vortec with occasional stumble

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poloz28

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I have tried to pick through all the searches and nothing exactly matches my issue.

2000 CCSB vortec 350

I have an occasional rough stumble when accelerating like it is running out of fuel. no pattern as to when it happens. 9mph on average. I have 62 psi when the key is bumped on, it goes down to 45 psi at times but generally hovers around 50psi.

compression is 180 on all cylinders, i am getting good spark at all cylinders. new fuel filter


i have an Autel MX808 scanner. these are the readings that i am clueless about:

Knock sensor: CONSTANT 4.86 or 4.85 volts
knock sensor activity: usually 0
Camshaft position sensor retard: 7 degrees at 1000 rpm. (i think this should be zero)
Fuel tank pressure: 14.01 mmHg on a scale of -32 to 10

i am thinking my evap system is shot and not venting and that my distributor was not installed/relearned correct when it was installed a few years ago by previous owner......?
 

poloz28

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evap can purge ON
evap duty cycle 20
egr duty cycle 0
actual egr postion 0
desired egr position 0
egr sensor 0.8 volts out of 5v
 

ozawkieng

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My 2000 GMC Yukon Denali was doing the same thing; it would go then stall out especially at slow speed. It never set a code and never ever tried to set a code. Finally it just quit. I put a new fuel pump in and it is running just fine. The Yukon has about 180,00 miles on it.
 

run96k3500

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I had this happen before and I was a fuel pressure regulator. It tested fine but after replacing it, the issue went away. I’m having the issue again on a different truck and I’m putting a new one in soon.


Sent from my iPhone using Tapatalk
 

blackburb

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I have tried to pick through all the searches and nothing exactly matches my issue.

2000 CCSB vortec 350

I have an occasional rough stumble when accelerating like it is running out of fuel. no pattern as to when it happens. 9mph on average. I have 62 psi when the key is bumped on, it goes down to 45 psi at times but generally hovers around 50psi.

compression is 180 on all cylinders, i am getting good spark at all cylinders. new fuel filter


i have an Autel MX808 scanner. these are the readings that i am clueless about:

Knock sensor: CONSTANT 4.86 or 4.85 volts
knock sensor activity: usually 0
Camshaft position sensor retard: 7 degrees at 1000 rpm. (i think this should be zero)
Fuel tank pressure: 14.01 mmHg on a scale of -32 to 10

i am thinking my evap system is shot and not venting and that my distributor was not installed/relearned correct when it was installed a few years ago by previous owner......?


I think you have two issues. Fuel pressure dropping to 45psi may cause the rough stumble you described.

CMP retard should be 0* +-2*. 10* or more will throw a P1345 code. If you have over 100k Miles your distributor gear is likely worn and the distributor(cam position sensor) is not holding timing. You can adjust is back to zero(CMP correlation) but it will not usually hold the +-2* required by the cpu. You can pull the distributor to check the gear... make sure to follow the correct procedure. Check 1A autos YouTube channel for the vortec distributor replacement procedure. If the leading edge of the distributor gear is sharp the gear can be replaced. If the distributor body has cracks around the distributor cap screw holes you will need to replace the distributor.
 

wheelman

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I have tried to pick through all the searches and nothing exactly matches my issue.

2000 CCSB vortec 350

I have an occasional rough stumble when accelerating like it is running out of fuel. no pattern as to when it happens. 9mph on average. I have 62 psi when the key is bumped on, it goes down to 45 psi at times but generally hovers around 50psi.

compression is 180 on all cylinders, i am getting good spark at all cylinders. new fuel filter


i have an Autel MX808 scanner. these are the readings that i am clueless about:

Knock sensor: CONSTANT 4.86 or 4.85 volts
knock sensor activity: usually 0
Camshaft position sensor retard: 7 degrees at 1000 rpm. (i think this should be zero)
Fuel tank pressure: 14.01 mmHg on a scale of -32 to 10

i am thinking my evap system is shot and not venting and that my distributor was not installed/relearned correct when it was installed a few years ago by previous owner......?
Do not know what you got there but if it is TBI.take the throttle body off.check for bad base gasket.mind was bad.on my 305 tbi engine.1988.but on my 96 350 vortec.it was acting up I used spray and sprayed out the throttle body.and it quit acting up.if you have the spider fuel injection.system and you are losing pressure.now and then.it might make it act up.when Chevy started fuel injection and electronic over drive transmission,s.there vehicles went all to hell.and they would not stand behind their vehicles and have recalls they left us all hanging.like the ml60E transmission,s.my van is going on three.and I only have 145,000 I had the second one.gone through by a Chevy dealer transmission man.he installed.after market trans parts.not the GM crap.so far so good.gm would not help on it.at all.so my next car was a Ford. Mustang.2005.not one problem.but the defective air bags.they were replaced by ford.no charge.
 

poloz28

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i have a 2000 vortec. thanks for the replies. the stumble is even worse now. i replaced the fuel pump and it does pull alot stronger up top now (when it does run well). i just found old reciepts and there is alot of hx regarding stumbling. the distributor was replaced 50,000 miles ago. i am wondering if they replaced it correctly. if i get some time, i plan on removing it and checking everything out.
 

someotherguy

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Get that cam retard number to zero or near as possible, spec is +/- 2 degrees from zero, *while* holding RPM's to at least 1,000 for a solid reading. If you adjust it at idle that is not the correct procedure.

Richard
 

Christian Steffen

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i have a 2000 vortec. thanks for the replies. the stumble is even worse now. i replaced the fuel pump and it does pull alot stronger up top now (when it does run well). i just found old reciepts and there is alot of hx regarding stumbling. the distributor was replaced 50,000 miles ago. i am wondering if they replaced it correctly. if i get some time, i plan on removing it and checking everything out.

Also, have you looked at the condition of the distributor cap? a 50k mile cap could be bad. Can you log misfires?
 
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