243

Engine is an L59 5.3, test run with a 97 Blazer 4.3 in tank pump that is rated 85-105 psi and 45-55 gph, running battery voltage is 14.1.

Pressures running at idle:

52 regulator vacuum disconnected
70 regulator vacuum disconnected - return line closed

42 regulator vacuum connected
75 regulator vacuum connected - return line closed

If the pump can provide 70-75 psi, is the regulator jacked if it only makes 42 psi?

ls1nova71

iTrader: (4)

I believe flex fuel engines run a lower pressure but didnt think it's that low?

243

I found this searching for flex pressure specs last night, it's a post from 74modified.

"I think it doesn’t matter as long as you get the correct pressure. Here is a little info on truck fuel systems. I like the return, most people don’t realize that returnless was installed to comply with emissions standards, not performance. 1999-2003 4.8, 5.3, 6.0 all had a fuel rail with 3/8" supply line and a 5/16" return line. The fuel pressure regulator is on the fuel rail, and has a vacuum line to the intake manifold. In 2004, All engines went to a single 3/8" supply line, with no return (returnless) except 5.3L L59 Flex Fuel vehicles. For 2004, Flex fuel engines KEPT the return line, BUT used a fuel pressure regulator with a lower pressure ratting.

2005 5.3L L59 Flex Fuel engines switched to a single 3/8" supply with NO RETURN line in 2005. Non flex fuel engines, fuel pressure spec is 55 to 62 psi with vacuum line disconnected, fuel pump running. 5.3L Flex Fuel engine 2004 and back, 48-54 psi with vacuum line disconnected, fuel pump running. 2005+ with returnless fuel rail all shared same fuel pressure spec, 55-62 psi. There is no vacuum reference on these, so fuel pressure should remain constant under all operating conditions. The computer is programmed differently for fuel flow rate depending on type of fuel rail. This is important to know when having a PCM programmed."

243

Here is a post from the Tahoe/Yukon forum that quotes the GM spec, the running pressure is the same as mine at 42 psi.

"Can't seem to find this spec anywhere GM's service manuel online only shows what the pressure should be with the key on and engine off "VIN Z Ethanol: 335–375 kPa (48–54 psi) " no where does it tell what a engine at idle should be producing. Here is what I currently get:

Key on pressure engine off 52 psi
Key off engine off 48 psi.
Engine running at idle 42psi
Engine acceleration jumps to 45 for a second and drops back to 42.

2004 Suburban 5.3L Z engine"

243

Found a GM Reference G083 in PDF that documents test procedures and pressures for many LS, appear to be all Gen III.

I was surprised to see 48-54 KOEO and 38-51 at idle for 02-04 5.3 Flex, Vin Z

Attached for convenience

CattleAc

iTrader: (7)

That's excellent reference material.

I own several of each...flex fuel-non flex fuel. The "flex fuel" regulators all have the vacuum port coming out of the top of the regulator...Like this


The "non Flex fuel" all look like this...

jakebenson6669

Ok, so I realize this topic is a few years old now, and I don't yet have a fuel pressure test set to check my numbers, but I have a question. I have a 2003 suburban 5.3 flex fuel 4wd. 220k when purchased and within 20k, replaced the fuel pump, filter, and regulator. Regulator was same as removed, which according to you, is for a non flex. My vin decodes as a flex, and I was second owner behind the owner of the original chevrolet dealership. Was the dealers personal vehicle. Anyway, I never used anything but 87 pump gas, and it ran excellent for 12 more years and another 110k. 350k on clock now. I may have messed up trying to tune it up. It's now got its 3rd starter, 3rd 4l60e trans, 4th fuel pump, new filter every time. New water pump, fan clutch, lower temp thermostat, and a 2 inch narrower radiator. Temp never reads above 165-170, and always had a code for 02 censors, so when I changed the plugs and wires and added a k and n intake, I developed a miss. Changed fuel filter, then pump after finding it to be too weak to hear. Made car worse, now it won't climb a mountain. Punched the cats, no smell mind you, now it climbs and hauls down highway at 80 better than ever, but still has a random multiple misfire that kills its power at anything under 2k rpm. And has to turn over a few seconds before firing, like the regulator is bad again. I plan on replacing, but question is......when still running regular gas, does the non flex regulator affect the way the vehicle runs when it is definitely a flex fuel engine? It never seemed to affect it before, but back when I first got it, I could get 28mpg on highway, same as my cobalt. Now im at about 12-15 ish, I'm sure the intake and still unresponsive downstream 02 sensor have alot to do with excess fuel consumption. But could it be so rich that at lower rpm it is sort of flooding tge engine? And maybe even more so if the regulator is bad or pushing more pressure. Heck, the 02 sensor might clear most of the miss up after a few drives. Back to the main reason I'm here though again. The regulator. Autozone most definately gave me a non flex regulator, when I know that telling them that it is a flex should be said before telling them the engine size so that they don't get click crazy. Would the regulator being wrong make a difference when still using regular gas? And could these couple things accumulate to a condition so rich that it barely pulls a small hill from a standstill, but once 2000 rpm is reached, no miss, lots of response and torque, and will then climb a 15% incline at 80 with throttle only halfway to floor? Oh, another note, I've been talking about it for a few months now, but haven't gotten the parts yet because I thought I had other issues. Timing chain is original, and even though I have no codes at all related to positioning sensors, maybe it's stretched to the perfect point where there's no code, but ignition is slightly off just enough that when combined with all new fuel and spark components, all 8 injectors and coils also inspected and or cleaned, it all adds up to a very sluggish ride until 2000 rpm, where it will then start to put the power down and pull better than when I bought it 130k miles ago. I keep thinking, maybe it's finally time to say goodbye, I have a 2011 suburban and 2007 escalade, as well as an acadia, monte carlo, and cobalt. But those sun's only seat 7, whereas blue, my 03, seats 9, and if I can get back to 28 mpg, or close, again, that's better what even the 4cyl clutch cobalt gets on an average day, with no check engine light and half the miles. At this point, it would be like getting rid of my kids or dog, I'd rather it fall apart around me than to give up before she's ready......I've had a spare engibe with only 180k for years, but I'm telling you, my 350k engine, with that 3rd transmission and k and n intake have so much left to give. Before this stuff, it was too heavy with 16 inch tires to even spin wheels in loose gravel. Now I have 17s, and before I changed the plugs and wires and everything went to ****, it would spin tire on dry blacktop, not smoke them, but you knew that one wheel was spinning anyway. Any and all input is appreciated. If it's not worth fixing, it'll first take alot of convincing, but my 2011 needs a radiator to get it road worthy again, and would you have ever guessed, it uses the same 2 different part numbered radiators as my 03. Not totally sure why there's a 2 inch difference in width between the part numbers, but blue went from the larger to the smaller and actually runs cooler because of it, and id be going from clutch fan to electric, so trying to force the shroud to fit a third vehicle, blue is it's 2nd, shouldn't be an issue this time around. Ok, I'm done, thanks to anyone that reads all this and throws me their theories and experiences.