Crackling sound

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Oct 7, 2011 | 12:54 PM

Poky1

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Crackling sound

Here's a strange one. You know that sound a catalytic converter or muffler makes when it's hot and the engine is turned off? I get a crackling, snapping sound like that, only louder, when I'm accelerating while towing a load uphill with my 04 F-250 V-10. It usually happens when the engine has been off for a while and I'm starting to drive. It seems to come from directly under the engine. Truck has the FX off road package, so I thought it might be from the skid plates and shielding on the exhaust or tranny but nothing is loose. Sound goes away when truck is going over 50. It sometimes returns, fainter, when truck is warm, only when climbing. When I lift the hood when truck is parked and idling, there's no unusual noise from the engine compartment. Engine idles smooth. Plugs seem secure and are not leaking. Any ideas?

Oct 7, 2011 | 02:16 PM

Bigpipes 35

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From: Forest lake minnesota

It sounds like predetanation or pinging My 5.4 does it sometimes, I think its usually caused by our wonderfull grade of fuels we have these days. You might try running a little higher octane and see if that helps.

Oct 7, 2011 | 03:23 PM

2000silverbullet

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From: Gilbert

Exhaust manifolds leaking?

Oct 7, 2011 | 06:14 PM

hotroddsl

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From: Gilbert Az.

X2 on ping check your MAF for dirt or filter debris on the wires!
Jim & fat Monty

Oct 7, 2011 | 07:47 PM

BCooke

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x3 on the fuel. It is especially noticeable if you are at higher elevation. One step up in grade should do you.

Oct 9, 2011 | 12:32 PM

Poky1

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Thanks all: I can't find anything loose on exhaust. Pocatello is 4500 foot elevation, and I run what's sold here as mid-grade (87 octane). I'll go to supreme and see. Air filter is new so that shouldn't be a problem.

Oct 9, 2011 | 12:54 PM

redford

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From: Stephensville WI

I would say that advice is incorrect. Higher altitudes actually allow you to run more timing and/or lower octane. From 30 Car Mysteries Solved: Low Octane Fuel at High Altitudes - Popular Mechanics "Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Being at higher altitudes actually reduces that chances of pinging. Ford used to sell heads for the flathead V-8 that were known as Denver Heads, they increased the compression ratio of the engine.

As for the noise, it is probably detonation or preignition, commony known as pinging. Your truck has a sensor in it that should detect that noise and retard the timing a bit until that noise goes away. It may be malfunctioning.

Other causes of pinging can include clogged sensors, failing fuel pump, clogged fuel filter, bad O2 sensor, a bad or dirty MAF (think of things that could lean out the fuel mixture), an overheating engine, or I have even seen pinging caused by a timing belt jumping a few teeth.