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oil pressure gauge bouncing/fluttering at hot idle

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Old 09-05-2006, 03:14 PM
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924RACR
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Lightbulb oil pressure gauge bouncing/fluttering at hot idle

I just wanted to get back with my findings, and a big THANKS! to rennlist!

I remember reading some time back that a fluttering oil pressure reading at idle indicated worn rod bearings; when I noticed this in my 924S, I figured I'd want to do them. I just pulled it apart over the weekend to both address the bearings, plus the leaking oil pan gasket, and to reseal the PS rack (rennbay!!! ).

Turns out the advice was spot-on - the #2 and #3 weren't looking that great, but the #4 was worn into the brass!!! Talk about caught it in time - I wouldn't have been surprised if they'd gone within 20kmi.

This is on an automatic with 157kmi. I think the higher revs turned by the 3-speed automatic (turns 4000rpm when my 931 turns 3000, cruising down the highway at 75) are a contributing factor to the wear...

As an aside, I'd agree the job isn't that bad - hardly had to break out the air tools for much - except for all the cleaning of filthy parts, and for the removal of the steering rack from the steering shaft - real PITA, that!

Thanks guys!
Old 09-05-2006, 04:22 PM
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2BWise
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Did it flutter all the time? Mine will flutter before the oil's fully warm, but will jump a little when I go on and off the throttle after that.
Old 09-05-2006, 04:34 PM
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JustinL
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Mine flutters because of the 18 year old wiring... in fact, mine will flutter when the engine isn't even running!
Old 09-05-2006, 04:58 PM
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2BWise
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Now thats spooky
Old 09-05-2006, 11:28 PM
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tjbreen
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Mine was fluttering so when I couldn't find any other reason, I replaced all the rod bearings. Old ones looked pretty good so I wasn't expecting a cure when I put the new ones in. From the moment it warmed up it went right back to fluttering. I even replaced the pressure sender.

Recently I went through Clark's procedure with a rheostat and multimeter to check the gauge's response. It did exactly what it was supposed to at each resistance. Also replaced water temp sender and checked with resistance, still not fully responsive. This winter I am pulling the cluster and polishing every connector and ground I can find.
Old 09-05-2006, 11:38 PM
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KuHL 951
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Originally Posted by tjbreen
...This winter I am pulling the cluster and polishing every connector and ground I can find.
That alone will solve a multitude of gauge and illumination problems. The OP guage on the 86 did a little dance every so often until I cleaned all the terminals and grounds under the dash.
Old 09-05-2006, 11:42 PM
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The DareDevil
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Mine is pegged at 5 bar. I replaced the sender, and the gauge. I even tried a completely different cluster. I suppose there is a break in the wiring somewhere.
Old 09-06-2006, 12:05 AM
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Calmchaos
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If it pegged that usually means its cross wired. IIRC

And when my gauge was fluttering... I spun #2 and broke a piston
At least I get the joy of rebuilding LOL.
Old 09-06-2006, 02:59 AM
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tjbreen
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I guess that is enough incentive to try to fix the electrical flutter - so it won't mask a mechanical problem.

Did you notice a certain regularity, frequency, or pattern in the flutter when it was a spun bearing?

My electrical flutter is like a bouncing ball that hits the floor three or four times then settles breifly before bouncing again. It is much too slow to be assosicated with the crank, doesn't change frequency with RPM, and goes away at 4 bar and higher.
Old 09-06-2006, 11:18 AM
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924RACR
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My flutter was only at idle, only while warmed up. Once you get on it, it smooths right out.

Got the new bearings in last night, and fired it up - it lives!!! Didn't warm it up, it's still up in the air for other stuff, so will be a while before that data point is gathered.

Rack stopped leaking real good once I tightened that last bolt I forgot! Looking forward to the car being dry and clean for a while underneath!
Old 09-06-2006, 01:39 PM
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Calmchaos
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tj,
I dont know if there was much of a pattern. But since I got the car it fluttered like yours does (and goes away above 3.5 bar)
But THAT went away when I tightened the nuts on the leads.
I can say that right before I got the knock the damn thing looked posessed! It would go up and down from 0-5 bar faster than I could see it. And the idiot light would come on which never happened with the purely electrical problem.

It seems like the light only came on when I had a REAL problem. It never came on when the wire was loose. So in my experience I would say really pay attention to the light, but try to fix the gauge problem if you can.

And you said you replaced the bearings and it still happens, and your problem sounds like my electrical one.
Old 09-06-2006, 05:29 PM
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mkd944
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I found this article from Skip at Paragon to be useful. It talks about cleaning / replacing the oil pressure relief valve and goes on to say that there can be any number of things that can be the cause of bad oil pressure readings...

"from higher than normal oil pressure (valve stuck closed) to low oil pressure (valve stuck partially open.) to no oil pressure (valve stuck totally open.). Other possibilities for low oil pressure include a bad oil filter, a blockage in the oil channel lines, low oil, a not tight enough crank bolt (155ft pounds or more), lack of a rubber o-ring behind the washer on the crank that drives the oil pump, a bad oil pressure sender, and a failing oil pump."

The full article is at: http://www.tech-session.com/kb/index...x_v2&id=88&c=4

Mike Dayton
'95 968 Coupe
'91 944S2 Coupe



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