Code 1 and 2. Bad fuel pump?

[roybotnik]

My car had some bogging and hesitation when I first got it, which I attributed to the new headers and high flow cats I had installed and the ECU needing to adapt. I reset it a few times and the problem went away for about 6 months. Now it's back and I'm getting a code 1 and 2 if I run the car at WOT in 4th gear going up a hill (I believe the manual recommends this for diagnosing fuel pump issues).

Tested my fuel pressure and it was only about 33psi idle. Removing the vacuum hose from the FPR did not increase the fuel pressure. Pinching the return line on the FPR didn't seem to make a difference in pressure either.

Guessing this is a bad fuel pump? Is my FPR acting up too?

 

[Larry Bastanza]

If you pinched the return hose the regulator is out of the picture. If you can only get 33psi of fuel pressure, the pump either has an electrical supply issue, or it is going bad. High mileage?

Regards,
LarryB

 

[Lude_2_NSX]

I have the exact same problem. I temporarily bypassed the fuel pump resistor and my fuel psi went from 30 to 40 at idle, and then jumps to almost 50 with the fpr disconnected.

I have diagnosed this as a failing fuel pump and will be ordering the walbro kit from SOS.

Larry, do you agree with this diag?

 

[Larry Bastanza]

I have the exact same problem. I temporarily bypassed the fuel pump resistor and my fuel psi went from 30 to 40 at idle, and then jumps to almost 50 with the fpr disconnected.

I have diagnosed this as a failing fuel pump and will be ordering the walbro kit from SOS.

Larry, do you agree with this diag?

But you do not have the same issue, he cannot get past 30 regardless of what he does, so it is not the same. I think you did the main relay already correct?

 

[roybotnik]

Actually my car only has 52k miles on it but it is a '91 . I haven't tried bypassing the resistor yet to see what happens. I was running the test with an annoying harbor freight gauge, but I'll be getting a B&M gauge in tomorrow to mount to the fuel filter. I'll do the resistor test then and double check the pressures when FPR vacuum hose attached/disconnected.

I hear the pump whirring up when the car is turned on and it's never died on me while driving or stalled out. Idle is smooth after warmup too. Starting takes a while after the car has been sitting though. Fuel filter was supposedly replaced ~5k miles ago by the previous owner.

 

[Lude_2_NSX]

But you do not have the same issue, he cannot get past 30 regardless of what he does, so it is not the same. I think you did the main relay already correct?

I have not done the main relay, but doesnt that just switch power? I dont see how the main relay could cause a low pressure.

I was having a hesitation under load below 4K RPM. Once I shorted across the fuel pump resistor connector, the fuel pressure at idle jumped from 30 PSI to 40 PSI. Before, it was stuck at 30 PSI with the FPR vacumm connected or disconnected (just like roybotnik). Now, after driving it, the hesitation was clearly gone, and I could not get code 2 to show back up again (I was able to kick the code many times before under low-RPM/High-load accelerations). I know this isnt the permanent fix, but I think it is a good troubleshooting tool to determine if your fuel pump is failing.

With regards to his problem, I dont think he has tried shorting across the resistor connector.

 

[Larry Bastanza]

If the relay contacts are burned, this can cause a voltage drop. Honestly I have only seen this on a Civic, not an NSX, but might be worth a try, since you do have voltage that is stepping up. BTW, have you measured the voltage at the pump?

Keep in mind this may very well also be the pump, but when I read that you can get 50psi out of the pump, I question that. Just thought it might be worth swapping the main relay.

Regards,
LarryB

 

[roybotnik]

I shorted the resistor connector and the car ran perfectly. Guess my fuel pump isn't running right on the lower setting. Considering I haven't ever had any problems starting the car or having it cut out on me, I assume the relay is probably good. Maybe if I get some extra time I'll take it out and check the solder just to be sure.

 

[Lude_2_NSX]

Yup, that's what happened to mine. I'm throwing a new fuel pump in this weekend. I'll let you guys know how it goes.

 

[roybotnik]

I just ordered the walbro 255 kit from SOS. How many hours of labor should I expect if I take this to a dealer or local shop? I don't have nearly enough room to do this install at home.

 

[jwmelvin]

The range could be from $300 to $800. As in 3-6 hours.

 

[Lude_2_NSX]

I just ordered the walbro 255 kit from SOS. How many hours of labor should I expect if I take this to a dealer or local shop? I don't have nearly enough room to do this install at home.

Just did the replacement yesterday. Only took about 3 hours by myself. I have done many fuel pumps on other cars, first on this car, so your hours may be different. I also posted a new thread documenting a couple of helpful tips I found during replacement. Good luck and PM me if you have any questions.

 

[roybotnik]

Awesome, I might just try this myself since the nearest nsxprime-certified tech is about 1.5 hours away from me.