2000 Sonoma Bogging

Hello I just bought this truck it has the 4.3 vin W bogging issue.
Both cat's have been replaced but it still has the issue[won't rev over 3 grand] when cold after it has warmed up the guy told me it's not as bad and will rev to over 3 grand.
So far they have taken it to a chevy dealer and 2 different shop's every one is baffled. NO codes and sensors and fuel pressures are in range.:banghead:

Hmmm. The usual culprits for bogging down are Cat Converter and stuck EGR. The EGR would throw a code though ... Cat would also probably throw some sort of code. It would also glow red color if it were clogged.

is everything mechanically sound with the accelerator pedal in the cab and throttle cable linkage under the hood? cleaned the throttle body butterfly lately? got a good air filter in there?

is the tach on the dash good? do you have a remote tach to verify things?





Hello I just bought this truck it has the 4.3 vin W bogging issue.
Both cat's have been replaced but it still has the issue[won't rev over 3 grand] when cold after it has warmed up the guy told me it's not as bad and will rev to over 3 grand.
So far they have taken it to a chevy dealer and 2 different shop's every one is baffled. NO codes and sensors and fuel pressures are in range.:banghead:

Both cat's were just replaced.At first they only changed the rear one then the Chevy dealer told them to change the pre CAT too.
They had it on the scanner everything is working like it's supposed too,the TPS O2 AND Map senors are all reading together when you accelerate
They even had the local CHEVY dealer check it and they couldn't figure it out, so now some local garage has it.
They said when it is cold it has no power but it clear's up when warm.
Air filter is new.
Thanx..

Sometimes it takes more than code reading.
Why was cats replaced?
How many miles on it?
What is the basic tune up history?
Any add on stuff on it?
Programers or chips or cold air intakes?
Is fuel trim going rich or lean?

A good factory trained tech or a good repair shop that knows what they are doing should be able to figure it out.

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.


Tips on finding a good repair shop.
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.

Run a basic on the road fuel pressure check and give us a vacuum reading at idel and at 2K RPM.
Post back vacuum reading and fuel mpressure readings.
MT

Thanks MT
That is the problem i bought the truck from a used car dealer and he is the one sending it around to get it fixed.
I paid for the truck i just don't have it yet[sounds crazy huh].
It has 100,000 on it.
I've been hanging around his shop in the morning[i work night's] and going to the auction to pickup car's with them,seem like good people.
I will probably give them till friday to fix it,and if they don't i will take it like it is and fix it myself.
After reading 100's of post's here i think it is the regulator,CFI,or nut kit.
Thanx for the reply's and i will post back when i find something out.

It does not have a nut kit.
That was on the older ones.
But a fuel pressure check on the road would tell you if fuel presure is good.
Also a vacuum test would help.
Good luck
MT

MT just a little feedback I picked up the truck friday they said it still ran funny when cold.
I drove it home and it ran good had plenty of power and all,put about 50 mi. on it and it started running bad [would not rev over 3 grand under load and sputtered a little].
So looking around it appeared to have original wire's and cap,so i gave it a good tune-up[AC plugs,Autolite wires and BWD cap and rotor]plug's well worn to .70 thou.

Running like a champ so far lotsa power .Hope it stay's that way.

In the proicess of soaking fuel line fitting to get filter off.


Thank's MT I have read numerous post's of your's and you are a factory shop manual in human form.Not trying to blow smoke you know where.:smokin:

MT just a little feedback I picked up the truck friday they said it still ran funny when cold.
I drove it home and it ran good had plenty of power and all,put about 50 mi. on it and it started running bad [would not rev over 3 grand under load and sputtered a little].
So looking around it appeared to have original wire's and cap,so i gave it a good tune-up[AC plugs,Autolite wires and BWD cap and rotor]plug's well worn to .70 thou.

Running like a champ so far lotsa power .Hope it stay's that way.

In the proicess of soaking fuel line fitting to get filter off.


Thank's MT I have read numerous post's of your's and you are a factory shop manual in human form.Not trying to blow smoke you know where.:smokin:

You are welcome and thanks for posting back how it went.
Yes the basic are the thing to start with.
Fuel filters can be a pain sometimes.
Good brake line wrench helps.
If all else fails you can crack/split the nut fitting on the old filter to get it off better.
Good Luck
MT

Well so much for that she started bogging again today.
fuel pressure is 60 lbs KOEO
holds to 55 for only three minutes at best.
with the engine idleing it holds around 50

still have to find my vacumn gauge and change the fuel filter.

Fuel pressure is to low.
You need 60/66.
If filter is not plugged the fuel pump or fuel pressure regulator is bad.


The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.
MT

MT another update,I changed the fuel filter this morning,i could not blow thru it.

As for the pressure reading the gauge i bought is not accurate,because man this truck run's like bear now.

I am taking that gauge back to get another one,really surprised me it was made in the U.S.A.
Gonna cross my finger's and hope that it keep's running like that.
It seem's that all the shop's even the dealer overlooked the obvious.
Thanx.

MT another update,I changed the fuel filter this morning,i could not blow thru it.

As for the pressure reading the gauge i bought is not accurate,because man this truck run's like bear now.

I am taking that gauge back to get another one,really surprised me it was made in the U.S.A.
Gonna cross my finger's and hope that it keep's running like that.
It seem's that all the shop's even the dealer overlooked the obvious.
Thanx.

You are welcome and.
Thanks for posting back how it went.
Glad you found the trouble.
Some of the Problem is.
Some mechanics are just lost if they can not get a code.
A good tech/mechanic always go over the basics first.
With fuel and air filter first on list and fuel pressure not far behind.
A pluged filter should show up on fyuel pressure gauge and fuel trims on a scanner reading.
Did you recheck your fuel pressure readings after filter replaced?
Good Luck
MT