Water Pump causing car vibrations?? - Mercedes-Benz Forum
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#1 (permalink) Old 02-04-2011, 02:45 PM
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Exclamation Water Pump causing car vibrations??

Hello all!

Well for about a while now ive been experiencing the weirdest vibration ever:S ok so when the car is idling, car is sometimes vibrating..

When i turn on my hazard lights, the RPM starts to fluctuate and the car vibrates accordingly..and whenever i turn on my headlights, the car vibrates stronger than it usually does in idle, and the RPM gets lowered a bit..

The vibration is not the kind that comes from misfiring, it is a kind of a high frequency vibration..

Ive replaced my MAF, Spark Plugs (6 months ago), Fuel pump, fuel filter, cleaned throttle body, cleaned injectors, replaced the air filter, changed engine and tranny mounts..

Well me and my mechanic were diagnosing the problem and we came up with an idea, which was to let it idle without the timing belt on to see if the vibration was motor related of from the pulleys bolted on the motor..sure enough the vibrations went away..

Then we noticed my water pump pulley had moderate slack in it and was wobbling, so did the idler pulley..thus deducing that the water pump pulley and idler pullley was causing this annoying vibration..under the logic that whenever i turned on my lights and/or flashers, the alternator increased its load on the engine thus making the water pump pulley start vibrating..

Can you guys tell me if our logic is sound? If not, why did the car stop vibrating when the timing belt was removed? Thanks in advance guys! Im sure youd be of great help

Last edited by wf.1990; 02-05-2011 at 03:57 AM. Reason: Additional info
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#2 (permalink) Old 02-05-2011, 03:59 AM
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Anyone?
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#3 (permalink) Old 02-05-2011, 06:59 AM
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I'll kick it off...

You are right. This is a weird one!

From your 2nd paragraph, the electrical effects are very strange, as the load on the generator caused by the hazard lights is quite minimal. The bigger electrical loads are the defrosters front & rear.

Now I'm really intrigued by your 'timing belt' experiment....Your V6 112 engine has a timing chain (a double chain) for this function, and the engine cannot run without it.

You must be referring to the 'poly V belt' (serpentine) at the front, which drives the a/c, the power steering pump, the generator, and the coolant pump. The engine can run without this belt, but not for long as it will soon overheat.

However, your experiment has shown that ONE of those above systems is the cause of the vibration - or a worn idler pulley. Why is the belt slack? There is a tensioner system to prevent that.

I think that you should examine each of the above pulleys again, with the belt off, so that any shaft wear can be eliminated.

I'm sure you are on the right track here..
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#4 (permalink) Old 02-05-2011, 07:41 AM
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First off, thanks for repliying

Well i was indeed talking about the serpentine belt, and what i meant by slack was that the pulley- when wiggled towards the motor and away from it- had some play in it...i was researching today, and i found out the harmonic balancer could also be a likely culprit.

Well how do i test the pulleys? Shall i just shake them back and forth or is there anything else i should try? Another question..can the culprit be a pulley that is not wobbling?

Do you indeed think that the vibration is from one of the pulleys? Thank you for your help
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#5 (permalink) Old 02-05-2011, 09:03 AM
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Your harmonic balance shaft sprocket is driven from the timing chain, so I doubt if that is your problem here.

I suppose that a little fore/aft movement is allowed at the pulleys. End-play on bearings maybe. I thought you meant that the belt was slack.

Regarding future checks, each pulley should rotate relatively easily, bearing in mind the function. The generator (alternator) has no touching parts, but the coolant pump is surrounded by water. The power steering pump, and the a/c system pump are also moving liquids, so there will be some drag expected there. Also check the 'idler' pulley.

If you have that help of a mechanic, he should recognize when something 'feels' wrong.
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#6 (permalink) Old 02-05-2011, 01:54 PM
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UPDATE:
I measured the following battery voltages under different loads through the "sensor mode" in the HVAC unit screen, i thought they could be useful:

Idling in Park then revving:
No items on: 14.1-14.2v
Headlights on: 13.8-14.0v while revving 14.1v
Seat warmers on: 13.7-13.9v while revving 14.0v
With rear window defrosters on: 13.5-13.7v while revving 13.7-13.9
With interior lights on:13.6-13.7v while revving 13.7-13.9v

Idling in Drive:

No items on: 14.1-14.2v
Headlights on: 13.7-13.9v
Seat warmers on: 12.8-13.3v
With rear window defrosters on: 12.1-12.2v
With interior lights on:11.9-12.0v

Note: Each item turned on is done so without turning on the previous one (ex.With interior lights on, the defroster, seat warmers, and headlights are also on)

Also, the lights dimmed when in P and revving the engine brightens them up. Im pretty sure the voltage fluctuations are not normal. So sir, do you think these values support of falsify my theory? Thank you in advance!! Id appreciate as many responses as possible!
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#7 (permalink) Old 02-05-2011, 02:46 PM
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Quote:
Originally Posted by wf.1990 View Post
Note: Each item turned on is done so without turning on the previous one (ex.With interior lights on, the defroster, seat warmers, and headlights are also on.
I guess you meant to say OFF in the sentence above.

It's late (and cold!) here, but I'll compare my car's voltages with yours tomorrow. Regarding loading the generator, your voltage regulator is there to stabilize the output, which it seems to be doing OK. Was the vibration occurring during this test?
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#8 (permalink) Old 02-05-2011, 02:59 PM
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Hehe..sorry again..yes i did mean "off"..

Well first of all thanks for all your help keyhole, id really appreciate it if we can compare values, but of course not in this cold..

Yes, the vibration was indeed occurring..so these values have nothing abnormal about them? The voltage regulator is working normally? and why would the voltage increase when the engine is revved? Do you think that my theory about the vibration is correct?

Sorry for all the questions i just want this problem to end with the least amount of money spent, and no where better to gain some knowledge and try to solve problems than with you helpful and knowledgable members.

Thanks Keyhole!

Last edited by wf.1990; 02-05-2011 at 03:01 PM. Reason: typo
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#9 (permalink) Old 02-06-2011, 04:48 AM
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I took a look through my WIS to find out what the MB voltage numbers are for the generator/voltage regulator system. (engines 111, 112 & 113 in models W202, W203, W208 & W209)

1. Checks are done at 3000 rpm with non-specified internal loads called 'consumers', and allow 2 minutes for VR to stabilize.

2. The voltage regulator clamps the generator voltage between 13.0vdc and 14.5vdc. If the measured voltage is below 13.0vdc, there is a generator problem. If the measured voltage is above 14.5vdc, there is a regulator problem.

Note: MB take their measurements from designated internal terminals, but there is no reason not to measure at the battery terminals. Apart from fractional voltage drops in the cables, it will be the same voltage there.

Results of my comparison test. (measured at the cluster)

Engine off: 12.2vdc
Engine running: no loads 14.3vdc
ditto: added headlights, no change
ditto: added both seats heaters, no change
ditto: added both front & rear defrosters, 14.0vdc
Engine off: 13vdc, falling and steady at 12.3 vdc after 5 minutes.

I did not find revving altered the voltage. I don't think that it should.
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#10 (permalink) Old 02-06-2011, 05:36 AM
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Thanks alot for your help keyhole?

Well, can we deduce that its the generator that's at fault? Thus causing the vibration, since the fuel pump is not getting enough electricity?

Or can we say that one of the pullies that are wobbling are causing drag thus lowering the rpm and making the generator not charge properly and the car to vibrate?

Or am I missing something else?
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