Possible clogged cat? (Placing in GT because it might not be)

[Pocket Chant]

So, I've been plagued with this problem for a while now. I'll go to start up my car, it'll run fine, then about 5-10 minutes in, the car starts to lose power. I'll put my foot down and that's enough to keep it at one RPM (as in, 2000 continuously), occasionally if I put it in neutral, it'll rev freely, sometimes it won't. It'll make a sputtering sound as I slow down, sounding similar to a truck's engine brake. If I rapidly pump the gas, I can get it back up above 2500 and it'll rev fine, but only above that. It'll backfire a couple times as I accelerate, and then be fine for the rest of the drive. However, if I turn it off and start it again half an hour or so later, the same problem occurs. Seems to me like it's a clogged catalytic converter, but I'd like to check before I drop $500+ on getting those replaced. FPR maybe? Thanks.

[dnguyen1963]

Sputtering and backfire are often the result of incorrect fuel:air ratio. I doubt that you have a problem with your cat. Tee in a fuel pressure gauge and perform a smoke test to rule out these possiblities before spending $500 for a new cat.

[Pocket Chant]

Thought it might be that, I had read somewhere the symptoms of a clogged cat and it seemed fitting.

Anyway, FPR? o2 Sensor? I don't have any vaccum leaks, I know that, but I have to get my hands on a fuel pressure gauge.

[603Racing]

Check fuel pressure first before you start replacing parts. If pressure is good after the 5 to 10 minute period then your FPR is fine.

Possible other causes could be bad coolant temp sensor, ECU, or O2. If it gets worse as the car warms up I'm inclined to think it's temp sensor related.

[Pocket Chant]

So, thought I updated this. Whoops.

Anyway, checked out a few things. I got a new o2 sensor around september, but it was spliced into the old wire (Long Tube headers, had to move the sensor farther away). I unplug it and notice a bit of corrosion on two of the prongs. Leave it unplugged and drive around, the problem is gone. Keep driving, eventually it repeats the problem constantly until I plug the sensor back in.

I get home, clean the contacts the best I can without a wire brush, the problem happens only every once in a while now, and it's much less aggressive. I have a brand new proper-length o2 from a 525i coming tomorrow, so I'm pretty sure that'll fix the problem.

[vert_this]

its sounds like the CPS (crank position sensor) is on its way out to me...

[Pocket Chant]

its sounds like the CPS (crank position sensor) is on its way out to me...

Thought so too. Replaced it just a week ago.

[vert_this]

Thought so too. Replaced it just a week ago.

ok how about the throttle position sensor? maf?

I'm also assuming the usual issues like cap, rotor, or plugs and plug wires have been addressed?

[Pocket Chant]

Plugs are new, cap and rotor are less than a year old, as are the wires. I assume they'll be next. TPS has been replaced, MAF is a possibility, but I've only had it since the end of last year.



So, interesting update. I pull the old o2, it looks like shit. Put the new one in, hook the battery back up and start it up. It's nice and smooth, as it should be. I drive it around, the whole car feels much better.

I had to go pick up some trim glue, so I did that, and once I got back in the car and started to drive away, it starts to cough and backfire, though only momentarily, and much much less than before. Doesn't happen every time, just occasionally. Thoughts?

[golde30]

check all battery and ground connections.

[Quadrajet]

If the problem happens again, loosen or remove the fuel cap. If the problem goes away then fuel tank isn't venting properly.