So after finally getting figuring out my pre-ignition problem(knocking sound) a wiring problem. I'm now having another problem i'm losing fuel pressure under WOT. I cant even launch it hard because the FP goes to around 25-30psi once under WOT and it fall on its face. But crusing around, it rides great. The fuel pump is a new Walbo 255, new filter and regulator. I have done a few searches but every thread i found didnt say what there problem was other than things i have already replaced. Any suggestions guys?

 

Clogged fuel filter? Bad ground on the pump? Bad ( original ) wires? Is there some way you can check voltage at the pump at WOT?

 

All of this is a good place to start! I had a clogged filter on my car and it was only a year old

 

factory fuel pump wiring, especially with age, leaves much to be desired. long run of small gauge wire can cause a decent voltage drop by the time it gets to the pump. on a couple of my cars, I grabbed a hot wire kit from Caspers that added bigger wiring and relay, but it doesn't look like they make one for the 3rd gens.

but as others mentioned, check all power connections, wiring, filter, etc.

 

Well i already replaced everything in the fuel system. Maybe theres i need a new tank and wiring?

 

i used one of these harnesses. it plugs right in. the new harness carries the load with the original wiring just activating the relay.

http://www.racetronix.biz/itemdesc.a...WH-005&eq=&Tp=

 

very nice find, I knew I wasn't looking hard enough. Tagging for a later time when I have money....

 

i used one of these harnesses. it plugs right in. the new harness carries the load with the original wiring just activating the relay.

http://www.racetronix.biz/itemdesc.a...WH-005&eq=&Tp=
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Thanks man, Well be ordering that kit pretty soon.

 

Well looks like i will be dropping my tank again to see whats going on? I used a Digital volt meter and took a crusie down the road. 13.11 and when i floor it 13.35-13.5. But fuel pressure still drops like crazy from 55-60psi to below 20 psi.

 

What regulator are you using?

 

The stock regulator.(new about a week old maybe two)

 

I had this once and luckily I made an acces panel to remove the pump easily and found that the pickup tube wasnt fully on the pump and created the exact same issues you are having.and sometimes the rubber pickup tube isnt the right type of hose to be submersed in fuel and begins to breakdown.just giving you ideas of where to look.

car drove fine at idle and cruise but hammer down and it just said no lol.only other things id suggest to check just for good measure are the injectors.could be sticking/clogged or stuck open but you would notice it running quite rich and poorly.

 

Well i went ahead and took the tank down. Took me about two hours, but the brand new sending unit had this junk all over it and the sock as well. So I'm betting that new filter isnt new any more. So I guess cleaning my or getting a new one is what is in store.

 

wow thats pretty gummed up :O lol

 

Do you guys think the pump is ok? Or should i just change that a well to be safe?

 

While it was down, I personally would change and go with even a bigger pump JIC future plans change.

 

I don't know what that means, but it appears your problem is inside the tank.

 

im assuming the corvette filter/regulator is what your using for the swap?

 

Negative, using the thirdgen filter and the 5.3 regulator thats on the fuel rail. I'm using the truck intake, fuel rail, and 8.1L injectiors.

 

what PSI are 8.1 injectors?

 

This may be a dumb question but how is your fuel system plumbed.I thought for lsx swaps you would need the corvette filter to regulate the psi to the proper rail pressure if the rail is a non return style.The regulator on the rail itself does not lower the fuel pumps 255lph rating?

Is it possible that he is running the intank pump all out and the feed line is going directly to the rail and may have blown the rail regulator?Im shooting ideas out cause I dont know if the 5.3 is any different than my ls1 swap.

 

All the stock lines for the third gen are the same. The intake had a feed and return already on it. So all i did was connect them to the thirdgen lines. And upgrade the fuel pump to a Walbro 255. The regulator on the fuel rail is a new replacement. I not sure what the max psi of a walbro 255 unit is, but I know that with key on engine I have 60 psi @ fuel rail and idle is the same. And with no load on the tires is also 60psi. But as soon it on the road it drops.

 

if he is running the truck intake more than likely it has a feed and a return on it. that way the in rail regulator will run it just fine.

 

From what i read the 8.1 trucks run at 50 psi. Thats at least what the stock regulator is. So what is great brand 340 pump or should another 255 be enough?

 

I'm having the same issues as mentioned. What came of it? What was the outcome? The fix? Do I need to away with the corvette regulator?

 

It ended up being a bad fuel pump, I got a free replacement because I had just brought it and it was faulty. That was the issue of the fuel pressure dropping.

 

I am having an issue which sounds like your preignition knocking problem, do you remember what was causing that?

sorry to bring it back from the dead again.

 

I hope you made sure the tank was clean, after seeing that pump and sock I would definitely flush it well.