1970T rough running and oil light...What's going on with this engine??

Tremelune · 07-27-2021, 03:16 PM

I just purchased a 1970 911T with a 2.2, and about an hour into my inaugural drive, the oil light came on. I pulled over and checked the oil (engine running at temp) and it was at about 3/4 dipstick.

Today I started it up and pressure was good. When the engine was cold, I pulled up the handbrake and the light came on. I put the handbrake down and the light went off. As the engine warmed, the light came back on. The druck press continues to register at least 10psi for every 1,000rpm, and at 5k RPM it was just over 60psi. The oil is pretty clean and green, so I assume it's PennGrade 20w50 semi-synthetic.

The engine has a pronounced shake at maybe 2,000-2,800rpm, under load or not. It does not like low revs (I'm not sure if this is related). Above 3,000rpm, it runs well, though not without a few farts and perhaps the occasional backfire (though it's rare when warm)...It's quite farty in general, but it seems happier at higher rpm and seems to pull to redline well. The car has a set of Weber carbs (that looked clean through the stacks) and a cracked plastic airbox with some extra speed holes put in it by a previous owner.

I'm much more familiar with a 3.2, and I'm a bit boggled by this oil light...I'm not sure where to start, and I'd really rather not pull the engine out of this car before I'm through the first tank of gas...Any insight would be appreciated! I got some video of the rough running and gauges:

https://www.youtube.com/watch?v=6K_RAo5kmsQ

https://www.youtube.com/watch?v=okelhShI6uo

timmy2 · timmy2's Garage

I’m thinking wrong gauge. No oil idiot light for 1970.
Likely the brake switch acting up. Unless it is a Sportomatic?

Tremelune · 07-27-2021, 04:17 PM

Interesting. The car is stick. The ideal outcome would be that I'm simply ignorant. My gauge looks like this, and for some reason it's in my head that the top red light is a combination handbrake and low oil pressure warning light (I shall reread the manual):

pkabush · 07-27-2021, 04:39 PM

I’m no expert but it sounds like your carbs are out of adjustment. Assuming you don’t have a AFR gauge installed I’d read your plugs to make sure your not running lean.

911obgyn · 911obgyn's Garage

Dont assume which oil is in it.
Unless you have documentation.
When you are driving and it comes on jiggle the handbrake.

timmy2 · timmy2's Garage

Love the little handbrake symbol on the gauge.
Pull the gauge. Should only be brown/yellow wires to that lamp.
Schematic for your year:
https://www.dropbox.com/s/32266dstkfqnwrx/SL35-Master.pdf?dl=0

Tremelune · 07-27-2021, 06:19 PM

I don't know where I got the idea that the handbrake light was also an oil pressure warning light...I disconnected the Br/Y wire from the switch under the handbrake...and the light's still on...I think I just have a short to ground somewhere. In any event, now that it's just a parking brake light, it's not that big a deal either way...

Time to mess with these carbs and plugs!

timmy2 · timmy2's Garage

Also a US market brake warning switch in the circuit.
Fluid level or pressure? Not sure, I’d have to look it up in a service manual.

Matter · 07-27-2021, 08:02 PM

Its not an oil light. Its park brake warning and brake failure light. Theres a sensor on master cylinder that if one circuit loses pressure it activates light.,

fizeus · fizeus's Garage

you should check distributor timing and then, as already suggested, your carbs.
has the engine recently rebuilt? is it possible that you are running a distibutor with a wrong curve?

peter leinberge · 07-28-2021, 06:28 AM

How 'bout this? : start at the start for reassurance...
Compression test. Valve lash adjustment, carb adjust (air, throttle rod sync, etc.) when warm, and go on from there.

Tremelune · 07-31-2021, 09:35 AM

Well, I cleaned the idle jets and things have improved substantially. It still has that shake from 2,000-2,200rpm, but manners are much improved. When warmed up and revving, it runs very well.

The "oil light" turned out to be the brake master warning switch.

It seems this engine isn't about to explode, so I'm calling this all a success. I think it needs more cleaning/syncing/tuning, but I can kick the can down the road until I do a valve job and timing and dwell and what not.