grdtii

I just purchased a 2002 996 C4S with 30,000 miles. I have noticed that the oil pressure gauge fluctuates a little even when I am maintaining a steady speed/rpms...I know the rpm & oil pressure readings are linked so that they correspondingly raise and lower, however, I am not so sure the oil pressure should fluctuate at all when I am maintaining a steady rpm level. Anyone have a similar experience?

logray

It should not fluctuate assuming warm engine at a constant RPM.

Search for the oil pressure sender unit here, there are a lot of threads about cleaning it and/or replacing it to solve that problem.

It could be other issues as well, but probably a good place to start.

grdtii

Thanks. Do you have any thoughts on what else it could be if not that?

logray

Baffles, oil pump spring, scavenge pump, blockage, instrument cluster problem, wiring, excessive wear, ummm.....

Seriously start with the sender it seems to be most common for that problem. At the very least cleaning the contacts on it.

grdtii

OK...thanks

knfeparty

mine is a bit jumpy too...it also was on the 944. I really only notice it when I'm holding the car at an elevated idle like when I am circulating coolant to help the engine cool. 944 spec racer lore says that it was a sign of a failing #2 rod bearing...but that was 944s.

silotwo

I just had the sending unit replace on my 04 C2 for the 2nd time. I had the "failure indicated" warning and gauge indicated zero pressure for a few seconds. Happened 2x in a few miles. I decided that since it is a pretty important warning I would just have it replaced so that the gauge had meaning I could trust.

When the dealer checked the car the diagnostics did show it as failed. They keep plenty in stock and as the mechanic said, there is a reason they have them on hand.

Looked like it would be a simple DIY for those with the time and basic skills.

back2porsche

Same issue on my 02 c4s with 60k mi. Had the sender replaced last fall and problem corrected. It's back again. At a steady 3000 rpm it can fluctuate between 3.5 and close to 5 within a couple of seconds. Think I'll try a DIY fix this time.

BTERRY1

Going to resurrect this thread since it is a couple years old to see if others have experienced and or determined cause of what I am seeing with my car. 2003 C2 51K on the odometer.

History – since I purchased I would see pressure of 4.3 – 4.5 on startup and RPMs above 4K and a low of 1.1 at idle. Never liked the low idle number. I noticed that I would randomly get pressure fluctuations when holding RPMs steady in higher gears.

Last week I changed the relief spring (read somewhere could be cause of jumpiness), and the sending unit. Now I am happy with pressure at cold start of 5 bar and warm idle after a long spirited drive of 1.4 bars.

I am still seeing fluctuations, even more than before. If I hold the RPMs at 3800 I see a pressure of 4 bar then it starts to fluctuate to 3.4 – 4.2. The longer I hold the RPMs the more fluctuation I see. If I let of the gas, then raise RPMs again it steadily rises and will not come back till I hold the RPMs again. It is random and not always there. I do not feel it is mechanical is the behavior is a little different than before the pressure sender change, and not always there.

Any thoughts guys or other things to check?

Kalashnikov

Oil pressure gauge operates from the crappy oil pressure sensor. They constantly go bad and produce irregular readings. Their life expectancy is roughly 10-20k miles. Replace your OP sensor and report back. OP sensor is located on the passenger side of the engine towards the front of the car.

BTERRY1

hi, thanks for the response. i changed the sender along with the relief spring this last weekend. Still seeing issue, just slightly more pronounced with new sender.

mse

I had a similar issue last year and brought it into my indy to get fixed. He told me that there is an oil pressure sensor AND oil pressure sender that can go bad. He replaced the sensor for me, and I haven't had any problems since. That might fix your issue.

BTERRY1

so wait... i replaced the "sender" following the common DYI. there is a "sensor" too?

BTERRY1

these are the items i replaced last weeked. I do not see a "sensor" listed on Pelican.

Ahsai

There's only one oil pressure sender/sensor, the one you replaced. Inside that sender/sensor, there's a pressure sensor inside, which drives the pressure gauge. There's also a pressure switch inside, which trips the oil pressure warning light. That's why the unit has two terminals, in addition to its metal casing which is grounded.