I recently replaced the drivers side Cylinder Head Gasket in my 93' CS Quattro.
The car ran super for 2 days afterwards. then suddenly developed erratic oil pressure at the gage. I replaced the oil and filter which brought it back to normal. ~5 Bar at 2500 RPM ~
Within 3 days, the oil pressure dropped below 1 bar (would increase when I accellerated) then dropped. After shutting down and restarting, the pressure is ZERO.
I've dropped the pan, inspected the screen and pickup tube. Opened the plate in the sump and blew compressed air through the oil cooler. All seems fine. This car has the older style Lubrication system for the AAH engine. I tried increasing the viscosity to help prime the system but no luck. I am at a loss (of ideas as well as pressure).
Are there any ports, which could have developed blockages or could the regulating valve near the filter be suspect? A Priming Process? The manner which it failed seems odd that it would be a Pump Failure as I understand that is very rare in this Engine group.
Can anyone help me out? I've tried the 80/90 forum without sucess.
A MUCH APPRECIATED FAN

Pressure valves, oil pressue switch, and oil pump come to mind. A blockage in an oil galley might lead to increased resistence and increased pressure, depending on where the blockage is occurring. What makes you think the oil pump didn't crap out all of a sudden?

Both the mechanical gage and light sending units seem ok. There is not oil distribution confirmed by the lack of oil spillage when I pull off the filter.
Does anyone know how to access and remove the regulating Relief Valve on the early AAH engines?

Any comments are appreciated.

After replacing the Cylinder head gasket, the car ran great for 2-3 days, then the Oil Pressure started to fluctuate and drop at idle,. After an oil and filter change, all seemed normal for 5 days until it started to drop off again at idle....after restarting, the Oil Pressure is ZERO. my first thought was inlet screen blockage. But the sump and screen were spotless. Do you know whether the regulating Valve near the filter could stick open? Does the one near the Pump housing have external access?
Thanks for your input!

then it will result in low pressure at low RPMs. I don't know where it is on the AHH. It must be near the oil filter.

If oil pressure is low at high RPM, then it might indicate worn crank bearings.

Thanks you.....this Valve was to be my next thought as well. There is one located near the filter housing. Not certain but it must screw in.
I don'yt think that I have a bearing problem as there is no knocking when it runs ....only valve lifters.....but I havn't left it running long enough to listen for more.
I'll post the results of this next task.
Meanwhile, can anyone post the access and removal of the regulating valve? It seems to be under a plate accessed when the sump is removed. Does the relief valve at the pump have the same effect?
Thanks!

I've heard a lot of problems AAH 92-95 v6 owners have had with oil pressures on higher mileage engines, even I suffer from zero pressure on starting the car after it has been shut down for a few hours and I know at least one other who visits the forums that has the same problem as me where the pump loses its prime even after changing the pump/gaskets, pick-up tube,pressure valves, retention valves and various filters.

Do you have any oil pressure on cold starts? if you do does your pressure read around 5bar, 3 bar or 0 bar? I've had the misfortune once to forget to look at my oil gauge and ended up with a spun no.1 main bearing this produced a drop in oil pressure of 2 bar across the range so at warm idle I would only have 0.5 bar and only 2.5 bar above idle speeds.

I've read on the Audifans 12v-v6 past archives (now lost)that some experienced a drop in pressure and sure enough the oil pump was the cause in fact one owner had to have the pump replaced twice! other times the cause was a loose oil pressure valve - there is one located in each head under the valve covers. Also be weary of the fact that the head gasket itself controls pressure as part of the gasket covers an oilway which controls pressure at the heads.

I would in your shoes check the pressure valves in the heads for tightness - as a precaution replace them - they need threadlock to be fully secured. Next, I would perform an inspection of the main bearings by dropping the upper oilpan and removing the bearing caps and examining the bearings for wear, especially no.1 main bearing next to the oil pump. If those are fine then progress to the oil pump, remove it from the front of the engine and remove the cover plate on the gears and inspect them for wear. Also examine the pressure relief valve on the side of the pump (see the pic!)- remove the bolt and check that the operation of the valve is smooth and that no debris has jammed the action. Be on the lookout for oil leaks as a serious one around the pump could cause a drop in pressure.

<img src="http://pictureposter.audiworld.com/18363/pumpopen.jpg.jpg">

Audi later upgraded the lubrication system on the AFC engine, perhaps their long-term tests showed problems on the AAH?

Thanks very much for your input....The manner which I lost pressure seems odd as it ran well after installing the new head gasket for a few days, then dropped low....but improved with increased RPM. AFter an Oil/Filter change, ALL was normal for 3 days then WHAM...very low pressure at idle. Now the pressure remains at ZERO when started. I won't rev the engine as I am afraid to damage a bearing. I suspect one of these relief valves. stuck open. Is the one at the pump accessable without removing the Timing Belt ? What about the one near the filter?
Thanks for your input.....

Does anyone know how to remove the Relief valve on the Ealier AAH engines? It loos as though it's about a 6mm Male thread, but I don't see anywhere to grab to remove it from the upper sump. This may be my culprit.

If you have the AAH engine there is no pressure valve in the sump area. There is only the pressure relief valve on the side of the pump. The only pressure valves are located at the heads, usually have an allen head socket. Only the AFC has a pressure valve in the sump area - where the plate is attached on the AAH upper sump!

To access the relief valve on the pump you're best bet is to remove the accessory belt and swing or remove the alternator out the way so you can get a 18/19mm? wrench on the hex bolt.

Sounds like a plan....but my diagram shows a relief valve in the sump on the earlier AAH's which activates on cold starts to regulate pressure at the filter......

Thank you for confirming that the Pump Relief is accessible by pulling away the alternator.
LB

Any suggestions before I rip this thing completely apart?

Thanks,