P300 and Sulfur Smell

[shyguy5885]

2000 gt 3.4 with 193,500 miles. I just recently replaced the idler pulley and the car was fine for about a week before new issue started. I pulled the codes and there was a P300 random/multiple cylinder misfire and Cam Sensor Circuit (i dont recall specifics, or code #). I replaced the Cam sensor and then cleared the codes. On first startup, the check engine light began flashing while idling after about 5 minutes. Turned the car off and rescanned, and it was Cylinder 6 misfire. I cleared code and restarted. The Cyl 6 code was gone, but the random/multiple P300 came back. Now, the light is always on, and once you go over 30 or 31 mph, the light will flash regardless if you are accelerating or coasting; once you come to 30 or less, light stops flashing and will be steady. There is also a strong sulfur/burning smell. When idling, there is a noticeable stumble/misfire felt. When first accelerating, theres a slight sound and feel of almost like a helicopter rotor or fan blade cutting through the air. Has anyone had this or seen something similar before? Does this sound like cat converter causing odor, or odor is more likely to be from misfire? Any specific places or sensors to check first? Any tips appreciated - wondering if its time to junk it

[Tech II]

Well, you obviously have a bad misfire, if the SES or CE light is flashing....

Cats usually smell when engines are running rich, or exposed to misfires....

Funny thing with misfires is this....when you have a misfire, you have unburned oxygen, and unburned fuel...the O2 sensor does not detect fuel, it detects oxygen...so when you have a misfire, the oxygen sensor goes lean because of the excess oxygen due to the misfire....the computer sees the lean condition, and adds more fuel to the cat, causing the smell....if the misfire is real bad, the PCM will make the SES or CE light flash, so that you will be aware of potential cat damage and either lessen the load on the car, or in extreme cases, shut the car down....continuing to drive a vehicle with a flashing SES or CE light, is begging for a new converter...ouch...

Not only that, but that unburned fuel can wash down your cylinder, get into your oil, and then you have bearing problems...

So stop driving the car....smell the oil on your dipsticK...if you smell fuel, drop that oil and oil filter....then get the misfire fixed...normally the problem is plugs and wires...possibly a coil(pull ignition wires one at a time and look for carbonning on the coil terminals), so do a coil output test......

Are you losing coolant?

Other possibilities are ICM, vac leak, bad fuel pressure regulator, injector, mechanical problem(valves/timing chain), etc.

[shyguy5885]

I was thinking cat because of issues in the past. I've had a p304 for quite some time - but it would come and go. 2 years ago I had a mechanic replace #4 injector, swap coil tower for #4 (and whichever cylinder is paired), replace plugs and wires, and still didn't solve p304. The compression at that time was ok - if i remember correctly, it was 160 in #4 and #6, and 140 in #2. The mechanic suggested it may be a burnt exhaust valve causing the issue. I declined more "fixes"/exploration due to labor cost. I ended up doing my own tinkering, and replaced the intake gaskets, during which, I also replaced the fuel pressure regulator, water pump, thermostat. During this time, I pulled all the injectors and sent them out to be tested and cleaned - the test results came back ok, so they didn't feel cleaning was necessary.

The timing cover gasket has also been leaking coolant for some time - this is the only coolant leak, that im aware of currently. I drained coolant and applied some vaccuum via the water pump housing and tried to get as much rtv/water sealant around so it wouldn't drip directly onto belt and start spraying everywhere. I also added the radiator stop leak stuff with the metal particles in it to try and plug the timing cover leak. This helped quite a bit. When changing the cam sensor, that was definitely some gunk on that side which seemed to be a mix of coolant and oil (or power steering) but nothing as a major leak or having to constantly add coolant.

I do have a scan tool, which I've mainly only used for reading and clearing codes in the past. If helpful, I could try to do a live data set, and paste the results. What are the proper levels of vaccum at idle and throttle? How do I go about the coil output test? Does the crank pulley, ac compressor, front wheel need to be removed to inspect timing cover/chain or is just easier? Could there be an issue with EGR or other sensors/components or more likely they wouldn't cause a situation such as this?

[xeroinfinity]

when you replace the cam sensor you might need to do the relearn procedure.
turn the key to the ON position for 15 mins, then turn it off for at least 1 min.

and from my Grand Am experience, 90% of misfires are the wiring harness or bad injectors. next would be plug wires and or coils/ICM.
But if one is stuck open, it will cause a rich fuel situation and you'll smell sulfur !

also the noise you describe while driving almost sounds like a cylinder is not firing. which when it misfires it temporarily kills the fuel or spark. usually giving it a few mins it'll snap out of it, unless theirs a major problem.

also sealing up the timing cover leak could force it inside, to the oil pan. which will ruin your bearings eventually.

and you might pull the EGR and see if the tube/port is filled with carbon. if it is that'll cause some issues.

[shyguy5885]

I ended up replacing the coil packs and ignition module. It fired up nicely and drove amazing the first day - it hasn't run like that with smoothness and throttle response in years. Unfortunately, the codes came back and went back to sluggish running - this time back with the p304. I replaced #4 spark plug and wire, and now it's back to the p300. As for the harness you mentioned, are you referring to the injector to the main connector or the main connector back to computer? I recall looking at the main connector when I did the intake gaskets. I tried checking resistance on main connector that goes to computer, but don't think i had the right slots. I did think it was peculiar that i had the p304 and all the injector wires to computer were 12356 on one, and 4 was on a completely separate connector at/or route to computer. Which terminals at main connector should have continuity, and do you know what the approx range should be? I only tried using stranded wire into female side, I was a bit nervous to backprobe or be slicing any wires on the main harness