Need help with fuel pressure
Need help with fuel pressure So I just installed the walbro 255LPH in tank fuel pump last night. I thought that changing the pump would fix my pressure drop under load and I was wrong. Before the fuel pump was changed it would idle at 62psi then under load it would drop to 54. Now with the new pump it is idiling at 66 and dropping to 58. When I did my first nitrous pull on the dyno my fuel pressure safety switch cut off the nitrous at 4400rpms so I am trying to please that thing by upgrading my fuel system and not blowing up my motor also. I am thinking about changing the rails and everything and if you guys have any ideas plese fill me in. Thanks in advance
Yeah that's right, the FP safety switch should be set quite a bit lower. Dropping to 58 is not a problem at all 
Set that switch in the 40s somewhere.
Also, if you were previously tuned, you will need to have your WOT touched back up, since the PCM is blind to fuel pressure. Your trims at part throttle will be significantly negative now too.
Set that switch in the 40s somewhere.Also, if you were previously tuned, you will need to have your WOT touched back up, since the PCM is blind to fuel pressure. Your trims at part throttle will be significantly negative now too.
I, too, have had issues with dropping fuel pressure under WOT conditions...
I'm trying a few things before going to a fuel rail mounted regulator with a Racetronix pump (my car is stock internally) and see if I can help it some.
I think it may just be an inherent problem with running the regulator in the tank. The other guys have you covered on the FPSS...what you are seeing for a pressure drop is about what I'm seeing (I idle at 58 psi, and drop to 51-52 psi under WOT).
I'm trying a few things before going to a fuel rail mounted regulator with a Racetronix pump (my car is stock internally) and see if I can help it some.
I think it may just be an inherent problem with running the regulator in the tank. The other guys have you covered on the FPSS...what you are seeing for a pressure drop is about what I'm seeing (I idle at 58 psi, and drop to 51-52 psi under WOT).
Ok so I need to adjust my fuel pressure safety switch then? How do you know what its set at? I am considering changing my fuel rails and mounting a adjustable fpr, will this fix my problem or will I be waisting money? The car is going back to the dyno in early january for another nitrous tune and I want to make sure I don't blow up my motor by adjusting the fpss too low. I appreciate ya'lls advice and I did the sea foam two days ago and its like I have a new car again!!!
Also excuse my ignorance but the car was being tuned on the dyno when the car was being sprayed for the first time, by WOT touched back up you mean?
Also excuse my ignorance but the car was being tuned on the dyno when the car was being sprayed for the first time, by WOT touched back up you mean?
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Maybe you just got really lucky with a bad pump 
I don't remember how the fps switch is adjusted, its been a while. If you do a search it was covered before or if you have your instructions that came with it that will be helpful also.
I don't remember how the fps switch is adjusted, its been a while. If you do a search it was covered before or if you have your instructions that came with it that will be helpful also.
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Verdad Gallardo Quite possibly...after this next round of fuel system mods (including new rails, and nice Canton Racing fuel filter, and braided line between the tank and fuel filter), I'll know whether or not it is the pump.
I'm hoping it was just my kinked plastic line going from the tank to the filter...it has been that way since the last time I changed the fuel filter, but I got most of the kink out. The kink is now worse than ever, so that line has to go.
I'd like to get my car back on the road since it has been on jack stands for at least 4 months now
With the snow, though, that prospect doesn't look good.
I'm hoping it was just my kinked plastic line going from the tank to the filter...it has been that way since the last time I changed the fuel filter, but I got most of the kink out. The kink is now worse than ever, so that line has to go.
I'd like to get my car back on the road since it has been on jack stands for at least 4 months now
With the snow, though, that prospect doesn't look good. 
sorry to hijack but I am curious if my press is good. Camrod you mentioned that you see about 55psi on wot, is that ok? I just finally got my elec fuel press gauge working today and I see 66 or so at idle and it drops to 58 at wot. To me this seems good cause stock press is 58. Thing is I start to lean out to 13.4-5 on some wot runs and to me that seems to lean. On the juice Im usually a good a/f of 11.8, I havent had time to see my press on the juice but Im fine with a a/f of 11.8 on my 100 shot. But the lean part on NA runs have me concerned. I have a 255 walbro and 42lb so fuel should not be a prob. So if 58psi is ok to drop to is it maybe my tune thats leaning me out. And I only start to lean out after 4500 or so, before that im usually at 12.8-0 or so. Hell 13.0 to me is fine for NA, its just the 13.5 that has me concerned....Just trying to keep this motor together. Thanks for any advice.
Wierd. My LS1 conversion uses a Vette filter/regulator combo and pressure is almost rock steady at just under 60psi at idle and about 56-57psi at WOT. I'm using an LT1 Walbro 255LPH pump. Is it possible the LS1 in-tank regulator is just crap??
Re'
Re'
I believe with the aftermarket pumps you see a bit more pressure. I'd say its in your tune as far as the leaning out. Out of curiousity what is your injector duty cycle on the runs?
I'm going through this as well guys here is my thread info
ok guys I have been fighting a loss in fuel pressure in my car. At WOT anything past 5800RPM I lose 18PSI of pressure.
So far I have hot wired the pump power and ground side so I know it is getting 14.8 volts. I have a Walbro 255HP pump with -6 lines for the supply. The tanks is over 1/2 full.
What could be the trouble here guys I have tried everything and it still just falls off at the top end. I think I have a bad pump thats they only thing I can see. Anyone else have something to add here. Oh it is doing this on the Dyno, and driving!
here is the pump before it went in the tank
really, I mean it works at idle and all the way up to 5800 then it drops off.
I was thinking of steping it up to this pump.
Bosch 040
The reg is like this one.
The filter is this size but not this one.
https://ls1tech.com/forums/fueling-injection/832298-fuel-pressure-drop-need-help.html
ok guys I have been fighting a loss in fuel pressure in my car. At WOT anything past 5800RPM I lose 18PSI of pressure.
So far I have hot wired the pump power and ground side so I know it is getting 14.8 volts. I have a Walbro 255HP pump with -6 lines for the supply. The tanks is over 1/2 full.
What could be the trouble here guys I have tried everything and it still just falls off at the top end. I think I have a bad pump thats they only thing I can see. Anyone else have something to add here. Oh it is doing this on the Dyno, and driving!
here is the pump before it went in the tank
really, I mean it works at idle and all the way up to 5800 then it drops off.
I was thinking of steping it up to this pump.
Bosch 040
The reg is like this one.
The filter is this size but not this one.
https://ls1tech.com/forums/fueling-injection/832298-fuel-pressure-drop-need-help.html
Not sure what the duty cycle was. I was so caught up in making sure the car was even running right. Just did H/C before I got tuned. Wish I would have found out though. No way Im maxing out the injectors...
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I'm having a simular problem with fuel delivery. The pressure is ok but the volume is low. I am using the same intank pump and fuel regulator and just changed the filter to a stock Gm filter. I am using braided steel fuel lines on all flex points and 3/8" steel lines onthe rest of the system. The car runs good at partial throttle but leans out on heavy throttle pressure. I have replaced the in tank pump, new fuel tank, fuel filter,fuel lines and still have the same problem.
If you are exceeding 58psi, the pump is outflowing the capacity of the stock regulator. In this case, it will drop back to the 58psi setpoint as soon as the engine uses suffucuent fuel to allow the regulator to regain control. This is normal. If it drops below 58psi, the pump or lines are now the limiting factor.
You should be good for approx 550rwhp on 1 pump. If you need more, I can fix you up with a twin intank setup that will take you to the 1000+rwhp range.
Happy Holidays
You should be good for approx 550rwhp on 1 pump. If you need more, I can fix you up with a twin intank setup that will take you to the 1000+rwhp range.
Happy Holidays
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Joined: Dec 2007
Posts: 4
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Thanks for the reply. This is a stock 2002 engine that had 800 miles when it was rapped around a pole. I installed the entire drive train in my 54 Corvette/Nomad. The only thing not replaced is the aeromotive fuel regulator. Is it possible that it is clogged up from crap in the original fuel tank? I replaced the fuel filter 3 times before installing a new tank, pump and different type of filter. The car runs fine except for hard acceleration and gets 30 mpg on trips.
Oldvett54,
The dirt would have been caught by the filter before it got to the regulator.
Also the press would be probably be low at idle if something was in the regulator.
What type of tank & lines are you running in that vehicle? Maybe I can help diagnose your problems. Is your tank or cap vented?
The dirt would have been caught by the filter before it got to the regulator.
Also the press would be probably be low at idle if something was in the regulator.
What type of tank & lines are you running in that vehicle? Maybe I can help diagnose your problems. Is your tank or cap vented?
An improperly vented tank does not allow air in when fuel is drawn out. This draws a vacuum in the tank under full throttle as fuel is displaced & that causes a drop in fuel flow because the pump has to work harder to pump the fuel.
I had an old '68 Camaro once with the wrong gas cap that sucked the tank bottom up 2" after running it hard. It would lay over on the top end & after trying to diagnose it, I pulled the cap off & the tank popped back into position.
Some cars had vented caps, some vented tanks & some have 1 way check valves that allow air in, but not out. It depends on your application.
A common problem is when people eliminate the tank evap lines & leave no means for venting. I'm not saying that is the problem but it should be ruled out before you start buying pumps & regulators.
I had an old '68 Camaro once with the wrong gas cap that sucked the tank bottom up 2" after running it hard. It would lay over on the top end & after trying to diagnose it, I pulled the cap off & the tank popped back into position.
Some cars had vented caps, some vented tanks & some have 1 way check valves that allow air in, but not out. It depends on your application.
A common problem is when people eliminate the tank evap lines & leave no means for venting. I'm not saying that is the problem but it should be ruled out before you start buying pumps & regulators.