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random misfire + rotten eggs odor

11-16-2010, 08:52 PM
Now I've a new problem with my Taurus 2002 OHV. When I started the engine from a hot start, I eard a very small cracking noise, and I smelt rotten eggs from my ventilation right away. Also my car stumble between 400 and 650 rpm like if it wants to stall. Then my check engine light come on. The codes was P0300 and P0316.
P0316: Engine Misfire Detected on Start-up (First 1000 Revolutions)
P0300: Random or multiple misfire
After few seconds, stumbling goes away and after 5 miles of driving, the CEL goes away from itself. But the rotten eggs exhaust odor is still there. It's exactly the same odor than I smell right now from the exhaust pipe and from under hood when hot engine is running. It's like if something metallic has melted or something.

This odor is very intoxicating because while driving I present symptoms myself like lack of energy, confusion, very relaxing. Like if blood was not saturated by O2. When I opened my windows to breathe pure air, my symptoms gone away.

I read somewhere it could be the catalytic that has failed. It's possible? How a catalytic converter can cause misfire?

I checked exhaust system condition, it seems perfect on visual. No exhaust leak (tested w/ flashlight the night). No damage or rust. Exhaust manifold and gasket good too. But the exhaust noise is like (poh-poh-poh...) no stable gas debit even if idling is steady at 580 rpm.

When I replaced my plugs 3 weeks ago, I see a lot of metal parts in decomposition around the plugs hole. I clean them, but when I remove the old plug, some very small metallic part fall into the combustion chamber. They could have destroyed the cat converter 3 weeks after of regular driving?

Or maybe my lean mixture damage my catalytic converter? Because I've a vacuum leak, so I run lean.

Few months before the problem, I see a lot of water drop under both cat converter and muffler. Could be related to the problem?

But actually I had the stumbling problem before all of that happened. But it's very intermittent. It's only after 2 hours of driving in city. When engine is very hot. Sometime idling is stable, sometime is not. It hesitates and lack of power intermittently. Because I also have a vacuum leak, but no CEL for that.

11-16-2010, 09:53 PM
The catalytic converters would not cause the misfire, but the misfire/vacuum leak could cause the catalytic converter to overheat and cause the smell. You need to fix the misfire/vacuum leak and hope the smell goes away. If not, the converters will likely restrict flow soon and will need to be replaced.


11-16-2010, 10:28 PM
How much it should cost approximately to replace the lower intake manifold gasket for this Vulcan engine at a garage shop?
One time I asked a quote for a cutlass supreme 3.1L, he saids 950$. For a Taurus it should be less, cause we don't have to pull the engine off, hopefully.

11-17-2010, 06:44 AM
You might try this site ( for an estimate.


11-17-2010, 08:34 PM
Alldata is showing labor at 1.8 hours for upper and 3.8 hours for upper and lower. So about 2 hours of labor at whatever your mechanic charges per hour.

12-07-2010, 01:22 PM
Thanks both of you for your answers. I replaced my lower and upper intake gasket manifold 2 weeks ago, it took 3.3 hours and they charge me a total of 400$ + the antifreeze.

The small side gasket parts at front and rear of engine were worn and a lot of antifreeze come out.

Ok, the odor in ventillation is almost not here. Sometime it comes on, but less strength that before. I discovered that the odor was in fact burned antifreeze, not the catalytic converter.

Now my car run a little better. I've better acceleration and almost no hesitation.

But sometime it stills stumble sometime at both idle and driving. Especially when it's more hot outside (40F and more) and after driving for at least 50 miles in city. When it does that, it doesn't response to the gas pedal instantly. It does that for about 10 minutes in 2 weeks (225 miles) so it's intermittent.

When I disconnect MAF sensor it doesn't change anything, so it's not emission control related problem. I check also ignition coil resistance when hot, it's good. Plugs, fuel and air filter are new. So maybe my fuel pump is a little weak. Anyway, I'll replace when it fails.

12-10-2010, 09:35 PM
I finally found the source of my problems. The stumbling and poor idle is caused by my camshaft sensor. Even if it has been replaced 5 moths ago, this part doesn't last on theses cars. The problem goes and disappears, so it was hard to diagnose. It last like 1 minute and work normally.

The antifreeze odor is coming from my heather core. It should be damaged. When I turn temp knob on cold settings, the smell goes off. But when I turn on hot air settings, I smell the antifreeze. Now it's all the time (even when engine is cold). But not burned like before, just natural antifreeze. Also my coolant level drop off. Heather lines are rusty as hell.

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