having misfires pls help?

Question

About a 3week ago on my way home my car starts trembling, shaking and lost power out of nowhere. Never experienced this problem before. The following day i got the codes pulled. Says im having misfire. P0420 catylyst eff below threshold.
P0341 cam position sensor. P0300 muti cyl. P0304 cyl 4 and p0305 cly5.. Called my mechanic shop. told him what the problem was. He said he would check it out. So i got my car towed there.The next day i received a call from him saying my catalytic converter was clogged bad, and thats a 90% chance thats causing the misfires. Got the converter changed with a gm direct fit gm converter. He called again saying the car is now misfiring on three cylinders the same side the converter was changed and that i would now need a tune up. I gave him the ok to do it. Called the next day. Said he changed all spark plugs, three ignition coil packs on the cylinders that was misfiring, Camshaft position sensor and some other part that had to be piggy backed along with it. He says Im still having misfires and dont know y suggest i replace the engine. Got the car towed back home to get a second opinion from somewhere else. Has anyone had this problem before or know what can still cause missfire after the work that has been done? Did he miss anything? Additional info. Cts v6 3.6 107,000 on the clock. Had fuel filter changed about two months ago. Only use shell and exxon gas. The day before i got it towed to the shop I Cleaned the throttle body. Car was on E put a bottle on techron fuel system cleaner and fresh gas. The same day i experienced the misfires i had my transmission fluid changed along with new filter and gasket. New brakes,rotors and calipers in the front. Pls any input would help. Thanx

Answer 1

The mechanic screwed you over. He never did a proper set of tests to diagnose a series of misfire codes, and a cam position sensor code, as well as the cat effluent code.

First thing to do: Connect engine analyzer and run engine at idle, Check alternator output voltage, fuel injector pulses, ignition system spark pulses, engine timing, manifold vacuum, exhaust and coolant temperature, and all sensor readings at idle. Based upon what is seen, shut it off and do comprehensive sub-system checks:

1) Compression check on all cylinders, and

2) inspect spark plug electrodes for pitting or impact abrasions, for cylinder temperature indications, and for oil or carbon buildup while they are removed for compression test

3) Fuel pressure check at the schrader valve, and pull and spray test each injector, test fuel injector relays, inspect injector o-rings and bores for leakage, sample fuel and check for contamination.

4) Ignition component tests and ground connector checks, and substitution checks with plug wires, coil packs, and the PCM, and any emission control sensors that gave weak or failed readings.

5) Inspect intake air system for manifold and hose leaks or faulty components.

6) Inspect timing chains and test VVT control unit for leaks, and check timing advance modulator valve not sticking or fluttering due to oil control problem.



From my own experience diagnosing problems on the 3.6 DOHC with VVT the VVT controller is the FIRST thing to develop problems if the oil system is contaminated with different oil types or the oil and filter is not changed every 5000 miles. Clogged vvt units will cause ridiculous misfires AND THE CAMSHAFT CODE !!!!!



And you have those two symptoms together, unlike most misfire situations.



Find a good mechanic. Stop getting screwed by small knowledge wannabe mechanics.



Basic conditions that cause misfiring in your engine: (incomplete fuel combustion in a cylinder despite fuel, air, spark, compression, and timing)

Low compression (bad sealing of cylinder during combustion, not enough pressurization of the air-fuel mixture to get a bang when spark is applied - leaking valve, scored cylinder wall, broken compression ring,leaking head gasket)

Low fuel delivery (injector is not opening long enough or is not spraying well or is not being given enough fuel, or the fuel is contaminated) or too much fuel delivery (PCM is all wrong on fuel mixture)

High air delivery (intake system has a vacuum leak at intake manifold gasket. fuel injector o-ring, or elsewhere, between throttle body and cylinder head, IACV is not fully shutting when it is told to,,,too much air for the fuel being injected) or Low Air delivery (clogged air filter, clogged manifold or throttle body...not enough air to combust the fuel)

Low Spark energy (alternator voltage is low, coil pack ground connections are cruddy, PCM command signals to coil packs are weak or coil packs are fried, bad plugs or dirty, burned or cracked plug wires are leaking some of the spark to the block instead of delivering all the electrons to the plug to make fire)

Incorrect Ignition timing (Bad camshaft sensor, bad timing alignment of camshafts with crankshaft - jumped a geartooth on the timing chain because the chain tensioner is busted, or VARIABLE VALVE TIMING control unit is on the fritz - oil control valve has a bad o-ring, modulator is sticking or has a bad spring, pressure control port is clogged, internal filter screen is clogged, the unit is leaking, or the command signal from the PCM is wacky or the connection is bad. Or the PCM itself is Dain Bramaged and needs repair or replacement....the cylinder is not at XX.X degrees from TDC on the compression stroke when the spark is applied, as is called for)



did you notice where I said "internal filter screen is clogged"? Just checking....

Answer 2

Okay. Like everyone says, your mechanic is a moron. A clogged catalytic converter will NOT cause misfires. It will cause the engine to bog down and lack power due to tremendous back pressure because the exhaust gases can't exit the tailpipe efficiently. Misfiring is when the air/fuel mixture fails to ignite at the proper time if at all. The misfiring results in fuel not being burned and so raw hydrocarbons are going into the cat and building up to block it off. This would result in a FLASHING engine light, which means severe damage to the cat. As for what is causing the misfiring, well, that could be an ignition system problem, compression problem, or a rich/lean condition caused by improper fuel pressure, sticking fuel injectors, bad oxygen sensor(s) or very rarely, a problem in the PCM. You definitely need to take your car to a certified, reputable mechanic who knows what the heck he's doing because obviously the mechanic you've been seeing is dumber than a box of rocks.

Answer 3

The most informative part of your statement is at the end. Apparently you failed to inform this intelligence challenged mechanic of your actions that contributed to the misfire. Are you a mechanic? Apparently not. Yet, you engage, probably like most people do with a combination of Good Intentions + Little Knowledge that = disastrous results. Look at your grammar as well. Exxon, Shell, CTS V6, no spaces between punctuation marks all indicated a teenager with poor experience and a new car that automatically makes new and young car owners "play mechanic." These are the typical results. A forensic analysis points to the fuel system dislodging dirt, rust, perhaps damaging old fuel lines and fuel filter causing improper fuel to air mixture. The car was OK before this work. The car was not OK after the work. Right? The mechanic also guessed because these codes are a starting point to troubleshoot issues, they do not point exactly the cause. The end result of the experience is to either get certified as a car mechanic or allow a decent, honest, qualified and experienced mechanic work on your cars. OK? All of this negative experience, and expense, could have been avoided. Sorry. Bye.

Answer 4

@ R Sorry if my writing skills Doesnt live up to your standards. Did not know i was writing a paper.English is a second language for me. U may know how to use puntuations but ur answer serves no purpose and is jus as helpful as a tumor. When i first encountered the misfires. I had the codes read by a licensed mechanic. Thats how i have the codes. I was told by him to clean the throttle body. It could be a culprit for the misfires. And to use fuel injector cleaner. the mechanic at the shop also knows about these events

Answer 5

The mechanic is clearly an idiot, I hope you didn't pay him for all the guessing. I suspect he's so stupid that he misread which side to work on. I am in the business and I see techs screw up bank1 and bank2 almost everyday.



OK, hopefully you're checking back because this is your problem. It's so common that you can buy the replacement part at your corner auto parts store. GM used crappy variable valve timing solenoids and the oil inlet screens deteriorated and their mesh got plugged and broke apart into the solenoid. Here's the link, I believe there are two, one for each head, thats why it's on one head but the other will fail soon so replace both. I promise this is your problem, if you're in San Diego you owe me a beer and in case he's reading, ef you "R".



Another update, I lied, there are 4 of these things, 2/head because each head has 2 variable valve timing sprockets. It's getting scary now because the dollars are adding up, probably best at this point to remove all 4 and clean and check them.



http://www.dormanproducts.com/gsearch.aspx?type=parttype&year=2004&make=Cadillac&model=CTS&parttype=Engine%20Variable%20Timing%20Solenoid&origin=YMM