Strange oil pressure problem

[RadoTD]

I'm having some weird issues with my oil pressure.
Engine is a 1.9L AAZ, freshly rebuilt.
After I put it together and filled it with oil, I ran the vacuum pump with a drill which turns the oil pump. It didn't take much spinning to hit 60-80psi on a temporary gauge, I held it in that range for about a minute to make sure the oil was well circulated. Started the engine up and ran it for the first day or two on the temporary oil pressure gauge, everything seemed fine. Yesterday, it was doing something weird... never showing anything but 20psi. It was just a cheap gauge, so I figured it was having issues. I put my good oil pressure gauge on today and... exact same thing.
Cold start... 20psi.
Once it's warmed up, 15psi at 600rpm, hits 20psi right around 800rpm, so those both seem quite normal, but if I rev it up, it NEVER goes over 20psi.

So then a few minutes ago, I pulled the vacuum pump out and ran that with a drill. The pressure seemed to go nicely linear, actually making it up to 32psi with the drill running at about 1100rpm, which I figure would equate to low-mid 2000rpm's.

Does anyone know what this might be or where I should start looking?
The fact that it stays so consistently at 20psi makes me think that the pump's internal bypass might be malfunctioning, but then how does it hit 32psi running off of the drill? 

[truckinwagen]

any sign of the im shaft pulley slipping on the back of the timing belt?
(look for scuffing on the back of the TB/transfer on the pulley itself)

how high can you get oil pressure with the drill when cold?
(should be right on where it was the first time you primed it)

-Owen

[RadoTD]

Yeah, I'll try that tomorrow.

Also, I'm going to run a gauge off of both the head and oil flange at the same time... if I'm thinking right, a bad oil pump, it'll be low on both, bad bearings it'll only be low on the head. Does that make any sense?

[rabbitman]

The pressure seemed to go nicely linear, actually making it up to 32psi with the drill running at about 1100rpm, which I figure would equate to low-mid 2000rpm's.

The fact that it stays so consistently at 20psi makes me think that the pump's internal bypass might be malfunctioning, but then how does it hit 32psi running off of the drill? 

I don't think the oil pump spins very fast at all. The IM shaft is driven at half crank speed and I think the gears that drive the vac pump slow it down even more. That would mean 1100rpm for the oil pump only happens at high engine rpm. I can check the IM revolutions vs. oil pump revolutions tomorrow with a partly disassembled 1.6D at work.

I spun my oil pump with a speed handle a while back and got 70psi, I think that would be about 100-200rpm.

Is the oil pump bolted on good and tight? The bolts could be loose or, like you said, the pressure regulator might be stuck.

[truckinwagen]

im shaft gear is larger than the oil pump gear, so it should step up in speed right?
probably similar to crank speed.

-Owen

[Powered by Spearco]

Oil pump bolts are only tourqed to 15lbs. Might want to check them.

[truckinwagen]

my bet is for the oil pump bolts being loose as well.

-Owen

[RadoTD]

I started driving home from Ed's house very easily and pressure dropped even further, so I parked the car on the side of a back road. I'll be driving another vehicle out there tomorrow (lucky I don't work tomorrow) with a new oil pump just in case and I'll be dropping the oil pan on the side of the road. Yay.

Hopefully you guys are right about it just being loose bolts on the pump. Would it make sense to tighten those bolts up any more than 15ftlbs? I think I may have torqued mine to 20 as that's the lowest my only (at the time) torque wrench went to. I now have a smaller one.

[rabbitman]

Hopefully you guys are right about it just being loose bolts on the pump. Would it make sense to tighten those bolts up any more than 15ftlbs? I think I may have torqued mine to 20 as that's the lowest my only (at the time) torque wrench went to. I now have a smaller one.

Torque them to 15ft-lbs and then with a regular ratchet see how they feel, I bet they'll feel too loose. Maybe use lock tite too.

I'll check the oil pump to IM shaft ratio tomorrow (if I remember), I'm curious now .

[myke_w]

my bet is for the oil pump bolts being loose as well.

-Owen

x3

[R.O.R-2.0]

Hopefully you guys are right about it just being loose bolts on the pump. Would it make sense to tighten those bolts up any more than 15ftlbs? I think I may have torqued mine to 20 as that's the lowest my only (at the time) torque wrench went to. I now have a smaller one.

Torque them to 15ft-lbs and then with a regular ratchet see how they feel, I bet they'll feel too loose. Maybe use lock tite too.

I'll check the oil pump to IM shaft ratio tomorrow (if I remember), I'm curious now .

pretty sure its close to 1:1

gassers have basically the same gears, but reverse cut, and they spin a dizzy with them, at 1:1 the rpm of the IM shaft. i know its not a gasser, but its just like one.

[Vincent Waldon]

My bet is that the oil pump turns at gasser distributor speeds (since that's its heritage from an engineering perspective)... which should mean the engine makes 4 revs for every rev of the oil pump shaft (and distributor, if its a gasser).  Four distinct TDCs, one for each cylinder, as the distributor makes its way around the firing order.

The IM shaft is half engine speed, and so the the oil pump would be half the IM shaft speed.

If I did the math in my head right that means that 4000 RPM at the engine is 1000 RPM at the oil pump.... and at idle the oil pump is doing something like 250 RPM.

All of the above is just me thinking out loud....  

[truckinwagen]

gasser distributor should spin at half of engine speed, many are simply run off the back end of the camshaft.

a distributor needs to be at cylinder 1 for each firing cycle, which happens once every two rotations of the crank, so it will spin one rotation for every two that the crank does.


that said, I am not sure that the diesel gears are quite the same as the gasser ones, I would not be surprised if the oil pump spins faster on a diesel to make up for the lower operating speeds.

-Owen

[Vincent Waldon]

Yeah you're right... these are 4 stroke engines.... and lots of them (16V gassers spring to mind) drive the distributor 1:1 off the cam.

K... let's call the oil pump 1/2 engine speed.   

[R.O.R-2.0]

just to throw a wrench in the spokes

the 16v engines had a smaller IM shaft sprocket.. so they did turn the oil pump faster..

i dont know what its ratio is, but its faster than normal..