Fuel Delay at WOT

I've been trying to solve a WOT fuel delay for several months now. The car will hesitate when going on/off throttle on heavy loads (shifting quickly or in and out of throttle).

To give some background, I went ahead and deleted the PPRV. While in there, noticed one of the fuel pumps was cracked and leaking (glad this was caught), so replaced both pumps with Deutchworks 340 LPH pumps. Unfortunately, this didn't resolve the issue.

The car had an unknown tune from the previous owner, so went ahead and got a dyno tune partially to try to resolve the lingering WOT hesitation, and also for peace of mind. The tuner was able to see a drop in fuel pressure after a few pulls on the street, but wasn't able to resolve the issue in the tune. Ended up putting down 403hp/432tq on a 4wd mustang dyno.

Ultimately, he recommended two options:

1) Hard wire the pumps (I'd rather not do this).
2) Go to a return style fuel system.

I think a return style system is overkill given I'm just running a 2.81" upper pulley on the stock eaton along with a bigger heat exchanger, tb, plenum, catted x, and a cat back. Eventually I'd consider going to a Whipple or VMP, but I'd rather not modify the car anymore given it has 18k miles and is in mint condition.

I've read plenty of posts about the PPRV delete or a tune resolving this issue, but I can't seem to get rid of it. Any suggestions are greatly appreciated.

Double check the hoses in the tank. Make sure they're not pinched or have a small pin hole. Generally a loss of pressure isn't from the tune. It's from a leak or a bad pump. If those are fine talk to another tuner.

Hoses and clamps are brand new. Inspected before they were put in. Its only losing fuel on - off - on throttle again. Outside of that, it runs great.

Boost a pump with wiring upgrade? Are the pumps losing volt's?

I think it's in the tune. Mine does the same thing when I'm quick in it, let out completely, stab throttle again. It'll do it

My 02 GT does the same. The PPRV delete helped when I first put the blower on the car. After switching to a DW pump, bap, and e85; the hesitation is back when shifting quickly and letting my foot off and back on again. Its annoying to say the least...

Are there any parameters to control what the pcm sends to the fpdm regarding fuel control in vacuum?

iudelt89 said:

Hoses and clamps are brand new. Inspected before they were put in. Its only losing fuel on - off - on throttle again. Outside of that, it runs great.

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Then I would talk to another tuner. There are adjustments that can be made in the tune.

slo984now said:

Then I would talk to another tuner. There are adjustments that can be made in the tune.

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x2

BLOWN9646 said:

I think it's in the tune. Mine does the same thing when I'm quick in it, let out completely, stab throttle again. It'll do it

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I agree it is in the tune. I also removed the PPRV and installed 255 lph pumps and that didn't really seem to help. I went back to the tuner and they were able to make it much less frequent. I thought they might have solved it 100%, but after putting some more miles on it the car I found that it will still occasionally does it. It seems to be on lazy shifts when accelerating hard. If I shift fast enough it doesn't give the pressure time to drop.

I've been working with my tuner on this. He's tuned cobras before and has always been able to eliminate it, but not this time for some unknown reason. Have tried just about everything we can think of and there is a still a significant fuel delay between WOT shifts.

I'm about at the point where I'm just going to take the hit and go return style. The price and fact its overkill given I'm still running the eaton is really holding me back though. Surely there is something we are missing, but out of ideas short of return style at this point.

I had the exact same problem, couldn't figure it out. I put a return system in and went away.

BlckBox04 said:

I had the exact same problem, couldn't figure it out. I put a return system in and went away.

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Gonna be a winter project at this point. Starting to dig into return style options. What did you end up going with? Any suggestions are appreciated.

Still running stock eaton with 2.81 upper and don't plan on swapping it out anytime soon, but I'd like to have a bit of headroom while I'm at it. Don't need anything crazy though. Just wanna get the fuel system to a point I would just need to swap out injectors and pumps should I decide to throw a whipple or VMP at it.

iudelt89 said:

Gonna be a winter project at this point. Starting to dig into return style options. What did you end up going with? Any suggestions are appreciated.

Still running stock eaton with 2.81 upper and don't plan on swapping it out anytime soon, but I'd like to have a bit of headroom while I'm at it. Don't need anything crazy though. Just wanna get the fuel system to a point I would just need to swap out injectors and pumps should I decide to throw a whipple or VMP at it.

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I have a lot of work done to my car so I went with a big return system for my Whipple. If you go on Lethal's website you can look at the options they sell as kits or you can try and piece everything together yourself. You're going to have to get your own injectors also, and since you're sticking with the eaton 60#'s are enough right now.

Lethal Performance Fuel Systems

Putting in a return system might not help you if your tuner doesn't know what he is doing. IMHO any tuner that recommends "hardwiring" your fuel pumps in a returnless system doesn't have a clue. Find someone else.

bigmoose said:

Putting in a return system might not help you if your tuner doesn't know what he is doing. IMHO any tuner that recommends "hardwiring" your fuel pumps in a returnless system doesn't have a clue. Find someone else.

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That wasn't a suggestion as much as a last resort option. Obviously we never intended to go that route.
From a tuning standpoint, its becoming really hard to find anyone to tune using anything but HP Tuning. Seems there are still some issues with the HP software for the cobras, unless they have been resolved in the past couple months. Anyone you suggest reaching out to on this?

My only worry is going with another tuner and dropping another $400+ only to have the problem persist. Car runs perfectly other than this issue. Dyno attched (Mustang Dyno)

iudelt89 said:

That wasn't a suggestion as much as a last resort option. Obviously we never intended to go that route.
From a tuning standpoint, its becoming really hard to find anyone to tune using anything but HP Tuning. Seems there are still some issues with the HP software for the cobras, unless they have been resolved in the past couple months. Anyone you suggest reaching out to on this?

My only worry is going with another tuner and dropping another $400+ only to have the problem persist. Car runs perfectly other than this issue. Dyno attched (Mustang Dyno)

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hp hasn't become fully compatible with our cars yet

BlckBox04 said:

hp hasn't become fully compatible with our cars yet

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Fueling seems to be a common issue with adding decent HP over stock. My BMW 335 has the same issue now. Fuel pressure drops to almost 1,000 psi right after a shift. Causes the car to go lean for a split second. Only happens occasionally just like the Cobra did.

Beetle6986 said:

Fueling seems to be a common issue with adding decent HP over stock. My BMW 335 has the same issue now. Fuel pressure drops to almost 1,000 psi right after a shift. Causes the car to go lean for a split second. Only happens occasionally just like the Cobra did.

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I was referring to hp tuners, my bad

Hey guys, just wanted to bring closure to this thread. Turns out, the FRPS was on it's way out.

The symptoms were odd because the car ran perfectly outside of the delay on/off heavy load, and it wasn't throwing any codes.

Was able to narrow it down when the car turned over but didn't start while I was pulling it out of storage. There was no pressure at the fuel rail test valve and the plugs were dry, but the fuel pumps were turning on so that helped with the diagnosis.

I had already purchased a new FRPS, so swapped it in and good to go. Also put the Kb resistor in front of it so hopefully it doesn't blow out again.

Hope this thread helps someone out before they go over the entire car with a multi-meter and do a bunch of dicking around with dropping the fuel tank to delete the PPRV.