ShauntK

Hi All,
I am new to the forum. but have been reading the threads for weeks now... lots of great information and experience here.

I have a 2003 Chevy Tahoe Z71, everything factory original (no mods), 113k miles. Last year I had a sudden drop in MPG and some power loss. since then I have done the following to the car, but no improvement and the MPG and power loss is slowly getting worse.

Things I have changed:
Spark Plugs (AC Delco)
Spark Plug wires (AC Delco)
Transmission - rebuild
Transmission cooler
Transmission shift kit
Air Filter (AC Delco)
Air Mass Flow Sensor (Densi/Denso?)
Fuel filter (AC Delco)
Front O2 sensors (Densi/Denso?)
Rear O2 sensors (AC Delco)
Coolant Temp sensor
Compression check - PERFECT with flying colors
Fuel pressure test - PERFECT with flying colors
cut the cats, both clean and PERFECT
passed smog perfect
I use 91 octane fuel
I use synthetic oil

I am getting no codes, no check engine light, but with some conditions the car drives like a weak 6cyl with the A/C full blast...

both my mechanic and muffler guy confirmed that the car is running RICH as there is excessive fuel in the cat creating lots of heat and backpressure.

but no one has been able to figure out why...

any help would be appreciated

Joe In NY

replace the injectors? They aren't very expensive. Replace the Fuel filter and run fuel system cleaner through. The newer burbs and tahoes have self cleaning injectors and dont have a return loop and no fuel filter. The older one have a fuel filter, return loop, and non-cleaning injectors. You can take them and have them cleaned, or just replace them. Had the injectors cleaned on our 2002 around 80K i would say along with air filter, fuel filter, and plugs. That thing ran so much better!

ShauntK

Hi Joe,

thanks for the response. My mechanic did mention that maybe one of the injectors might be dripping instead of spraying... but wouldn't bad injectors cause misfires? is there a way i can test the injectors first?

Joe In NY

Injectors wear out. Leak, and not have a nice spray to them. There are ways of testing them. I would have your mechanic hook up a proper injector cleaner to the fuel system and see if it makes a difference. I believe injectors aren't very expensive. Especially compared to the other things you bought and replaced.

ShauntK

Hi All, so are Delphi injectors good? should i consider it? or just go with Delco??

73shark

IIRC Delphi is a GM supplier.

ShauntK

sorry, what is IIRC?

also, is there any upgrades to the injection system? and is there a difference with the multiport and standard injector?

73shark

IIRC = if I recall correctly.

ShauntK

oh, I feel stupid

ShauntK

so any upgrade mod to the existing injector system? i keep reading about the spider assembly... but i am not sure if this applies to me... i am not a mechanic and dont really understand too much, but i also dont want to get creative by changing things on my car.

i would just like for the car to function like it did before. it was totally fine.