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2008 5.4 misfire/popping

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Old 07-24-2014, 04:21 PM   #1
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Question 2008 5.4 misfire/popping

I have a 2008 Expedition EL (munchkin transport) with 148,000 miles.
A couple of months ago we started having a mild misfire / loss of power / rough idle. Nothing much. I investigated and found that the heater hose was leaking into the passenger side spark plug wells.

I replaced the heater hose and changed all of the spark plugs (broke #'s 6, 7 and 8). After that, there was a new problem... a LOUD popping/rattle and shuddering misfire starting at about 2500-3000 RPM, and only under load (won't happen at idle or if revving it in park or neutral- making it very hard to troubleshoot). Still have low power - it will get to 75 MPH or so, and downshift on small hills at that speed, causing the popping to start. The misfire is now throwing a code.

I have an Auto Enginuity scanner, and it is giving a #3 misfire code every time the popping happens.

I have replaced the #3 COP and boot for a new one.

I switched the #2 and #3 injectors - they looked clean, though - I changed the fuel filter about 10k miles ago.

Air filter is good.

Compression test is good (#3 tied for lowest @ 152, but also got that on 4 and 5; highest was 167 psi on #7 and #8).

Verified that there is a spark from #3 COP, at least at idle.

Ran with #3 injector and COP unplugged and still had the popping noise, so it's not fuel getting into the exhaust header (at least, not from #3).

Also, still have a rough idle, but it got better after the spark plug change. I did run some seafoam in the vacuum line, but no improvement from that.

What could cause the popping under load?

Could a cam phaser / timing chain problem do this?

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Old 07-26-2014, 12:31 PM   #2
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Sounds like a bad timing chain tensioner. (The "popping" noise is the timing chain slapping around) Does your scanner have live data? If it does, pay attention to the cam timing or VCT when it starts to misfire/pop and see if the timing advances or retards. I had a very similar issue on my 06' 5.4 and it was the timing tensioner. On my Edge I would watch the cam timing and it would be around 40-45* then once it started misfiring/popping it would drop to 0-2*. Mine would idle fine, rev up fine, and drive fine through 1-2 gear but once I got above 45-50 mph and around 1,700-2,800 rpms it would start misfiring/popping anytime I'd try and slightly accelerate through that rpm range.
- JimmyB
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Old 07-28-2014, 09:56 AM   #3
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That's it... The chain on the drivers side is loose (I just have the valve covers off so far), so probably a failed tensioner or guide.
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Old 08-05-2014, 12:58 PM   #4
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Ok. After changing the timing components (both tensioners had the gaskets blown out... guides and chain looked okay, but I changed them anyway), it still had the problem. Took it to the muffler shop for a backpressure test, and the passenger side cat is bad.
At least now I know...
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