Ok I have a 92 s10 5.3 flex fuel with a bad idle. Its dbw return style fuel rail powered by a walbro 255 fuel pump that was installed during the swap. I have about 40 psi at idle according to the Russel gauge I installed after the fuel filter. A buddy hooked up his EFIlive program to it and its saying the computer is asking for more fuel according to the o2 sensors for the fuel air mixture. I know my setup asks for 48-52 psi so how do I get a higher pressure required for it to run right? During load and normal driving it runs fine and revving it brought the pressure up to 50psi. It idles poorly and seldomly hesitates during a takeoff from a dead stop. Other than that she runs like a bat outta hell. Any suggestions?

 

what are you running for a regulator?

 

Not running a regulator. Was told the intake had one built in. The program they hooked it up to was able to richen or lean it out so I'm sure it has the regulator built into the intake. Where is it located on the intake?

 

the regulator will be on the fuel rail. not sure about flex fuel but you should be running close to 58psi on all ls motors i have seen and with an oe regulator that is where it should be given its the same. but 40 is low none the less and id hate to say this but i think you need to pull the pump and check the hose that connects from pump to pick up tube. i have seen a run of these hoses fail with the walboro pumps recently. i do not even use the hose they provide anymore. just replace with a piece of fuel injection hose and use good fuel injection clamps. as for adding fuel in the tune that has nothing to do with the regulator its a mechanical piece

 

What's the walbro 255 pump rated for? I only bought it cause it was recommended for it. I think I might have to pull the tank again anyways cause my sender is acting up. Does the regulator have a vacuum line running to it on the driver side? Is it a circular little fitting? Im almost to the point of buying an aeromotive a1000 if I can get this fueling problem fixed.

 

yeah the regulator is the circular one with the vacuum line on driver side. walboro is good for about 500 na hp. i would check that hose and make sure you are getting 12v ang ground to the pump. i think either pump is not running fully or you are losing pressure in the tank

 

Walbro makes a high and low pressure 255... sounds to me like you have the wrong pump with 40psi at idle. GM calls for 55-60psi for the motor to run properly.

 

I purchased the walbro gss342. Its the high pressure in tank pump. Im wondering if there's an. Obstruction in the tank. Like I said it runs perfect after takeoff and on the highway just won't idle right.

 

Ok good, next up is to check things out, what size fuel line, any obstructions or a bad regulator. Are you running a hotwire kit on it?

 

New lines. 3/8 fuel injection hose all the way to intake rail. 5/16 hose return. No hot wire kit. Basic oem wiring with stock relay. Pcm controlling relay.

 

The regulator is more what I'm leaning towards now cause that's about the only thing I havent checked out. I removed it and cleaned it but that's about it. I still think its the fuel pump cause I don't know why its only putting out 40psi at idle. The highest it jumps is 50psi but only when I rev it up.

 

Ok so after long hours of troubleshooting and triple quadruple verifying no obstruction in the fuel lines it came down to the inevitable. Tearing everything down and starting from scratch! Luckily for some reason I decided to remove the spark plug wires. Low and behold the number 3 cylinder wire was melted to the header and the number 7 had a slice from a sharp edge of the steering shaft that had worked its was into the rubber. Replaced all the wires and decided to remove all the spark plugs just for fun. Turns out the gap was incorrect as well. They all were sitting at .034 and AutoZone said its supposed to be at .040. Regapped and installed. Fired up the beast and she is purring beautifully! No misfires or sensor codes and everything is back to normal. Oddly enough the fuel pressure still seems a bit low only averaging about 42 psi at idle and 52 during revs. I'm not complaining though cause it runs and drives the way it should now.

 

Actually, being low on pressure means it is NOT running the way it COULD....

It is still fuel deprived and that means running lean. Which could cause you some problems. Something is still amiss in the fuel system, so I would check into upgrading the size of either the power wire to the pump, or a larger fuse if it has one in line.

 

Hey guys, hang on a minute.........

I just looked at napaonline.com and they actually show a regulator for BOTH 50 and 62 psi.... So some of these engines were actually set to run at the low pressures.

I looked that up on my 01 GMC yukon 5.3L specs on their website.

http://www.napaonline.com/Catalog/Re...0030%202030087

There is even a regulator that runs at 56.56 PSI..... WIERD!!!!!!!!!!!

On top of that, I looked up my friends 08 tahoe that is flex fuel and it does NOT show a regulator for that vehicle. It does show a pressure sensor connector.. but no regulator.

 

Well if its running lean how would I tell without the pcm showing any codes? Even the normal o2 sensor codes aren't showing up anymore. I'm wondering if the type of regulator I have on it is supposed to run low. I read somewhere it is supposed to lower fuel pressure at idle and raise it as demanded by the vacuum and sensor readings. Like I said I don't see anymore problems with my truck. Its running real good and even more responsive than before.

 

Well I typed in the vehicle that the engine came from and it shows it has the 50 psi regulator so I think I'm good on fuel pressure.

 

IF it shows one for the donor car at that pressure you should be fine.

Congrats on getting it figured out and back up and running. I am still in the build stages on mine so I have a bit of work left to do... I wish it was less, but unfortunately its not.

I am about to go back into the heat stroke zone and find the oem exhaust pieces that have the O2 sensors and get those swapped to my header collectors, than get them bolted to the headers..

 

Yea seems like it shows the donor vehicle had a 50psi regulator. What kind of headers are you running now on your setup? I bought the Sanderson ceramic shorty headers that were for the Ls swap setup and I've been running them since completion of the build with no problems. They come with collectors that have provisions for the o2 sensors. My only downfall to them is the clocking location of the o2 port. The drivers o2 points down and toward the engine making it easy to access. Didn't think about the location of the passenger port before I got the exhaust welded so it now points towards the top of the engine and tranny. Next time I have to replace them I will be cutting off my newly installed exhaust and repositioning the passenger side collector.

 

You can see the complete teardown/build-up of my project by clicking on the link in my signature.

I went with a set of Racing Innovations headers. They were just $212 or a hair more.

Not too bad a set of headers, but I pointed out a couple things that could have been done differently to improve the design. Would have made for an easier installation also. Drivers side had to have the steering shaft removed to get them in, passenger side was primarily just the plug wires and dipstick out of the way. But you do have to run 45 degree plug boots in two spots that I see so far. It is all pointed out in the build pages. I even got a video of mine running the lower pressure like yours for the fuel pump. I installed a fuel pressure gauge to my fuel rail. Now I also have a spot to tap in for the wet nitrous kit as well. Just as soon as I decide to drop $500 for one of the ZEX kits that has the EFI smart box. No switches to install except the power switch. It taps into the TPS wiring for its full throttle signal. Plus, the solenoids are enclosed in the box so its a cleaner installation.

 

I took a look at your build and it seems like you're on the right track for everything. I was able to use the stock shifter on my build but the problem is the shift lever throw. I don't have the lower gears but I have the basic prnd. If I adjust the other way around I would have 1-reverse and no park. No big deal for me since I'm not using it just for drag purposes. I didn't have to remove my steering shaft to install driver side header I just use a lot of patience lol. I'm a aircraft mechanic so I'm use to tight spaces and busted knuckles. I agree with a better design for the spark plug wire boot clearance. I have another s10 that I'm wanting to throw a 6.0 from a gto in it with a t56 if I can find a good combo for less than 2500. Its probably a longshot. That originally has the 2.8 and 5spd and a better body. If I do end up doing another swap to that truck ill definitely take a lot of pics for progress.