Vortec 5.7 stumbles and backfires without giving and check engine codes

[LilWee247]

Also this has no emissions. No egr or rear O2. Plus they are tuned out of the computer.

 

[L31MaxExpress]

Also this cap and rotor are only 2 yrs old with about 5000 miles worth of driving.

If its a cheap parts store unit or a crappy Delco piece, I wouldn't rule it out as being bad. In the 24 years we have had my 97, nothing but problems when I tried Delco ignition parts.

 

[L31MaxExpress]

Also this has no emissions. No egr or rear O2. Plus they are tuned out of the computer.

So should be able to rule out a plugged cat or bad egr.

Does the engine make any extra mechanical noise on the upper end? Like a collapsed lifter, flat lobe, broken rocker stud, broken spring?

 

[stutaeng]

Best I can tell, trims look fine

...like less than 10% on both LTFT and STFT for both banks...at various RPMs, and under driving conditions?

 

[LilWee247]

I don't hear or notice any different noises. Just runs like crap with some backfires and loss of power.

 

[jaxcob]

I know you said your fuel pressure was fine, just wanted to chime in that the symptoms sound like they're mimicking the ones i had when my fuel pressure regulator went out. I didn't ever get the opportunity to test the pressure but after a new maf, plugs, wires, temp sender, I dug back into the intake and swapped the regulator and that fixed it.

 

[LilWee247]

So with the fuel pressure, I only checked at the valve before the intake. Could the regulator be dropping pressure after that point as to affect the injection?

 

[L31MaxExpress]

So with the fuel pressure, I only checked at the valve before the intake. Could the regulator be dropping pressure after that point as to affect the injection?

No, but was the engine idling or under load when you tested the pressure?

 

[LilWee247]

I did both while having the gauge on the windshield so I could see changes. That all looked fine to me.

 

[L31MaxExpress]

What is fine? Poppets need 66 psi under load and the MPFI spider needs 58.