Low Oil Pressure at Idle
 

I figured since I was boosted, this would be an appropriate area to post. I also searched the forums and the information in all the threads was a bit lacking.

The past few days I have noticed that when I am warmed up and at idle, my "low oil pressure" light comes on my dash as well as my Oil Pressure gauge. I checked my oil levels, right where it is desired. I found no leaks after checking numerous times, but on a lift and looking for a puddle on the ground. When I am driving it is at roughly 60psi when I am coasting at 3k rpms, which from my understanding is normal. Car drives normal, no strange sounds or any other engine symptoms.

I plan on changing out both of the oil pressure sending units next oil change, sometime this week after I find an OEM one online to buy, I can only find ones for the z32 on z1motorsport's website, I am waiting for an email response to see if they have any for the z34.

Does anybody have any other suggestions?

First thing that came to mind for me was the sender was on the way out. Don't recall what kit you are running but I believe most of them get turbo oil feed from where the factory sender is located. Could be it got slightly damaged during install. Check the harness too and make sure it isn't damaged. Might have to resplice a wire if one got nicked.

Partsgeek.com if you just need the OEM sender.

Thanks jwick, I'll give it a look.

The weird thing is it just started up a few days ago. Not a single pressure issue for he past year.

It is super hot lately, that's when it started acting up.

Oil pressure dips pretty low when it's hot out. I have an external gauge (Depo), and it can dip as low as 25 PSI range. I question the accuracy, though, since the external oil temperature gauge is off by 15F.

When I am at temp and idle, my Prosport reads 0psi or 1psi. When it was cooler out, mid 70s, it idled at around 14psi or so.

I'm sure the heat outside has a big problem with it, I am just paranoid whenever I see the warning lights at idle. When I blip the throttle in neutral both go away and act normal, so it's strictly a stand still at idle problem.

I don't like that one bit... Mine is around 15-20 at idle and drops a bit if I drop the RPM letting the clutch out. Running 5-30 Mobile FS.

I would look hard at that, having that low of pressure, even at idle, is not good... perhaps as jwick says it's the gauge. If the pressure was really that low, you would be able to hear her knocking.

It sounds completely normal though, that's the thing that is giving me some hope. Once the stuff I ordered comes in, I'll rip it all apart and check it out, run a mechanical gauge and see if my electronic one is at fault.

Low Oil Pressure at Idle
 

Don't think I've ever checked idle in the heat. Of course I don't drive it much during the Texas summers. I usually just monitor oil temp, boost, AFR and fuel pressure.

That doesn't make sense at all at 0-1 PSI with the engine idling fine. I think the lowest was 12 PSI as I get in 1st gear at low RPM. I'm sure you'll be hearing all sorts of nasty mechanical noise if oil pressure dipped that low. IIRC, isn't there a warning light on the dash for that? I don't think it's a low oil level indicator.

Cold start, my gauge shows 90 PSI. Then hovers to around 60. It'll be around 40 PSI at 3k RPM or so. That's my gauge indication, though.

Had the same issue. On a hot day my oil light would come on whenever at idle. It would instantly go off once on throttle. Adjusted the tuning and raised the idle rpm. Never had an issue since.

hook up a mechanical pressure gauge, could be a bad gauge.

We had a sentra a few days ago, oil pressure was only like 1-2 psi on the gauge.
it wouldnt pop on the oil light, we found that the oil filter came apart inside and was restricting flow.

Ouch, what brand of filter?

If I recall it was a Napa Gold line filter.

Happens to mine too. What i noticed is that when i pulled the dipstick i heard a hissing noise as if there was too much crankcase pressure building on hot days. Im planning on running a catch can setup to help with the excess pressure in the pcv system.

Check sender and check any oil feed lines running to turbo...

I have a twin catch can setup with a check valve, as suggested by Sh0velman. Maybe I will tweak my set up and see if that helps.

I plan on doing some maintenance this week when my shipment arrives, oil change / oil pressure sender replace / turbo air filter replacements.

Update - Changed out the sending units when I did an oil change yesterday, didn't fix anything.

I have a feeling the cause is the check valve in the OCCs. I thought the heat was just a coincidence, the day after install is when the temperature sky rocketed.

With the check valves removed, wouldn't it pressurize the cans when I am in boost and essentially make them useless?

Ideas?

Hey, I replied to your Facebook message too, but I'll post here for posterity's sake.

There's absolutely no way that oil pressure is being affected by anything related to your catch cans. Even if they were plugged closed you'd have the same oil pressure, air is compressible, oil isn't, and a a pump like an oil pump thrives on back pressure.


Does the gauge show pressure at start up that falls off after warm up? Are your "under load" pressures identical to what they were before?


It sounds to me like a conductor has gone high-impedance on the sensor circuit, causing an offset that drops to zero or near zero once you get the normal pressure drop as the oil thins out. Was ANY modification done to ANY wire related to the sensor or to anything else in the same harness?


Is it possible that you jiggled something loose or perhaps inadvertently got a harness somewhere where it got heat damaged? The insulation on the OEM wiring isn't particularly high temperature, exhaust parts or gasses will melt and burn it in short order.


This is on the assumption that you are piggybacking the OEM sender for your external gauge. If you have TWO senders on completely different circuits both agreeing that you have low pressure, it's hard to argue that there isn't a real issue.


If your external sender is on a sandwich plate, it's going to be on the part of the oil circuit that is going into the oil filter, if you have low pressure right there at idle, but normal pressure at speed, I have to think the pressure regulator in the pump is faulty in some way. I believe it's just a spring-type regulator, and if the spring has failed it will be venting most of the flow back into the crankcase, at speed the pump will have the flow to overcome that, at least partially.


My advice in the immediate sense is to not go above 4K RPM unless absolutely necessary, I'm going to check the FSM and find an oil circuit diagram. I'll post what I find.

The pressure at start up seems normal and then it tapers off after a few minutes of running, under load pressure seems very similar if not the same as before.

The aftermarket sensor is located off the GTM adapter when I have my oil temp sensor, the OEM wires and the aftermarket ones are in the same heat proof shield that GTM used when they did my initial install last year. So I believe they piggy pack off each other, but I did not remove the heat shield to double check.

I thought I was careful in the catch can install, none of the wires should of been knicked or knocked loose, when I had it on the lift Friday everything seemed ordinary.

I'm thinking what you said in the FB messages could be correct, maybe the oil pump is gummed up. I'm going to drop it off at the local dealership tomorrow and get the head techs opinion. He has worked on my car before the catch cans and knows the ins and outs of my set up.

Thanks again everybody, I can't say how thankful I am for the help and knowledge.

I just want my Z normal again, I hate not driving her!

Ill

Your prosport oil pressure gauge has its own sensor. The GTM oil block has both turbo feed lines,the factory sensor and I believe the sensor for your prosport gauge. The heat proof shield around the wires might just be some split loom.

I don't think anyone has asked you yet but what viscosity oil are you using during the summer?

Update

Received a call from the tech yesterday when I was at work. I don't remember the specifics but one of the gaskets blew out in my upper oil pan and there was a crack in the bolt for the oil pump. Waiting for parts to come in and then they will reassemble everything and it should be good to go, no major damage was seen anywhere else.

I'm going to go after work to chat with the tech and get more information and the diagrams showing the damaged parts.

It's going to be pricey to fix, but it could've been worse.

Fyi VHR engines don't have oil pan gaskets. Its all "Nissan bond" and I would highly recommend reusing the same stuff to re seal it. The oil pump bolts to the engine block hopefully that's not what's cracked.

Did you figure out what the culprit was. Was it the gasket and oil pump bolt after all?