire. The waveform was picture perfect at this time.

I left the vehicle running while I answered a phone call.
Ten minutes later I went back to the vehicle and the waveform had flat lined on the scope but the vehicle was still idling away merrily!

I switched the vehicle off and tried a restart. One or two cranks and the vehicle started but still no waveform on the scope!!

This can't be right I mutters to me self! So while the engine was idling I disconnected the -ve probe and the engine stopped running. The engine would not restart!

I reconnected the PicoScope -ve probe and the vehicle started!
I did the -ve disconnect/reconnect a couple of times with the same results.

Okay .. I knew the crank sensor was cactus ( I bench tested it with a hair dryer and ohm meter plus I was getting no rpm data on the scanner ) but how come the PicoScope kept this vehicle running when the cranksensor dropped its bundle??  ;D

The new cranksensor ohmed out at 800ohms @ 20°C.
The old sensor ohmed the same but would go OL went I applied some heat to it.
I had to get this one out the door pretty quickly so I didn't get to experiment any further but it does have me wondering! ???

Cheers!
Kevin

Hi Kevin,

I don't show that model here.  I also show that engine with a hall effect CKP.  I assume you were working with a VRS type since you refer to ohm values.  I was looking it up to see if it was a floating sensor or not, but have no diagram for that.

I can see how the signal may have weakened and not shown up on the scope well without reducing Volts/div to see it, but how the scope kept it running is a mystery to me.  Now you have me wondering  :P

There are some hand held scopes that will kill a perfectly good runnning engine when hooked up due to low impedence, but to keep it running?!   :o  

Hi Gang,

Tom : I hope ya don't think I'm 'crackers' on this one matey!  ;D

It is a VRS type sensor and although I said ' it flat lined ' on the scope, that was not strictly the case. A very, very small waveform was still visible.

I know what you are relating to with scopes/impedence.

One of our big box scopes is a perfect candidate for this.

On certain vehicles fitted with a L.E.D/optical type crank angle sensor, I can pick if a non OEM sensor assembly has been fitted. This comes in handy if the vehicle has a driveabilty issue and the client says " I've replaced the crank sensor ".

Not something I rely on but hey! it works in a pinch, especially on those pesky intermittents!

The PicoScope also affects some aftermarket crankshaft sensors on a particular GMH vehicle we have here in Aussie. The PicoScope will always pick the non OEM sensor. The vehicle will stall out everytime when I use the PicoScope to check the cylinder I.D wave. I change the sensor out, driveability issue is solved and the PicoScope works flawlessly!

Not bad aye! ;)

Cheers!
Kevin