PCV Rattling, Even After Replacement

[ConfederateTyrant]

My Grand Marquis is having a rattling sound under the hood, which is noticeable inside the car. It is noticeable in Park, and Drive/Reverse at idle, but as I accelerate it diminishes (or at least I can't hear it). The engine has not always done this, I first heard it last year when I was flushing my transmission.

The rattling seems to come from the PCV valve, as when I remove it, the rattling COMPLETELY goes away. I even replaced it with a brand new Motorcraft PCV valve, and the rattle is still there.

There is no oil consumption going on, and no Check Engine Light is showing up. The PCV vacuum line is completely clear of debris, so I do not believe there is something limiting air flow into the intake.

Is this an issue? I would think it is stressing the PCV valve spring inside.

Any idea of what could possibly cause this? Blow-by, IAC valve, MAF sensor?

Thanks in advance.

 

[Eddie]

Blow-by

 

[punisher]

Thats a new one. Usually the rattle complaints we had were due to metal replacement PCV valves. The black plastic Motorcraft valves were usually quiet.

You didn't mention the model year. Make sure nothing is laying on that plastic PCV line that can transmit the clicking to the interior. Other than that you might try another Motorcraft PCV to see if it behaves the same. Verify the part # is correct for your application. You might also try a vacuum gauge to see if there is some sort of manifold vac pulsation that is causing the PCV to thrash around.

 

[punisher]

Just to add, a clicking PCV is not out of the ordinary on a modular Ford. The longer I think about it I remember a lot of noisy PCVs but I pretty much ignored it unless the customer complained about it.

 

[ConfederateTyrant]

It's a 1995, and I was using a Motorcraft PCV valve before as well, the Fram/Purolator/etc would not stay securely in the engine. I checked on Motorcraft's website for correct part numbers, and the ones I received from Rock Auto were the same number. Even the local Ford dealer is offering the same model number that I am using.

 

[boxcartommie22]

fords products have a much higher tol. then the stuff at an auto store in my opinion i would stay with motorcraft

 

[55Test]

Desrcibe the rattling sound, I can't remember if my old 93 Crown Vic made that noise.

 

[ConfederateTyrant]

It is just a rapid rattle, I am not entirely sure what spark knock sounds like, but this makes a knocking type sound. When I pull the PCV valve, the knock/rattle is gone, but I can feel the PCV pulling a vacuum at the same rate as the knock/rattle, it is just not loud.

I think it is more annoying than harmful.

 

[CorvairGeek]

The rubber tee on the passenger's side and the rubber union on the driver's side joining the large plastic vacuum lines are prone to becoming porous and leaking on the Ford 4.6L. Check them in case you may be bleeding off some of your vacuum.

 

[ConfederateTyrant]

There is no noticeable hissing sound or surging to indicate a vacuum leak. Any other way to check for a vacuum leak?

 

[CorvairGeek]

I would physically pull them both off and just take a look at them (the union on the driver's side is harder to get at). I was suprised at how brittle and porous they can be. I've simply replaced them with an appropiate size hose to reconnect the plastic lines (driver's side) and a tee with hose on the passenger's side. This may not be your problem at all, but I was suprised at how these pieces can deteriorate.

 

[ikeepmychevytoo]

I have the exact same thing with my '84 Chevy. Just replaced the thing with the same AC Delco which began to rattle when idling cold and yes, this sounds like a spark knock. I'm a bit luckier for it is not noticable after dropping the hood down. Could this be designed in to remain clean longer

As a side note.. I can't see half the humdrum of the "replace the PCV valve too" mantra on the service manual. All it says remove it, place a finger underneath if it snaps then and after releasing it is OK. Mine was 20 y.o . and ok per the manual (and wouldn't buzz).

Quote:

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You might also try a vacuum gauge to see if there is some sort of manifold vac pulsation that is causing the PCV to thrash around.

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Punisher... What if it pulsates? This means vacuum leak? Could anyone relate what the vacuum dwell is? Have some specs but I don't know how to use them... Never had a vacuum gaugage but I bet it would pulsate to some extent

 

[punisher]

A vac gauge will pulsate to some extent, usually it will be 1" or less from the average. It is when the needle jumps +/-4" or so is when you look for a bad valve. Vac pulsation also depends on where a reading is taken. Readings taken near or at an individual port runner will pulsate more than a reading from the plenum nearer the throttle body. In a perfect world, on a generic production engine, manifold vac will hang around 18". Retarded timing, excessive camshaft duration, and retarded cam timing will all throw vac readings to the low side (numerically, not absolute).

 

[ikeepmychevytoo]

hmm... vacuum reading sounds like a very useful info. Thank you for the insight.

 

[ConfederateTyrant]

Well, it appears that the rattle has quit, I haven't noticed it in the past week or so.

I played around with my exhaust pipe to get it to stop vibrating, but I tightened everything back up, and the rattle was still there for a couple of days. But now it appears to be gone. I don't think that could have fixed it, as I didn't have an exhaust leak to begin with.

Perhaps it was blow-by. I have been using FP60 since August, would it be possible that it slowly cleaned carbon off the rings which gave them a better seal, and thus lessened blow-by?

 

[ConfederateTyrant]

Ok, ignore that, I noticed it quite a bit this morning. I'm not going to worry about it as it seems to be normal.