91 NSX Crank No Start, No Fuel Pump Prime

[Senna36]

Hello fellow NSX enthusiasts. I have owned my NSX for almost 9 years now. It's hard to believe that it's been that long and even harder to believe that I have never had to get it towed until recently. I’m somewhat knowledgeable about working on the NSX and I know how to do some basic maintenance, but when it comes to the more complicated problems I could use some help. I’m hoping someone here can steer me in the right direction.

I recently went for a short drive to visit with family and when I was leaving, the car took a very long time to start. The engine just kept cranking, but wouldn't start. It eventually started and ran fine until I foolishly made a stop on the way home. I decided to get gas, thinking that maybe the fuel gauge was off or something fuel related was going on. I tried starting the car again and I immediately noticed the fuel pump wasn't priming. I tried starting it numerous times with long breaks in between to no avail.

After having the car towed home, it sat for over a week before I finally had time to work on it. I should mention that the CEL never came on. I was looking through the service manual and I noticed that it references using a jumper to count the CEL flashes. I turned on the ignition to see if the CEL had come on and of course now the fuel pump primes and the car starts just fine.

Obviously something is failing, but whatever it is, it's working at the moment. Some other symptoms that may or may not be related: the car often has trouble starting when parked on an incline and sometimes it takes longer than usual to start when the engine is already hot. I have been suspecting the fuel pump might be failing for a while, but the fact that it always runs fine after it starts makes me think it might be something else. Any suggestions on what the most likely culprit is or what to test/check would be greatly appreciated.

 

[drew]

Main Relay. Tap moderately hard above the center speaker just below the rear window when starting.

That is presuming the dash lights are bright.

If not bright: then you have an ignition switch issue.

 

[docjohn]

what he said^^^ my car had some glitchy no start/stall issues and after a new ignition mechanism in the dash its like auto Viagra..

 

[Senna36]

Thanks for the suggestions. I don't recall the dash lights looking dim, so I will start with the main relay.

 

[Old Guy]

This is pretty much a reprise of Doc & Drew's comments.

When you turn the ignition switch to the run position, the CEL should come on for 2 or 3 seconds and then go out. That is the self check routine for the CEL. If the CEL does not illuminate then the ECU is not getting powered up and the likely candidates are:
- the main EFI relay
- the ignition switch (the dash lights will likely not come on if its the switch)

If the CEL does come on for the self check; but, the pump does not prime then the likely candidates are:
- the main EFI relay
- the fuel pump

The main EFI relay is a 2 for 1 special with two relays in it - an ECU control relay and a fuel pump control relay and failure of either of those relay circuits can kill the car. If your 1991 is still running with the original main relay that would be the #1 candidate. The relays typically fail by a fracture of the solder joints on the relay circuit board which is why Drew's 'hit it test' can sometimes get them to work again. However, sometimes they stay dead so the rap test does not always work. In most cases, reflowing the solder on the circuit board with a soldering iron is an effective repair.

Unless the CEL light is not illuminating, don't immediately jump to replacing the main EFI relay. Check the fuel pump by testing for voltage by back probing the connector at the fuel pump resistor. If you switch the ignition to run you should measure 12 volts at the fuel pump resistor for 2 seconds - the fuel pump prime pulse. If you don't get that 2 second prime pulse then its likely the main EFI relay. If you do measure 12 volts and the fuel pump does not run then the fuel pump is likely dead.

Depending on the mileage, on a 1991 the main EFI relay, the ignition switch and the fuel pump are all candidates for age and wear replacement. On my 2000 the main relay died in 2021 and I preemptively replaced the ignition switch around the same time. I have a new Denso fuel pump sitting in a box to cover the time when it eventually fails.

 

[Senna36]

Thanks @Old Guy for all the info. My CEL does come on like normal when I turn the ignition to run, so I will do the checks you described to narrow the problem down. I'm really hoping it's the main relay, because I heard replacing the fuel pump is not fun.

 

[drew]

One super important thing: you're not going to find "CEL" in the Manual... it's a MIL- Malfunction Indicator Light

MIL (aka Money Light)

 

[Old Guy]

One super important thing: you're not going to find "CEL" in the Manual... it's a MIL- Malfunction Indicator Light

MIL (aka Money Light)

I admit that I don't recall the three letter abreviation 'CEL' in the Honda manuals. However, in the service manual section covering trouble shooting the fuel injection they refer to "Check Engine Light" and the light does have the little word 'CHECK' on it if you have a US model (my 2000 is a USDM car). Canada being officially bilingual gets the bilingual light which has nothing written on it. Just for fun, the Electrical Trouble Shooting manual does refer to it as the Malfunction Indicator Light and uses the abbreviation MIL - even though the light symbol in the ETS says 'CHECK'. The owner's manual does refer to it as a malfunction indicator light.

So, you may not find CEL; but, you can find Check Engine Light depending on which manual you look at. NSX trivia!

 

[FlopShot]

Carrying a spare Main Relay is part of the NSX starter kit. Original relays are known to fail. Tapping on it (and hopefully getting your car started by doing that) is a short-term solution.

 

[wavy]

This is pretty much a reprise of Doc & Drew's comments.

When you turn the ignition switch to the run position, the CEL should come on for 2 or 3 seconds and then go out. That is the self check routine for the CEL. If the CEL does not illuminate then the ECU is not getting powered up and the likely candidates are:
- the main EFI relay
- the ignition switch (the dash lights will likely not come on if its the switch)

If the CEL does come on for the self check; but, the pump does not prime then the likely candidates are:
- the main EFI relay
- the fuel pump

The main EFI relay is a 2 for 1 special with two relays in it - an ECU control relay and a fuel pump control relay and failure of either of those relay circuits can kill the car. If your 1991 is still running with the original main relay that would be the #1 candidate. The relays typically fail by a fracture of the solder joints on the relay circuit board which is why Drew's 'hit it test' can sometimes get them to work again. However, sometimes they stay dead so the rap test does not always work. In most cases, reflowing the solder on the circuit board with a soldering iron is an effective repair.

Unless the CEL light is not illuminating, don't immediately jump to replacing the main EFI relay. Check the fuel pump by testing for voltage by back probing the connector at the fuel pump resistor. If you switch the ignition to run you should measure 12 volts at the fuel pump resistor for 2 seconds - the fuel pump prime pulse. If you don't get that 2 second prime pulse then its likely the main EFI relay. If you do measure 12 volts and the fuel pump does not run then the fuel pump is likely dead.

Depending on the mileage, on a 1991 the main EFI relay, the ignition switch and the fuel pump are all candidates for age and wear replacement. On my 2000 the main relay died in 2021 and I preemptively replaced the ignition switch around the same time. I have a new Denso fuel pump sitting in a box to cover the time when it eventually fails.

I have a 1993 that's been sitting for a few years, trying to get it running and I am having similar issues.


Am I checking for voltage after the sending unit correct?

Also is there a way to feed power to the pump directly to check if its seized or not?

 

[Old Guy]

Not sure what 'sending unit' refers to.

Yes, you can access the fuel pump + supply wire at the main EFI relay or the fuel pump relay or the fuel pump resistor. Go to NSX Prime Library and follow the links to find a .pdf of the 1991 service manual. The wiring diagrams start on page 23-350 of the SM and wiring diagram #14 shows the fuel pump circuit with the wire colors. Section 13 of the service manual shows where all those parts are located.

 

[crishallam]

Thanks to those who contributed to the great advice on this thread.

My '97 totally failed to start last night... thankfully outside my house, so not a big deal. The symptoms were exactly as described here, and a light re-soldering of the main relay got me going again. RockAuto are sending a new one, and I should be good for the next decade or so.

Definitely a win for the NSX Prime forum!

 

[TiksAng]

Thanks @Old Guy for all the info. My CEL does come on like normal when I turn the ignition to run, so I will do the checks you described to narrow the problem down. I'm really hoping it's the main relay, because I heard replacing the fuel pump is not fun.

Wondering if you ever resolved this issue or if indeed it came back to haunt you. I have been having intermittent periods where it takes a little longer to start up than it used to. Have replaced the main relay already and don't have any issues with the CEL coming on. Have ordered the fuel pump relay and resistor and will replace those when they arrive, and have also put an order in for a new fuel pump so that I can fully remove these all as variables.

 

[Senna36]

Unfortunately the problem did return. I replaced the main relay first and the car started every time and ran great for a couple of months, but then it started doing the exact same thing. I think my fuel pump is finally dead, but I haven't had time to do all the checks yet. Good luck with yours. I hope it's something simple. Where did you order your parts from?

 

[Old Guy]

Wondering if you ever resolved this issue or if indeed it came back to haunt you. I have been having intermittent periods where it takes a little longer to start up than it used to. Have replaced the main relay already and don't have any issues with the CEL coming on. Have ordered the fuel pump relay and resistor and will replace those when they arrive, and have also put an order in for a new fuel pump so that I can fully remove these all as variables.

I have been having intermittent periods where it takes a little longer to start up than it used to.

If the problem is intermittent, that specific problem is pretty common for an ageing NSX. It is typically caused by:
- leaking fuel injectors
- a leaky check valve on the fuel pump
- a leaky fuel pressure regulator

When you shut the engine off, the fuel system is supposed to trap fuel and maintain pressure in the fuel rail which insures fuel availability for a fast start. If any of the above result in pressure loss then there is no / insufficient fuel for a fast start and you have to crank longer and may get what I will refer to as a rough start . If you switch the ignition key to run (do not engage the starter motor) you will hear the fuel pump run for about two seconds which primes the fuel system. Unless your leaks are really bad, allowing the fuel pump to complete the prime cycle before trying to start the engine will usually get you a fast start. It is when you switch from key off directly to cranking the engine that this problem typically occurs.

If this problem occurs intermittently, then the problem is not leaky injectors. A leaky regulator is not too hard to replace. The fuel supply check valve is part of the fuel pump and requires replacement of the pump so most people are not going to go through the hassle of a pump replacement just to fix an intermittent problem if the problem is fixed by allowing the prime cycle to complete. If you are obsessive, you can confirm that there is a pressure loss problem by hooking up a fuel pressure gauge and watching the fuel system pressure after you shut the engine off. I don't recall Honda providing a spec for pressure retention; but, on my 2021 Audi A4 the service manual specifies that the low pressure fuel system should still be above 3 Bar 10 minutes after shut down.

My 2000 suffers from this problem on occassion. I just try to remember to let the fuel pump prime cycle complete before starting the engine.

 

[TiksAng]

If the problem is intermittent, that specific problem is pretty common for an ageing NSX. It is typically caused by:
- leaking fuel injectors
- a leaky check valve on the fuel pump
- a leaky fuel pressure regulator

When you shut the engine off, the fuel system is supposed to trap fuel and maintain pressure in the fuel rail which insures fuel availability for a fast start. If any of the above result in pressure loss then there is no / insufficient fuel for a fast start and you have to crank longer and may get what I will refer to as a rough start . If you switch the ignition key to run (do not engage the starter motor) you will hear the fuel pump run for about two seconds which primes the fuel system. Unless your leaks are really bad, allowing the fuel pump to complete the prime cycle before trying to start the engine will usually get you a fast start. It is when you switch from key off directly to cranking the engine that this problem typically occurs.

If this problem occurs intermittently, then the problem is not leaky injectors. A leaky regulator is not too hard to replace. The fuel supply check valve is part of the fuel pump and requires replacement of the pump so most people are not going to go through the hassle of a pump replacement just to fix an intermittent problem if the problem is fixed by allowing the prime cycle to complete. If you are obsessive, you can confirm that there is a pressure loss problem by hooking up a fuel pressure gauge and watching the fuel system pressure after you shut the engine off. I don't recall Honda providing a spec for pressure retention; but, on my 2021 Audi A4 the service manual specifies that the low pressure fuel system should still be above 3 Bar 10 minutes after shut down.

My 2000 suffers from this problem on occassion. I just try to remember to let the fuel pump prime cycle complete before starting the engine.

Thanks very much old guy, I had read about the fuel pressure retention and have recently been letting the fuel pump prime, but there is still the odd occasion that it didn't crank perfectly the first time even with the prime.

It would start well after maybe the third crank or the alternate remedy at such times appeared to be a quick application of the throttle.

As you say it's a bit intermittent (one out of every 10 starts perhaps) but just enough for me to start digging around and start replacing old parts as preventative maintenance in any case given the NSX is a long term hold.

 

[TiksAng]

Unfortunately the problem did return. I replaced the main relay first and the car started every time and ran great for a couple of months, but then it started doing the exact same thing. I think my fuel pump is finally dead, but I haven't had time to do all the checks yet. Good luck with yours. I hope it's something simple. Where did you order your parts from?

Oh that's a bummer. I ended up ordering my pump and some reconditioned injectors from ATR and the various relays/resistor from yahoo.jp. I decided to buy spare injectors and then get my original ones cleaned as well. I seem to just like collecting NSX parts now.

 

[Senna36]

Oh that's a bummer. I ended up ordering my pump and some reconditioned injectors from ATR and the various relays/resistor from yahoo.jp. I decided to buy spare injectors and then get my original ones cleaned as well. I seem to just like collecting NSX parts now.

Thanks for the info. It's not a bad idea to stockpile parts for these ageing cars.

 

[Old Guy]

Thanks very much old guy, I had read about the fuel pressure retention and have recently been letting the fuel pump prime, but there is still the odd occasion that it didn't crank perfectly the first time even with the prime.

It would start well after maybe the third crank or the alternate remedy at such times appeared to be a quick application of the throttle.

As you say it's a bit intermittent (one out of every 10 starts perhaps) but just enough for me to start digging around and start replacing old parts as preventative maintenance in any case given the NSX is a long term hold.

Since you seem to have ruled out the common pressure loss problem, a few more details would help.

Is this a drive by wire car or cable throttle and is this a hot start or cold start problem or does the problem occur regardless of the engine temperature?

If this is a cold start problem and you have checked and ruled out a constant low fuel system pressure problem, possible causes might be:
- dirty injectors which are not delivering enough fuel during cranking (your replacement injectors should rule out that as a possible cause)
- during cranking, the ECU typically calculates fuel injector pulses on the basis of an engine coolant temperature look up table. If the coolant temperature sensor for the ECU, which is different from the gauge temperature sensor unless your car is 2002+, has gone out of spec then the cranking pulse widths may be incorrect making for a harder start. The service manual has the specification for the sensor resistance. You can check the resistance to rule it out as a problem.
- you mentioned that applying throttle sometimes helps. On a cable throttle car there is a thermostatic warm up air valve that allows more air flow when the engine is cold. If applying a little throttle helps, the warm up valve might not be opening sufficiently. On a drive by wire throttle the ECU opens the throttle for fast idle and the amount that it opens is controlled by the ECU which is based upon engine coolant temperature (so check that sensor resistance). If the cold temperature fast idle is within spec then the warm up valve / DBW cold idle spec is probably not the problem.

All of the above can also cause hot start problems. The big wrinkle is that all of the above problems would normally cause starting problems most or all of the time. Not intermittently. Your problem still sounds like a cranking fuel pressure problem. Have you done a resting fuel pressure test where you prime the fuel system and then watch to see how quickly the pressure drops? It is possible that you have a completely stuck open or super leaky check valve or a very leaky fuel pressure regulator and even when you allow the fuel pump to prime before attempting to start the fuel system is not achieving operating pressure. If you prime the fuel system and it comes up to pressure and stays at pressure then it is likely some other mystery problem.

All this assume that the engine is in good condition (no underlying issues) and that the spark plugs are in good condition.

 

[TiksAng]

Old Guy thanks very much for the thorough analysis, mine is a 91 so cable.

I have not yet had a start issue first drive of the day (proper cold start) and each of the few times that the car took longer to crank was what I guess I would term a warm(ish) start up, after say an hour or two of rest.

I will definitely be checking resting fuel pressure as you suggested after letting the pump prime for a bit as a first port of call. The unfortunate (or is that fortunate) thing is that the car behaves more often than not at the moment and suspect I will end up not seeing too much until the problem becomes more regular.