AlphaCrow

Hi again

Sometimes my '00 blazer will idle rough and I notice the tachometer drops a few hundred. It will generally do that until I tap the gas or quit on its own if left alone for a bit. Does not always do it, but usually when cold start and idle or sometimes after running for awhile.

If I try to accelerate when it is idling rough (say from a red light), it lacks power and will not shift into the next gear, though the RPM's are reporting it's near 5000 rpm.

What does this sound like to you guys? Vacuum leak or spark plug or wire? I performed a tune-up a little over a year ago. I did not change the wires though, because of the cost at the time. Also did not change the PCV valve.

Thanks

MT-2500

What engine and mileage?
Any check engine lights?
Any codes?
Is the fuel pressure up to specs?
Any engine miss or misfires?

__________________
Remember proper testing gives us the answer to many problems.
MT

AlphaCrow

Which letter in the vin is the engine again? 4.3L, I'll figure out the VIN letter and get that.

Just turned 100,000 miles. No SES or codes at all. Usually when it's code, usually when idling. If I do try to accelerate when it is idling rough, I lack power. After a minute, it will lunge forward with normal power and runs fine.

Last problem I had with it was the MAF sensor being dirty and not reporting right. Cleaned and cleared codes.

I wonder if its the MAF again or possibly the O2 sensors.

Not sure how to check fuel pressure. I do have a faulty fuel level sensor that I'm going to replace when I get the 0-ring for the fuel pump in.

Thanks

MT-2500

The 8 letter/diget in vin is engine code.

100k is time for a good time for a full tune up.
Ac-Delco plugs and check dist cap and rotor /replace wires

I would get a GM fuel pressure gauge and make sure fuel pressure is up to par.

Also a good engine capable scanner may have a lot of info on past /present /history codes and missfires.
Also check camshaft retard readings on scanner.
Are you using a aftermarket or oil type air filter?
Clean MAF again and test drive with it unpluged.

__________________
Remember proper testing gives us the answer to many problems.
MT

AlphaCrow

8th Letter is "W"
Fram air filter, standard one.
Most things are about 1 year old, about 10k miles. AC plugs, rotor cap, fuel filter, etc.

Things I did not change are PCV valve and wires. Got wrong ones from parts store and got lazy and forgot to get new ones.

Do you think MAF needs replacing? Or O2 sensors?

MT-2500

I would replce the plug wires.

On the MAF sensor try cleaning it an the unplug it test.

Make sure you fuel pump and fuel pressure is up to specs.

You need to get it on a good engine apable scanner and check all sensor and fuel and camshaft retard readings out.
There may be codes or miss fire readings that do not turn on the check engine light.
Also a good scanner will read out MAF sensor and 02 sensors.

Guidelines on fuel pump and pressure test.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.

__________________
Remember proper testing gives us the answer to many problems.
MT