fuel pump resistor bypass

[metsuki]

Hi everyone,
long story short, my 93 nsx was experiancing some acceleration hesitations, sort of missfires, and not so much power from the day i bought it.
i was blaming my old coils, or even a bad timing belt job....but i try the fuel pump resistor bypass and bingo, everything seems to become fine.
what can i conclude with this?
do i need a new pump? do i need a new resistor? do i need both?
can i drive the car with the bypass for a long time without issues?

thank's a lot guys

[goldnsx]

Most likely, your fuel pump is dying. How long you can drive with the old one? Don't know. But it should last a little bit longer.

OEM is expensive, aftermarket is junk if you are unlucky. With the labor and time involved to change it I'd go the bullet proof way. Don't ask me how I know. Or are you planning going forced induction?

[metsuki]

thank you goldnsx,
the car will remain stock.
so there is no problem driving the car with the bypass?
i drive the car maybe 2-3000 miles a year, if it can buy me some precious time...

[darock]

I drove one complete season now with the bypassed resistor.

The only issue I had was the emission test during the yearly inspection. The engine runs rich at idle. It seems that it has a bit too much fuel pressure.

I have to do a back to back testing next spring with the resistor bypassed and connected.

Other than that, the car runs strong.

Bernhard

[goldnsx]

thank you goldnsx,
the car will remain stock.
so there is no problem driving the car with the bypass?
i drive the car maybe 2-3000 miles a year, if it can buy me some precious time...
The mechanic of the fuel pump inside wears out over time. By bypassing the resistor this process is now accelerated. But at 2-3000 miles a year you might have 10 years to go but don't blame me if it doesn't. :) The next time you will notice a problem is in the high fuel demand range -> high rpms, high load. That's where you want to guarranty a healthy fuel supply for sure.

[metsuki]

just to let everyone know, finally after replacing all my coils, i can tell you that my problems was coming from them and not from a fuel deliverance issue.

[metsuki]

Hi everyone, and happy new years!

i come back to this thread because the problem was not solve in fact...

the hesitations are gone only for few miles after unpluging the clock fuse.
i don't understand what can cause that???
it seems the car run fine as long as the ECU is learning and then the hesitations come back (around 2000rpm mostly, and at very light throttle)

in two years i changed to solve this:

6x spark plugs
6x coil pack
2x O2 sensor
SS exhaust manifold
SS cats delete
SS exaust TAITEC

it is not a big issue, i can live with it, but i feel the car is not as smooth and powerfull it could/shoul be.

[goldnsx]

but i feel the car is not as smooth and powerfull it could/shoul be.
That's the keyword here.

A weak fuel pump can have two symptoms:

1. hesitation below 4k rpm
2. less torque/acceleration below 4k rpm

No. 1 gets detected first while you get used to no. 2 over time. No. 1 can be intermitting in an early state of failure/weakness (mainly when cold outside) while no. 2 is not unless you compare your car to another one and wonder why the other car pulls (much) stronger at low revs then yours.

The reason is the dual stage fuel pump voltage supply with a relay switching from 9V (measured it once but not sure anymore) to 12V at 4k-4.2k. If your fuel pump is weak less fuel will be delivered at 9V. The ECU adjusts for that by reducing the power/torque. At 12V the fuel pump still can be capable of delivering the needed amount of fuel up to 8k rpm WOT but at 9V AND below 4k rpm it fails to do so. When the amount of fuel is too low to be adjusted by the ECU hesitation can be observed. Surprisingly the hesitation occurs mostly at part throttle not at full throttle. Not sure but the reason might be the FPR but anyway. If your wonder why the problem doesn't occur at 8k rpm WOT first the explanation is simple: the fuel pump is choosen to supply more fuel than the car actually ever needs.

It took me three years to get behind the seldom hesitation of my car and that was 10 years ago with around 70k miles on the odo. Back then I got a chance to drive another NSX, mildly modified but I was very surprised why the hell it had SO MUCH MORE TORQUE below 4k rpm. I did dyno pulls on a yearly base back then and none of them ever showed less power, in fact it was VERY powerful. When I bypassed the fuel pump resistor my car had the torque like the one I testdrove and the amount of torque you'd expect from a 3.0 V6. So it was clear by then that the fuel pump was weak. I changed it and the car was as powerful as it should be again.

The fuel pump is prone to fail after 70-80k miles as the plastic gears wear out over time. The harder you drive it the sooner it fails. It's not due to time, it's mainly due to miles. You can continue to drive it with bypassing the resistor for a long time but the weaker it gets the next time it will show symptoms will be at 8k rpm, not a thing you'd like to have. Honda did an intelligent job to design it the way it is even though I believe the fuel pump resistor was there to reduce noise at idle.

The negative side-effect is that it can be read in all forums that people have thrown ££££/$$$$ parts at the car to get wrid of the symptom. Even though these parts (o2, coils, spark plugs) CAN be the scource in most cases the fuel pump is the culprit, esp. if it has done more than 60k miles.

[UnhuZ]

Hi,

well Thomas... mine is at 220.000kms :).... but i already have a aeromotive one to install when i finally fix my NSX;)

Thanks,
Nuno

[metsuki]

In fact I just put back the bypass yesterday and the car still have the same hesitations at light throttle. Just like I was playing with the throttle very softly.
And If I press hard on the throttle at very low Rev, the car nearly stop and then rush.
Do you think the fuel pump is just so shot that even with the bypass it do not feed the engine sufficiently?

[goldnsx]

Did you measure the fuel pressure? What's the pressure at idle? That's the first thing I'd check.

Not sure about the fuel pressure regulator...

[britlude]

i'm having the same issues at the moment, i checked my fuel pressure and that seemed within spec at both pump resistor in line and bypassed, and with the pressure regulator vac line disconnected, and connected....

the hesitation i have isn't regular and repeatable enough to fault find easily, but as mine is JDM it has temp sensors in the cats. these flagged up an over-temp condition on the motorway. this was after a brief period (seconds) of the engine 'missing' while on a constant cruise on a slight incline. this was was experienced with AND without the fuel resistor in line with the pump

with the help of Kaz's knowledge, the JDM overtemp warning light implies raw fuel at the cats, burning in the exhaust, heating the cats. as i checked the fuel pressure, i didn't see any evidence over fuelling, so i'm leaning towards an ignition issue.

to that end i have a couple of used ignitors winging their way to me, so i can eliminate that side of things.

[metsuki]

I started this thread nearly two years ago, and i have Still the samedi issue.
I am searching for a solution since then
Last day I found a fellow primer with a TPS issue sounding like what I endure for so long.
I disconnected my TPS and beside the CEL light coming on, I can tell that the car seems to ride perfectly. I reconnected it and the issue was restored.
Can i drive with the TPS disconnected waiting for the part to arrive?
I only found TPS for 95/05 nsx wich I bought anyway. I found divergent informations about it. Some says that it turn the wrong way, other says that it is ok all honda's TPS are the same, other says you can invert the polarity.
Has anyone have any real good informations about this stuff?
I will clean my throttle body and check the idle at the same time

[britlude]

As a quick (if late) update to my symptoms, I replaced the ignitor and ignition coils, and, touch wood for luck, all has been ok since....