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2004 V6 problems (no codes show up)

918 Views 2 Replies 3 Participants Last post by  wmburns
Okay guys, so Ive been bouncing around the manual and online to find out whats going on with my car and so far I have many answers.

Heres the deal. My car starts a little funnier than it used to about 6 months ago. it seems like it takes .5 seconds longer to start. may not seem like much but its definitely noticeable. Once started it begins to idle, a bit rough and feels like its miss firing since it will thud randomly every few seconds. When initially putting it into drive/reverse it thuds when you touch the accelerator. when coasting it seems to not really vibrate but knock a bit. Once I push on the accelerator more it seems like it lags and sputters while also shaking (especially when uphill from a stop light, also when going uphill a strong odor is smelt, not fuel but it ranges from exhaust smell to rotten egg smell). When I hit the highway it sputters whenever I push the accelerator but if I keep pushing further it smooths out. A lot of the vibration and knock comes in around 1,750 rpm. Also there is a loud rattling noise when I approach a stoplight. Im thinking its my catalytic converter because when I crawled under I made a fist and lightly pounded on the exhaust pipes and it started rattling(of course the engine was off). That should be it, ohh and also there are no codes showing up on two different OBD 2 readers. also definite noticeable loss in power, feels like a four cylinder now.

So far what I've replaced are the spark plugs and wires( I've checked the plugs since changing them and they're properly gapped and theres no sign of anything like oil/carbon build up or anything else). I also replaced the fuel filter and have checked it since replacement and it seems fine. I checked my differential like someone said to and the fluid was fine. driveshaft is completely stable so I'm guessing its not the universal joints. I bought a cold air intake and its clean so its not that either.

So far the symptoms gave me a list of things that could be wrong. Someone said the EGR valve or system. Another said the catalytic converter. Theres also piston damage, faulty distributor, fuel system problem and others.

Sorry this seems so long and detailed but I love my butt stallion and I want to keep her alive. Any suggestions will help will help. Thank you
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What kind of scanner do you have? if it is capable of datalogging, or watching live data, look for fuel pump duty cycle, or fuel pressure, or fuel pressure at the rail, and make sure its at least 30-35. if that number dips significantly while driving or accellerating, the fuel pump, sender, or other fuel pump related device is malfunctioning.

If the duty cycle is the setting your watching, it would jump very high while accellerating if theres a problem.

if your reader cannot show this data then,
get a pressure gauge, and test the fuel pressure under the hood. schrader valve, passenger side of the intake manifold i believe.
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Suggest starting with the "basics" before looking deeper.

Have you:
  • Cleaned the MAF?
  • Changed the PVC valve?
  • Tested the alternator for excessive AC ripple (bad diode)?
  • checked the fuel rail pressure intake vacuum reference for leaks?
  • checked for vacuum leaks?
  • Checked for exhaust leaks? (don't cut corners here!)
  • Checked the motor mounts?

Double check the spark plug routing. Have all factory standoffs and looms been used?

Try this. Cycle the key on/pause/off several times without cranking. Now crank the motor. Does this improve starting? If so, suspect fuel pressure leak down as part of the problem.

The V6 is prone to carbon build up in the intake/value covers. Check out:

Then check the cats for blockage. Often the cats will glow red if blocked or the motor is running rich.

Honestly, if you suspect "piston damage" then your first test should be a compression test.
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