BigFish246

2000 Astro Van
4.3Liter Vortec V6
It used to hesitate and engine code P0300 : multi cylinder missfire.
The the radiator cracked and it over heated. When it started to overheat, also it started to lose power. Not sure if the overheating is connected to the loss of power.
It started to loose power gradually, at this point I can hold the pedal down to the floor and barely get moving. It sounds like it's starving for air or fuel...


Replaced:

• Radiator & hoses.
• Spark plugs & wires
• Distributor Cap & Rotor

Performed Fuel Injection Cleaning.
Checked Cylinder Compression. All 6 are at 200+psi
Checked Fuel Pump Pressure; it's at about 60psi at Ignition On position
Checked if the Intake Manifold gasket is leaking, it's not
Checked vacumme pressure, it seems fine. Air filter is ok.

BigFish246

Computer read code P0102 Mass Airflow Sensor Low Input. I swapped the MAS and nothing changed.
When you say "lower intake manifold" which one do you mean. Because I have sprayed everything from brake cleaner, water, to starter fluid around the intake manifold. Around this: http://monsterautoparts.com/CHEVROLE...ES/1380002.jpg

BigFish246

The strange part is that it idles very well. No noises or anything like a vacume leak.
When I clear the codes, is there a way to make the computer do diagnostics again?

Diagnostics to be performed the Fuel Trim, and Purge Flow, the O2 response, air Intrusive, EGR, Purge, Misfire.
Perform these diagnostics without driving 50 miles? Obviously, the vehicle is not drivable at this point.

BigFish246

Checke Throttle Position Sensor. It reads from 0.53v to 4.38. It was as smoth as I was pressing the pedal.

http://idsllp.com/temp2/MVI_1768.avi

BigFish246

Yes, Checked Throttle Position Sensor. It reads from 0.53v to 4.38.
Voltage rise was as smooth as I was pressing the pedal. Did not notice any voltage drop during the test.

I uploaded the video. not sure if you can see it: file://idsllp.com/temp2/MVI_1768.avi

BigFish246

I agree with you. I will do this test tonight, and post results. I'll have to makeshift a vacuum gauge and the connections to exhaust O-2 port.
It's either that exhaust blockage or I will need to convert from CentralPort to MultiPort FI.

MDTAHOE

There is a good possibility that the head gasket is blown. But if we take into consideration that it was running bad before the over heating we will start with something that could cause the random misfire code, the mass air flow code and the loss of power. 1Gary maybe on the right track with the converter. Do you have a real vac gauge can not be something make shift as that may cause false readings. Connect the vac gauge to a direct intake vac source and get a idle vac reading, then rev it up and hold it if vac goes to zero you most likely have restricted exhaust. Now you can try to remove any pre cat o2 sensors and repeat the test if the vac reading is higher then you have your answer. Now if it is not the is another possibility, the from y-pipe on these truck is double walled I have seen the inside pipe collapse and cause the same symptoms as a bad cat. You may need to unbolt the front pipe. If you do not have a vac gauge this would be the easiest thing to do. Also post the idle vac reading because if this is low you could have a whole other problem

BigFish246

Thanks for the post. I really appreciate it.
Status Update:
I did use a Vacuume guage as pictured below. But I did not get a chance to do the test to a direct intake vac source...

I did Removed the driver's side Pre-Cat O2 sensor. I attached the rubber grummet through the O2 sensor hole. Reading was over 4+psi at idle, and way off the scale (10+) at throttle rev. Based on the "How To Articles," stated the backpressure should not exceed 2.5 psi at 2000rpm rev.
The Cat Canverter is clogged. Made sense. I cut out the CatConverter. The honey comb on input side was broken up in chunks, and the rest sure looked clogged up.
Purchased a Universal CatConv, and now having a good time trying to make it fit. The universal cat has 3 inch ID but the chevy exhaust pipe is 2 3/4 OD. So that 1/4 of an inch is too much of a gap to hose camp down.
Tried to expand the exhaust pipe, but that was not sucessful. Broke the expansion tool.
I am now trying to find couplers and adapters that would take from 2-3/4 to 3 inch. But it seems that the auto stores these days do NOT sell anything that is either not shinny or glowing colors...
I know there are exhaust reducing bushings out there, but just can't find any in due time. Will try to find a CatConverter that is 2 3/4 OD.
Will keep you updated.
Once again, thank you!

BigFish246

Thank you Gary & Pat for all of your assistance.
It was definately the clogged Catalytic Converter. Most likely when the Radiator cracked and overheated, it burnt out the CatCanverter.
Replaced with a Universal Fit CatConverter (as pictured). Now the van runs like new!

Thanks again!

BigFish246

After about 1,000 miles the Cat Converter is clogged-burnt out again. Very upset about it since it's the 2nd time and it left me stranded. So there is some causing this.

I can definitely smell the strong odor of sulfur.<O</O
No computer codes came.<O</O
Car just lost power and shut down.<O</O
I let it cool off and hammered it a little, and then the car ran fine again. So I must have dislodged the clogged part.
<O</O<O</O
Is it true that faulty 0-2 sensors will burn out the cat? I heard if the 0-2 sensors do not respond quickly enough then that causes the computer to over compensate…. But can it burn it out?