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Afm Questions

zinkrb250

By zinkrb250,
in Engines & Forced Induction

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zinkrb250 Enthusiast

zinkrb250

Posted
Posted

Here is a graph from my last dyno tune...

dynograph2.jpg

My A/F ratio is a little high and i'm getting high knock levels at high rpm...

On a post earlier someone suggested that it was my walbro 255lph fuel pump that was giving out and not flowing enough fuel...

However, I'm still using a sII rb25det afm and making 371hp...

Would this be a problem causing my high knock levels or the fuel pump?

I turned up the fuel pressure to 50psi and my injector duty cycle is set at 87.0% on 550cc injectors.

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Abo Bob Grand Master

Abo Bob

Posted
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Dude I've figured out now that you are in the US somewhere (probaby Georgia) but you should state that since 95% of us are in Australia and use different methods of working out horsepower - we actually prefer kilowatts but anyway...

So to your question; Yes the AFM should be well and truly maxed out. What ECU are you using? That said we have been using these walbro's and they are shit. You are right in the area where flow becomes a real problem.

Here's an easy test for you.

Put car on dyno.

Take off fuel return line and point into a bucket or tin.

Run the car up at full power.

If the return flow reduces to a trickle or even worse stops completely (as it did mine) take the pump out and sell it to someone who has less power than you.

This test is cheaper than replacing your pump just in case and since we don't know what ECU you have or the tuner's methods we can't comment on the afm really.

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted

running 50psi base rail pressure? Do i read that correctly?

Thats astronomically high for 550cc injectors that should pump out (in your terms) over 450rwhp on the stock 38psi base.

I would say the fuel pump is not working, remembering that walbro's are nothing but a waste of money.

Make sure the pump is seeing the correct voltage.

If it is, rip it out and put a bosch/nismo pump in there and be done with it

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zinkrb250 Enthusiast

zinkrb250

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Yesterday I hardwired the fuel pump to the battery... It's now recieving 13. + volts and I'm still getting high knock levels in the high rpms..

I'm using a PFC and my car was tuned at a certified excel tuner facility..

So are we saying that I could be getting high knock levels because my afm is being over flowed? The reading on my pfc is saying my afm is seeing 5115mv or something along those lines...

So it looks like i'm getting a new fuel pump... prolly not the nismo because it's twice as much as a bosch pump... what do you guys recommend? I see a lot of people on here using 040 and the 044...

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r33_racer Grand Master

r33_racer

Posted
Posted

yep sounds good mate....practically everyone runs a bosch these days...they do the trick very nicely.

Yes your airflow meter is out of range for the airflow your seeing. You need to get a z32 or q45 to cope. What rpm is it showing 5v?

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