issue with fuel flow - too much

[PaulC-turbo5.0]

got a fox body with stock lines, rails, and pump hanger and ever since upgrading to a larger pump I have had issues with too much flow. I originally had a 340lph and bumped it down to a 255lph which helped lower the pressure at idle but I still have issues with fuel trim swings due to overheating the fuel I believe. upsizing the return line would likely be the best solution but at this point I think I would have to change just about everything to avoid having the 1/4" restriction somewhere. I am looking for options on the simplest and least expensive way to remedy this issue.

would increasing my base fuel pressure help? this would still require some work since I dont have room currently for the kirban adjustable regulator on the stock rails

could I somehow lower voltage to the pump? lowering just at idle and low load cruise would be ideal but lowering it overall could be possible too since I likely have enough headroom. piggybacking this idea could a pmw controller for the pump be a good option?

would a 190lph pump flow enough up top for my needs?

any and all suggestions are welcome

[decipha]

cheapest option would be to get a fuel pump resistor for a harley/lightning truck and put that on the fuel pump ground wire.

Then modify a wot switch to use as a closed throttle switch and and when you come off closed throttle or any given amount of throttle you want wire up a relay that gives the pump full ground.

/done

[PaulC-turbo5.0]

thats an interesting solution I'll have to research this a bit. first concern that comes to mind though is if the switch or relay decided to fail and I mash the pedal would it possibly be super lean from the pump voltage being reduced?

[red5.0fogger]

Alt idea. you could find what's the lowest the fuel pressure will go at idle. then retune using that psi for the whole tune.
(I think it would just be the injector slopes.)
I have a 255 lph. Mine was tuned for 55psi vac line off at idle. no issues.

[PaulC-turbo5.0]

it'd be nice if it was that easy but I dont think it is. My fp gauge is showing 36 psi with vac connected and 44 disconnected with I think is within fords spec. I think the fuel is either circulating way more then needed or I am getting captivation from the return line restricting flow which makes the fuel pickup heat. I see a 2 psi drop on my gauge after the car has been running for a bit. It makes for larger swings in my fuel error then I'd like and also have some minor startup stuff that cant be dialed in perfect because of the fuel temp changing so much

[decipha]

yeah it would lean out if the relay failed to answer your question above

cavitation is a damage mechanism that happens inside of a rotating component when air bubbles form and pop, has nothing to do with the return line

your fuel pressure sounds perfect. couple psi isn't going to affect fueling.

startup is simple just kick up the fuel pump prime time and the hot fuel will be pushed back to the tank and it won't be vapor locked on hot starts if thats your concern

otherwise nothing your saying is going to affect dialing her in properly or cause her to run poorly or give you any issues

[PaulC-turbo5.0]

Cavitation was something I read in searching about this and listed the symptoms I see.

The issues are very minor and most would prob my not care but I feel like it could be better and that bugs me.

I have fuel pump prime time at 3 secs, is that long enough? I’ve posted here about this before and you mentioned my fuel pump being too big. If I get her up to temp shut it down and restart all will be well. If I drive for an hour and shut down for a few mins and restart it will be lean and the startup is not smooth. Not terrible just not smooth.

The biggest thing that I see is my fuel trims changing 15-20%. When she first kicks into closed loop it will be removing 10% which can give me lean stumbling on the first few shifts. As it gets up to temp trims get closer and closer to perfect. Then the longer it runs it’ll get leaner and start adding 5-10%. My kams never end up in that perfect spot I’ve been striving for. I have dialed in maf curve to the point of insanity lol.

[decipha]

have u given her more hot startup enrichment?

sounds like its going in to closed loop before the hegos are fully warmed up

[PaulC-turbo5.0]

yes. it will continue to change though by how long the car has been ran.

whether it goes in at 1 min or 5 mins the error will still be off by the same amount. just now idling in my driveway before i left it was pulling 8-10% and up to about 300 ad counts was the same, after my 15 min ride in it was pulling 3-4%. it only seems to be in the idle and cruise ranges 350 ad counts and above seem to be more consistent.

[decipha]

thats perfectly fine no problem