Fuel pressure drops @ WOT
Thread Starter
Teching In
Joined: Jan 2016
Posts: 9
Likes: 0
From: Louisville, KY
Fuel pressure drops @ WOT On my 2014 Camaro 1LE I am consistently seeing fuel pressure drop from about 60 psi to the low 50s on a WOT run in 3rd gear (see attached). Car is stock except for a Rotofab CAI and SCT X4 tune and still under warranty. I'm trying to figure out what the most likely point of failure is here and if I should seek a warranty repair or if I need to be looking for an aftermarket solution. Does anyone have any experience with this on a basically stock setup?
Thanks,
Larry
Thanks,
Larry
Thread Starter
Teching In
Joined: Jan 2016
Posts: 9
Likes: 0
From: Louisville, KY
I don't have a wideband to know for sure but I am getting a bunch of knock retard right when the pressure drops so my concern is that it is going lean.
Thread Starter
Teching In
Joined: Jan 2016
Posts: 9
Likes: 0
From: Louisville, KY
Ran with stock ECU, it had more knock retard than the mail order tune, and the fuel pressure behaved the same. I asked the dealership if the fuel pressure drop is normal and they say it is. So now I'm getting about 60/40 saying not normal vs normal. Clear as mud.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo Thread Starter
Teching In
Joined: Jan 2016
Posts: 9
Likes: 0
From: Louisville, KY
Thanks for the suggestion.
A regulator could be faulty, you could have a dirty filter, or the pump could be failing. All possible, but...
Pressure drop in a fuel line is directly related to the velocity of fuel through the line, just like flow in a pipe. When you send more fuel through the regulator path during normal driving conditions, the volume of fuel demanded by the motor that flows through the feed line to the injectors is lower. When that's the case, in a bypass-style regulated system, flow through the path to the injector has a low velocity and therefore a low pressure drop. When you go WOT for a period of time, the injectors relieve the pressure at the end of the system and pump flow preferentially flows toward the rails/injectors instead of the regulator. The (typically) longer flow path of fuel causes more pressure drop in the stock lines.
Most people don't notice this because they don't have a FP gauge or wideband on their car... but you'd be surprised how many cars suffer this from the factory. Of course, the characteristic is mostly compensated for in the factory tune. OEM tunes add more fuel in strategic places to accommodate.
I'd bet if you did nothing but change the feed lines to the motor to a larger size, you'd see less pressure drop. And if you put a fuel pressure regulator closer to the motor with a return running the length of the car, your pressure drop would level out even more.
Pressure drop in a fuel line is directly related to the velocity of fuel through the line, just like flow in a pipe. When you send more fuel through the regulator path during normal driving conditions, the volume of fuel demanded by the motor that flows through the feed line to the injectors is lower. When that's the case, in a bypass-style regulated system, flow through the path to the injector has a low velocity and therefore a low pressure drop. When you go WOT for a period of time, the injectors relieve the pressure at the end of the system and pump flow preferentially flows toward the rails/injectors instead of the regulator. The (typically) longer flow path of fuel causes more pressure drop in the stock lines.
Most people don't notice this because they don't have a FP gauge or wideband on their car... but you'd be surprised how many cars suffer this from the factory. Of course, the characteristic is mostly compensated for in the factory tune. OEM tunes add more fuel in strategic places to accommodate.
I'd bet if you did nothing but change the feed lines to the motor to a larger size, you'd see less pressure drop. And if you put a fuel pressure regulator closer to the motor with a return running the length of the car, your pressure drop would level out even more.
I'm no expert, but as long as that pressure drop is expected and accommodated for in the PCM appropriately, you can suffer 10+psi drop at WOT and still be fine. For example, if you consistently drop pressure over a known time at WOT, you can play with VE or PE to accommodate it. When I got my car tuned at a shop in the Northern Delaware area, they nailed 12.6-12.8 AFR through my dyno pulls. Later, I discovered that my fuel pressure drops at WOT. But they had already accommodated this inadvertently by tuning to AFR rather than fuel pressure.
The real problem begins when your tune accommodates it, but you do WOT pulls through 2nd vs 5th gear... because you're not sweeping through the RPM as quickly and some cells may have expected to have more fuel pressure than they actually do due to the slower sweep.
Something else to consider is the injector behavior at different pressure drops.
So there may not be a limit to acceptable fuel pressure drop at WOT, but 0psi drop is best.
The real problem begins when your tune accommodates it, but you do WOT pulls through 2nd vs 5th gear... because you're not sweeping through the RPM as quickly and some cells may have expected to have more fuel pressure than they actually do due to the slower sweep.
Something else to consider is the injector behavior at different pressure drops.
So there may not be a limit to acceptable fuel pressure drop at WOT, but 0psi drop is best.