Oil Pressure Dropping When No Load On Engine.

[Simon-S14]

has an interesting problem and im not sure if itts engine related or haltech + oil sender related.

Both my rb25 and rb30 engines (both with different oil pumps, restrictors etc) show up in data logs with dips in the oil pressure when you back off. so for example when your on the throttle. boost is up, rpm is up oil pressure is up. when you back off quickly.. (straight line or corneriing, does not matter.) the boost turns to full vac and tps to 0 oil pressure dips down to 15-20 psi for 0.1 of a second or something. RPM remains the same since im still in gear..

its not oil surge. sump is way overfull as it is. does it in a straight line, turning left or right. and its random too.

if anyone switched on wants a copy of the data logs i have them..

it seems almost to me that once the load is removed from the engine, oil flow goes up and pressure goes down. as soon as load is put back on, oil pressure goes up.

[Simon-S14]

sample of log

http://imageshack.us/f/3/datalog.jpg/ might have to magnify to view

[scotty nm35]

Lazy pressure relief valve perhaps? Interesting log, wish I could run the Haltech...

[Simon-S14]

well thats the thing,... i have logs from when i ran the rb25 bottom end with nitto pump (brand new) and it shows the same characteristics as this. just the numbers are different.

makes me wonder if its an overly sensitive sender issue or a real issue

[zebra]

Any crank case pressure will increase oil pressure, so when you back off the pressure will drop.

Can look at the log as I'm on my phone so can't see if it is a major drop or not

[Simon-S14]

yeah i really have no idea atm

[GTSBoy]

Yuh, I was going to say, blow by pressurising the crankcase.

Make up an adaptor to hook a MAP sensor or boost gauge onto a crank breather line. Go for arun through 3rd gear and watch how much pressure you get. Could be interesting.

[Simon-S14]

so nothing to worry about then? since pressure is down flow must be up...

[The Dan]

Crank case pressure can cause the oil pressure to read higher/lower but not by the amount being seen there.

If you had that much crankcase pressure that it caused massive spikes up or down you'd be blowing rear main and oil pump seals out of your engine. You would also be literally pumping oil out the breathers into your catch can and popping your dipstick out.

From the engine I've seen with massive crankcase ventilation problems, they actually made oil pressure read much lower as load was applied. Both times it was broken ring lands

I would be checking ECU and signal earths. It sounds like a sender/signal problem tbh.

The only other thing that could effect oil pressure like that 'might' be crank end float but shit you would have to have a tonne of it

[kitto]

Interesting issue.

I would be putting another oil pressure sender in. One sender at the outlet of the oil filter plate and have the other one in the main oil gallery (im assuming this is where you have your curreny one).

Then do a run and log it. Youll be able to see any difference between pump output pressure and engine oil pressure.

[r31 25t]

Are you confident the sensor is scaled correctly in the ecu settings?

[DJRIFT]

Log it stationary. Give it a big rev then let off and do it 5 times in 20 sec then put the log up. The rpm signal is very ruff and doesn't seem right. It mite be logging to frequently

[Simon-S14]

will do. cheers

[Simon-S14]

refresh rate for logs is 100ms if that helps

[kitto]

The rpm signal is very ruff and doesn't seem right.

Thank the Nissan CAS for the rough RPM signal.

Simon, just looking at the graph, i see a maximum oil pressure of 64.2 PSI and a maximum RPM of 6734RPM. Your peak oil pressure is on the low side for that RPM.

[Simon-S14]

rb30e pump.. what can i say.still its not far off the mark going by the old 10 psi per 1000 rpm rule.

in my incar footage you can see the oil pressure light (red light on left of dash) come on when engine is unloaded or backing off. dash is fed info from the haltech and light is set to come on under 20 psi .

https://vimeo.com/46565580

[kitto]

Hmmm, red light is dancing away like mad.

Maybe its a good idea to fit an accusump?

Yeah your just on the verge of the 10psi/1000RPM rule. 75-90 PSI would of course be a lot better.

Another idea you could do, hook up a mechanical oil pressure gauge. Watch the gauge and/or film it and see if that gauge drastically dips.

[Simon-S14]

yes thats on the cards... will hook up a mechanical gauge asap and see if theres any dips.. need to borrow on tho, dont have one lying around do you?

[kitto]

yes thats on the cards... will hook up a mechanical gauge asap and see if theres any dips.. need to borrow on tho, dont have one lying around do you?

Nah i dont have one lying around. Just go and buy a speco meter one, $30odd.

Even though i'll have the racepak in my car i'm still going to have some gauges.

Accusump will be a good investment.

[abr33]

Im not up to scratch on the logging side of things but oil pressure should have sweet f/a effect from engine load unless your sucking air? If im thinking correctly?