Stumbles/hesitates while accelerating Vortec

[Josh104626]

I have a 97’ k1500 with a 5.7. I’ve had a problem with my truck accelerating from a stop to 10-20 mph then it goes just fine. Any help would be appreciated.

 

[HotWheelsBurban]

When was the last time you replaced the throttle position sensor? If it's the original one, by now it's probably about done. I just replaced the one on my '97 crew cab 5.7 Vortec a couple of weeks ago. My issue was at idle but if this sensor is going bad, it will affect the throttle response.

 

[Komet]

Plug a scanner in, look at your data. Check fuel pressure.

 

[Schurkey]

Plug a scanner in, look at your data. Check fuel pressure.

Took the words right out of my mouth. Thank you.

How old are the usual "tune-up" items? Cap, rotor, plug wires, spark plugs, fuel filter, air filter? When was the last time you verified the spark advance, PCV, and EGR operation? Charcoal canister?

 

[L31MaxExpress]

Mine always had a noticeable egr induced stumble from day one. GM commands the EGR valve full open at about 3 mph on a stock vortec and the hesitation is easily noticed. Drive one without EGR sometime if you are a doubter, it is night and day different. Took me driving a Mexican non-egr L31 to realize it was the way GM intended it to run. The EGR literally eats about 30-40 ft/lbs of torque just off-idle when you are trying to accelerate from a stop against the factorys lame excuse for gearing and tight torque converter.

 

[drifterwanb666]

so im having the same issue and its drivin me nuts, just fixed a vacuum leak that i been chasin for weeks. (valve cover bolts werent sealing, pcv was pulling vacuum thru the washers) just did delco iridium plugs and replaced my cap and rotor a few weeks ago (2 to 3) with delco parts. wires are maybe four or five months old, EGR os blocked off cause im runnung a set of shorty headers, my EVAP system is ok. idk what else to look ar any ideas? ive been on this for six months and im at a loss.

 

[Komet]

so im having the same issue and its drivin me nuts, just fixed a vacuum leak that i been chasin for weeks. (valve cover bolts werent sealing, pcv was pulling vacuum thru the washers) just did delco iridium plugs and replaced my cap and rotor a few weeks ago (2 to 3) with delco parts. wires are maybe four or five months old, EGR os blocked off cause im runnung a set of shorty headers, my EVAP system is ok. idk what else to look ar any ideas? ive been on this for six months and im at a loss.

Normally I'd say something like:

Plug a scanner in, look at your data. Check fuel pressure.

But your EGR being blocked off is ruining your tune. You need to either hook up the EGR, or tune it out.

 

[drifterwanb666]

Normally I'd say something like:

But your EGR being blocked off is ruining your tune. You need to either hook up the EGR, or tune it out.

id try and hook it back up, with 35" tires and 3.42 gears id like fuel economy but i cant figure out how. i know fuel pressure and filter are clean, pumps not even a year old yet and i did filter with it.

 

[L31MaxExpress]

EGR is disabled with the valve unplugged. With error codes for the unplugged valve, the PCM will not enable fueling/spark correction used in conjunction with a functioning EGR.

I unplugged my EGR diagnosing a hesitation I felt years ago. The hesitation I was feeling was ironically from a properly functioning EGR system. Vortecs use very aggressive EGR dilution off-idle under high load and it results in a perceptible stutter when you drive one back to back with earlier well tuned small blocks.

 

[Schurkey]

just fixed a vacuum leak that i been chasin for weeks. (valve cover bolts werent sealing, pcv was pulling vacuum thru the washers)

How is this possible? The crankcase is not intended to be sealed, there's a huge open hose drawing fresh air into the crankcase. There'd be no vacuum to pull air through the valve cover bolts/washers.