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Registered
Join Date: Jun 2005
Location: Central Florida
Posts: 136
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Please Help, Oil pressure drops after warm up - 74 Carrera
Hi all, I just got the 74 Carrera back on the road after a two year layover. The car received a new suspension pan and some new sheetmetal in the nose. The fuel tank was cleaned out, new gas put in. I did the typical start up procedure of purging the fuel system, removed the spark plugs, disconnected the coil. I could not find any fuse and/or relay for the fuel pump so while cranking the engine to build up some oil pressure some gas did spray out. Can anyone tell me where this fuse/ relay is?
The engine started up good and I was able to let it warm up. The oil pressure would read about 60 psi and when you blip the throttle it would jump up close to 100. After doing this for a few minutes I took the car on its first test run and to bed in the new brakes. During the run the oil pressure stayed good, between 40 and 60 psi. I had already turned around and was headed back to the house when I noticed the oil pressure staying around 40, but soon it was more like 20 psi and by the time I'm back near the house it would be between 20 and 0!! The whole time I'm driving nice and easy. After the car cooled down and I started it up to put it away the oil pressure was back at above 40 with the occasional blip up to 60 or slightly above. My question to you folks is, where should I look for a problem? I checked the oil level while the engine was running and it was where it needed to be and the color was clean. Should I look under the sump plate for anything? I'm sure the guage is working properly. Simply stated, the pressure drops dramatically after warm up. What's next? Thanks everyone. Here's a picture before it was finished.  later, Flank
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Flank |
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05-24-2009, 08:46 PM
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Band.
Join Date: Dec 2003
Location: Denver, CO
Posts: 13,313
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When the car is warm, you should expect about 10-15 PSI per 1K of RPM. If the engine is warm, and you accelerate to 4K RPM, seeing between 40-60 PSI of oil pressure is how it's supposed to be. At a stoplight with a warm engine, if the pressure gauge is at 0, don't worry.
In addition, you never really can know where your oil pressure is until you check it without the gauge. Maybe the sender is bad. Don't worry yet.
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1983 SC Coupe 1963 BMW R60/2 1972 Triumph Tiger 1995 Triumph Daytona SuperIII |
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05-24-2009, 08:50 PM
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You didn't say you changed the oil and filter after a 2 year lay over. That's the first thing I'd do.
Your car doesn't have a fuel pump relay. I think they started using them in 1978?
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Rex 1975 911s and 2012 Range Rover Sport HSE 1995 BMW R1100RS, 1948 Harley FL |
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05-25-2009, 05:11 AM
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Join Date: Jan 2006
Location: Santa Barbara, CA
Posts: 2,307
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If the motor follows the about 10lbs per 1000 rev rule above, which it sounds like it does, you have a perfectly functioning motor.
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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05-25-2009, 06:01 AM
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grateful user
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relay
///walter is right, the latest prod. date i have seen so far with a relay is 10/75
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fully disassembled, blasted, customized and restored 75 targa with factory hard top, 993 style turbo ft fenders, steel flares, C2 bumpers and rockers, 82 3.0 sc 9.5/1 engine with PMS flywheel, 964 cams, flowed heads, ssi's short geared 915 w/lsd, polybronze, bilstein,working lambda, modified and highly tuned cis, tensioners, pop valve, backdated exhaust and heater, 2300 lbs. no bolt left untouched. 1970 911E. Nice car but needs a re-do. |
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05-25-2009, 06:21 AM
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Make My Day
Join Date: May 2003
Location: Northern NY
Posts: 1,305
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seems normal, 60 at startup, drops to 20 (and below) after warmup.
My car has a red fuel pump relay.
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74 911S Targa ROW Building Designer/Business Owner |
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05-25-2009, 07:14 AM
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Location: Central Florida
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Hey all, thanks for the responses. I was debating about when to change the oil. I felt it would drain better if it was hot rather than cold from sitting for a couple of years. It was changed soon before it was taken off the road.
I'm concerned about the oil pressure because it is dropping off after the engine warms. The rpm is staying steady at 3 grand but the pressure was down to below 20 psi. Could a simple oil change help this or do I need to take off the sump cover and see if there is a build up of anything? If the 74's did not have a fuel pump relay, where is the fuse for it? I could find it anywhere.  Thanks again for your help, Flank
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Flank |
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05-25-2009, 09:40 AM
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Fuel pump relay.......
Quote:
Tony |
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05-25-2009, 10:17 AM
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Make My Day
Join Date: May 2003
Location: Northern NY
Posts: 1,305
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I have 3 relays at the rear fuse compartment 1-red, 2-black, when the red one is pulled out, the fuel pump will not run. My workshop manual does not list this relay, nor does it show up on the wiring diagram, but the manual is for USA cars, and the relay is present and connected to the fuel pump none the less.
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74 911S Targa ROW Building Designer/Business Owner Last edited by wowzer911; 05-25-2009 at 10:36 AM.. |
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05-25-2009, 10:34 AM
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Air Medal or two
Join Date: Jul 2003
Location: cross roads
Posts: 14,081
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If you install cam oil restricters you will have more O.P @ the gauge..there was a raging debate if it was good or not to do this
I did soon after rebuild and could not be happier with them.
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D troop 3/5 Air Cav,( Bastard CAV) and 162 Assult Helicopter Co- (Vultures) South of Saigon, U Minh Forest, Delta, and all parts in between |
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05-25-2009, 10:43 AM
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1975 Porsche 911s
75 Porsche 911
bike
1970 porsche E
