SQLGuy

Since I picked up the GTS, I've noticed that its oil pressure rarely exceeds 4 bar. On the S4, it's often pegged. Today, in slow moving traffic, and with the A/C on, the GTS oil pressure fell low enough that it started complaining about insufficient pressure at idle.

Does this sound more like an oil delivery problem or an oil pressure sender problem... or how can I tell?

BTW, I have verified oil level, and it is correct.

Thanks,
Paul

Hilton

First question - are you running a suitable 20W50?

If so, then I'd suspect an actual oil pressure problem - possibly the check valves in the heads are stuck open?

Is this the car with S3 cams in it? Did the installer of the cams remember to block off the uncovered oil journal on the passenger's side? (there's a journal that needs to be blocked with a grub screw or similar where the S3 cams have a different surface to S4 ones).

edit: Changed drivers to passenger Its the rear of the right-side exhaust cam, which is RHD driver's side.

ROG100

Paul,
As Hilton said you need to be running 20W50 - I use Royal Purple in my GTS.
In high ambient temperatures - 100F here in Dallas - the idle oil pressure can be very low at maybe 1 to 1.5 bar.
If your light is coming on that is far more accurate than the gauge so pay attention.
My car rarely goes above 4.5 bar.

Also the oil cooler under the radiator is useless in stop and go traffic.
Jim Mayzurk and I are installing a cooler in the radiator and using Greg Browns hoses to use both coolers.
Hope that helps.
Roger

SQLGuy

I would expect/hope that Dave Lomas and his team over at Motorsport would have known how to properly install the cams. Speaking with them, I got the impression that they had installed a few sets of these Elgin grinds. I will call and double-check, though.

As for oil, the invoice says only Fuchs Synthetic Oil, but no indication of weight.

This was all done about 2 months ago.

ROG100

Mine already has S3 cams in it - what a difference 8>)

Mrmerlin

you might do well to remove the valve covers and check that the oil block off pins that are in the unused cam journals are replaced with the new style pins the S4 and later had the rubber holder pins and these will fall out thus reducing the oil pressure with similar results as you are seeing

Mrmerlin

Read through this link it has pictures of the bad parts.
https://rennlist.com/forums/928-foru...t=oil+pressure

SQLGuy

Hi Stan,

In that thread Erkka mentions the later style being a metal plug. How "late"? I would have thought 92/93 was pretty late....

Cheers,
Paul

Hilton

The rear-most cam journals may not be unused in this engine.

If the S3 cams were not shortened to be the same length as S4 cams they will be using that final bearing surface, and one of the journals will be exposed and need to have been blocked when the cams were installed. Shortening the S3 cams to the same length as S4 cams enables using the aluminium plugs to block the 5 oil holes.

Either way, the best course of action is to pull a cam cover - to check the length of the cams, and status of the plugs.

Other possible causes I can think of would be a broken oil pressure bypass valve above the oil pressure sender (should open at 10bar - I believe if the spring's broken it might be opening too soon?), or the check valves in the heads.

I certainly wouldn't drive the car any more until you've found the cause and fixed it.

hinchcliffe

Where do you buy the replacement pins/plugs? I didn't read through the whole link yet.

ROG100

928 105 262 00 and we sell for $1.25 each - you need five.

hinchcliffe

Those are the new style, not the original rubber ones, right?

SQLGuy

I spoke with one of the guys at the shop, and the oil in question is 5W40. When coldish, and just started, the dash reads about 4 bar.

As to the head modification for S3-based cams, are you guys talking about blocking an oil passage in the bearing socket towards the back of the head as circled here? I took this shot from this thread: https://rennlist.com/forums/928-foru...n-s4-head.html.

The set of Elgin ground S3 cams used in that thread was extended on what they say is the driver's side exhaust (though it looks like US passenger's side from the picture - from the original thread and reattached here), to use the rearmost thrust bearing. Is this what you're talking about? If so, one of the questions is whether this extension was done by Elgin or the installer.... IIUC, with the extension, nothing needs to be blocked?

Edit: Added the third pic, from Stan's thread. This shows the hole that's there if the plug is missing and if the cam is not extended. Hilton, were you suggesting putting a screw into the oil hole shown here instead of, or in addition to, the plug... or were you talking about something else?

Thanks,
Paul

Hilton

I haven't yet fitted my modified S3 cams yet as I'm waylaid by another 928 which needs to go back together before get around to more work on my 89.

Anyway, AFAIK the area circled in the first pic is where the problem hole in the heads is if you're running the S3 cams at their original length, rather than cutting them down to S4 size. There are two journals on that cam bearing surface at the rear of the head (right-side exhaust, using Porsche's convention for left/right on the car). If the S3 cams are using that last bearing surface, one of the two holes needs to be blocked, and it is the one shown in your third pic - e.g. tap and use a grub screw (being *very* careful to remove all tapping debris).

These pics from Erkka shows the problem - see the groove outside the bearing surface on the cam? It exposes the feed journal and pumps oil into the heads, resulting in lost oil pressure.



If the cams are cut to S4 length, you just use the stock part Roger listed above to block all 5 holes on those rear surfaces (1 per cam and 2 for the exhaust identified above). I've fitted the pins to a couple of my S4's and will shortly be doing so on a third, and will likely just cut down my S3 cams prior to installation because it simplifies this issue, and its not like they can be installed in an S3 motor anyway.

You can read all about it in this thread here:

https://rennlist.com/forums/928-foru...ce-gain-2.html

edit: Seems all GTS should have the metal pins to block the journals, from factory. So your problem is either the cams weren't cut and the pins were removed, or a failure elsewhere (oil check valves, pressure relief valve, oil pickup etc.).

edit2: 5W40 isn't ideal, but should still result in better than 4bar cold idle pressure. I'd change to 20W50 with ZDDP (Brad Penn, Royal Purple etc), and take the opportunity to cut open your oill filter to check for metal.

SQLGuy

OK. Just checked again with the shop, and they confirmed that they did cut the cams to stock (GTS) length and did not remove the factory plugs on the end passages. They also feel that, with the oil they're running, the dash complaining about low oil pressure is probably normal, and the car should be fine as long as it's showing 4 bar or higher under full pressure. Cold, this morning, it was showing about 4.5 bar from just off idle to higher RPM's... seemed to peg there. They felt this should be fine, but suggested maybe going to 20W50 at the next oil change for warm seasonal use.