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I have a 94 Corvette 6 speed LT1 coupe that has a custom remote mounted Precision Turbo 7675 in by the rear diferential. I was having oil scavenge problems when I switched turbos to the Precision Turbo so under the advice of Precision I added a small remote oil tank to catch the oil off the turbo and the scavenge pump returns from that tank back to the engine. I took it out with this new setup and it seemed like it was running good my oil scavenge problems seemed to be fine then I noticed a dramatic drop in oil pressure. It seemed like if I put the motor under load the pressure would go further down, but it would idle almost at a normal oil pressure. What should I do to diagnose this to figure out what is causing the falling oil pressure. Right before I got to my house the pressure dropped to 0 and the check gauges light came off and that is when I shut the car off and coasted it home. It turned back on so I could back it in my driveway and ran fine other than having low oil pressure.
There is oil in the car and its on the high mark on the dipstick. The scavenge pump is new but I am wondering if it isn't scavenging all the oil fast enough and the additional 1/2 Liter remote oil tank is taking enough oil out of the motor putting the engine in a low pressure situation.
Does anyone have any theories or ideas on where I should start looking
Last edited by Impala Balko; 03-04-2021 at 01:43 PM.
Don't take this the wrong way, but you are driving a turbo small block c4 and do not understand the basic stuff to check? That's kind of scary. Have a buddy that's into cars help you out. The sbc oiling system is very simple, robust, and there isn't much external to go wrong with it. Throw a trusted gauge on it and see what's going on. It could just be a bad sensor. If it actually lost oil pressure you'd have likely heard a lot of noise, experienced excessive heat. Etc etc. Obviously check all the turbo oil lines and the return pump for proper operation
Don't take this the wrong way, but you are driving a turbo small block c4 and do not understand the basic stuff to check? That's kind of scary. Have a buddy that's into cars help you out. The sbc oiling system is very simple, robust, and there isn't much external to go wrong with it. Throw a trusted gauge on it and see what's going on. It could just be a bad sensor. If it actually lost oil pressure you'd have likely heard a lot of noise, experienced excessive heat. Etc etc. Obviously check all the turbo oil lines and the return pump for proper operation
I dont take offense, but not everyone that owns these cars and mods them are mechanics. I know how to change parts and have a basic understanding on how things work but I am not a mechanic as to where I know the proper diagnosis techniques. I am still learning, this is why I am seeking advice on what I should do. I understand it could be a oil pressure sensor and this will be the first place I plan on looking
speaking from experience, pull the intake manifold and inspect the oil pump drive stub shaft; either a stripped gear on the stub shaft (my experience) or a cracked stub shaft housing. Google it; it's frightening.
I replaced the oil pressure switch and the oil pressure sensor last night and the pressure still reads low, and sometimes bounces around. Now I have a new problem, when I shut the car off and have the keys out the fuel pump still continues to run. Could the pump be related to replacing these sensors?
Attached is a quick video of the car idling in the driveway
I replaced both the oil pressure switch and the oil pressure sensor, I had a defective switch causing the fuel pump to run constantly even with the power off so I swapped that out with the stock one that appears to be in perfect working order. HOWEVER I still have the low oil pressure..... but now it will increase with rpm to a normal level. I noticed after running it down the road that oil was coming out of the breather for the turbo oil catch pan and quite a bit of oil. I think my scavenge pump just isn't up to the task of getting rid of this oil out of the turbo causing it to back up and leak out of the breather and turbo. This leak may be causing the pressure drop.
Well it's confirmed.... it just started making noises that sounds like a bearing is gone, and I found metal in the oil... does anybody have any recommendations for engine builders around the Central Massachusetts area that knows these engines.
I noticed after running it down the road that oil was coming out of the breather for the turbo oil catch pan and quite a bit of oil. I think my scavenge pump just isn't up to the task of getting rid of this oil out of the turbo causing it to back up and leak out of the breather and turbo.
Oil drain from the turbo will be a foamy oily mess. The scavenge pump should have much higher capacity than oil flow to the turbo because it should eat all foam and still have extra capacity to draw some air in thru the breather.
The TurboWerx pump I had supposedly could pump 1.75 GPM and I ordered a new pump that is advertised at 3 GPM. I think the new pump should be adequate. Now I just need to find an engine builder.
Last edited by Impala Balko; 03-13-2021 at 11:14 AM.
03-04-2021, 01:39 PM
Loss of oil pressure
