Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

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Bluegizmo83
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Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

Post by Bluegizmo83 »

I have a 2010 F-150 5.4L 3v truck and its barely running. It died on me on the freeway and ran really rough when I tried to restart it, so I towed it home. Its misfiring really bad, backfiring (through the intake I think), dies when trying to idle, and starts spark knocking badly when in gear and any throttle is applied.

I think it may have jumped timing, so I took an oscilloscope reading from both camshaft position sensors. My scope does not have isolated grounds between each channel so I cannot do a cam/crank relationship test, so I'm forced to read both camshaft sensors simultaneously and try to interpret timing from that by comparing to known good waveforms from Picoscope's Waveform Library...

If I'm reading this waveform from my truck properly, it appears the timing relation between banks is off by almost 90 degrees!

Known good waveform from library (Bank 1 in blue, Bank 2 in red):
Higher resolution photo: https://ibb.co/vJnvwJ1
Cams_Known_Good_Timing.png

Waveform from my truck (Bank 1 in blue, Bank 2 in red):
Higher resolution photo: https://ibb.co/4grjxWq
Cams_My_Truck_Timing.png

I thought this engine is an interference engine, so wouldn't timing being out that badly have caused valves to slam into the pistons and cause catastrophic damage? There is no valve ticking, no lower end knocking, no smoking out the tailpipe.

Here is a YouTube clip I took of the truck during a cold startup (relatively speaking, it was 75 degrees outside), engine idling, and throttle was never touched during this clip (it has an exhaust leak due to the passenger side manifold being cracked, but that's an old problem that's been there for at least a year so ignore that): https://youtu.be/_AKQ7HI33kQ

liviu2004
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Re: Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

Post by liviu2004 »

I don’t understand why you cannot do cam crank measurement. If crank inductive, connect signal wire to one sensor wire and the black lead to battery minus?

Bluegizmo83
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Re: Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

Post by Bluegizmo83 »

liviu2004 wrote:
Mon May 23, 2022 5:12 am
I don’t understand why you cannot do cam crank measurement. If crank inductive, connect signal wire to one sensor wire and the black lead to battery minus?
I can measure the crank or camshaft independently, and they are both inductive, but when I try to measure both simultaneously it shorts the crank sensor and the truck won't start at all. My understanding is that the crank sensor and cam sensors use different grounding paths or something, and if your scope does not have isolated grounds between channels then you just can't do it. You gotta have a scope with isolated channel grounds. I tried it anyway, but like I said it won't start at all until I disconnected either one of the signals (cam or crank), then it would fire up.

liviu2004
TwoWaves
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Re: Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

Post by liviu2004 »

I never heard of such a thing and please tell how you connect all your leads and where exactly, besides the usb cable.

A channel blue wire where black wire where.
B channel red wire where black wire where.

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Grant_Baker
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Re: Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

Post by Grant_Baker »

Bluegizmo83 wrote:
Mon May 23, 2022 1:39 am
My scope does not have isolated grounds between each channel so I cannot do a cam/crank relationship test, ...
See the following forum post with a reply by Steve Smith for how to connect your scope inputs and grounds

topic22834.html?&p=103142&hilit=common+ground#p103142

Bluegizmo83
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Re: Am I interpreting this Oscilloscope reading correctly? (Ford 5.4L 3V)

Post by Bluegizmo83 »

Thanks for the help guys. I found the issue with the truck though. I decided to remove the passenger side valve cover (as that was the side where all the Check Engine Codes where saying the problem was) to inspect the timing chain and variable valve sprocket, and I found the entire plastic upper timing chain guide in pieces inside the valve cover and down inside the timing chain cover. Pieces of the guide must have gotten between the chain and sprockets, causing the timing to jump a few teeth.

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