Hello, was wondering if anyone might have tips or tricks to help me diagnose a chirping squeaking sound on acceleration. 2003 DII 4.6, 160K miles.

Sounds to me like a bad bearing somewhere. Only happens on acceleration when the engine is under load and the car is moving. Does not happen when decelerating, coasting, idle or parked no matter how much I rev the engine. I even put it in drive, smashed the brakes and hit the accelerator, no noise then either. Also pauses when the transmission shifts. To me that all says drivetrain. The higher the engine load, the louder the chirp - so up a big hill is the worst. I should also mention the chirp slows as the transmission shifts through, so loud and fast in 1st, pause for the shift, a little less loud and a bit slower in 2nd, pause, etc., etc.

Last time this happened, it was the front drive shaft. U-joints were shot. I replaced the front drive shaft about a year ago. I saved the old shaft and rebuilt it, installed it, but the exact same noise remained. Replaced the u-joint in the rear shaft, same noise. Replaced the pinion bearing in the front differential, no change, same noise. Flex coupler on the rear shaft was replaced about a year ago also.

It's difficult to diagnose because it only makes the noise when the truck is moving. Before I start digging into something else, I wanted see if someone has a suggestion or experience diagnosing an issue like this. I've replaced all the obvious, typical disco failure points. At 160K, most of that stuff (excepting the pinion bearing) needed replacing anyway. It’s also pretty loud, so it doesn’t sound like an internal component (like a transfer case bearing). Some forums posts have suggested engine pulleys, but that doesn’t seem likely to me since it only happens when the car is in motion.

Any suggestions would be most helpful.

 

front drive shaft

 

Did you replace the centering ball? What u joints did you use to rebuild the driveshaft?

I'm going to join ZG and say just replace the front drive shaft.

 

I have 2 front driveshafts. The first is one I bought about a year ago and has about 10K miles on it. The noise started a couple months ago with that shaft on the Disco. I saved my old driveshaft and replaced the u-joints with standard u-joints from a local parts store. I did not replace the centering ball, but I did take it apart and load it up with grease before I reassembled the shaft. Swapping the year old shaft with the rebuilt shaft does not change the noise at all. It's there, unchanged with exactly the same symptoms no matter which shaft is on the Disco. I agree, it feels like a front shaft problem, but I would think that if both shafts were bad, the noise would change at least a little bit with the different shafts. I do plan to reinspect this weekend.

 

The centering ball is what fails, not usually the u-joints. That's also what makes the chirping sound

 

I agree.

Check your serpentine belt system next and look at your motor mounts.

 

I have the same thing going on and I think it's either the idler pulley or the fan touching the shroud. If it's the later then it will either be engine mounts or fan clutch.

 

So, I figured this out. One of two things - either a bad power steering pump or a blown head gasket. I wasn't getting anywhere with the drive train, so I started checking pulleys. I fired a shot of lithium lubricant behind each one, one at a time. When I got to the power steering pulley, the noise changed slightly, but did not go away. PS fluid was a little low, it has 160K miles on it, and steering was always a little stiff, so I diagnosed it as a bad pump. While I was waiting for the pump to arrive, the squeak, squeak was replaced with, or drowned out by, the loud puff, puff of a blown head gasket at cylinder 6 (turned out to actually be 4 and 6). So tore the top half of the engine down, replaced both HGs, and the PS pump with the new one I ordered, and the noise is gone. I think the HG was really the cause, I've heard stories about them sometimes making odd noises when they are about to blow.

 

Head gasket, I just went through the same thing. mine was blown externally on cylinder 6 I believe. The chirp started out very faint but after about 1000 miles it sounded like someone cut the mufflers off of it. It never changed the performance or raised the temps, it just got worse the more I drove it.

 

Shady milkman when this happens to you did you have to have your cylinder heads resurfaced, I'm experiencing the same symptoms as you did. T.I.A.