A restricted cat will definitely produce a temperature drop from the inlet to the outlet. The restriction causes the heat to build and once the exhaust gases get past the restriction, they will expand & cool resulting in lower temperatures.

A similar phenomenon can be seen in high RPM engines when run on a dyno. The outside of the bends in the header tubes gets hot faster due to the increased flow of hot exhaust gases overpowering the cooling from the exterior.

Increased flow or increased pressure causes a build up of temperature.

 

Ok, I will buy that. But doesnt he state that he lacks power mostly when cold? My gut says it isnt the cat.

 

I really don't think it's the cat either. Just responding to your question. Its easy enough to check for and rule out though.

 

True that. Im 41. Ive had my fair share of beaters. (Too many to count!) Funny thing is, in all my years of rebuilding and keeping things on the road, I have only had to replace one cat.(Rattled). In your expirience with the 4.3, do they eat them of have I been just really lucky all my life?

 

The problem with the 4.3L is the fuel system (prior to the MFI spider anyway). Once the fuel system starts to act up due to failed FPR, poppets leaking or otherwise not spraying correction, etc, more raw fuel gets pushed to the cat where it gets burnt and over time it can melt down the catalyst. Lack of maintenance (tune ups, injector cleaner, etc) is the biggest killer of catalytic converters.

But enough on that.

To the OP, have you cleaned the MAF sensor and/or EGR valve? Either of these can cause a performance issue on cold starts. When was the last time a full tune up was performed (plugs, wires, cap, & rotor - AC Delco is preferred for these items)?

 

Thanks for cat chat.

I would be interested in what the temperature sensors are reading. IAT or coolant temp have caused problems for me in the past. A data stream would probably provide alot of information with this problem

 

well everyone it was not the cat. so i hooked it up to the tech 2 again.... the maf sensor is working properly.... back to the fuel pressure gauges?>

 

I hooked up the fuel pressure gauges and drove for a week and same results as last 55- 70 lbs .... so i unhooked the maf sensor and the intake sensor and it runs like a top .... throws two codes reading fuel to lean . off subject but where is the cabin air filter located in the 2000

 

So.. that leaves the IAT as the probable culprit, right?

 

What do you mean on the iat sensor