04 Sierra surge

[SargeSlaughter]

Long story short, truck has a new fuel pump, maf, transmission. Holding the pedal steady at 2000 rpms it willnsurge up and down between 50 and 100 rpm. Not a lot but definitely noticeable. Does it in park, and while driving. Far more noticeable while driving uphill. Could the new fuel pump be bad or possibly something else?

 

04 Sierra 5.3l lm7 4x4 4l60e

[Jsdirt]

The sad reality of today is, new parts are always suspect. You could have a bad new pump, or a bad new MAF. Also could have an air leak through the intake gaskets.

 

Full throttle in a SAFE area (usually keeping it in 1st gear is good enough) should peg the o2s full rich (.7v or higher) with no switching. If they're switching or full lean, you're going to have to check fuel pressure while driving.

 

Usually a snap throttle test will show the problem right off - pressure should increase slightly on a snap - if it decreases, it sucks but you're going to have to do the job twice, thanks to 21st Century parts. Warranty the pump, and hopefully better luck with the next one.

 

If the o2s are rich, focus on the MAF.  Hopefully you still have the old one (if it functions correctly) to get a baseline grams per second at idle and full throttle, to compare with the new one. Set the scan tool on graphing view to watch these parameters. Any changes will show up great there.

[88m53453]

Had the same problem with an 03 Tahoe and an 05 Sierra. The Tahoe was worse , replaced the O2 sensors and plug wires. It's been years, but I believe the sensors were the fix. Also try, just for grins premium fuel 

[Jsdirt]

No need to run premium if it isn't knocking or pinging - you're throwing your money away if it isn't.

 

Only benefit would be if you live in a state (like NY) that does NOT put ethanol in premium fuel - then it's worth buying. Here in MA, we have no choice, and get ethanol in EVERYTHING at the pump.

[mjm-1957]

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Don't know where you got that information from but thats incorrect. NY has ethanol in high test also. On Long Island we can't by ethanol free gas either.