Fuel Injector Mystery - Premature Maxxing Out

[satanic]

Hi everyone, need some technical advice or explanation on what the go is with my current situation...

I have managed to somehow max out my stock injectors to 99% duty cycle with a power figure of under 200rwkw. Something is definitely not right as this translates to 266hp which is below the figure that the stock injectors on a R34GTT are capable of sustaining.

Is there any possible reason that this could be happening? Has anyone had something similar happen to them and what was the cause/solution?

It's got everyone scratching their heads - hoping that someone will have an answer.

Thanks

Stan

[ferni]

Gotta state the obvious - could be a crap tune/tuner?

[TurboX]

You dont state the pressure your running?

Have you replaced the fuel filter and is the pump voltage OK to sustain the correct pressure that rises with boost pressure?

[Sydneykid]

Hi everyone, need some technical advice or explanation on what the go is with my current situation...

I have managed to somehow max out my stock injectors to 99% duty cycle with a power figure of under 200rwkw. Something is definitely not right as this translates to 266hp which is below the figure that the stock injectors on a R34GTT are capable of sustaining.

Is there any possible reason that this could be happening? Has anyone had something similar happen to them and what was the cause/solution?

It's got everyone scratching their heads - hoping that someone will have an answer.

Thanks

Stan

Hi Stan, first guess is always fuel pressure. Get your tuner to plumb in a pressure sensor (or guage) and run it up on the dyno, that will tell you what is going on.

cheers

[R31Nismoid]

Yep, check the fuel pressure on the dyno.

Then its easy. That will then give us info... Once you get that, we can all help

[satanic]

Sweet guys! I'll have the pressure checked tonight if I can... do I need to run it on a dyno again?

From what you guys are saying, would it be that I'm running to little pressure through the fuel system?

More Information:

My fuel system comprises of a Bosch 040, a Nismo Fuel Reg and brand new fuel filters (1 week old). This week the 040 will be scrapped in place for the stock pump running into a fuel surge tank and then a Bosch 044

[Sydneykid]

Sweet guys! I'll have the pressure checked tonight if I can... do I need to run it on a dyno again?

From what you guys are saying, would it be that I'm running to little pressure through the fuel system?

More Information:

My fuel system comprises of a Bosch 040, a Nismo Fuel Reg and brand new fuel filters (1 week old). This week the 040 will be scrapped in place for the stock pump running into a fuel surge tank and then a Bosch 044

You should have said that in the first post.

Who set up the "Nismo Fuel Reg"?

What base pressure did they use?

Standard pressure should be 36-38 psi (plus or minus boost / vacuum)

They DO NOT come out of the box preset to the standard pressure.

cheers

[satanic]

I don't think anyone has set it up... so should I just set it to say 38PSI if I find out it's a lot less?

[Beer Baron]

whoever installed the fuel reg should have set the base pressure when it was installed. I would take it back to wherever did the reg install and get them to set the base pressure, and then slap them one.

once the pressure is set, and then checked on the dyno to make sure it's not dropping pressure up top (insufficient pump flow) if it's still hitting 100% duty then the most logical answer is tuning. what was the AFR? if you are running an AFR of say 10:1 under load then of course they will be maxing at quite low power. leaning off the AFR will have two outcomes. more power. less duty cycle.

[satanic]

We installed the FPR ourselves and it was set to 39PSI from memory; unless it's been changed since I cannot say much else about it.

Pump flow should be ok as it's coming from a Bosch 040. We ripped it all out for an inspection the other day before the track day and it was doing fine. We even replaced the fuel filters while we were at it.

Tuner says that at no point throughout the tune was the A/F ratio ever above 12:1 - he said it was tuned to pretty much a flat line across the 12:1 ratio.

If we do find that the pressure is very low right now; should I wind it back to say 40PSI? More? Will this affect the tune in any way? or will it adjust by itself...

[R31Nismoid]

Pump flow should be ok as it's coming from a Bosch 040. We ripped it all out for an inspection the other day before the track day and it was doing fine. We even replaced the fuel filters while we were at it.

not if the fuel pump itself is not seeing the correct voltage.

You cant run bigger pumps like that off the stock loom. It requires a re-wire.

Also, why the need for a fuel reg? The stock one is perfectly fine.

Both of these things (even setting base pressure on an FPR) should have been checked by the workshop doing the tuning.

If they have not, and are stumped by something this basic, i wouldnt be taking the car back there as if they cant check a fuel system, i wouldnt trust them to tune.

I'd had to see your motor die, or alternatively you get a half baked tune @ full cost

[satanic]

Hmm that's interesting... any links to how to re-wire the pump? Should I even bother considering the stock pump will be going back in and a Bosch 044 used instead of a 040?

[fatz]

relay and hard wire it to the battery

had a similar problem high rpm and the voltage broke down

relay and direct wiring = lots of volts for happy fuel pump

[satanic]

Is that the direct-wire modification that Cubes did on his 32? If so then that sounds like an easy fix. I'll have the pressures checked tonight, will correct it to stock levels if we find it's not doing so good

I'll look more closely at the re-wiring as well.

Thanks guys, help is greatly appreciated - if anyone has anymore bright ideas/solutions - please post it up!

[Beer Baron]

before you go through any of the solutions check the base pressure. you said before that no-one had set it, but now it may be 39psi, either way check it. then run it up on the dyno and watch the fuel pressure gauge and the duty cycle and make sure that the fuel pressure climbs 1:1 with boost and that when it reaches it's peak pressure that it stays there right to redline (assuming boost control is working properly). if it does then your problem is not fuel flow from the pump but most likely a tuning thing. if the pressure starts dropping off then you may have a pump problem/wiring problem. HTH.

R

[Sydneykid]

For your benefit and others, when I do a dyno (tune or power run) I ALWAYS get a graph of;

1. Horsepower (or kw for the metrically minded)

2. Boost

3. A/F ratios

4. Fuel pressure

5. Torque

6. RPM not mph (or kph for the metrically minded)

Then, in your case for example, I can simply overlay the boost curve and the fuel pressure curve and detect any issues with the fuel flow and/or pressure.

Separate, dedicated (non standard) electrical supplies for Bosch fuel pumps are essential. They are a high torque (for flow and pressure) pump and hence require decent sized wiring.

cheers