48 psi fuel pressure at idle

Lsxtrucker · February 12, 2020

Just got done testing for failing fuel pump. I'm getting between 48 and 50 lbs at the rail on my 4.8L, is this within normal parameters?

davester · February 13, 2020

For '04, the 4.8, 5.3 and 6.0 all should be from 55-62 psi. Yours should be the same. So, yours is low.

Don't just check fuel pressure with the engine off. Also check with the engine running, and with it sped up. For example, when I bought my truck, eventually I figured out that while the fuel pump could get up to just over 55 psi at idle, once the engine went faster and needed more fuel, the fuel pressure would drop like a stone to between 10-15 psi and stay there. It's ok for the pressure to briefly drop as the engine speeds up, but it should quickly return to full pressure once the rpm becomes constant again.

Lsxtrucker · February 13, 2020

I'll do as you instructed this morning and return here with the results. Thanks for the advice.

Lsxtrucker · February 13, 2020

I'm getting 50 PSI this morning at idle and at 2k RPM it drops 4-5 pounds to 45 then quickly returns to 50-52 Lbs. At 3k RPM it does the same, same again at 3,500 RPM still hovers around 50 pounds. Back to idle it's at 50 PSI steady.

riverbanks · February 13, 2020

You didn't mention in this thread,is the po300 gone and the sputtering?

Lsxtrucker · February 13, 2020

5 minutes ago, riverbanks said:

You didn't mention in this thread,is the po300 gone and the sputtering?

Yes, the P0300 and flashing CEL hasn't been back for 100 or so miles. I was thinking about having the back pressure tested before I do the exhaust system I was planning on this month. I'd hate to spend the money having it welded in only to have the cats be the culprit and have them do the work twice. I'm glad the CEL is gone, at least for now, though that's for sure. Any more ideas? I am noticing a spitting noise from one or two injectors on the passenger side.

It's Tim · February 13, 2020

Lsxtrucker · February 13, 2020

Much obliged

Chevyevan · February 16, 2020

i have 2 2002 5.3s they both idle at 45-50psi and will spike up under hard throttle. Seems normal. What was the culprit to the p0300?

Lsxtrucker · February 16, 2020

2 hours ago, Chevyevan said:

i have 2 2002 5.3s they both idle at 45-50psi and will spike up under hard throttle. Seems normal. What was the culprit to the p0300?

Faulty spark plugs wire

Chevyevan · February 16, 2020

22 minutes ago, Lsxtrucker said:

Faulty spark plugs wire

Did yours do it all the time or only at a certain rpm? I ask because I'm getting a p0300 and pinging at about 3500rpm. Im a little stumped on it. Runs perfect until 3500rpm

Lsxtrucker · February 16, 2020

3 minutes ago, Chevyevan said:

Did yours do it all the time or only at a certain rpm? I ask because I'm getting a p0300 and pinging at about 3500rpm. Im a little stumped on it. Runs perfect until 3500rpm

No mine didn't do it all the time. It did it when it felt like doing it. That's what stumped me. I just hope it won't come back. If you haven't changed the plugs and wires lately I'd probably try that first. Plus it wouldn't hurt to at least check out the connections and make sure they're secure. I did the plugs and wires before I looked at the coils. Anyways have you any loss of power? Maybe you collapsed/bad catalytic converters? I'm testing mine tomorrow.

Chevyevan · February 16, 2020

21 minutes ago, Lsxtrucker said:

No mine didn't do it all the time. It did it when it felt like doing it. That's what stumped me. I just hope it won't come back. If you haven't changed the plugs and wires lately I'd probably try that first. Plus it wouldn't hurt to at least check out the connections and make sure they're secure. I did the plugs and wires before I looked at the coils. Anyways have you any loss of power? Maybe you collapsed/bad catalytic converters? I'm testing mine tomorrow.

I did the plugs a few days ago, I'll do the wires soon as well. Im thinking a cat went bad, I'll probably end up taking them off to see whats going on. The power seems good up until 3500. Thanks!

Lsxtrucker · February 17, 2020

2 hours ago, Chevyevan said:

I did the plugs a few days ago, I'll do the wires soon as well. Im thinking a cat went bad, I'll probably end up taking them off to see whats going on. The power seems good up until 3500. Thanks!

Mine was acting funny somewhere around that rpm range as well. I'm convinced the problem isn't solved. I'm looking at my cats too. That's why I ordered a infrared temp gun from Amazon for around $10 to test my pre/post cat temps at operating temperature. It was cheaper than getting the vac Gauge and fabricating it to attach to the 02 port because I don't have an old 02 sensor to cut and I was too cheap to buy an backpressure tester ($40) lol..

If this solves the issue I'll let you know, heck I'll update the thread anyways. Good luck on your quest too man. Regardless of the headaches I love these trucks. But honestly that new GM crate engine 6.0/450HP 24x for $5k and change is looking sweeter everyday. If only I could get my 3rd gen Camaro sold and get it. Talk with ya soon brother.

Edited February 17, 2020 by Lsxtrucker

Chevyevan · February 17, 2020

23 minutes ago, Lsxtrucker said:

Mine was acting funny somewhere around that rpm range as well. I'm convinced the problem isn't solved. I'm looking at my cats too. That's why I ordered a infrared temp gun from Amazon for around $10 to test my pre/post cat temps at operating temperature. It was cheaper than getting the vac Gauge and fabricating it to attach to the 02 port because I don't have an old 02 sensor to cut and I was too cheap to buy an backpressure tester ($40) lol..

If this solves the issue I'll let you know, heck I'll update the thread anyways. Good luck on your quest too man. Regardless of the headaches I love these trucks. But honestly that new GM crate engine 6.0/450HP 24x for $5k and change is looking sweeter everyday. If only I could get my 3rd gen Camaro sold and get it. Talk with ya soon brother.

Im starting to think one of the cats went bad as well. 99-07 was the best generation haha. My family has owned 5 or 6 of these, one with 580k original engine still being used to this day. And We own 2 now with 280k. Theyre tanks. A crate motor would solve all of my problems! Looking forward to what you figure out!