Help from those with oil pressure senders at the pump

[boca rat]

Hey there

I have a separate sender at the pump, that is hooked to my AEMv1 and then outputs to gaugeart.

Gaugeart shows this PSI when hot and steady highway cruising for a bit, on a hot day.

RPM PSI
1000 14-18
2500 42
3000 53
3500 61
4500 77
5000 75
5500+ 78-80

I use Mobil 1 10w30, I am 1100 miles or so since the last oil change. Motor is SCed, intercooled, 157k on it, 400rwhp

Question 1: how do these numbers look? Seems it maxes at 5.5 bar or so. If so, I will presumably never see more than that at the gauge, right?

Question 2: does anyone know what the factory spec/tolerances are for pressure at the pump?

Question 3: I swapped out the factory sender for an SOS one. The gauge never gets above 3.5 bar, and at hot idle is actually less than zero. Could I have a bad gauge or (another, they promptly diagnosed and replaced the first one) bad SOS sender?

Question 4: has anyone hooked up some kind of gauge at the factory sender? Obviously it would be good to know what the true reading is at that point.

Talking to other local NSX guys, they said that when I do engine out TB/WP, hoses etc in a couple of months time, looking at the cams will tell us immediately if there was ever oil starvation issues.

But it would be nice if I could get harder data ahead of time to minimize downtime

Thx!

 

[Mac Attack]

The aftermarket oil pressure sender readings look fine to me.

The factory specs are in the SM. IIRC, they hook up a gauge at the pump discharge and check at idle and 3k RPM.

Dave

 

[boca rat]

The aftermarket oil pressure sender readings look fine to me.

The factory specs are in the SM. IIRC, they hook up a gauge at the pump discharge and check at idle and 3k RPM.

Dave

Thx Dave. I checked the SM, 10psi at idle, 50psi at 3000rpm.So I think I am good to those specs.

However, interested to hear what other primers are seeing, especially at top end.

Any thoughts on the other questions?

Thx again.

 

[smooth]

I recently checked oil pressure at the factory sender location. Readings were generally about the same as what you listed.

I was getting fluctuating readings and sometimes no indication at all with the factory gauge. Very unsettling to say the least, but I guess the factory gauge/sender problem is common on some of the '91s. I ordered and installed the SOS sending unit and got the same as you, max ~3.5 bar, and under zero when idling. It sucks to see under zero at idle IMO, and even 3.5 bar max is not a true reading. So I put a T inline with the SOS sender, added an analog gauge and took the readings.

The wire that comes with the SOS sender has a 10ohm resistor in it. After some movement of the wire during gauge install/removal, the leads on the resistor broke and I was getting no reading on the factory gauge. I replaced the connector on the sender wire, leaving out the resistor. Now the factory gauge reads just barely below one bar at idle, and between 7-8 max. I'd rather have that than the below zero/negative reading at idle.

 

[boca rat]

Thx Smooth, Of all the responses, the last one I expected to see was someone with the exact same issue that I had, and I even saw the same thing with bypassing the SOS resistor. I think I/we need to go back to them on the quality of the sender.

Do you have pics/more details of the analog gauge and the T? I was thinking of doing the same thing as a sanity check.

Can anyone else confirm their numbers at the pump?

Thx!

 

[smooth]

At idle


At ~5k


Tee

 

[RYU]

Are those readings when engine is under load or are you revving in your driveway or something? Not that it matters too much. Also, that's at normal operating temperature right?

I run a denso sensor to my HKS Camp2. From vague memory your numbers seem about right.

If I remember, I'll check this wknd

 

[nsxspdfreak]

Your numbers are fine. I read as high as 100 at the filter pancake, but never that high at the dash, and I have a SOS sender installed. The purpose of the SOS sender is not increased accuracy over the OEM sender, but is only to reduce the possibility of failure of the sender from exposure to heat and vibration from the motor. I had a wiped cam bearing last year so I spent hours going through the oil system making sure it wasn't a oil pressure problem. My gauge still reads 1 (14.2psi) at an idle and around 4 (60psi) at 5000. When the oil is fresh it rises slightly due to the increase is resistance to flow that comes with new oil. The location of the tap for sensing oil pressure is sort of semi useless when it comes to reading pump pressure. The oem gauge reads oil pressure just before the front Vtec solenoid and downstream of the oil circuit (crank and cam journals), and not at the pump so it's affected by resistance to flow within the rest of the system before it ever gets to the sending unit port. The pressure is affected by the condition the crank journals and when vtec solenoids open. Tight clearances on the crankshaft journals will increase pressure and opening vtec solenoids will result in slightly lower pressure on a gauge connected to the cylinder head tap. I would prefer to have oil pressure readings from both the oem location and at the pump.

http://www.nsxprime.com/FAQ/Troubleshooting/oilpressure.htm

 

[boca rat]

Good stuff, thanks guys. I did some more reading and seems the gauge can be a weak spot, and I have seen with ignition on thegauge reads about 0.5 bar below zero. Is that normal? An extra 0.5 in my favor would be nice but not sure that counts for a whole lot.

So courtesy of a good friend, sourced a new temp/pressure gauge set from Acura. I should have that in 10-14 days, will install and report back.

Meanwhile I will also look at Teeing off the sender as Smooth has done.

Thx!

 

[nsxspdfreak]

Good stuff, thanks guys. I did some more reading and seems the gauge can be a weak spot, and I have seen with ignition on thegauge reads about 0.5 bar below zero. Is that normal? An extra 0.5 in my favor would be nice but not sure that counts for a whole lot.

So courtesy of a good friend, sourced a new temp/pressure gauge set from Acura. I should have that in 10-14 days, will install and report back.

Meanwhile I will also look at Teeing off the sender as Smooth has done.

Thx!

Do you mean a negative .5 bars with the ignition on, but the motor not running? If that's the case I wouldn't worry about it. The accuracy of the gauge and sender or not that good to begin with.

 

[bngl3rt]

Tangent: Could one not also run a "T" here (at the base of the SoS sender) if one wanted to run an oil temp sensor?

 

[NSX2398]

I have had the SOS sender almost from when it was introduced. Shortly after installing, the pressure readings were normal then a day later they went to zero. Chris diagnosed it to a piece of what looked like Hondabond coming loose and plugging the sender. It then worked fine for quite a while .. then gave very low readings at idle but 3-4 as the revs rose .. and now will rise to 0 and stay there most of the time although it will occasionally drop below 0 while running. I'm going to be pulling it apart soon to see if more gunk has wandered into the sender or line.

But my real reason for mentioning this is that it seems there is always this unknown about whether it's the gauge or the sender. Both are electrical so I'm sure it's a simple matter or someone fabbing up a test circuit with a couple of resistors to simulate a couple of pressures and if the gauge doesn't respond properly, then we known it's the gauge and not the sender. This shouldn't be rocket science! Now if it's not the gauge, then I'm not sure how you prove it isn't the sender. And, if you could prove it isn't the sender or the gauge, it sounds from the discussion here like there's a number of reasons why the pressure reads low; fluctuates; etc.

 

[boca rat]

Forgot to report back.... I am feeling a lot more comfortable now.

I got the new gauge installed and the gauge now reports slightly less than the AEM sender at the pump across the full rev range, although a little less that that at hot idle.

Thx for all the feedback guys.