Update #3: Replaced fuel pump, fuel filter, fuel tank check valves (just because) and the car is running much better, but the issue is not completely solved. The CEL issue seems to be resolved (still test driving, but so far, so good). My mechanic pulled a fuel sample for me to examine and I was shocked. The 93 Octane fuel looked like green pond scum, and there was residue at the bottom of the clear container. I am going to run the tank almost to empty, then refill with the 93 or 94 Octane fuel and continue to test.
Update #2: Car back in shop, replacing fuel filter to see if that can fix the issue. If not, Square 1 here we come...
Update #1: I am sad to report that replacing the fuel pump resistor did not solve the problem. The car is still indicating O2 sensor codes are the issue, but since we just replaced them, we (the Acura tech and myself) think it may be something else. The car goes back in the shop Monday. Just for grins, we are going to replace the fuel filter (not sure when it was last replaced) and then we will go from there. Current symptoms = engine "flutters" with normal on-throttle application, usually at any rpm below 4k, although on rare occasions it may occur slightly above 4k rpm, but I don't think it has ever happened at 5k or above. On occasion, the engine will still "hunt" for idle, maybe 2x in 5 minutes. Normal idle appears to be 800 rpm, and it may fall to 500 and then quickly go back to 1k, settling in at 800 rpm all in the space of less than 5 seconds. Check engine light may still come on every now and then, resets when ignition turned off.
Sidebar: When I removed the fuel pump resistor and got to the mounting screws on the back side of the resistor heat sink, the phillips head screws had either been secured with nuclear locktite, or they had corroded a bit, or a combination of both. No amount of swearing, WD40, hair dryer heat, and taping the screw heads with a screwdriver and hammer could budge them. I went to my local gas station mechanic and begged help. 30 seconds later, problem solved. The mechanic had a pair of mini-vice grips with tapered jaws. He secured the vice grips to opposite sides of the screw head, parallel to the mounting bracket, and broke both screws loose with twisting torque...easily. Thought that I would mention this so others might be able to try this in similar situations.
Update number two to follow some time next week...
I have searched the forum and found some discussion about CEL issues, but I also have a Loss of Power (LoP) issue too, so I'm hoping the collective owner knowledge at Prime can help me. I have my suspicions about the cause, but I don't want to share that until I get unbiased feedback here first. I'm hoping to share what you suggest with my Acura mechanic to help shorten the trouble-shooting process.
History: I purchased my 91 NSX about 7 years ago, and I am at least the third owner. I'm sure the original owner loved the car, but the person who had it before me...not so much. So, this has been a labor of love to get the car back to perfect condition.
The CEL issue has been occuring even before the following mods were installed: Downforce air induction scoop; Downforce air induction system; DC Sports headers, SoS exhaust. SoS red powder coated intake manifold and valve covers are also installed, but I don't see how they could be creating any of the issues below.
1. On occasion (maybe once every 5 min or so, sometime less), engine will "hunt" for idle rpm. Normal idle appears to be about 800 rpm. Sometimes, this slowly drops to what appears to be 500 rpm, then the engine auto adjusts to 1000 rpm, and falls back to normal 800 rpm.
2. Check engine light still comes on (after my mechanic replaced O2 sensors, adjusted valves, checked coils and plugs), but less often. Turning off the engine and restarting resets the CEL. Typically while driving in 2,500 - 3,500 rpm in 3rd or 4th gear, the CEL will trigger under sustained load or if I gradually accelerate (perhaps on the Interstate to maintain speed going up a slight rise or hill).
3. Engine "flutters" (no backfire or other strange noise that I can hear), typically while driving in 1,000 - 4,000 rpm range and accelerating, any gear, and exhaust note changes (lower). Normally, when rpms reach >3,500 rpm, the issue clears itself and the car takes off as if VTEC had kicked in, only a bit more pronounced.
4. None of the above appears to occur once engine rpm reaches 4,000 or higher. The main "trouble spot" appears to be between 2,000 - 3,000 rpm, but that may just be because the engine spends more time in that rev range. Once above 4,000 rpm, the engine appears to run fine, accelarate fine, etc.
FWIW, I always run 93 Octane or a bit higher if I can find it, but nothing lower than 93 Octane, and no additives.
Anything that you could suggest would be helpful at this point. If I can just solve this issue, the car will be perfect! :smile:
Update #2: Car back in shop, replacing fuel filter to see if that can fix the issue. If not, Square 1 here we come...
Update #1: I am sad to report that replacing the fuel pump resistor did not solve the problem. The car is still indicating O2 sensor codes are the issue, but since we just replaced them, we (the Acura tech and myself) think it may be something else. The car goes back in the shop Monday. Just for grins, we are going to replace the fuel filter (not sure when it was last replaced) and then we will go from there. Current symptoms = engine "flutters" with normal on-throttle application, usually at any rpm below 4k, although on rare occasions it may occur slightly above 4k rpm, but I don't think it has ever happened at 5k or above. On occasion, the engine will still "hunt" for idle, maybe 2x in 5 minutes. Normal idle appears to be 800 rpm, and it may fall to 500 and then quickly go back to 1k, settling in at 800 rpm all in the space of less than 5 seconds. Check engine light may still come on every now and then, resets when ignition turned off.
Sidebar: When I removed the fuel pump resistor and got to the mounting screws on the back side of the resistor heat sink, the phillips head screws had either been secured with nuclear locktite, or they had corroded a bit, or a combination of both. No amount of swearing, WD40, hair dryer heat, and taping the screw heads with a screwdriver and hammer could budge them. I went to my local gas station mechanic and begged help. 30 seconds later, problem solved. The mechanic had a pair of mini-vice grips with tapered jaws. He secured the vice grips to opposite sides of the screw head, parallel to the mounting bracket, and broke both screws loose with twisting torque...easily. Thought that I would mention this so others might be able to try this in similar situations.
Update number two to follow some time next week...
I have searched the forum and found some discussion about CEL issues, but I also have a Loss of Power (LoP) issue too, so I'm hoping the collective owner knowledge at Prime can help me. I have my suspicions about the cause, but I don't want to share that until I get unbiased feedback here first. I'm hoping to share what you suggest with my Acura mechanic to help shorten the trouble-shooting process.
History: I purchased my 91 NSX about 7 years ago, and I am at least the third owner. I'm sure the original owner loved the car, but the person who had it before me...not so much. So, this has been a labor of love to get the car back to perfect condition.
The CEL issue has been occuring even before the following mods were installed: Downforce air induction scoop; Downforce air induction system; DC Sports headers, SoS exhaust. SoS red powder coated intake manifold and valve covers are also installed, but I don't see how they could be creating any of the issues below.
1. On occasion (maybe once every 5 min or so, sometime less), engine will "hunt" for idle rpm. Normal idle appears to be about 800 rpm. Sometimes, this slowly drops to what appears to be 500 rpm, then the engine auto adjusts to 1000 rpm, and falls back to normal 800 rpm.
2. Check engine light still comes on (after my mechanic replaced O2 sensors, adjusted valves, checked coils and plugs), but less often. Turning off the engine and restarting resets the CEL. Typically while driving in 2,500 - 3,500 rpm in 3rd or 4th gear, the CEL will trigger under sustained load or if I gradually accelerate (perhaps on the Interstate to maintain speed going up a slight rise or hill).
3. Engine "flutters" (no backfire or other strange noise that I can hear), typically while driving in 1,000 - 4,000 rpm range and accelerating, any gear, and exhaust note changes (lower). Normally, when rpms reach >3,500 rpm, the issue clears itself and the car takes off as if VTEC had kicked in, only a bit more pronounced.
4. None of the above appears to occur once engine rpm reaches 4,000 or higher. The main "trouble spot" appears to be between 2,000 - 3,000 rpm, but that may just be because the engine spends more time in that rev range. Once above 4,000 rpm, the engine appears to run fine, accelarate fine, etc.
FWIW, I always run 93 Octane or a bit higher if I can find it, but nothing lower than 93 Octane, and no additives.
Anything that you could suggest would be helpful at this point. If I can just solve this issue, the car will be perfect! :smile:
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