Low Engine Power before 4k RPM

[jsullyboy]

I am fairly confident that its the fuel pump. I am trying to get the gas as low as possible to make it easier to drop the tank. Is there no low fuel warning light on the 1991 model year?

View attachment 194652

For the future reference of others if you get the gauge to this level the tank is manageable to remove without being a body builder. With a floor jack I was able to get it out and back in on my own. I didn't spill a drop! This project did inspire me to buy a fire extinguisher for the garage though. Just in case. The fire extinguisher did set off alarms with my wife though regarding my garage activities. Another tip. If you are using quick jacks make sure you have them spread as far apart as possible. The tank is very wide. With the rubber block that contacts the jack point in the middle of the quick jack it was too tight.

 

[NSX78__]

yeah, reading your post over and over again, it does click to me it could be the fuel pump because it was better the first drive after the bypass and then it "deteriorate" after more drives. I changed my fuel pump before to walbro 255 but that was 8 years ago. probably faulty by now. Would you guys suggest the walbro 255 or going back to oem?

 

[Wild Turkey]

So glad to hear you're back in business. We all know how frustrating it can be when the diagnosis is unclear. Good call replacing the regulator as well since it's cheap could cause similar symptoms, & of course a new fuel filter. For future reference with similar symptoms, it's hard to say whether it was the fuel pump, the resistor, fuel filter, the regulator, or the wiring? 3 of those options are much easier to deal with than replacing the fuel pump, & might be worth ruling out first.

Even though it was probably the fuel pump, would it be wise in future to attack them in the order of ease of replacement?

1. Replace the fuel filter if not changed recently since it needs to be changed regularly anyway.
2. (5 minutes) Bypass the resistor at the relay behind the driver's seat. If that solves the problem, it's probably the resistor or the wiring to it? Check by bypassing at the resistor instead - if that also solves the problem, it's the resistor; otherwise look at the wiring?
3. Replace the regulator because it's cheap and easy.
4. Replace the fuel pump.

Agree the fuel gauge is rather pessimistic & you have to go well below the red line to trigger the fuel light, & then still have ~6 l, or about 50k.

 

[Old Guy]

(5 minutes) Bypass the resistor at the relay behind the driver's seat. If that solves the problem, it's probably the resistor or the wiring to it? Check by bypassing at the resistor instead - if that also solves the problem, it's the resistor; otherwise look at the wiring?

Maybe yes, maybe no. The resistor by-pass test is useful in that it indicates that it could be the pump or the resistor. If the pump has developed wear issues that result in the pump being unable to develop the pressure specified in the service manual, by-passing a healthy fuel pump resistor will cause the pump motor to run faster which may mask the pump problem. However, if the fuel pump resistor is dodgy it can cause the pump to run slower than design which will result in low fuel pressures and by-passing the resistor will restore pressure. Because the pump is a consumable, on a higher mileage car if the resistor by-pass restores fuel pressure, a coin flip on the cause is heavily weighted to the pump being the problem.

There is no single step definitive diagnosis for a failing pump until the pump goes 100% dead. If you are not set up to do a fuel pressure test the differential diagnosis would follow your suggested four steps. However, I suggest that step 2 should be inspect the resistor and the associated wiring. Unfortunately, Honda has not provided a resistor spec so we cannot test the resistor. However, if you search on Prime there is a thread where some users have posted the pump resistance. If the resistor and associated wiring look OK they are probably OK.

If you are set up to do a fuel pressure test then I would add a step and reorder the steps
1 - test the fuel pressure to confirm that it is out of spec
2 - do the regulator fuel pressure test because it is easy to do once you have the gauge set up
3 - replace the filter
4 - do the resistor by-pass test / inspect the resistor
5 - replace the pump

If you don't want to do the full diagnosis, in the failure rate roulette wheel of fuel pump, fuel pressure regulator, fuel filter and fuel pump resistor, 27 of the slots are probably marked fuel pump. Most people will win if they just jump to fuel pump; but, not always.

 

[NSX78__]

Aight, a little update on my situation, i removed the bypassed and the anchoring/hesitation came a lot faster and obvious. Decided to just order new parts from honda and rule out this issue for the next years to come. Also, i recalled few years back i had this hesitation issue and i replaced the speed sensor, it seem to remove the symptoms but came back years later. Installed a new one a month ago hoping it was the same problem but turn out to be the same.