Hi all,
Truck is a '99 4x4 with the 5.9
Ever since I bought my truck a few months ago there's been a rattling noise coming from the engine bay. It only happens under load with a lot of throttle, usually with rpms over 3000. Changed spark plugs, wires, distributor cap, rotor, cat, and muffler and it hasn't gotten any better. I've also run 83, 89, and 93 octane at different times and there was no difference. Anyone know what this could be? I'm wondering if it could be pinging, but I've never actually heard pinging before so I'm not sure. Any help is appreciated. Thanks

 

Catalytic converter is going bad. Tap it with a hammer to see if it rattles.

 

More than likely it is pinging (also called spark knock). is it reproducible at a very specific rpm? Does it sound like a rhythmic and metered clickity clack, or just a bunch of random clicks and clacks like coins in a coffee can?

 

Buy a stethoscope and put it on the valve covers. If the loud noise is coming from that area, it may be a stuck lifter. This is likely the case if you are hearing a "ticking" noise. It may also be an exhaust leak.

If the sound is more profound and rattle-like, it could be many things. Possible causes could be rod knock, detonation, spun bearing, piston slap etc.

First I would check the valve covers though. If that checks out, do a eninge compression test.

You can also examine your old plugs for detonation if you still have them.

 

what did the spark plugs look, good bad?? because they say sum times a bad Plenum can cause a knock sound.

 

Why do I always go straight to conclusions?

 

I dunno, but I wouldn't have guessed cat after he said he replaced it.

 

I did'nt even see that!!


What a Fu<king Dumb@$$!!

 

I have a brand new magnaflow cat, so that can't be it. It happens anywhere from 1500 to redline when I mash the gas. Some days the sound is more noticeable than others. I noticed that when I replaced the spark plugs #8 was destroyed. I think it was #5 that was a little wet. All of them (except #8) where a nice shade of golden brown. Here's a pic of the #8 plug...


And a pic of the distributor cap...


The noise is a rhythmic clickity clack I guess, and it's pretty loud. I would try the stethascope idea but the noise only happens when the truck is under load and accelerating hard. I can rev the engine in neutral all day and the noise will never happen. I don't think the plenum is bad because I don't see any oil pooling in the intake, and my gas mileage is still okay. Any ideas?

 

that cylinder is running hella lean if that's what's left of the #8 plug. You probably have a bad/clogged fuel injector. Might very well have burnt a valve or blown a head gasket if it got that hot.