I've got an odd problem, which I believe is either A) FPR being overrun or B) something that I don't understand

My fuel trims last week were 'stuck' at something like 81.2%, all three, low - mid and high.

I reset the ECU last night for shits and giggles and driving to work, Low is back to 81.2, Mid is around 90, and high is about 99. They are gradually going down, and I would assume they will be back to 81.2 rather soon...

Is this just the ECU reaching a limit on how much it can lean it out?

I currently have a Supra pump, hotwired, I don't plan on running outrageos amounts of boost, should I downgrade the pump to a stock VR4 one?

Thanks,

Nick

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1991 Stealth RT/TT

Remind us -- what fuel controller are you using and what injectors, and how are you coming by these numbers?

Best,

SJ

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Sorry about that, should have been in my original post.

Current im running stock 360s, SAFC zero'd out. All numbers are reported by MMCd.

Thanks,

Nick

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1991 Stealth RT/TT

best way to tell would to be hooking a fuel gauge onto the fuel rail, and see what type of presure your getting...

I suppose another way to test it would be to put the stock resistor/relay combo back in the loop. this will make the supra pump give the line less fuel at cruise and low boost conditions, switching over to your hotwire line when you get on the throttle.

stock cars have run this set up for a long time, and it works fine. The only reason I have ever heard for the change to straight hot wiring I have heard is people believed that the relays were taking to long to switch over, and there cars would dip lean when switching over to the hotwire, which was more pronounced the bigger injectors you went to, as the ECU kept pushing the "change over" point further and further into higher boost.

I would say because you run stock injectors you should be fine.

I will also say (but prolly shouldn't) that if someone thinks a millisecond of switch over in the relay is the cause of lean spot on a fuel map... well, I'm gonna stop there...

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Bad decisions make good stories.
Look at it! LOOK AT MY @SS AND TELL ME IT'S PRETTY!

Fuel pressure at the rail is 40psi at idle with the vac. line attached to the FPR.

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1991 Stealth RT/TT

I'm trying to return stuff to stock to figure out the root of my problems... I have a small question.

On the fuel pump, what the heck holds the o-ring on around the neck of the pump? I have this little top hat looking piece, and the o-ring itself, however I don't have a clue to how it fits into the whole assembly.

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1991 Stealth RT/TT

Does this make sense...


Car running, FP gauge at the rail reads 41-43 psi, remove the vaccum line and it still reads 41-43psi, shouldn't it jump up w/o the line connected?

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1991 Stealth RT/TT

Remind me again, are you using the NA FPR? Where exactly are you hooking the FPR vac line to?

NA FPR is 47 to 50psi with the vac line disconnected. Connected it should be around 40psi.

The way you look for FPR over run is to mount a fuel pressure gauge in a place where it's easily visable inside the cabin and go for a drive. While cruising, if the fuel pressure jumps around spiratically, then you have FPR over run.

Truthfully, it's overrated. Just like fuel trims. If you get a 1:1 FP to boost ratio, you're good. Cruising FPR overrun can be tuned out.

Fuel trims are just a guide. They show you what the ECU is doing to correct the a/f ratio. I don't even really look at them any more because you can never get them to behave the way you think they should. Especially if you're tuning for power/gas mileage. The stock ECU settings aren't exactly optimised for either.

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06 Blue EVO 9