Is this compression loss? [Archive] - GrandAmGT.com Forum

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DLISH
02-26-2009, 02:47 AM
Symptoms:

low end power loss
loss in mpg
rough idle in drive
high idle in neutral or park
cel for P0420 (lower catalyst efficiency blow threshold)



[B]backstory[B]

about a year ago i was getting p0420, so i replaced the cat once, few weeks later it came back, so i replaced o2 sensors and the cat again i think, the light comes back, this time with a noticable misfire, so i take it to the dealer and they say im leaking coolant into cylinder 1, so i get the head gaskets replaced at an out of state dealership.

as i leave the p0420 comes on a few days later. i call them and they say the coolant had killed my converter, so i repalce the cat again...... so ok i got a new cat and new gaskets, idle starting to roughen up again and p0420 comes on again.

i take it to a local dealer, and they say they cant work on my car because i dont have a stock airbox on (just too many modifications), so i take it to another dealer and they say they dont know whats wrong with it and say i need a gm catalytic converter for the car to operate...they even scanned with the obd masterscanner and all my sensors checkout just fine and everything.

so time goes by and i make a trip to the dealer that changed my head gaskets, and they tell me the same exact thing...."its your catalytic converter it isnt OEM" i argued for a few days with them and eventuallly left empty handed.

so thinking my cat was out of spec, i decide to order the S&S header combo with cat, knowing of its good results, thinking it would fix my problem. so knowing i would have to install the system myself i decide to cut my cat out to see if any change in the matter happens. so i cut my cat off put in a test pipe and plug my simulator in.

i start the car and the problem still exists.....so if i put on the S&S system there wont be a change....

i have no idea what to do, all my sensors read fine, and the only code i ever get is the lower catalyst below threshold.

im pretty sure that is a result of a problem, and i cannot find a dependable mech to even look at my car, they all just turn thier shoulder to it "because its not stock"

thing is lost my job last month and dont know how to pay for someone to do a wet/dry compression test or any form of diagnostic for me..




any suggestions :(

DLISH
02-26-2009, 01:11 PM
k guess no one knows

lone_wolf025
02-26-2009, 01:32 PM
Check the wiring from the rear sensor to the computer. If you're still getting a code even with a sim in the pipe, it has nothing to do with the actual sensors themselves.

Oh, and look for a vacuum leak too. Generally that fits the high idle and power loss.