02 silverado 4.3 timming retards (sometimes) during hard acceleration

[silveradojosh]

hello every 1 new to the site i have been reading alot on here and decided to become a member. my problem doesnt happen all the time, but it does happen alot. the problem is that my timming
retards when hard accelerating from a dead stop, i have no codes showing nor pending i have seen many problems like this mostly with 98 to 99 blazers, i have a actron cp9180, vacuum test gauge and fuel pressure test gauge. i want someone with knowledge to lead me in the right direction thanx

[MT-2500]

Originally Posted by silveradojosh

hello every 1 new to the site i have been reading alot on here and decided to become a member. my problem doesnt happen all the time, but it does happen alot. the problem is that my timming
retards when hard accelerating from a dead stop, i have no codes showing nor pending i have seen many problems like this mostly with 98 to 99 blazers, i have a actron cp9180, vacuum test gauge and fuel pressure test gauge. i want someone with knowledge to lead me in the right direction thanx

How much is it retarding?
Or how much more when it does it?
Is it showing any knock sensor signals?
What does the engine do when it does it.
Any engine running problems?

[silveradojosh]

hey thanx for the fast reply the most retard i have seen today is -5 the most i recall seeing is -19, at idle i am getting +20 while going down the road i get +27 to +30.
not sure where or how to check for knock sensor signals.
the engine falls flat on its face butt i watched the timming and from the negatives it starts slowly going up in intervals of 5 every 1 or 2 seconds peaking out at about +15 to +20 the truck has 130 thousand miles would the 02's be going bad causing it to (slowly) come back to life?

[b1lk1]

I throw this response out alot, but my truck did something like yours is doing and cleaning my mass airflow sensor straightened it right up. It is free to do so I would give it a shot just to see if it is part of the problem. My truck would do this randomly and fall flat on its face if I hit the gas too hard at a start.

[silveradojosh]

Originally Posted by b1lk1

I throw this response out alot, but my truck did something like yours is doing and cleaning my mass airflow sensor straightened it right up. It is free to do so I would give it a shot just to see if it is part of the problem. My truck would do this randomly and fall flat on its face if I hit the gas too hard at a start.

hey thanx for the help
yes i have tried that a couple days ago i did notice that it only does it when there is high humidity should my motor tlose that much power because oh humidity dry days it runs awsome well if any has any sugestions let me know

[MT-2500]

Originally Posted by silveradojosh

hey thanx for the help
yes i have tried that a couple days ago i did notice that it only does it when there is high humidity should my motor tlose that much power because oh humidity dry days it runs awsome well if any has any sugestions let me know

As said MAF sensor will do that along with a lot of other engine sensors that feed information to the VCM.

I would find a engine running trained tech to read out computer and sensors.
And do not forget to check for proper fuel pressure.
Good Luck

[silveradojosh]

Originally Posted by MT-2500

As said MAF sensor will do that along with a lot of other engine sensors that feed information to the VCM.

I would find a engine running trained tech to read out computer and sensors.
And do not forget to check for proper fuel pressure.
Good Luck

i tested the vacuum and it held a steady 18 then snaping throttle to about 2500 rpms then let off it would drop to 0 then right back to 18 every thing seems to work exactly how the book says for a good sound engine then holding throttle at 2000 rpms it goes to 21 and holds soon as i let off it returns to 18 so i shouldnt have any vacuum leaks
i will check the fuel pressure today and let u know the results
as for the trained tech i guess the chevy dealer would do me best
thanx agian i will let you know the results asap

[MT-2500]

Originally Posted by silveradojosh

i tested the vacuum and it held a steady 18 then snaping throttle to about 2500 rpms then let off it would drop to 0 then right back to 18 every thing seems to work exactly how the book says for a good sound engine then holding throttle at 2000 rpms it goes to 21 and holds soon as i let off it returns to 18 so i shouldnt have any vacuum leaks
i will check the fuel pressure today and let u know the results
as for the trained tech i guess the chevy dealer would do me best
thanx agian i will let you know the results asap

Sometime dealer is best and sometimes not.
Not all dealers have have trained techs.
Or just let the grease monkey test it.

Check around Ask around
Word of mouth.
Family friends coworkers neighbors business people and delivery people.
Mailmen and parcel delivery people get around and notice a lot of stuff.
Even a good parts house knows what shops are good and not good.
Chamber of commerce and better business bureau and city hall.
If you find a good referral to a repair shop go look them over and talk to them.
Look for a clean looking busy place with nice people running it.
Ask a few questions and ask about their qualifications and training.
Not all places have trained tech/mechanics.
If they do not find a place that does.
Even all dealers do not have all trained techs/mechanics.

Tip on going to the dealer
Ask that only a factory certified gasoline engine performance specialist work on your car.
Not all dealerships are concerned with how repairs are dispatched, and not all dealership techs bother to take advantage of the training offered by factory (the vast majority of which is paid training). If the dealer is uncooperative, ask for your money back and call around for a dealer that will accommodate you.

[silveradojosh]

hey mt thanx for the help i got tired of messing with it, so i changed the mass airflow sensor and both pre cat 02 sensors and fixed the problem i have another thread i wanna start but i cannot find how to start 1 can u help me?

[MT-2500]

Originally Posted by silveradojosh

hey mt thanx for the help i got tired of messing with it, so i changed the mass airflow sensor and both pre cat 02 sensors and fixed the problem i have another thread i wanna start but i cannot find how to start 1 can u help me?

You are welcome and thanks for posting back how it went.

Look for the New Thread button upper left side top of forum.

http://www.automotiveforums.com/vbul...wthread&f=2072
Good Luck