The conditions were better last night than when I was trapping near 111 mph a few months ago. The only difference between the two times is a new Walbro 255 fuel pump and a PCMforless tune.

Before I replaced the fuel pump, I was seeing 30 psi @ idle and 25-28 psi at WOT above 4500 RPM. With the new pump, the fuel pressure is right where it should be...42-45 @ idle and around 40-43 psi at WOT.

I think the tune may have a little too much timing in it up top and may be running a little lean.

Can some of you guys take a look at this file and tell me what you think?

The best ET last night was 12.7 @ 109.8. The track prep was non-existent and I couldn't get the car to hook up at all, but I would think with the tune and better conditions the car would go 112ish. I appreciate any input.

http://www.public.asu.edu/~dbump/danielcc305.bin

Thanks.

 

The tune may be a little lean (and I would also try removing a degree from WOT 2800-5000 timing) and you may be getting some knock retard, but I'd email Bryan directly and ask him for an opinion, rather than post the file on the board.

Another thought would be that if you do not have an adjustable fuel pressure regulator, the pump may be pumping fuel at a higher pressure (seen that before) which would make the injectors flow more than the PCM knows about. Check your fuel pressure and see where it's at.

 

Thanks for replying. I had him tune the pcm mainly for the obd1 conversion and to have a baseline tune. I have Tunercat and a laptop...I'm just waiting on a cable. I plan on doing the rest of the tuning myself so I just wanted some input from some of the more knowledgeable tuners on the board.

As far as fuel pressure goes:

Before I replaced the fuel pump, I was seeing 30 psi @ idle and 25-28 psi at WOT above 4500 RPM (car was scary lean on the dyno). With the new pump, the fuel pressure is right where it should be...42-45 @ idle and around 40-43 psi at WOT.

 

OK... fuel pressure sounds right then. Hook up your laptop and check for knock retard. That's most likely what's slowing you down.

 

Das what I figured. Thanks.

 

Ion, I think you're a little backwards . With the stock regulator, the FP should be ~43.5 regardless of what pressure the pump is supplying - unless its lower than 43.5 ofcourse .

Ryan

 

No clue. I've seen myself 50 PSI on a car with a stock regulator and a Walbro 255 Hi Pressure unit. Maybe the regulator was bad...

 

What do you do about the knock retard?

 

If real and programming induced, correct the air to fuel ratio and/or timing.

 

My car goes anywhwere from 40 to 50psi with the Walbro, but its generally understood that that is normal. That is the whole point of a regulator. Now...if its pretty far off, your regulator is bunk :-).

Ryan

 

50 PSI is a 15% increase over the stock 43.5... AFAIK, the normal range for a PCM to compensate is ~10% and that at part throttle. At WOT, you will definetely see the difference in pressure.
But this is already O/T.... so feel free to PM me if you want to argue more.

 

Exactly what I'm seeing right now. 52 psi, stock regulator, walbro gss340 high pressure pump.