5.3 woes

[mooseknuckles]

Hi. I'm having some issues with the 5.3 in my '63 gmc. It runs fine in the garage or parked, but under load it seems like it's not getting enough fuel. doesn't throw any codes...it chugs and bucks, struggling to get up to highway speed....forget about passing! Im running a walbro 392 in-line pump, wix vette filter/reg, -6 fuel line from tank to fuel rails. the same setup as my 6.0, I even swapped pumps out of my 6.0l to make sure.. it also has longtube headers, a cold air intake, and an edelbrock pro flo intake, now I did use the stock 5.3 injectors and got them to fit the pro flo intake and billet rails. is it possible that I need bigger injectors? I don't know what else to check. thanks.

[TwinsSpeedShop]

I researched those intakes one time wanting something different looking on this build, and found that this was a common problem. Low end bucking is an issue but ultimately you need some to scan it and see if it's lean when it's acting up. If so, injectors for sure. Good luck and keep us posted!

By the way, that engine looks so TITS

[BR3W CITY]

Are you getting fuel pressure and maintaining it under load?

Is this a MAF or SD tune, and who/how was it tuned?

IIRC your setup doesn't have any wild internal mods or a max effort cam or anything, so stock injectors should be able to run the engine alright, at least under light load if anything. You may very well be at high injector duty cycle, but it shouldn't prevent the engine from running under its own power.

Do you have HPT? Can you send my a log?

[mooseknuckles]

Originally Posted by BR3W CITY

Are you getting fuel pressure and maintaining it under load?

Is this a MAF or SD tune, and who/how was it tuned?

IIRC your setup doesn't have any wild internal mods or a max effort cam or anything, so stock injectors should be able to run the engine alright, at least under light load if anything. You may very well be at high injector duty cycle, but it shouldn't prevent the engine from running under its own power.

Do you have HPT? Can you send my a log?

it's MAF, PSI Conversions harness and tune, stock junkyard motor. I guess my next step is to check fuel pressure...

[Heavymetl]

Originally Posted by mooseknuckles

it's MAF, PSI Conversions harness and tune, stock junkyard motor. I guess my next step is to check fuel pressure...

I've never been much of a fan of mail order tunes, they'll "get it running" but that's usually about it. PSI does a nice job, but I did tune a buddy's 5.3 swap that ran terrible from the start. Turns out PSI had used Flex Fuel injector data as opposed to the correct non-Flex fuel injectors installed in the vehicle. The result was lean bank 1/2 codes and extremely lean WOT performance.

If everything checks out mechanically, a real tune may be the next step.

[mooseknuckles]

Originally Posted by Heavymetl

I've never been much of a fan of mail order tunes, they'll "get it running" but that's usually about it. PSI does a nice job, but I did tune a buddy's 5.3 swap that ran terrible from the start. Turns out PSI had used Flex Fuel injector data as opposed to the correct non-Flex fuel injectors installed in the vehicle. The result was lean bank 1/2 codes and extremely lean WOT performance.

If everything checks out mechanically, a real tune may be the next step.

that sounds like the PSI that I know....

[TooTall]

start with the fuel pressure first. It needs to be at 58 psi at the rails

Check the spark plugs. Are they oily wet or dry or smell like fuel

Junk yard injectors or newer ones?
easiest way to check is to pull the injectors out of the manifold, and either watch them fire while cranking or suspend them over a paper towel and check the spray pattern.

[mooseknuckles]

Originally Posted by TooTall

start with the fuel pressure first. It needs to be at 58 psi at the rails

Check the spark plugs. Are they oily wet or dry or smell like fuel

Junk yard injectors or newer ones?
easiest way to check is to pull the injectors out of the manifold, and either watch them fire while cranking or suspend them over a paper towel and check the spray pattern.

Plugs were dry and light brown. I did have 2 cold cylinders when I first fired it up, so I swapped out the two dead injectors for two out of another 6.0...ordered a new fuel pressure guage, and a new filter/reg , so I'll check the pressure tomorrow....

[mooseknuckles]

Still buckin' like a mule...checked fuel pressure today 58 psi with key on, running its 70+, down the highway and on the gas it drops to 68 psi.... throwing po327 and po332 knock sensor codes now. ...witf?

[TooTall]

Originally Posted by mooseknuckles

Still buckin' like a mule...checked fuel pressure today 58 psi with key on, running its 70+, down the highway and on the gas it drops to 68 psi.... throwing po327 and po332 knock sensor codes now. ...witf?

you're hardness is either unplugged, or both knock sensors have corosion in the connector and or sensor.

They're known for getting water intrusion. Replacements are pretty cheap from Rockauto

[mooseknuckles]

They were a little rusty in there..if they're cheap enough I'll replace them and see what that does...

[hugger6933]

If you can find a buddy that has a motor [or like me 5or 6] for core, you can take the knock sensor harness and unplug what you have then screw the newer sensors into the back of the heads. Then clear the codes that will tell you if indeed the knock sensors are bad. I would say 1 out of 20 to 25 in my area have those codes and also has the gas fill problem.[field truck in dirt,] then they clean them with steam cleaners causing water intrusion in the valley

[mooseknuckles]

replaced both knock sensors, didn't make a difference except no codes now, still bucking...kinda reminds me of the vss issue I had with my 6.0/4l80... knowing PSI they probably have something pinned wrong again.