Fuel Pressure Dip/Recovery at WOT

[pmor4243]

Hoping to get some thoughts here. During some roll racing a while back, I noticed I was getting a pretty big drop in fuel pressure when going WOT. It would only be for a moment, and then would jump back up to 60-70psi for the duration of the pull. I grabbed a log to a couple of days ago essentially matching the same conditions to see how things were doing, and noticed that my fuel pressure dropped down 19.9psi then jumped back up once again.

Quick details on the car. 19 GT, Procharger P1x @ 9psi, LP52 injectors, Stock Fuel Pump, Meth injection

Datazap log link: https://datazap.me/u/pmor4243/fuel-pressure-dip?log=0&data=9-26-31

Im not sure what to make of this. I understand that fuel pressure will drop in this scenario regardless, but dropping down to 19psi seems problematic. I tried a BAP to see if that helped and it made almost zero difference. I also want to point out that this "roll race" type condition is literally the only scenario where this happens - high rpm, stab the throttle, immediate jump to near max boost, etc. In all other scenarios this is not a problem.

I understand that the easy answer I may get here is "add a fuel system" and I do agree that would probably be a good idea, and who knows, maybe that IS the answer. That said, the car makes 695hp at the tire, and I am not intending on going any further, at least for a while which makes a fuel system less appealing to me.

So I'm curious if there are other potential options to help alleviate that initial drop in pressure.

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[Proshop]

First of all… OMG man buy yourself a damn fuel system come on! Second of all how much gas was in the tank at the time of this occurrence?

 

[pmor4243]

Gas was around 3/4 of tank. 19.9psi is by far the lowest I have ever seen that go. Usually 25-27psi is what I have noticed in previous logs I had from roll racing.

This is an honest question, if the current fuel system is able to feed enough fuel to support the power levels I am at (according to Wengerd, it is) what would throwing $2-4k+ at a fuel system actually get me? The car doesn't lean out up top and it holds pressure all the way, so I am genuinely trying to understand.

I'm also legitimately curious if someone with a full fuel system were to replicate the same thing, what their logs would show. I would think more flow should result in far less drop compared to what Im seeing.

Like I said, maybe that is the only answer here. But once again, if the only place this dip happens is when I go WOT at 5500 rpms, which is almost never as a street driven car, I just have a hard time justifying a full blown return fuel system. But I am open to the idea that it may in fact be what I need to do.

And if that is the case, I am also open to dropping my boost levels down to better align with a power level that my stock fuel system is capable of supporting.

 

[haze324]

Does anything else drop? I'm having a quick dip/drop in load on my log similarly when doing WOT pulls, but did not check to see fuel pressure changes. Curious if they are similar issues.

 

[Proshop]

Gas was around 3/4 of tank. 19.9psi is by far the lowest I have ever seen that go. Usually 25-27psi is what I have noticed in previous logs I had from roll racing.

This is an honest question, if the current fuel system is able to feed enough fuel to support the power levels I am at (according to Wengerd, it is) what would throwing $2-4k+ at a fuel system actually get me? The car doesn't lean out up top and it holds pressure all the way, so I am genuinely trying to understand.

I'm also legitimately curious if someone with a full fuel system were to replicate the same thing, what their logs would show. I would think more flow should result in far less drop compared to what Im seeing.

Like I said, maybe that is the only answer here. But once again, if the only place this dip happens is when I go WOT at 5500 rpms, which is almost never as a street driven car, I just have a hard time justifying a full blown return fuel system. But I am open to the idea that it may in fact be what I need to do.

And if that is the case, I am also open to dropping my boost levels down to better align with a power level that my stock fuel system is capable of supporting.

Ultimately even a split second lean spike especially a drop like that can cause you to spend a lot more money than what a fuel system would cost. I asked about the fuel level because it reminds me of gas tank slosh but if you had that much in it that is not the case. You don’t need to spend 2-3k on a fuel system unless you are going e85. You can spend around $700 and get a nice radium setup. That stock pump could be getting worn out from the use and abuse and this my have been a sign of it starting to go.
http://www.radiumauto.com/Fuel-Pump-Hanger-2011-Ford-Mustang-P2165.aspx

 

[Cory S]

Yeah. Somethings really odd. It should never drop below around 40psi, unless there’s a significant fuel delivery issue. Is Lambda being maintained during this drop? Are STFT’s trying to add more than 8-10% fueling?

My buds Procharged Gen3 makes well over 830+ with a DW400/BAP + 28gph of 80% methanol injection. Lowest his rail pressure drops is 43psi and recovers almost instantly to 50+.

 

[pmor4243]

All good to know. @Proshop that's good info. I'll definitely check out the Radium set up. We don't have E85 in Utah other than 1 station so I can't rely on that for a car that gets driven often. So a more robust system for the pump gas I'm running and 700hp would certainly be justifiable.

To the other questions, that downward spike happens so fast its hard to see anything huge. But what I do notice is that in that split second, the commanded vs measured lambda values are quite a bit off. Commanded drops down to .75 but measured stays around .98. This is also the only time I really ever get knock (likely due to going lean for that split second) It then adds a little fuel on the short term trims but at about the same time 18gph of 100% methanol are getting in there and helps keeps things somewhat in check (as far as I can tell)

@Cory S, with your buddy's set up, the only thing I would be curious about and would elaborate on in my case is this only happens when I do a high RPM "roll race" type start around 5,500 rpm. If I come into the power in a more typical way that you would normally drive a car, the fuel pressure never drops below 57psi. The log below shows a more typical pull. Fuel pressure is rock solid (blue line in the second line chart).

 

[pmor4243]

So I guess if anyone wanted to try and replicate going WOT at around 5,500rpm or around a 40 roll in second gear, Id be very interested to see what the log looks like.

 

[Proshop]

Have you brought this drop up to Mr. Wengerd? If so what are his thoughts on it?

 

[pmor4243]

I did send an email a couple of days ago referencing it as I wanted to make sure adding a BAP would not create any issues with the current tune. He did not mention anything in relation to the fuel pressure drop.

It seems problematic to me so I figured it was likely a hardware issue and not software.

 

[Proshop]

I did send an email a couple of days ago referencing it as I wanted to make sure adding a BAP would not create any issues with the current tune. He did not mention anything in relation to the fuel pressure drop.

It seems problematic to me so I figured it was likely a hardware issue and not software.

Yes I doubt it’s a software issue also. But he is a pretty knowledgeable guy and figured he might throw in his 2 cents if asked.

 

[Cory S]

I did send an email a couple of days ago referencing it as I wanted to make sure adding a BAP would not create any issues with the current tune. He did not mention anything in relation to the fuel pressure drop.

It seems problematic to me so I figured it was likely a hardware issue and not software.

I would 100% add a BAP. Or…. Do a DW400 pump swap in your basket.
Can you send me that log?

 

[pmor4243]

I would 100% add a BAP. Or…. Do a DW400 pump swap in your basket.
Can you send me that log?

Added a BAP but unfortunately it didn't change anything. Happy to share the log file. That link I added in the first post for Datazap is the full log so it has a lot of parameters that can be checked on and off as well.

 

[Cory S]

Added a BAP but unfortunately it didn't change anything. Happy to share the log file. That link I added in the first post for Datazap is the full log so it has a lot of parameters that can be checked on and off as well.

Can you send the original file to:
[email protected] ?

 

[K4fxd]

There is always going to be a lag between requesting more fuel and it being delivered. That said a drop to 20 Psi is a bit much. I'd add the DW400 pump.

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