Zero oil pressure at idle but comes back with a little throttle. Serious WTF.

[illwillem]

BACK STORY-----
So I took the NSX out to the track this yesterday and ran hard for a few sessions. I'd I blown my oil gear on track a couple years ago and i've been fighting with an intermittent vtec solenoid CEL (code 22) since. I'm not positive the two are related but thats when it started. It typically occurs when ive been on track for a few laps and i'm up to temp, oil about 200-240* all pressures looking good, then about 5 seconds into a rev though a long sweeper or down a straight ill suddenly get a CEL and the car will go 'limp'. Ill pull into the pits and sure enough, its the front bank vtec solonoid, code 22.

I reset the code wait a few min then fire it up and everything is fine for the next session, until i repeat the above steps. It has never occurred on the street or on the dyno, only under track conditions. I have cleaned screens, I have replace BOTH front and rear solenoids with new OEM ones and added an external oil pressure gauge thats reading post sump/cooler before the sandwich plate return. This also happens when accusump is on and when it is removed from the equation.
Im running 10/30 mobil1 and oem filter. Motor has the Dali billet oil gear, new OEM pump housing, 3qt accusump, baffled oil pan. Ive also replace all the accusump switches and valves for new upgraded ones. I've rerun them off different 12v circuits and installed a dummy light inside the cabin to verify the sump pressure switch is getting 12v power. Oil cooler lines and fittings are appropriate length and width (-6an) and im using a zero restriction check valve before the sump 'T'.

I am seeing normal solid pressures at idle and under vtec conditions as read from both gauges; OEM dash and after-market Defi unit. OEM reads pressure from the head per stock and Defi reads post sump and gages pressure in the ancillary systems (external oil lines, oil cooler, sump return, back to motor)

All in all I have a pretty clear picture of what happening in the motor at a glance.

I have found in the past that slightly over filling the motor oil level had helped in postponing the CEL. My hunch was that as I was revving the engine and building pressure the 3 qt sump it was storing oil enroute to the motor, as it should, but this and causing a drop or insufficient pressure when the solonoid was looking for the 'OK' to go into vtec. Ive always slightly over filled all my vtec hondas on track and this seemed to help the issue for a bit.

As annoying as all this is I can still take the car out and put down some quick times. Ive become pretty accustomed to the problem its SUPPER aggravating but to continue to test my fixes and trouble shoot it a solution I have to take it too a track day and drive it hard to see if i was able to fix the problem, since I haven't been able too yet, ive done able 6-8 track days in a car that i will only do 3 maybe 4 laps in before I have to pull it in. Thats maybe 15 laps a day TOTAL including warm up laps. its getting old and frustrating becasue i haven not cut any corners in trying to get this resolved.


Problem as of yesterday---
So yesterday was more of the same, I had changed the oil and removed a shift light that was on the same circuit as the sump and installed an aviation grade power switch in the far off hopes that any of these things could be a miraculous fix.

End of the third lap of the first session and "hello my old friend" CEL pops on again. pull in read code 22. damn it. run two more sessions, 3 laps in same issue both times. pull in.

I check the engine oil and determine that it could use about half a qt more as id discovered to help. I power on the sump and rev the car so I can fill it with oil and switch it off so it is storing its 3qts capacity and is removed from the system. Now I can read just the engine oil on the dipstick and fill it appropriately. I add about 1/2 a qt or less while the car is at idle @ about 180 deg oil temp. I go and sit in the driver seat to check pressures and verify everything is in spec, at this point ive done this a million times....

Thats when I notice that at 900rpm idle the pressure reading at my defi gauge (post oil cooler and 8 inches from the sandwich plate intake) is dropping under 5psi... then reads 0psi i qiuckly blip the throttle and oil pressure responds and bounces back up to about 15psi, it then settles back down and down and goes too 0.
At this point im thinking i have a malfunctioning aftermarket switch becasue the OEM oil light switch triggers the oil light on the cluster if it drops under 5psi and so far its not come on. I watch the oem oil pressure dial and it looks normal for idle for about 10-15 seconds then it too drops to flat line. still no oil pressure light on the dash. i blip the throttle again and they both respond back to life and go within normal range. i let them settle and do this a couple more times to verify its really happening and not a fluke. Sure enough pressure in the external system at idle drops first then I see the pressure in the head drop a shortly after that and return to normal with any throttle or if i switch the sump on.

So this is new.


I call it a day and dont let it idle anymore for the whole drive home with left foot braking.


Where im at---
Its a mechanical system, the he oil pump is driven off the crank, if i rev and everything is withing spec this should not be happening at idle. BUT its being verified by two separate gages at two separate places but not on the oil pressure switch dummy light which id expect to light up as it was dropping as it did when i blew my oil gear and had no system pressure.

I guess i can start by seeing if something has a blockage it that can only be moved by more than the 9psi thats happening at idle? Seems like thats a long shot, but hell I don't know anymore...

This is on top of the front bank code 22 problem.... anyone wanna buy and NSX?

 

[Mac Attack]

I'm not sure how precise the 5psi pressure switch is on the oil cooler. My point is, it might only be ~3psi or so.

BUT, if your other two senders are responding when revved slightly, then my guess is you have a trapped piece of debris that is blocking open the oil pump spring-loaded bypass. That could explain why you have little oil pressure indicated at low RPM (pump volume and discharge pressure), but it is registering under higher RPM.

The oil pickup sump screen is pretty coarse and would allow debris to pass up into the pump suction where it could get trapped in the bypass bore and cause the plunger to stick. Certainly makes sense, because the OEM oil pump is rated at 6000 RPM at the point where the bypass is designed to normally open. I'm sure you spent a lot of time that day above 6k RPM where that plunger was sliding down and up.

If you're brave, you can go out and take the engine above 6k to try and clear the debris out of the bypass. But, this may not work depending how the debris could be lodged in there. Your best bet is to drop the pan and filter the oil to see if anything shows up visibly. Then remove the TB and oil pump to open it up.

My guess is that not all of the old disintegrated oil pump gear got cleaned out of the engine during the rebuild. That's also probably the cause of your front head VTEC issue. Sorry man. Good luck.

Dave

 

[illwillem]

^^^ thats is EXACTLY along the path I was thinking after brain storming. Very good to hear it echoed from you. Well, sounds like I have my work cut out for me.

 

[Mac Attack]

If you aren't ready to remove the front head, TB, and oil pump yet, you could always just drop the pan, check the oil, and check the oil pump bypass.

As you know, the oil pump bypass can be opened up from the bottom of the pump when you remove the pan and oil pickup. That way, you can see if it was sticking or not. Or at least remove the spring-loaded plunger, clean it, and inspect the top seating area surface if it's boogered up.



When you rebuilt your engine after the gear failure, did you replace the oil cooler? This would have been the prime spot for debris to get stuck in. It took me two cans of brake cleaner to completely clean out mine, and that didn't have any debris in it... just gunk. I would recommend oil pump cooler replacement for any failed bearings, pumps, etc. The oil cooler just has way too many crevices for that crap to accumulate in and not be able to get it all flushed out.

 

[liftnot]

Will, do you have a mag oil drain plug? any shaving in sight? not sure when you install the Dali billet oil gear but the flatness callout on it maynot be as tight as the Comptech/TODA gear. I have seen this in another track car.

>Thats when I notice that at 900rpm idle the pressure reading at my defi gauge (post oil cooler and 8 inches from the sandwich plate intake) is dropping under 5psi... >then reads 0psi i qiuckly blip the throttle and oil pressure responds and bounces back up to about 15psi, it then settles back down and down and goes too 0.
sounds like you've check everything else.
the clearances of the gear to pump housing needs to be checked thoroughly but the common excuse seems like is "they all do that".

 

[Mac Attack]

Back when I was evaluating oil pump gears (including the TODA and SOS), I came to the conclusion that the best and tightest-tolerance manufacturing process would be to EDM 4340 alloy and then micropeen it for stress relief. Was prohibitively expensive. So, after more research, I bought the Dali gear, which was sourced from the same provider that supplied SOS's gear (from my research). This may have changed in the past five years - I don't know.

FYI - my Dali oil pump gear clearances with my old 130k mile used OEM housing are published on this site in the for sale section. There were absolutely no issues with the Dali oil pump gear tolerances and a lot of people are using this gear without issue.