I just installed a Radix on my 01 Sierra C3 (LQ4), and have been trying to figure out some issues i've been getting with the fuel trims and pressure. I've checked for vacuum/boost leaks via pressurizing the system, and using carb cleaner and watching my STFT's spraying my injectors and have found no issues for leaking.

The other day, after running fine,with slightly lean fuel trims the truck started to bog and die out if i tried to launch or give more than 50% throttle. I checked the fuel pressure today and got about 53psi at idle, and 65ish under boost while easing into the throttle slowly. If i really stand on it the pressure drops tons...ok so there's the problem...

Basically I isolated it down to a bad in tank or in line fuel pump. I have the factory in tank pump as well as an inline walbro255 (from magnuson) right after my fuel filter. Both are under a month old, under 1000 miles.

I bypassed the inline today and went for a drive monitoring my wideband and fuel pressure and with just the factory pump it keeps up the pressure while launching, but goes lean pretty quick in higher rpm as expected...no jerking though and not irratic dip in pressure, just a slight drop of before i backed out of it.

Figuring the Walbro's bad, I flow tested it with just over 2 gallons of gas, timing the amount to flow and it seems to pump the proper amount if you do the conversion from 255litres per hour. My question is though, if under load is this maybe when the walbro is failing or is there something else that is casueing my problem???I seems to flow the amount, but maybe not under full pressure? I'm assuming its the walbro, are my assumptions correct?

Any input helps, thanks guys!

-Brian

 

recheck and reinstall your fuel pressure regulator. Quick vacuum to boost on it may be causing it to bypass the needed fuel for the rails. You sound like you have many avenues of troubleshooting. If you have the ability, put a fuel pressure gauge right after the walbro as well. That's before the fpr so the pressure should stay fairly constant. Nevertheless you can watch to see if pressure dips hard there as well. If it does then you know it's one of your pumps. If not, it's in the rails which is almost always the fpr.

 

Thanks, ill try that to meter the pressure right after the Walbro. I should have said I have already checked and changed the fuel pressure regulator and block. Maybe ill swap back to the original one and see if it changes anything.

 

I put a pressure tester right before the fuel regulator because i didn't have the right fittings to do it right after the pump and get 53PSI at idle and 65ish under WOT with the in tank pump only. Is this due to the voltage change to the pump, or is the pressure supposed to be stable under all conditions before the regulator?

Anyways, put the in line back in and get a 51-53psi at idle, sort of unstable, then 5 psi when the truck bogs under heavy throttle....so ill call maggie on monday and see what they say.

Anyone else have issues with Walbro inlines?

 

Actually, I have never tested psi before the fpr. LOL I just assumed it would be fairly stable. In a return system the inline and intank are always runnning at the same voltage (pretty much) and all the time. The fpr just allows more of that to come to the rails as boost comes on. So maybe some drop in pressure is acceptable before the fpr.

What boost are you running? I've been thru 3 inlines in 70K miles.

 

Running a 2.9 inch pulley on the 112, with the 6.0 and haven't been able go full throttle yet lol so i dont even know how much boost. I have heard it should be somewhere in the range of 7-8psi.

3 in-lines in 70k, wow that seems a bit much! Is this due to not being cooled or have you had other issues? Are they expected not to last long?

 

No, just a fluke I assume. The 3rd one I am on has been on for a while. The first two were like bam bam.

I asked about your boost because with a 6.0 and the 2.9 there is no freaking way the stock in tank by itself will support that. Right around 4 to 5 psi your fuel pressure should slowly die away if you have a bad pump. Heck if the inline is bad, you see it die quicker because now it becomes a restriction in your system.

Don't forget to tell magnacharger about the fpr. Some many problems are solved with the fpr it is just not even funny. So they should suspect that right away.

 

so I'm stumped...

new pump from Magnuson and the same issues are occurring. Leans out really easy as you get into it and if you stomp on the gas it will just backfire. Swapped the fpr again to the other one I have and no difference.

I figured it must be the relay or wiring, so i swapped relays and checked them everything looks good. I checked voltage at the pump, and even metered it will driving when it starts to lean out and there is no voltage drop at the pump...every time i stop, or don't have exhaust noise i hear the damn Walbro whining, so its not like its intermittent.

what the heck am i missing here, there is no chance its a bad pump again..or is it lol?

The fuel trims are all off again and going positive with the new inline installed, where as with just the stock pump it seemed pretty close to 0 all the time.

Could my stock in-tank somehow be bad, and cause it to look like its the inline pump? The truck runs great with just the in tank pump, without the inline, but obviously i cant get into it too hard without it starting to lean out....but still with the inline and in tank together its worse! WTF???

Any insight???

 

Have you checked for voltage drop at the stock intank pump? Have you done a hot wire kit to the stock pump? Just a thought. Hate for this to be something you have to keep throwing parts at it to fix one problem.

 

Haven't checked voltage drop at the in-tank pump. The weird thing is that it flows much better without the inline and just the stock pump. Do you think with both pumps in there its pulling power from the in-tank, even though all i am using is the stock pump signal to fire a relay totally isolating the walbro and stock pump?

What is a hot wire kit?

Today I swapped grounds for the in-line pump relay, as well as the pump ground and also changed where it pulls power from for the pump without a change at all.