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Old 03-26-2010, 09:24 AM
Howser Howser is offline
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Join Date: Mar 2010
Posts: 4
Default '02 Ranger jittery oil gauge

~100K miles. 3.0L Manual transmission. Problem started last summer. Would only do it on longer drives. Turn off truck, start back up, would be OK until driven a while. Always changed oil and filters at regular intervals. No leaks. No smoke. No rattling, grinding, pinging or other noises. No antifreeze in oil, or oil in antifreeze. Spark plugs look OK, all exhibit similar wear, and were changed at 83,000 miles.

Always only does it after fully warmed up, and only as coming to stop, and settled to idle, but intermittent.

First, replaced sender. No help. Shortly after, noticed CPS was starting to squeal. Had that replaced. Still did it.

Replaced sender again with higher quality one. No difference.

Had a mechanic temporarily connect an actual oil pressure gauge and monitor it. Said it was actually still pumping oil, and SHOULD be safe to drive. He also temporarily installed another sender, but that didnít help.

What I have noticed, and he agreed after I mentioned it, is that after good and warmed up, and coming to idle at a stop, sometimes the tach shows the idle to drop a few hundred RPMs, and the engine seems to idle a bit rough. Thatís when the gauge bounces. The slightest bit of throttle causes the gauge to stabilize. I have no idea how accurate the ďtachĒ is (if itís anything like the speedometerÖnot very) but on a cold start, it goes to just over 1000, maybe 1100 RPM. After short runs, it idles to just under 1000, maybe about 800 RPM. When the gauge starts bouncing after longer runs, it seems to drop to what would appear to be about 600 RPM, and idle a bit rough.

So, Iím starting to wonder if the lowered idle is causing the oil idiot-gauge to not see quite enough pressure to work properly, and causing the bounce? Iím wondering if something in the emissions control system is causing that?

I cleaned the IAC valve and throttle body. I also cleaned the MAF sensor. Helped smooth things a bit, but still has the problem. I suppose it still could be a bad one of those? Maybe the IAC valve isnít working quite right, and causing low idle after warmed up?

How about the ECT sensor? Could that be fooling the engine into thinking itís too hot, and thus, trying to reduce idle to cool down? Is that how it might work?

Iím fairly convinced the jumpy gauge is caused by the lowered idle. Does that make sense? Or, am I chasing the wrong thing?

Iíd appreciate any ideas. This is driving me crazy, and Iím nervous about driving much at all until itís resolved properly.

Thanks,

Howser
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