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Discussion Starter · #1 ·
I have a 1993 Allante and, within the last few days, the engine started revving very low when I am stopped or idling. Several times, it felt like it was going to stall but it recovered. Previous to this, I had also been noticing that the oil pressure indicator drops significantly when I'm stopped. I've only had the car for 6 months and maybe it always did this, but I never noticed it before. Finally today, when I was parked, it did stall and the oil pressure warning light came on (no chime like it says in the owner's manual - it just came on when the engine stalled). It started right back up and I drove it home with no oil pressure warning light, but now I'm nervous. The oil was recently changed and is full, so it's not a low oil issue. There are no visible oil leaks. I saw a generic YouTube video about an "oil sending unit" that may need to be replaced. Should I continue driving the car? Any suggestions or advice?
 

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I have a 1993 Allante and, within the last few days, the engine started revving very low when I am stopped or idling. Several times, it felt like it was going to stall but it recovered. Previous to this, I had also been noticing that the oil pressure indicator drops significantly when I'm stopped. I've only had the car for 6 months and maybe it always did this, but I never noticed it before. Finally today, when I was parked, it did stall and the oil pressure warning light came on (no chime like it says in the owner's manual - it just came on when the engine stalled). It started right back up and I drove it home with no oil pressure warning light, but now I'm nervous. The oil was recently changed and is full, so it's not a low oil issue. There are no visible oil leaks. I saw a generic YouTube video about an "oil sending unit" that may need to be replaced. Should I continue driving the car? Any suggestions or advice?
First and foremost- what are the codes?

Codes are the first step in the diagnostic process, and we can’t go any further unless you find and post them.
 

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Discussion Starter · #3 ·
First and foremost- what are the codes?

Codes are the first step in the diagnostic process, and we can’t go any further unless you find and post them.
Thanks for getting back to me so quickly. Can I buy a diagnostic machine to read the codes myself? I do not have this, so I have no idea what the codes are.
 

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Discussion Starter · #4 ·
Thanks for getting back to me so quickly. Can I buy a diagnostic machine to read the codes myself? I do not have this, so I have no idea what the codes are.
Okay, so I've done a little bit of research on OBD2 readers, but they all say "for 1996 and newer vehicles". What reader should I get for a 93 Allante?
 

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First a scanner is built into the Allante. Turn ignition On (does not need to be running) and press the OFF and WARM buttons at the same time. Hold until display blinks. Error codes will display in the DIC. Second for ALDL cars I like an OTC 2000 with the '93 or later Pathfinder cartridge and GM cable. They show up on eBay often. Third if really want to get into it see the ALDL products on MOATES.NET
 

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Discussion Starter · #6 ·
First a scanner is built into the Allante. Turn ignition On (does not need to be running) and press the OFF and WARM buttons at the same time. Hold until display blinks. Error codes will display in the DIC. Second for ALDL cars I like an OTC 2000 with the '93 or later Pathfinder cartridge and GM cable. They show up on eBay often. Third if really want to get into it see the ALDL products on MOATES.NET
Thanks so much. I'll try this tomorrow morning.
 

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Discussion Starter · #7 ·
First and foremost- what are the codes?

Codes are the first step in the diagnostic process, and we can’t go any further unless you find and post them.
Okay, thanks to Padgett, I was able to run the diagnostics and get the codes. Here's what shows:

Code P025 History
Code P041 History
Code R034 History
Code R061 History
Code S044 History
Code S060 History
No Lighting Codes
No BCM Codes
No TCS Code

Any help figuring out what this all means would be greatly appreciated.
 

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Check the sending unit for the oil pressure gauge. If you're getting a pressure drop and no warning light it may be a faulty gauge.
 

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Discussion Starter · #10 ·
Check the sending unit for the oil pressure gauge. If you're getting a pressure drop and no warning light it may be a faulty gauge.
Thanks for the advice. So, the pressure drop on the gauge when idling has been happening for a month or so. Yesterday is the 1st time that the oil pressure light came on. Do you think the 2 are related? This morning, when I put the key in the ignition at the accessory position, all the dash lights come on as expected, but the oil pressure light stays on after the other ones go out. It does go out when I start the car. Any additional thoughts?
 

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2002 F55 STS, 2014 Explorer XLT, F-150s
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0 engine rpm = no oil pressure
Idle rpm (650 - 800), hot engine = normal low oil pressure (no warnings)
Highway cruise rpm (1750 - 2300), hot engine = highest normal oil pressure.

GM likes about 12 - 25 psi hot idle, 40 - 50 psi hot cruise. The oil pump has internal bypasses and pressure regulators to prevent excess oil delivery and excess pressures. The oil pressure sending switch is set for some lower-than-normal pressure, maybe 5 or 6 psi, so an extremely low rpm hot idle may trip the warning light. An engine stall WILL trip the warning, every time. Oil pressure is internal settings and mechanical condition; flow is lubrication and cooling.

Owner's manual . . . . .
 

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Okay, thanks to Padgett, I was able to run the diagnostics and get the codes. Here's what shows:

Code P025 History
Code P041 History
Code R034 History
Code R061 History
Code S044 History
Code S060 History
No Lighting Codes
No BCM Codes
No TCS Code

Any help figuring out what this all means would be greatly appreciated.
Yes, now that have recorded them, clear all codes then drive a bit and see if any come back but none are current.

GM oil pressure sender has two separate elements: oil pressure switch (usually trips at 6-8 psi) and gauge. The switch is usually interconnected with the fuel pump so will not run long if too low.
 

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Discussion Starter · #15 ·
Yes, now that have recorded them, clear all codes then drive a bit and see if any come back but none are current.

GM oil pressure sender has two separate elements: oil pressure switch (usually trips at 6-8 psi) and gauge. The switch is usually interconnected with the fuel pump so will not run long if too low.
So, I cleared all codes and the only ones that comes back up after driving quite a bit is the S060 code, related to the Ride Control system. However, I'm still having the stalling issue at idle and erratic oil pressure gauge. Now I'm not even sure if there is any issue with the oil pressure or if the stalling is something totally unrelated??
 

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Discussion Starter · #17 ·
When oil light comes on the fuel pump is supposed to turn off.
Is this a safety feature to prevent the engine from running if oil pressure is low? If so, am I back to replacing the oil pressure sending switch?
 

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It's a safety feature - some vehicles have the shutdown circuit, some don't. Brand/model/year/engine specific.
 
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