SOLVED: 1998 S70 base - rough idle, odor, undrivable (culprit was distributor cap) Topic is solved

[MagicBus]

it possible to have such a sudden, spectacular failure of the exhaust system

Exhaust system failures can appear to be sudden, once the condition produces enough back pressure. Material from resonators and mufflers can act like a rag getting sucked into the system.

Fair enough, but wouldn't that throw codes for the CAT itself?

As of now, I only have the aforementioned P0300, P0301, P0302, P0304, and now a P0102 (I disconnected the MAF and started the car to test that - no change in behavior), but I don't consider that one to be real.


It's still cold as anything here, so I haven't done much yet. I crossed my fingers for a quick fix this morning and ran across the street to Advance Auto right as they opened and bought a brand new, non-returnable ignition coil. I installed it and fired the car up. It started with a bang, but that seems to have been a one time thing (it started fairly normally tonight after work).

I THINK it ran the tiniest bit better with the new coil, but I ran out of time this morning and had to hop in the other car go to work. I was running late.

This evening, I started the car again. It didn't fight me this time and started up fairly easily. After all the times I've started it. I'm no longer suspecting that fuel supply is an issue. But, it's still running rough like it's not firing on all cylinders. After warming up a few minutes, the live misfire came back and the sulfur odor with it. So, I shut the car off and called it a night. No new codes.

This Saturday, I'm planning to run a compression test, just to see what's going on, especially with cylinders 1, 2, and 4. That'll give me a good excuse to check the condition of the spark plugs, too. Can a malfunctioning coil damage a spark plug? I'll probably also do a more detailed check on the fuel pump, relay, and may, per the suggestion above, check fuel pressure at the rail.

[RickHaleParker]

but wouldn't that throw codes for the CAT itself?

P0420 Catalyst System Efficiency Below Threshold (Bank 1)? A clogged exhaust system would not effect the efficiency of the cat, just how much passes through the cat.

After warming up a few minutes, the live misfire came back and the sulfur odor with it. So

So floor it, let up when the engine reaches 5000 RPM ... if it will rev that fast and keep the windows down so you can listen.

[MagicBus]

but wouldn't that throw codes for the CAT itself?

P0420 Catalyst System Efficiency Below Threshold (Bank 1)? A clogged exhaust system would not effect the efficiency of the cat, just how much passes through the cat.

I wasn't thinking any particular cat code. For that matter, what, besides the cat itself, could actually clog? And with what?

[MagicBus]

but wouldn't that throw codes for the CAT itself?

P0420 Catalyst System Efficiency Below Threshold (Bank 1)? A clogged exhaust system would not effect the efficiency of the cat, just how much passes through the cat.

After warming up a few minutes, the live misfire came back and the sulfur odor with it. So

So floor it, let up when the engine reaches 5000 RPM ... if it will rev that fast and keep the windows down so you can listen.

Listen for what, exactly?

[RickHaleParker]

"For that matter, what, besides the cat itself, could actually clog? And with what?"

Back pressure would prevent the cylinder from pushing out exhaust effectively, screw up the air/fuel mix ratio in the cylinders causing misfires. The back pressure would also keep the engine from revving past a certain RPM. When the back pressure is equal to the force of the pistons pushing the exhaust gases, the engine will not be able to rev any higher. Floor it see if you can get to 5000 RPM.

[MagicBus]

"For that matter, what, besides the cat itself, could actually clog? And with what?"

Back pressure would prevent the cylinder from pushing out exhaust effectively, screw up the air/fuel mix ratio in the cylinders causing misfires. The back pressure would also keep the engine from revving past a certain RPM. When the back pressure is equal to the force of the pistons pushing the exhaust gases, the engine will not be able to rev any higher. Floor it see if you can get to 5000 RPM.

I'm pretty sure it will get to 5K. I think I had it up to 4K without issue tonight. I'll check that when I'm back out there with the car on Saturday. But, a few questions still stand. Physically speaking, what part of the exhaust system, aside from the cat itself, could be prone to clogging, and with what?

Also, when I am revving to 5K, and I put the windows down, what then am I listening for?

Thanks

[RickHaleParker]

"Listen for what, exactly?"

A High pitch whistle like the sound a tea kettle makes when it ready or a boiling a radiator makes when it is boiling over. Your listening for the sound of high pressure gases escaping through the small imperfections in the exhaust system joints.

PS: The sound of a steam pipe when it is about to blow.

[RickHaleParker]

besides the cat itself, could actually clog?

Resonator and muffler.

[MagicBus]

"Listen for what, exactly?"

A High pitch whistle like the sound a tea kettle makes when it ready or a boiling a radiator makes when it is boiling over. Your listening for the sound of high pressure gases escaping through the small imperfections in the exhaust system joints.

Gotcha. I had the car idling thought and exhaust gases are clearly exiting the tailpipe. That's not enough to go on? (don't get my wrong - revving to 5K and listening is easy enough and I will do that)

[RickHaleParker]

That's not enough to go on?

If you turn a garden hose on to a trickle the water flows without any opposition. If you turn on the water full blast the water has to fight to get through the hose. If you restrict the flow with a hose nozzle it has to fight even more.

Your trying to find out if large volumes of exhaust gasses are fighting like hell to get through. If large volumes of exhaust gasses are fighting like hell to get through, there is only one thing that can cause it, excessive opposition to flow ...a clog.