91 NSX Fuel Pump Test

[GearHead55]

Hello,

I have a 91 NSX with 80,000 miles and I have the crank, no start problem. The ignition switch has been replaced a couple weeks ago as I had the start and die problem that is common and I have a main relay coming. I have a fuel pressure gauge and it is not showing any fuel pressure and I don't hear the fuel pump priming, although I don't really recall ever hearing it. I disconnected and tested at the resistor and I do get voltage at the BLK/YLW for 2 seconds, but it is less than 1V. I assume I should see 12v+. The fuel pump relay does activate and release after the 2 seconds. I want to apply 12V directly to the pump to rule it out, but not sure which connector. Would it be at the resistor connector or the fuel pump relay behind the seat. I do have the service manual, but it wasn't quite clear to me.

I do not have any CEL codes (although I haven't jumped the ECU to test) and have never seen the light come on, other than when you first turn the key per usual.

Any help is appreciated.

Chad.

 

[GearHead]

I should also note that I was driving it Saturday and everything was fine. Put it in the garage and went to take it out sunday and no fuel pressure.

(and I found my original user account.)

Chad.

 

[chudson1549]

To confirm you're getting fuel, you can remove the service port on top of the fuel filter. Have a towel to cover the fuel coming out of there. It will be under pressure. Maybe clogged filter

 

[Larry Bastanza]

Sure sounds like a main relay. Move the passenger seat forward, and just about where the passenger headrest is, give the back panel a good smack with your fist. I have had many NSX's with bad main relays start after a good smacking.

HTH,
LarryB

 

[GearHead]

Sure sounds like a main relay. Move the passenger seat forward, and just about where the passenger headrest is, give the back panel a good smack with your fist. I have had many NSX's with bad main relays start after a good smacking.

HTH,
LarryB

Larry,

I did give it a couple taps, but not a good smack. I've fixed a few electronic devices with a good whack as well. I will get a bit more aggressive with it and see what happens. I have it out at the moment and was going to look at the solder while I wait on the new one. I didn't figure the fuel pump would just die overnight sitting in my garage, it should have started to degrade first I would assume.

Thanks.
Chad.

- - - Updated - - -

Update, it is in fact the main relay. I plugged it in without the cover and twisted it around and good to go. I will redo the soldering and have a spare new one in a few days.

Thanks.

Chad

 

[ftuhy]

Glad you found your problem!

When you redo the solder, if you can, remove the old solder and flow in some flux with new solder to remove any small amounts of oxidation within the cracked areas for a more reliable repair.

This failure is so common, I simply have re-flowing the solder every 6 years or so as routine maintenance for my NSX. The cracks come about because engine & road vibration cause the relay (a relatively heavy item compared to resistors and capacitors) to vibrate, which causes the solder joints to crack. Fastening the relay to the board with a mechanical strap or even hot glue can reduce the stress on the solder joints. This problem occurs not only in automobiles, but in many outside mounted electronics that are close to roadways - including telecommunications equipment and traffic control signals.