Hi,

Sorry for such a long first posting, but this problem is driving me nuts and I have posted on other board with good responses, but nothing that turned out to be the correct problem yet. Hopefully someone here can lend some insight.

I have a 2000 D2 with 128k on it, and over the past few weeks I started noticing a tapping or rapping sound, but only at highway speeds.

It first started at about 70 MPH/2500 RPM and sounded more like a piece of the wheel-well rubbing on a tire and clicking, or possibly something contacting the fan, not a really "metallic" sound it didn't seem.

The sound seems to go away immediately when I let off the gas, but comes back as soon as gas is applied again, so it seemed to be only under load at speed, so I thought perhaps something was rubbing or hitting the fan, but couldn't find anything.

When stationary the noise does not happen and engine sounds fine from idle right up to high RPMs.

Oil is fine. Reads a bit high on dip stick, but has since mile 1 that I have owned it and I always drain well, and fill with amounts spec'd in book. That has never been a problem for 128k now. Just a wierd stick I guess. Diff's and T-Case are all full as well.

Took out plugs and replaced with new champions. Still the same. New Magnecor 8mm wires last summer.

Front driveshaft out...same noise. Viscous fan out...same noise

Had a shop look at it and they thought it might be the flex plate, but scoped it and couldn't tell from that. Said most likely $800 + just to get in and check it. Ouch.

Followed up on the cat idea from another board and driver's side cat had a rattling to it, so I replaced them in the hope it was one of the bisquits in the cat rattling around and then flipping back into place when speed/pressure changed, but that didnt help. At least I have new high flow cats and was going to have to swap cats anyway sooner or later it seemed.

Any ideas? I would hate to pay someone to pull the transmission off to check the flex plate and have that not be it.

It doesn't make sense to me that it would only do it after a certain speed or under a really heavy load, say up a steep hill, at decent speed only. Once it starts now it will do it at pretty low speeds as I slow down but keep load on it, but once I stop I cant hear it anymore to check. But with flex plate, isnt it constantly spinning? Would speed really effect it so much it would go from perfectly normal to a pretty loud banging/tapping sound? Also, no loss of drive from transmission, just lack of power when it gets really loud and starts to bog down.

Deffinetly changes with RPMs. At say 1500-200 after it has started it is a low pitched sound but deffinetly not 1500-2000 times a second. More like only a few. Kind of like a manifold to Y pipe leak sound, but rev it and frequency increases as does pitch of sound. More a rapping sound then, and louder. but again. I could drive 40-50 miles of side roads and it drives fine. Only have I noticed it on highway or going up a very long, steep grade at over 40 MPH. That is more recent. At first it was only on highway.

I did look inside front inspection hole and found the allen screw I have seem mentioned in other posts. It was indeed showing that it had been rubbing something at sometime, but after removal they problem still exists, same as with it in there, so that wasn't it.

I was getting some missfire codes and the p0171, P0174 fuel trim codes after it really does it bad, and do now notice a lack of power when it is happening and then service engine light blinks till I let it coast a bit and then back to normal. Also getting some p03xx missfires here and there and an intermitant "Gear 3 incorrect ratio" code. The p0171, P0174 fuel trim codes I have not seen again since new cats were welded on.

Really driving me nuts now after swapping out cats with that not being the cause, and looking at possibility of pulling transmission off to the same end.

Anyone else have an idea I might try to look into?

Thanks far any help. Seems a tough one to diagnose.

John

 

Sounds like an interesting (and irritating) problem. To me, it sounds like a valve issue. Maybe something wrong with the tappets. No being there to hear it, it is difficult to guess....

Good luck,

Tim

 

Almost sounds like a knock sensor has gone out.
If your not using premium fuel start.

 

My 2000 discovery with 95,000 miles just started making a strong vibration sound and feel under acceration. I think it is the rubber roto-flex coupler on the rear drive shaft. It has a lot of cracks in the rubber. A front U-joint also just started making a loud crack sound when I put it in drive. So I will be changin all four ujoints will greasable joints this weekend. I bought my rubber roto-flex coupler from Rovers North for $89. the dealer wanted $137 ! It sounds like you have a different sound but it woulded hurt to check it out. All Discovery II owners should ckeck the roto-flex and u-joint condition. It would suck to have a u-joint break on the highway.

 

John,

A question for you that I didn't see any mention of in your post. When you are driving and the noise increases, does the engine develop any kind of misfire that you can feel? I'm thinking you might have a valvetrain problem. Possibly a weak or collapsed lifter. However-- in most cases that noise is present even at idle.

Unless....what is happening is that your oil pressure is not adequate at higher rpms, and the valve train is then clattering when it becomes starved for oil. This we have seen. We replaced rocker shafts, arms, and lifters on a Discovery. The noise came back within a few days. We then removed the oil pressure sending unit and fitted a pressure gage to that location with a long hose on it, and drove the vehicle. Sure enough, when under load the oil pressure dropped. We ended up having to fit a new timing case cover and oil pump to get back the pressure and volume the engine needs.

A cracked flex plate is something we have seen on both the Discovery and the Range Rover. And with the engine idling, you can hear a very distinctive noise, equal in frequency to engine rpm. Some people confuse the noise with that from a Catalytic convertor that is coming apart internally. But if you get under the vehicle while it is idling and listen right at the torque convertor/bell housing area, you can pinpoint it. A cracked flex plate also affects the running of the engine as the crank sensor output is erratic from the flex plate fluttering. And when under load, the flex plate distortion from the crack and inertia effects cause the noise to increase in amplitude.

Hope this helps.

Regards,

Geoman
www.eurotekapg.com