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Discussion Starter · #1 ·
I replaced my fuel pump with a new Walbro, so had to adjust my fuel rail pressure. I have an LM2 so can read the AFR in realtime and play it back.

What should the AFR be on boost? The chart below is one pull up a hill, the black line peaks in RPM are
the shift points. The purple line is AFR. When the boost comes on, the AFR drops below 10-1. It was actually worse
but I reduced the Fuel Pressure from 55psi down to 45psi.

Is 10-1 acceptable? Seems awfully rich to me, but at steady state is it right at 14.7-1 so the
computer is working and it's only rich when the boost comes on.

Best Regards, Philip

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It does seem a bit rich but the factory computer is on the safe side of things.
One thing for sure is changing fuel pumps should not require you to adjust the fuel pressure so there’s definitely an issue somewhere. Have you swapped injectors?
 

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Discussion Starter · #3 ·
I put a Walbro fuel pump in the car probably 10 years ago, maybe more, so I just presumed the new Walbro would
generate a bit more pressure.

This car had 20+ injectors in it, but it ran very very rich so I put standard injectors in it.

I've also tested all three versions of the FWD Performance ECU maps. They go from just letting the turbo run
out to 15 PSI, to insanely rich. You would really need some crazy HP to run the Stage-III chip.

At steady state it's right at 14.4 to 14.7 AFR so it runs fine on the highway.

As soon as the boost begins to build, the AFR drops immediately, probably a protection mechanism to
prevent lean engines when the boost comes on. It just seems excessive?

Best Regards, Philip

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It does seem a bit rich but the factory computer is on the safe side of things.
One thing for sure is changing fuel pumps should not require you to adjust the fuel pressure so there’s definitely an issue somewhere. Have you swapped injectors?
 

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Generally the fwd cals do need fuel pressure adjustment to be spot on, also +20 injectors are more suited to a 3 bar setup or an engine with porting work done. I had run the stage 3 cal for an 1989 2.5 car before and also the MP cal, the car seemed to work much better with the MP cal but this was before I had a wide band or a adjustable fuel pressure regulator. I eventually stepped up to the FWD stage 5, 3bar and +40s and I did need to drop the base pressure a bit for the wot a/f to be good.
I found it best to check your wot pulls on a cold night so you don’t take too much fuel away.
 

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Discussion Starter · #6 ·
Yes, that's what I was thinking. I'll dial down the pressure another notch and see if I can get it in the 11s when the boost is on. As I noted, when running steady state down the highway it is spot-on at 14.7.

Best Regards, Philip
 

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All fuel pumps run at maximum pressure/volume all the time, it is the job of the FPR to regulate rail pressure so 53-57 PSI is always maintained at the injector tip under all load conditions.
I have a Walbro 255 in my All Stock VNT and never had an issue with excessive rail pressure or running rich.
(Other than an AFPR that the diaphragm ruptured in about 15 years ago, the AFPR was only 6 month's old, I reinstalled the factory FPR and have had no issues since)

At idle and no load cruise the car is in "Closed Loop Operation" so the O2 Sensor output tells the controller if it is rich/lean so the controller can maintain a 14.7/1 (Stochiometric) A/F Ratio.
During acceleration/WOT the fuel system is operating on a fixed fuel/spark advance program in the controller, the controller has no idea what fuel pressure is or what injectors you may have in the car, it "assumes that both are correct for its programming.
 

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Discussion Starter · #8 ·
NAJ,
Following that logic, the chart/graph of AFR I have makes a lot of sense. With the +20 injectors and the fuel rail at 55PSI the car was crazy rich. I switched to standard injectors and the car is still rich, 10:1 but not like it was with the +20 injectors. I can turn down the fuel pressure one more notch and the AFR should got to about 11:1. I presume 11:1 is about where it should be but I don't have another Turbo-II to test against, my other car is a VNT.
>>>>>>>>>>>>
During acceleration/WOT the fuel system is operating on a fixed fuel/spark advance program in the controller, the controller has no idea what fuel pressure is or what injectors you may have in the car, it "assumes that both are correct for its programming.
>>>>>>>>>>>>
Best Regards, Philip
 

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10/1 AF @ WOT is probably normal for a stock vehicle, rich is safe.
 

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Remember what I said about outside air temp, you will be leaner when the air is cool and dense. Just be aware of that when you make your adjustments, the factory ran them a bit rich for a reason.
 
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