rattling noise when accelerating up hill

s2dglt · Post by **s2dglt** » 22 Apr 2012, 19:29

I bought a bottle of duralube instant quiet, because my 95 850 fly makes a strange rattling sound when I'm accelerating up hills, before I use this new product I thought I would see what the experts had to say.

Post by **jblackburn** » 22 Apr 2012, 21:06

Where does it sound like its coming from? Can you take a video with a phone or something and upload it?

s2dglt · Post by **s2dglt** » 23 Apr 2012, 10:22

It sounds like It's the valves in the engine, I've already done the pcv job

Post by **jblackburn** » 23 Apr 2012, 10:27

I would pull off the timing cover and have a very close look at your timing belt, tensioners, and timing marks on the cams. Turn them around to TDC so that the marks line up with the notches in the timing cover. (see Lee's topic "850 140k maintenance for a how-to).

Lined up properly and at high RPM, you should not hear any valve noise unless the timing or something is off.

s2dglt · Post by **s2dglt** » 23 Apr 2012, 10:44

Thanks, I will try that after work and let you know what happens.

Post by **fazool** » 23 Apr 2012, 13:07

Try a simple experiment first.

Get a fresh tank of 93 octane and try it again. If it sounds like a coffee can with marbles in it, shaking around it might be pre-ignition. Under load (accelerating uphill is the greatest load) then you could simply be suffering engine knock. If your knock sensor is out of whack it could sound like that.

Post by **jblackburn** » 23 Apr 2012, 13:45

The knock sensors should, for all intents and purposes, stop audible knocking from happening WAY before it can be heard by your own ears by cutting back timing.

Then again, if one is bad, and the check engine light is on (which many people ignore)...all bets are off!

s2dglt · Post by **s2dglt** » 23 Apr 2012, 17:39

Well the timing is good, I'm not sure about the can of marbles, I will have to grab some of my sons marbles and compare the sounds.

The only lights that are lit on my dash are service and abs. How would I determine it it is the sensor, or would the check engine light not being on rule it out?

Post by **jblackburn** » 23 Apr 2012, 18:24

If the knock sensors are reading out of spec, the check engine light would be on (it does light when you start the car for a brief second, right?)

Hmmm...

Oil starvation maybe? If you pull off the oil cap while running, do you see oil splashing around the rotating cams up top? Hear any knock from the top or bottom end at idle?

The injectors are very loud on these engines, but they are more of a high-pitched ticking than a knock, if that makes sense.

Post by **MoVolvos** » 23 Apr 2012, 18:35

To test for pre-ignition or detonation as you are going up hill and it begins to knock let off the accelerator pedal halfway (be sure no one is behind you) and see if the sound lessens? You can also shift to the lower gear and as the revs go up does the knocking go down? Finally a long shot but maybe it is catalytic converter starting to break up as the sound is pretty loud (Marble) from your description.

Blessings,
BKM
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