DYNO PROB with DUTY CYCLE

hey folks,


i will be picking the zed up from the dyno tommorow arv.. but they ran into a strange problem and i hope some of the guru's here will have a better idea then i do of the cause and solution..

The zed was going to be tuned to 20psi and should be around the 400+rwhp however she has been tuned somewhat conservatively at the moment to 296RWHP at 14.5psi, which seems about right for that boost level.,
Now the problem is that we couldn't tune to the 20psi we wanted as the injectors are at 80% Duty Cycle which seems strange for nismo's and we dont know the cause.. 80% at 20psi would seem a little more correct.
Screwing more fuel pressure through the reg wasn't working either.,
we cant figure why the injectors are coming so close to maxxing out at only 14.5psi
other then that my tuner pete says everthing is running fine..anyone know what could be wrong..
car has the following parts that may relate this if it helps some of you guys diagnose

-new fuel lines and filter
-turbosmart FPR 800
-Nismo S2 injectors (yellow top 615cc)
-GT600R turbos (GT28R)


cheers
scotty

 

Hows the fuel pump?

 

not sure on the fuel pump condition.. its standard TT and seems to work fine ATM, could possibly getting tired??

 

Bypass the fpcu, see if that helps at all.

 

Thanks Eric..Well i wont be able to try untill i get the car back..

Would that even cause the injectors to be up there on duty cycle at low boost psi??

Doesn't it work by varying voltage and allows the fuel pump to just operate at different rates and send the appropriate amount of fuel to the injectors. It doesn't act to regulate the fuel pressure, but works in conjunction with the fuel pressure regulator to insure proper fuel flow.?

i thought when this unit fails doen't it usually mean the car will not start, because the fuel pump will not operate or will only supply low pressure??

mine is apparently running fine at 14.5psi just the 615's are maxxing out WAAAAAAAYY to early

 

Turn the fuel pressure up.

 

I bet money its the age old pump!

 

in the OP we tried screwing up the fuel pressure but wasn't helping

 

thats weird

I had my 615cc at about 95% with all stock fuel system pushing decent numbers.

injectors real nismos?

 

I'm thinking this could also be the case but want to know for definate if the pump is getting old it would cause the injectors to be running so high on duty cycle?? im gussing yes. if the pump isn't.. well pumping lol enough fuel for whats required at certain boost lvel then the injectors are having to work harder to supply the fuel needed thus running out of headroom early..

the pump "WAS" fine before on the stock 370cc's. i guess not when now having to push harder with 615cc its having a " Arghh GET OFF ME" moment

 

yes they are BRAND new genuine nismos from coz.. or maybe Z1 cant remenber which bundle of parts they came in from..

but agreed all seems strange

 

One way to test it is to get a new pump, push out 400 odd hp and then consider if it was the pump

 

:rofl: true but want to try and diagnose before i have to shell out another squillion cents for a new one :bash:


thanks for all the help so far guys

 

if the pump isn't running properly (pumping its rated volume) how will it cause your injectors to run at a higher duty cycle and max them out? ??

 

I'm getting 430rwhp on stock fuel pump, stock fuel lines and stock regulator @ 19.5psi running 750cc injectors.
So with all your extras, there should no reason to max out your injectors at that boost & power level.

As said before, it's possibly a tired old stock fuel pump, or an issue with the Regulator unit. So, bypass the regulator for starters (it costs nothing) and see how you go, if no luck, then it may be time to put a new OEM fuel pump in. Those two steps would be a good starting point.

 

Hmm i dont know. by the way i posted i imagine but i im not certain thats how it would work??
i.e injetors having to run at a higher duty cycle because the pump cant supply enough fuel for them to suplly enough fuel at a lower duty cycle

 

LOL thanks benny im aware of your beasts levels and was hoping for similar sorts..

reg is brand new so dont thingk that would be the prob

 

If adding fuel pressure doesnt lower duty cycles i would look at the fuel pump, or a blockage in the line.

 

Yes Scotty, i've seen this first hand before on a dyno aswell. Stock everything (including fuel pressure regulator operating normally) and first power run on the dyno see's the duty cycle maxing out during high boost, second run on same boost (but with stock fuel pressure regulator bypassed) runs with less duty cycle due to the higher line pressure, and achieved a higher HP on dyno run obviously.

I think it might have been member r33k many years ago at a Brissie dyno day, but i've killed many brain cells since then so excuse me if i've referred to the wrong member.

 

The injectors could be open at 100%, but it?s not going to be delivering much if there is relatively only a trickle of fuel coming through.