1996 Volvo 850 GLT Wagon --> Random Misfires

[jose456891]

My car is getting horrible MPG's, and now it's sputtering really bad. Here is a recent history:

Replaced front O2 sensor with OEM 300 miles ago.
Replaced fuel filter 50 miles ago.
Cleaned PCV system 3k miles ago.
Cleaned MAF 5k miles ago.
Replaced TB 3k miles ago (did it my self correctly).

Current Problems:

I'm getting RPM interference via all AM stations on stereo (not FM). This happens to independent handheld radios too, pointing to a problem in the ignition system.

I blew my Cat because 50 miles ago. (Yes, I recovered some melted honeycomb cat pieces from my exhaust).

Other variables:

I have cheap plugs, I just ordered OEM.
I have no idea when the rotor/distributor/wires were changed

Other:

This problem is intermittent, the check engine light comes on, but after 50 miles it goes off. It comes on when it wants to die.

Smells like it's running rich.

[rspi]

What codes are you getting?

[jose456891]

P0300, P0301, P0302, P0304 and p0305

[rspi]

Sounds like you need to finish the tune up with rotor, cap, etc.

[jose456891]

I'm debating to replace the ignition coil, should I?

[jalwlb]

Start the car after dark, pop the hood, cup your hands over the coil to block out any ambient light and take a peek. If you see fine blue lightning over the surface of the coil, it's time for a new coil. A bad coil will cause random multiple misfires. Misfires have allowed unburnt gas to enter the hot cat and damage it by igniting there.

[erikv11]

Keep in mind it is rare for the coil to go bad on these cars. If the test described so nicely by jalwb is not definitive, I'd wait to put in new Bosch cap, Bosch rotor and Bougicord wires before moving on the coil.

[jose456891]

Misfires will allow unburnt gas to enter the cat and damage it.

My cat is already gone, it literally blew. I found pieces of melted cat honeycomb on my tailpipe the other day.


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Can bad vacuum lines do the same??