8/19/05
Just got back from dealer. Dealer says bad 02 sensor, valvetrain clatter indicates mechanical problem, pirometer indicates 200 degree temperature rise between front and rear of cat converter- claims cat clogged, car has 72,000 miles on it 1.is my motor junked at 72,000 miles? 2.can clogged cat converter cause engine noise? 3. is 3.4L a weak motor?

8/15/05
I need help! My 1996 Monte Carlo Z34 (3.4L) has been running horribly. The car ran fine one day this summer and the next day the car would bog down and hesitate upon pressing the gas pedal. I have had it at a Chevy dealership and two mechanics. None of them have been able to fix it. Chevy dealer thought it was fuel pressure :nope, one mechanic thought catalytic converter was clogged:nope, other mechanic thought it was fuel injectors:nope. When the car has just been started it runs OK. But when the motor warms up anytime it is below 4000 RPM the car hesitates and bogs down aka its horribly slow! However it runs fine as long as you keep the motor above 4000 RPM. Does anyone know what could be wrong? Please help I've been having this problem for 2 1/2 months. It is driving me crazy.

well its the 3.4 dohc if i am correct.. i suspect a timing belt slipped possibly....The 3.4 is a great motor when its running properly, i had a 3.4 dohc in a 92 lumina...and wow that thing had power...the only problem i had was the intake gasket...also any other symptoms besides this bog....rough idle, etc how's your oil pressure, at idle when hot, etc..if it runs crappy when hot it may be something to do with a am/crank sensor...let me know more info so i can help ya

[QUOTE=montecarlossfan]well its the 3.4 dohc...

Yes its the 3.4 dohc. Timing belt huh? I have considered that because I have never had it replaced. But no one that I have taken it to has even suggested that. Could replacing it solve the problem? Or is the apparent mechanical damage (the engine clatter) irreversible? When should a timing belt be replaced on a car anyway? Do you think the bogging down could have something to do with the catalytic converter being clogged? Or do you think the cat and engine clatter and bogging down are all connected? What is "am/crank sensor"? I appreciate your help!

I have a 95 Monte 3.4L, I have replaced just about everything in mine, when it stalled like that it was my fuel pump. I would ask the mechanic exactly how much pressure the gauge said when he checked it. Mine was pushing 20 and I believe the injectors are 29psi, after the fuel pump I could burn the tires again. Other than that, it could also be dirty fuel filter, Wal-mart has them in stock for $10 easy fix. I doubt the injectors are bad. Mine has 170,000 and it runs great. Can't think of anything else right now.

[QUOTE=Mole826]I have a 95 Monte 3.4L...

Got my 96 3.4L back today from another shop. The verdict is that there were two knock sensors that were misenterpreting the engine clatter for knocking and retarding the timing causing it to bog down like it was. The tech. removed both sensors and it ran perfectly! However, the check engine light was on, so he plugged one back in, the light went off and now the engine runs almost perfect with one sensor. I am so happy to have my Monte back in working order ready to blow the doors off Civics again!