txhokie4life

Ok sort of stumped here:

This is where we are at -- and where we have been.

Picked up a 951 18 months ago.
Never had great OP -- 4 bar tops startup cold,
-- would idle warm/hot down to 2 or a tad below.

On track -- got LP light -- sub 2 bar -- eventually going to sub 1 bar
and could creep to 3 with revs.

She ended up spinning #2 rod bearing while idling.

Rebuilt the whole engine.
new bearings (rod & main), replaced #2 rod. replaced and cross drilled crank.
replaced oil pickup tube, put in a new to me oil pump. New rings, new sleeves.
Rebuilt turbo -- i.e. -- a large chunk of change.

Block was completely torn down -- completely clean.

Put it all back together -- and we still get maybe 4 bar at startup.
Then just at or below 2 bar at warm/hot idle (no track session, just street driving (below 4k) and when warm -- barely over 3 bar at 3-4K rpm whether
under load or unloaded.

Replaced OP sensor (as the original was damaged during rebuild).

Thought the OPRV was binding, replaced it with another 3 piece, Same behavior Bought a NEW OPRV/seals (ouch $$) -- still same. (might have gained 1/2 bar at startup -- but back to about the same when warm).

Running 20/50 Valvoline racing oil -- with 1 QT 60W -- dumped all that after rebuild -- and redid same thing -- no change. Inspected filter -- nothing out of the ordinary for a rebuild.

checked front pulley bolt torque -- at least 150 ft/#.

Car has RX7 oil cooler upfront as installed by PO.

even measured the voltage on the op sender
9.5v @ 2bar warm
8.7 idle (1100 rpm) 8.7 cold 3 bar
8.2-8.4 revved 4000rpm -- semi-cold.

Pulled the dash and cleaned the instrument pod connections -- no change.
(I trust the gist of the gauges -- as last year they read about the same
and the bearings spun when it dropped pressure)

Since the behavior hasn't seemed to really change before/after the rebuild....
I don't think we've found the root cause -- and I'm not risking the engine to another failure.

My mechanic and I (and a few local 944/51 folks) are stumped.......

thanks,

Mike

jimbo1111

My gut instinct would suspect the oil pump. Unless you knew for sure it's new. I had a similar issue that turned out to be a faulty oil pump. After investigating the usual suspects and later installing a new oil pump and a set of rod bearings. That I had replaced for precaution the oil pressure was fully restored to 5 bar.

951Tom

Maybe try hooking up an external gauge like the factory shop manual shows to get a more accurate reading? Did you use the special alignment tool when installing the oil filter housing?

Chris White

Here is a bunch of thoughts-

Very little can go wrong with the stock oil pump, they don't wear out. They can be reinstalled badly but that's about it.

Most important - any modified 944 turbo that is tracked should have a good oil pressure gauge - and a good oil temp gauge!

Cold Oil pressure should peg the attack gauge - it is up to 100psi (over that on new engines).

The Oil Pressure light comes on below 1bar.

Did your rebuilder check all the bearing clearances? sounds like something is off in that area. Maybe the oil pressure valve in the head was not reinstalled.

Don't track the car....it won't last.

on the original failure - most likely the rod bearing was damaged earlier and finally died at idle. Not enough force on unloaded rod bearings to fail at idle - in fact they can run on residual oil for quite a while as long as they are not super hot.

BTW - hot oil pressure at the track down to 1 bar at idle is not uncommon (make sure your gauge is accurate!). even cars that make 5 bar cold can get down to 1 bar at track temps. Oil temp has a very big impact on pressures.

Willard Bridgham 3

Get a calibrated oil pressure gauge. Have you checked pressure with a calibrated mechanical gauge (not the stock one)?

txhokie4life

We'd been through just about everything including a complete new block.

We've been chasing this issue for 2.5 years, cost me one engine.

You name it we inspected and then replaced it to no avail.

Finally Took the cam tower off
Pulled the cam and found a gouge in one of the cam journals.

Sourced a cam tower and rebuilt.
Installed it today and oil pressures are solid
Nearly 5 bar cold and slowly dropping to 3 bar after 25-30min of idling. Rev to 3k yields 5 bar.

Haven't confirmed on the street and track, but I'm confident we finally nailed this.

Need to continue testing and finish buttoning it up.

I don't even want to think how many $$ and hours went into this.

Prev owners rebuilder should be shot
Never addressed debris in turbo (complete rebuild)
Left debris in oil pump (replaced)
Debris left OPRV sticking (upgraded)
And clearly missed this as well.

Oh well someone's going to a heck of s car when I'm finished.

Also have a stout racing block to move along...

Cheers,

Mike