Slow humming sound after spark plugs changed

[TXScott]

Just changed all my spark plugs and the PCV. Not my first rodeo, gapped the plugs to spec(they were pretty much there already), coil packs looked fine, replaced the air plenum gasket, put on anti-seize lube on the plugs after I was burned owning a Mustang where they broke off inside during a change. Anyway, when I start up now, still in Park, there is a low hum that comes and goes like I have some sort of alien reactor technology around .3 Hz. Since I had to remove the air plenum as part of the replacement, at first I thought bad vacuum hose connection when reattaching, but they all seem snug and no hissing sound. I used all Ford parts. Any ideas what's causing the slow, ominous humming?

 

[peterk9]

Welcome to the Forum.
Just curious if you also get the hum in accessory mode without the engine running?

Peter

 

[TXScott]

Welcome to the Forum.
Just curious if you also get the hum in accessory mode without the engine running?

Peter

No, it's only present when the engine is started. I couldn't find my ForScan ODB-II dongle so I ordered a new one which will arrive on Friday. I used a dongle off my wife's Kia, which is much more basic, but it didn't show any codes.

When I drive it around, it seems fine, even a slight bit more peppy since it was nearing 100k and needed those new spark plugs.

 

[Explorer75]

Just changed all my spark plugs and the PCV. Not my first rodeo, gapped the plugs to spec(they were pretty much there already), coil packs looked fine, replaced the air plenum gasket, put on anti-seize lube on the plugs after I was burned owning a Mustang where they broke off inside during a change. Anyway, when I start up now, still in Park, there is a low hum that comes and goes like I have some sort of alien reactor technology around .3 Hz. Since I had to remove the air plenum as part of the replacement, at first I thought bad vacuum hose connection when reattaching, but they all seem snug and no hissing sound. I used all Ford parts. Any ideas what's causing the slow, ominous humming?

Did you re-install the intake manifold using the following sequence?

There´s also a bolt underneath that maybe you forgot to torque it. I believe it´s this bolt:

 

[Gary Crist]

I hate to ask but is that .3 or 1/3 HZ as in as infrasonic?

 

[Mbrooks420]

I hate to ask but is that .3 or 1/3 HZ as in as infrasonic?

Indeed. You can’t remotely hear anything nearly that low.

Did you use the exact match on the plugs with what came out? Are you sure you didn’t change the routing of the wires?

 

[TXScott]

Did you re-install the intake manifold using the following sequence? View attachment 327892

There´s also a bolt underneath that maybe you forgot to torque it. I believe it´s this bolt:

View attachment 327893

Thank you for your input, I will need to try this. I have one of those digital torque gauges that fits between the ratchet and socket but it was dead even after changing the coin battery so I just went with ye olde "tight+1/4 turn" when putting the air plenum back on(with a new gasket) and the new plugs. I will get a torque wrench and see if correct tightening helps.

Also, got the ODB-II dongle for use with FORScan in the mail today and hooked it up but there were no real problems detected.

FWIW - some CPU's and other FRU chips use this ordered tightening sequence method as well

 

[TXScott]

Indeed. You can’t remotely hear anything nearly that low.

Did you use the exact match on the plugs with what came out? Are you sure you didn’t change the routing of the wires?

Hz can also used to measure frequency in terms of time intervals, or in this case about once ever 3 seconds.

I changed the plugs one at a time so as not to worry about wiring mishaps, altho tbh there is much excess wire off the harness to get them confused. I used the stock Motorcraft platinum plugs(part numbers matched old plugs) and even bought them direct from Ford so as not to worry about scammers on eBay or Amazon selling cleaned/used or outright fake parts.

 

[Roushford6]

Just changed all my spark plugs and the PCV. Not my first rodeo, gapped the plugs to spec(they were pretty much there already), coil packs looked fine, replaced the air plenum gasket, put on anti-seize lube on the plugs after I was burned owning a Mustang where they broke off inside during a change. Anyway, when I start up now, still in Park, there is a low hum that comes and goes like I have some sort of alien reactor technology around .3 Hz. Since I had to remove the air plenum as part of the replacement, at first I thought bad vacuum hose connection when reattaching, but they all seem snug and no hissing sound. I used all Ford parts. Any ideas what's causing the slow, ominous humming?

The old 4.0L OHV Explorers used to develop a humming sound from the IAC. Since that function is now incorporated into the new style electronic throttle body I would look at all of the air intake connections. If you end up getting P0171/P0174 codes you know it is definitely a vacuum leak.

 

[TXScott]

Got the new ForScan ODB-II dongle but it didn't throw any error codes. Got a cheapo $15 torque wrench and torqued the upper intake manifold plenum down. First bolt, snapped it loose. Got a new, less cheapo torque wrench for $25 with a good Amazon rating. Removed upper intake manifold plenum. Thankfully it was the bolt that sheared so the threads on the captive nut were fine. Called all over town on a Saturday afternoon to find a Ford parts shop with the bolt in stock. Between all the calling and part numbers, I called four different dealerships, each one saying they didn't have it and giving me a different "correct" part number to call the next dealership with. One dealership said the next dealership had it in stock, but called ahead and got it verified that while the inventory system says it was there it was in fact not, lol. Finally, the last dealership said the part number I *really* needed was 5F2Z-9Y450-A. It came in a pack of 4 but they removed two and sold it to me for $2.50 apiece(I wanted a spare bolt just in case).
Removing the sheared bolt was surprisingly easy, went after it with a tissue and screwdriver against a shard of metal sticking up. Removing the upper half of the bolt from the plenum was just a matter of a knock with a mallet. It has a captive sleeve that pops out along with the bolt.
With my new torque wrench and replacement bolt, I popped the replacement bolt into the plenum and torqued it down in rotating sequence as mentioned above(first resistance, then down to 10 Nm (89 lb-in), then another 45-degree tightening). For good measure, also sprayed down the MASS air sensor with some MASS cleaner, let dry and re-installed.
Fired up the engine and the slow, oscillating hum is gone.

HOWEVER, now the engine idles a bit rough. ForScan found no codes. Thinking there is a vacuum issue but all hoses are snug, no hisses, cracks, etc. Also thinking maybe all this jacking around knocked some oil residue loose and maybe a bottle of SeaFoam at my next gas fill-up might help? Could it also be the MASS has to do some mileage to re-learn?

Lastly, I'm not a ForScan guru, quite the opposite, are there some tests I can create/program within it to narrow down potential issues?

Cheers

Did you re-install the intake manifold using the following sequence? View attachment 327892

There´s also a bolt underneath that maybe you forgot to torque it. I believe it´s this bolt:

View attachment 327893

 

[Explorer75]

Got the new ForScan ODB-II dongle but it didn't throw any error codes. Got a cheapo $15 torque wrench and torqued the upper intake manifold plenum down. First bolt, snapped it loose. Got a new, less cheapo torque wrench for $25 with a good Amazon rating. Removed upper intake manifold plenum. Thankfully it was the bolt that sheared so the threads on the captive nut were fine. Called all over town on a Saturday afternoon to find a Ford parts shop with the bolt in stock. Between all the calling and part numbers, I called four different dealerships, each one saying they didn't have it and giving me a different "correct" part number to call the next dealership with. One dealership said the next dealership had it in stock, but called ahead and got it verified that while the inventory system says it was there it was in fact not, lol. Finally, the last dealership said the part number I *really* needed was 5F2Z-9Y450-A. It came in a pack of 4 but they removed two and sold it to me for $2.50 apiece(I wanted a spare bolt just in case).
Removing the sheared bolt was surprisingly easy, went after it with a tissue and screwdriver against a shard of metal sticking up. Removing the upper half of the bolt from the plenum was just a matter of a knock with a mallet. It has a captive sleeve that pops out along with the bolt.
With my new torque wrench and replacement bolt, I popped the replacement bolt into the plenum and torqued it down in rotating sequence as mentioned above(first resistance, then down to 10 Nm (89 lb-in), then another 45-degree tightening). For good measure, also sprayed down the MASS air sensor with some MASS cleaner, let dry and re-installed.
Fired up the engine and the slow, oscillating hum is gone.

HOWEVER, now the engine idles a bit rough. ForScan found no codes. Thinking there is a vacuum issue but all hoses are snug, no hisses, cracks, etc. Also thinking maybe all this jacking around knocked some oil residue loose and maybe a bottle of SeaFoam at my next gas fill-up might help? Could it also be the MASS has to do some mileage to re-learn?

Lastly, I'm not a ForScan guru, quite the opposite, are there some tests I can create/program within it to narrow down potential issues?

Cheers

I suggest you disconnect the battery for 30 min and reconnect. Start the engine, let it idle with all lights off, radio off, etc.
Which spark plugs did you use?
Use no other than Motorcraft 520, bought from the dealer.

 

[TXScott]

I used those, bought them direct from Ford's agonizingly slow website just to make sure I wasn't getting used or fake plugs like on eBay or even some Amazon sellers. Will try the re-learn and see if that helps!

I suggest you disconnect the battery for 30 min and reconnect. Start the engine, let it idle with all lights off, radio off, etc.
Which spark plugs did you use?
Use no other than Motorcraft 520, bought from the dealer.

 

[Explorer75]

I used those, bought them direct from Ford's agonizingly slow website just to make sure I wasn't getting used or fake plugs like on eBay or even some Amazon sellers. Will try the re-learn and see if that helps!

OK, good luck, keep us posted