Would a camshaft that's off a tooth show up on a CKP/CMP waveform?
07-16-2015, 11:10 PM
#1
Would a camshaft that's off a tooth show up on a CKP/CMP waveform? In the morning I'm going to start diagnosing a 02 T/A at work. Customer installed a hot cam/blue springs and the car ran bad. He took it to a shop and had it "dyno tuned" and the car ran worse. He took it back four times and the shop never figured it out.
Customer originally called and asked for us to dyno tune it. When he dropped the car off we spent some time talking and I have a feeling that cam was installed a tooth off and suggest we do some diagnostic work before putting it on the dyno which he agreed to.
I use a scope a lot at work. Anytime I can find a reason to break it out I do.
I did a retaliative compression test and all cylinders are the same.
I then used an in cylinder pressure transducer w/ an ignition pickup to see where the spark plug was firing in relation to TDC. Looking at the waveform I felt that it was firing way before TDC.
However, I use a Snap on Verus Pro that has a scope. One of my few complaints about it is that it will only display time based on the bottom axis and not crank rotation degress compared to a dedicated scope like a Pico.
Since there is no way for me to know how many degrees the ignition is firing BTDC I can't make a 100% call on the cam timing being off. I took the Verus home and hooked it up to my 00' Firehawk that is pretty much stock except for exhaust and wouldn't you know it, the waveform looked identical to the T/A at work. Well hell.
I got to thinking if I could make a determination by scoping the CKP/CMP signals and see what they look like.
I'd like to be 100% sure before I pull the cover off it and waste a bunch of time going down the wrong path.
The car idles very very badly and will die if you don't nurse it. Random misfires on most of the cylinders but not enough to kick the CEL on.
BARO is fine. MAP voltage is 2.5 at idle. IAC counts are 275+. The customer also said the previous shop drilled the hole bigger in the throttle blade to keep it working. TPS, inj p/w and all the other stuff appears normal. MAF is showing around 7 g/s.
I figured a cam that small would probably run "OK" even on a stock tune, at least in neutral.
Sorry this post ended up being so long. I don't know anyone else that uses a scope and thought someone in here that tunes and actually knows what a waveform is might have some insight.
Thanks for reading.
J
Customer originally called and asked for us to dyno tune it. When he dropped the car off we spent some time talking and I have a feeling that cam was installed a tooth off and suggest we do some diagnostic work before putting it on the dyno which he agreed to.
I use a scope a lot at work. Anytime I can find a reason to break it out I do.
I did a retaliative compression test and all cylinders are the same.
I then used an in cylinder pressure transducer w/ an ignition pickup to see where the spark plug was firing in relation to TDC. Looking at the waveform I felt that it was firing way before TDC.
However, I use a Snap on Verus Pro that has a scope. One of my few complaints about it is that it will only display time based on the bottom axis and not crank rotation degress compared to a dedicated scope like a Pico.
Since there is no way for me to know how many degrees the ignition is firing BTDC I can't make a 100% call on the cam timing being off. I took the Verus home and hooked it up to my 00' Firehawk that is pretty much stock except for exhaust and wouldn't you know it, the waveform looked identical to the T/A at work. Well hell.
I got to thinking if I could make a determination by scoping the CKP/CMP signals and see what they look like.
I'd like to be 100% sure before I pull the cover off it and waste a bunch of time going down the wrong path.
The car idles very very badly and will die if you don't nurse it. Random misfires on most of the cylinders but not enough to kick the CEL on.
BARO is fine. MAP voltage is 2.5 at idle. IAC counts are 275+. The customer also said the previous shop drilled the hole bigger in the throttle blade to keep it working. TPS, inj p/w and all the other stuff appears normal. MAF is showing around 7 g/s.
I figured a cam that small would probably run "OK" even on a stock tune, at least in neutral.
Sorry this post ended up being so long. I don't know anyone else that uses a scope and thought someone in here that tunes and actually knows what a waveform is might have some insight.
Thanks for reading.
J
Last edited by LilJayV10; 07-16-2015 at 11:17 PM.
07-17-2015, 01:32 AM
#2
TECH Senior Member
Some time ago I posted a pic of CKP/CMP waveforms taken from a Picoscope... the CMP transition is supposed to line up with the 4th CKP pulse out of the 5 sequential narrow pulses...
I'll see if I can locate my post.
I'll see if I can locate my post.