Fuel pressure problem that i cant make heads or tails of

[ttribejr]

I will post a fix for this when I find out for future searches

87 GN. All stock except for TT street chip, test pipe, catback, kn filter and comp valve springs.

A couple months ago I installed brand new parts to get ready to turn the car up:

Walbro pump/sock/hose
Casper HW kit
Fuel filter
Accufab FPR with Marshall fluid filled gauge

Car ran the same. Recently I installed more parts:

Fast XFI
120lb precision injectors
GM flex fuel sensor in the return line
car is now on e85


Problem #1

I cant get the fuel pressure below 50psi static. When i put the vacuum line back on it, it quickly dips to about 48psi, then immediately jumps back to 50psi. If I drive the car for a while, the static fuel pressure drops to 45psi (line on or off does not make a difference. The vacuum source is good.

First thought here is a restriction in the return line. But ....

Problem #2

When I blip the throttle, the fuel pressure drops about 10 psi. This is dead opposite of problem #1. I suspect It is not raising under boost either but i cant see the gauge while driving. I suspect this because I had to add a lot of fuel to the VE table under boost to get the AFRs right.


Why would fuel pressure change after the car warms up? I dont believe it is a faulty gauge because I can see the O2 corrections and it correlates to the fuel pressures shown on the gauge.

If there is a restriction in the return, why is fuel pressure dropping when it should be increasing?

I am looking for any advice to speed up the diagnosis. The flex fuel sensor doesn't appear to be restrictive.

 

[Gene Van Horn]

Im not positive with this but im thinking maybe that accufab cant handle what your now pushing at it. I recently was talking to Don Cruz about fuel rails and he told me i would also have to upgrade my regulater due to more volume. Just a possibility. My ? Is why do all that to a stock engine, maybe that has something to do with it also. Either buy or borrow a fuel gauge to go on windshield and see if its rising 1to1. Im not to familiar with the FAST but isnt it supposed to tell you all that stuff.

 

[Reggie West]

I have seen that issue before. It's the regulator.

The corrections are caused by the mechanical problems coming from the regulator. In other words a mechanical problem is causing the XFI to compensate for it.

How do you have the fuel lines routed and what size are they?

 

[ttribejr]

I will eventually upgrade everything, but in steps as my wallet allows.

Its all stock fuel lines. Walbro is the smaller, 255 one. Same part number as everyone uses on these forums. I still have the stock regulator. I suppose i could reinstall it and see if my FP issues go away.

XFI doesn't know my fuel pressure. I do not have the sensors for it. It simply reads the air fuel ratios. If i tune the VE while its at 50psi, then when it drops to 45psi, the o2 correction goes up a little. And vice versa.

That will suck if one of my brand new parts is defective.

 

[Pronto]

You could use the stock to test but the stock fp is probably too low for any real driving. BTW, the Accuflub has known machining issues. You could have gotten one that was milled on the day the Taco truck came by with a load of weed.

 

[RmvBfrFlght]

Accufab FPR with Marshall fluid filled gauge

If I drive the car for a while, the static fuel pressure drops to 45psi (line on or off does not make a difference. The vacuum source is good.

A liquid filled gauge is only accurate at room temperature. As the gauge heats up the liquid expands and puts additional pressure on the Bordon tube. This causes the gauge to show a lower then true reading.

GM flex fuel sensor in the return line

Possibly an added restriction causing high fuel pressure issues? I don't know but figured it as a maybe.

RemoveBeforeFlight

 

[84BuickGNYorkPA]

Hello ttribejr,

Just a couple of thoughts, are you able to log and post it up? I'm not familiar with XFi and I'm not sure how much unpaid assistance you will receive. But you need to start logging fuel pressure to see what's going on exactly. I had to drill out my return line at the A arm junction on the driver's side when I first upgraded my fuel pump years ago as I was not able to get the pressure below 50 psi. Full throttle has the fuel lines on sale right now that will take them out of the equation as part of the problem. Perhaps it's your regulator, is there anyone close by that will let you swap it out for testing?

Chuck

 

[Chuck Leeper]

Why would fuel pressure change after the car warms up?

A fluid filled ga may be affected by heating of the fluid.

 

[BEATAV8]

Most likely an issue with the regulator or the return line. With engine off and pump on, the fuel pressure should be fully adjustable from low to high just by turning the screw. If it wont go low there must be a restriction in the return. You can make the pump run (engine off) by jumping 12V to the fuel pump test lead terminal located on the driver's side of the engine.

When blipping the throttle the injectors take a gulp, that may be why the rail pressure drops?

on an somewhat related note, that single walbro 255 pump can only support your 120lb injectors to about 50% duty cycle. probably less.

 

[Nick Micale]

[QUOTE="ttribejr, post: 3720946, member: 513]06"............First thought here is a restriction in the return line. But ....

Problem #2

When I blip the throttle, the fuel pressure drops about 10 psi. This is dead opposite of problem #1. I suspect It is not raising under boost either but i cant see the gauge while driving. I suspect this because I had to add a lot of fuel to the VE table under boost to get the AFRs right...........

If there is a restriction in the return, why is fuel pressure dropping when it should be increasing?

I am looking for any advice to speed up the diagnosis. The flex fuel sensor doesn't appear to be restrictive.[/QUOTE]

First of all, the flex fuel sensor IS a restriction in the return line.

Second, to run with 120# injectors with stock lines is insane, I would NEVER take that chance, especially with e-85 if you need 120# injectors for your build.

Third, if you have not replaced ALL your 30 year old rubber stock lines with alcohol resistant lines, you are inviting a disaster.

Fourth, I had a similar case with a GN and an aftermarket dual pump set up that would lose pressure as boost increased? After replacing all the line and wiring, the problem was solved.

Fifth, be aware the stock, or replacement in-tank sender, is a major restriction as the metal return line size is also 1/4".

My solution in a build like your's, I would replace all the stock lines, wiring, stock type filter and in-tank stock-type sender to assure an adequate and reliable fuel delivery system.

One hic-cup at WOT will cost more in engine repair than upgrading to the proper fuel delivery system.

 

[Jerryl]

.

 

[TURBOELKY]

I once upon a long time ago, had the return and vent line mixed up somehow. Fuel pressure went backwards, would drop under load. It only cost me an engine. No big deal.....

I'm with Nick in this one. New lines and proper setup is cheaper than a new engine.

 

[ttribejr]

I hear you guys, we are on the same page. If I had the money, I'd do it all at once. Car had stock injectors, I put in 120s knowing I will grow into them. I am only tuning the car to around 20 psi on stock turbo/e85 until the next round of upgrades.

I am sick as a dog right now, but will jump back into this soon. Looks like they have quite a few options on that pump/sender kit. Doesn't say how much power they support. I wonder how much e85 power those single pumps (340 / 450) LPH can support? Quite a bit cheaper than the dual pumps. Any input on these options?

I saw this:

A Racetronix FPWH-006 fuel pump wiring harness MUST be used with this sender in order to properly support the power demands of the Racetronix 340LPH high-performance fuel pump.

and this:

Customers who can't afford to upgrade their current hotwire harnesses may use our FPAH-076 to adapt the power connector on this hanger to the factory-type Weather-Pack connector found on first-generation hotwire harnesses. This hanger MUST NOT be run off of the factory wiring PERIOD!

Sounds like they are saying you have to use their hotwire? Looks just like the caspers one i bought a few months ago.

 

[BEATAV8]

Which Walbro pump did you install? The 255lph or the 450lph?
I had assumed the 255lph?

 

[ttribejr]

yes it is the 255 one. I installed it before I decided to go e85. Full Throttle just told me not to use the racetronix double pumps with e85. Said only the single 450.

 

[Toby_Goodmk]

oh the subjects of proper fuel delivery. I can say I earned my wings learning from this subject. I pissed away thousands of dollars thinking I had proper fuel delivery. I'll tell you this. This is meant to scare you as well, as no one came out and scared me till my wife about divorced me on the second engine. Dont fuck with fuel, period. Buy the best damn products and the least restrictive lines, most voltage supplying wiring out there.

This is what I dont have anymore.

Factory type wiring connections (plugs)
Factory fuel lines
Factory style sending units

If I were you I would stop while ahead. Save some cash, before you end up like me.

FAST SYSTEM: I too have a fast system, and that system only helps fuel correction with sensors, which you commented you are not using. Sensors are cheap, and when you upgrade lines, the sensor fitting comes with the Racetronix kit. Buy a ceramic sensor off ebay for $20, and the caspers harness connection for another $60, and you can log fuel. It is very helpful to see on a graph what your fuel and IDC are doing together with other params to stave off starvation or other issues.

Your lines need to go. People on here will claim you can use the factory lines and they have used them for years with no issues. Good for them, I side on the "better safe than sorry." I run RT teflon lines (which is a very nice product) and have a continental FF sensor in the return AN-6 line. I run BOTH MY PUMPS (340 DW) ALL THE TIME and can drop my pressures to 30 psi....no sweat. That is how much of an advantage to having restriction removed from fuel lines. Guess what....if send too much fuel to the rail it goes back to the tank! If I dont supply enough fuel, it blows up engines!

People on here will say they run a single 340 Dw, or a 430 walbro on E85 with no issues. Good for them. I have studied the factory sender, hell I know where it is made. There are a couple suppliers in the world, one is in Taiwan, one is in Canada, these are the good ones. There may be one in China that is a complete hill of shit now, but I have lost track. The good ones both follow the OEM design. For less than high performance builds, this sending unit is more than adequate. You start stepping into delivering ethanol and supplying 120lb injectors......throw the OEM design out the window. It may work for you, but why risk it????? See my original paragraph.

I don't work for Nick Micale, but he has treated me well enough and honest enough when discussing fuel delivery. So I am going to give him an advertisement below about his products I now use. I also headed words of advice and instructions and what to look for in the logs of my FAST system from Cal Harltine. Dave Fiscus lives near me, and occasionally we hang out and talk, he too shared the same comments that I expressed above.

At minimum you need to replace your fuel lines now since you have all kinds of pressure issues. I would use at minimum Nick's sender and 430 pump with 120's. My vote is for dual 340's but that is me, the 430 was not enough with my build. My injectors were gasping for fuel with the 430.

There is not a better in tank sender, period. There are no restrictions. There are no factory weather pack connections. The wiring is as good as you can get. The wiring is held into the unit with bulkhead connections using a nut and ring. The relays are continuous duty. The wiring has no disruptions, and runs directly into the BATTERY, both positive and negative. At no time, I want anything to interfere with voltage to the pumps, period.

Lines. I used Racetronix line set, because Nick did not have his ready yet. Still, it is a good product. AN-8 feeds from the tank to the rail with a proper E85 filter to the rail in line. The fitting used to adapt saginaw to AN was custom machined to the same diameter as the AN-8 to remove any restriction. My AN-6 return is also machined at the filling to remove restriction and has the continental FF sensor inline, then drops into the sending unit return.

I know this is long and drawn out. Ethanol changes the game. Dont F with fuel delivery.

 

[ttribejr]

Toby, thank you for elaborating and telling me about Nick. I don't know him.

Does Nick have a website I can see these products on? I need to see what he offers and prices before I lose the chance on the sale from another vendor.

We probably have the same Continental FF sensor. Is it any restriction in a -6 line? I got mine off ebay, i think for around 40 or 50$.

I am going to place an order soon from somebody. I can not tune this thing with inconsistent fuel pressure.

oh the subjects of proper fuel delivery. I can say I earned my wings learning from this subject. I pissed away thousands of dollars thinking I had proper fuel delivery. I'll tell you this. This is meant to scare you as well, as no one came out and scared me till my wife about divorced me on the second engine. Dont fuck with fuel, period. Buy the best damn products and the least restrictive lines, most voltage supplying wiring out there.

This is what I dont have anymore.

Factory type wiring connections (plugs)
Factory fuel lines
Factory style sending units

If I were you I would stop while ahead. Save some cash, before you end up like me.

FAST SYSTEM: I too have a fast system, and that system only helps fuel correction with sensors, which you commented you are not using. Sensors are cheap, and when you upgrade lines, the sensor fitting comes with the Racetronix kit. Buy a ceramic sensor off ebay for $20, and the caspers harness connection for another $60, and you can log fuel. It is very helpful to see on a graph what your fuel and IDC are doing together with other params to stave off starvation or other issues.

Your lines need to go. People on here will claim you can use the factory lines and they have used them for years with no issues. Good for them, I side on the "better safe than sorry." I run RT teflon lines (which is a very nice product) and have a continental FF sensor in the return AN-6 line. I run BOTH MY PUMPS (340 DW) ALL THE TIME and can drop my pressures to 30 psi....no sweat. That is how much of an advantage to having restriction removed from fuel lines. Guess what....if send too much fuel to the rail it goes back to the tank! If I dont supply enough fuel, it blows up engines!

People on here will say they run a single 340 Dw, or a 430 walbro on E85 with no issues. Good for them. I have studied the factory sender, hell I know where it is made. There are a couple suppliers in the world, one is in Taiwan, one is in Canada, these are the good ones. There may be one in China that is a complete hill of shit now, but I have lost track. The good ones both follow the OEM design. For less than high performance builds, this sending unit is more than adequate. You start stepping into delivering ethanol and supplying 120lb injectors......throw the OEM design out the window. It may work for you, but why risk it????? See my original paragraph.

I don't work for Nick Micale, but he has treated me well enough and honest enough when discussing fuel delivery. So I am going to give him an advertisement below about his products I now use. I also headed words of advice and instructions and what to look for in the logs of my FAST system from Cal Harltine. Dave Fiscus lives near me, and occasionally we hang out and talk, he too shared the same comments that I expressed above.

At minimum you need to replace your fuel lines now since you have all kinds of pressure issues. I would use at minimum Nick's sender and 430 pump with 120's. My vote is for dual 340's but that is me, the 430 was not enough with my build. My injectors were gasping for fuel with the 430.

There is not a better in tank sender, period. There are no restrictions. There are no factory weather pack connections. The wiring is as good as you can get. The wiring is held into the unit with bulkhead connections using a nut and ring. The relays are continuous duty. The wiring has no disruptions, and runs directly into the BATTERY, both positive and negative. At no time, I want anything to interfere with voltage to the pumps, period.

Lines. I used Racetronix line set, because Nick did not have his ready yet. Still, it is a good product. AN-8 feeds from the tank to the rail with a proper E85 filter to the rail in line. The fitting used to adapt saginaw to AN was custom machined to the same diameter as the AN-8 to remove any restriction. My AN-6 return is also machined at the filling to remove restriction and has the continental FF sensor inline, then drops into the sending unit return.

I know this is long and drawn out. Ethanol changes the game. Dont F with fuel delivery.

 

[ttribejr]

i googled and found him.

 

[Toby_Goodmk]

yea, AZGN.com

You may be best off to call and speak with him as well. Not only a good person to shoot the breeze with , but will also go over any questions you may have and explain any differences that I may not have outlined above.

 

[Toby_Goodmk]

Toby, thank you for elaborating and telling me about Nick. I don't know him.

Does Nick have a website I can see these products on? I need to see what he offers and prices before I lose the chance on the sale from another vendor.

We probably have the same Continental FF sensor. Is it any restriction in a -6 line? I got mine off ebay, i think for around 40 or 50$.

I am going to place an order soon from somebody. I can not tune this thing with inconsistent fuel pressure.

I forgot to answer your ques concerning a restriction in the FF sensor. I assume there is a small amount, but is not apparent with my setup. I used the quick coupler connection to AN -6 found at summit, and made by earls I think.