Upgrading pumps to fix hesitation and fuel supply

91svtcoupe

TTop SVT Coupe
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Fuel pump questions/issues

03 Swap into 02 GT (possible fuel pump or pumps failure or going bad)

Mods include:

Stock blower
2.9 pulley
Kooks Longtubes and H pipe
Single blade tb
JLT short CAI

Lund Tune

(75k miles)
Stock tank
stock pumps
Stock FPDM with wire upgrade/relay

1) Was experiencing hesitation at the top end of 3/4 throttle boost pulls and with the Aeroforce scan gauge showing 95% fuel pump duty cycle

2) 2nd or 3rd gear stab of throttle , extreme fall on its face reaction.

remedies......remove stock hat to remove pprv , installed aftermarket hat with stock pumps back in it's place.

same results as mentioned in 1 and 2 above

I have (2) 340lph pumps, I am going to install, feeling that fuel demand/supply is the issue

question??

Lund said with upgraded fuel pumps I would not need a revision tune.

I did not clarify I was going with 340 pumps when I sent my question to him, so does anyone have experience with this and do you see any potitienal problems, by installing 2 larger pumps with no tune revisons?

anything else that maybe be happening to cause the issues in 1 and 2 above?

Trying to get the car so I can enjoy it a little more but with the issues , I've been to afraid to push in on it.
 

MG0h3

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If the fuel pressure is the same which it will be, then just changing the pumps wont require a tune revision. The problem could be as simple as a plugged fuel filter.

The stock pumps can handle your power so I dont think an upgrade will necessarily fix the problem unless the pumps are aged and failing.

If you have a handheld I would datalog fuel pressure or just grab a gauge and put it up against the windshield and do a quick pull.
 

cj428mach

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If you're running a stock cobra hat, I say just add a BAP and be done with it.

These cars do have some adaptive learning that takes place on the returnless fuel system so they can do some adjusting. Especially with the pprv delete done you shouldn't get the massive fuel pressure spikes on shifts.
 

91svtcoupe

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I didn't mention I have a fuel pressure gauge on the car via Aeroforce interceptor. pressure is steady at idle 39-40

but when going into a pull pressure drops, instead of rising, same symptoms as mentioned before still no wot pulls.


installed the 2 340 pumps....today

same situation again....

however I am only running one stock FPDM with a wire upgrade not a modified FPDM.

will installing a second FPDM help?
 

BoostedSVT03

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I had this same issue with my 03 Cobra and TVS. I spent a lot of money chasing this gremlin and some say it's in the tune. I went to a return system and drivability has never been better. I prefer it over stock! Do a search and find my thread with this issue.
D
 

bubblehead93

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the system maintains 39 psid across the injectors, so 39-40 psig at idle seems high... i'm confused by the Lund don't need to modify the tune after upgrading pumps... pprv delete is a mechanical fix to a tune problem... works for some not all... lets assume something was lost in translation talking with Lund, there is tuning to be done here, adaptive learning will fix a lot, but is not a substitute to properly modified fuel tables...

since fuel pressure drops under boost, you have another problem, what is fpdc telling you when this happens, what is happening to injector d/p, should stay at 39 or so... number of PIDs to log under these circumstance to try and diagnose the issue...

been awhile since I played with this in my tune, need to go back through my notes, others with PRP can probably chime in...

r/
Andy
 

bubblehead93

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also, i'm not smart enough, how do you turn off your signature block on this new site... used to be able to turn it off in the options... sorry OP...
 

MG0h3

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Well you didnt need two FPDMs before and it worked. Ive never experienced thermal shutdown so I dont know if its a completely dead unit at that point or just cant carry the load.

CJ had a good point though about the BAP, it would cure that possibility.
 

cj428mach

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the system maintains 39 psid across the injectors, so 39-40 psig at idle seems high... i'm confused by the Lund don't need to modify the tune after upgrading pumps... pprv delete is a mechanical fix to a tune problem... works for some not all... lets assume something was lost in translation talking with Lund, there is tuning to be done here, adaptive learning will fix a lot, but is not a substitute to properly modified fuel tables...

since fuel pressure drops under boost, you have another problem, what is fpdc telling you when this happens, what is happening to injector d/p, should stay at 39 or so... number of PIDs to log under these circumstance to try and diagnose the issue...

been awhile since I played with this in my tune, need to go back through my notes, others with PRP can probably chime in...

r/
Andy


Do you mean voltage tables? or fuel tables? if the fuel tables are off then yes he has an issue but if I remember correctly the ecm can learn to modify the voltage tables in order to help maintain pressure.

His aeroforce could be reading pressure drop across injectors pid which would show 39 psi all the time, or it should.

It definitely sounds like OP has a problem, if it was me I'd throw a return style system on and retune. Actually thats what I did and I couldn't be happier not having to try to tune the returnless fuel system anymore.
 

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