ShauntK

Hi All!
I have a currently with 140k miles. Around 3 years ago at approximately 115k miles, the performance changed. (I have always used and 91 octane fuel) Every part of the car is factory stock (except for the muffler, )

Car feels sluggish, likes is towing 5 tons or binding... (checked brakes, no binding, no issues)
MPG went from 14-18 down to 12 and is always at 11.9 or 12 now...
can still tow a boat, but not really on an incline and its too much for the car now...
wants to upshift very quickly
sometimes after a full stop, when you start again, it feels like the trans didn't go back to first gear and then kicks and starts...


NO CODES!!

since then I have repaired / replaced the following and still no change:

***everything OE***
spark plugs
spark plug wires
air filter
air mass flow sensor
coolant temp sensor
thermostat
fuel pressure regulator
fuel filter
battery
O2 sensors front and back
Cat and Muffler is completely clean
throttle body (improved response a bit)
injectors
rebuilt trans
put shift kit
rebuilt transfer case

I have taken it to the dealer and a private transmission shop to diagnose the trans, they say it runs fine... i think they are just checking the scanner and since no codes, they say its fine...
I had a compression test done, and the compression was excellent.
The only existing issue there is a small exhaust manifold leak.

any help or ideas with this???

cleveland63b

has anyone ever checked fuel pressure or fuel trims? No codes of any kind?

ShauntK

ive checked the fuel pressure and it was very good... no codes!

i was driving yesterday in the high heat and the car performance was horrible... i must have some sort of back pressure... but the cats are clean and clear...........

Scotiapilot

disconnect them and go for a drive. if power clears up then you know. Maybe the mufflers have collapsed

ShauntK

ive cut the cats and inspected, it was perfectly clean and see through... i disconnected the exhaust manifold before the cats and drove like that it... it actually drove worse...

i did remove the muffler and drove without the muffler either, no change...

what else can cause backpressure?