Philly Miata

iTrader: (1)

Just finished building and installing my new motor: 99 head, 97 block, low comp Wiseco pistons, Manley rods, bearings: rod ACL .001" oversize STD size, main ACL .001" extra oil clearance STD size, Boundary high pressure oil pump, reading through AEM digital oil pressure gauge, using 10w-30 synthetic from Napa to break in with a Fram oil filter. EDIT: also I plugged my oil squirters on account of that thread y'all know about since I have the Wiseco forged pistons. Motor is still NA, built for turbo just waiting to break it in and make sure it won't blow up first.

Still tuning idle a bit, having some oscillation when shifting into neutral (example rolling to a stop light), engine slows to 1k and then will dip to about 500 rpm and then oscillate back up to 800-1k for idle. Idle pressure hovers from 8-10 and pressure does increase by about 10 per 1k RPM, so in the 30s and 40s while cruising at highway speed.

The concern is that during these idling oscillations, the readings on my gauge will read pressure going down to 0 briefly at the lowest RPMs and then while it's oscillating go from 2-8. I'm new to engine building and tuning so I've been working with one or two of the veterans on here who have gotten me this far. I would reeee-heee-heeeeally love to not have to pull my motor so soon after getting things running, so roast away and let me know your thoughts.

mmmjesse

i can tell you this much. i have a boundary stage 2 and my full temp oil pressure is around the same at idle with semi syn 10-30. its up to 50 or so under cruise. It worries me however it seems to be consistant with others?

Philly Miata

iTrader: (1)

I'm just hoping I don't damage my motor by starving it of oil when it drops briefly. Oh I have to add to OP I have plugged oil jets.

rwyatt365

After losing a brand new engine build to spun main bearings (and discovering the cause was a stuck bypass valve on a brand new Boundary Engineering pump) I was very paranoid about low idle oil pressures.

My engine is similar (99 head on a 99 block, Eagle rods holding up Supertech pistons, with squirters - "similar", not the same) and I was really spooked when the oil pressures barely got above 5psi during idle. I switched to 10w-30 Rotella T6 and pressures stay closer to 10psi at idle, but - even after almost a year - it still makes me nervous.

Advice? Use heavier oil. Install an Accusump, Install an oil cooler. Put in a second pressure sensor hooked to an idiot light as a visual "shut the damned thing off!" warning. I did all of this...

Philly Miata

iTrader: (1)

Thank you for the advice. Heavier oil is an easy solution, I'm not sure what an accusump is but I'll do my homework, oil cooler could be in the works down the road. I have a sump temp gauge (is that what an accusump is?) and my oil temps are under 190 at highway and in stop and go and heavy foot mode go a bit over 200. I have the 949 crossflow radiator and a coolant reroute and that does an amazing job keeping everything cool.

Philly Miata

iTrader: (1)

Searched up and read about accusumps, this seems to be a worthwhile investment

AlwaysBroken

I'm not sure it's the relief valve, but you need to address this. Your oil pressure consistently dropping to below 5 psi (especially with the clutch in during idle) is going to cause abrasion sooner or later and that means metal debris accumulating in the can journals. Been there done that.

I have the 949 BE pump and I get 25 psi hot idle. I'm running slightly oversized clearances and unmodded squirters. This is with 5w40 but other viscosities don't differ significantly.

Philly Miata

iTrader: (1)

I do want to address it. Short of pulling the motor, where can I start trying to diagnose the issue?

hornetball

iTrader: (4)

Have you verified the accuracy of your oil pressure gauge setup?

AlwaysBroken

Yeah, I would diagnose the gauge first. Run some tubing up to a 10 dollar Grainger gauge and start the car then go under the hood and look at the gauge as it idles. That will at least tell you it's ball park or not.

BTW, what is cold idle vs hot idle like? Is the cool idle like 20psi with hot being low? It is cold idle like 0 with hot idle normal? When I had a stuck relief valve many years ago I would get no oil pressure at cold start and then the relief valve would unstick as the pump housing warmed up. It got worse over time and eventually my rear intake cam journal accumulated enough crud to block the oil flow and weld itself into place and snap the timing belt.

If you need to get to the oil pump, you can drop the front subframe to access the oil pan and relief valve. Replacing the oil pump will also require removing the harmonic damper obviously. But you don't need to pull the whole motor if you don't want.

Philly Miata

iTrader: (1)

I was planning on swapping my 1.6 pressure sender in just to see if it's the gauge, but maybe an actual analog gauge would be better just to make sure.
Cold pressure is great, 70-80 right off the bat and it obviously goes down as the oil warms up. The car seems to trend towards the lowest pressures when I'm stopped on an incline, but it's possible thats coincidence.

Philly Miata

iTrader: (1)

Sample of pressures with idle oscillation

Philly Miata

iTrader: (1)

Self bump. Conferring with Stefan this seems characteristic of a stuck open pressure relief valve. I'm not too thrilled about having to pull my motor after just getting it in. Will try to verify it's not just the gauge next.

AlwaysBroken

Every time I've bet on the gauge being wrong I regretted it.

Every time I saw oil pressure drop and stopped, it was the right call.

Don't drive the car without oil pressure. Drop the pan, fix the pump. Or you'll be doing another teardown. At this point there isn't a downside to verifying the gauge to be sure, but I bet it's right.

JasonC SBB

Big bearing clearances reduce oil pressure at both idle and high RPM.
But not to near zero.

Philly Miata

iTrader: (1)

Yeah we're gonna verify it isn't the gauge and it sounds like I'm gonna have to pull the motor. Better to pull trans and motor together or just motor?

rwyatt365

I don't know if it's systemic, but I don't think this is the first time that a BE pump came BNIB with a sticky relief valve.

Better safe than sorry...

Philly Miata

iTrader: (1)

I definitely don't want to be sorry! If it means car is garaged for the next week or two, so be it I guess. Just trying to pool my resources before I tear her apart again.

psyber_0ptix

iTrader: (4)

I've got a boundary pump street/strip pump with one shim and noticed that with my new oil pressure gauge, hot idle pressure is about 12psi. I thought it'd be higher with a shim. This is lowest I've read compared the old poop quality gauge and wonder if i've been having wack oil pressures all along. Squirts intact. I do have some difficulty with VVT oscillating trying to reach target but as soon as I blip the throttle and oil pressure shoots up, it works fine. I'll be watching this thread

I too would hate to pull the motor because of a damn relief valve.

stefanst

iTrader: (1)

The shim doesn't do anything for your hot idle pressure. It just increases the pressure needed for the relieve valve to open. Since hot idle pressure is far below that pressure, it has 0 impact.