I think it is a bad cat....[Update - KISS]

Update:

Keep It Simple Stupid.

I finally had some time on Sunday to check up on the E28. Based on input my plan was to inspect the fuel connections, then get it running and see if there was an exhaust obstruction when it was running poor.

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Popped the hood and was looking through the fuel connections from the hose to the rail to the injectors. Then I stood for a second and just thought.

“I should go ahead and just check the spark plug wires”

Sure enough, one was a tiny bit off, and one was mostly off. I must not have pushed them back on all the way when I was checking for spark during the no-start issue (which ended up being a disconnected crank sensor).

Started up and ran no problem. Went for a pleasant drive, turned it off and let it sit for 5 minutes, then drove it again. No issues.

In other news, we are slated to get our first cool front in Houston today, which means I’ll be able to work on the BMW without sweating through my shirt in minutes.  Hope to get the cat cut out and bumpers tucked in soon.

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Original:

So the E28 has been running erratic lately.

Short version: Heard a rattle from the cat, car runs fine sometimes, then other times stumbles, almost dies, and backfires.

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Long version:

About three weeks ago I was going to take the E28 on a quick errand on a Sunday morning. Got in, started right up, didn’t really let it warm for more than a minute, and set out. I was halfway down the street when I started hearing a new noise - rattle that seemed to move with RPM’s.

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I can’t recall where I was headed, but it was time dependent, so I turned around, parked the BMW and took the Suburban.

When I got back later in the day I started to try and troubleshoot, and from the outside it quickly became apparent that it was the cat rattling.

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OK, not a huge deal, no emissions testing in Texas for a car this old. I’ll either take it out or buy a cheap universal cat (even though it isn’t required, I don’t HATE the environment). Either way, doesn’t seem critical to get done now.

A week later Tropical Storm Imelda hit Houston. Those of you that haven’t read my sparse posts - I live near a bayou in a flood plain. From 2015 -2017 I lost 5 cars to flooding (somehow never my car, wife’s and minivans). So when we had warning I moved the E28 to my parent’s driveway, which while only a mile away didn’t flood in Harvey when we got 44" of rain in two days. Since it was in the driveway and I still have no idea if the seals around windows / trunk are actually good (normally in my garage) I put a cover on it.

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Imelda wasn’t bad for my area of town though we got a short burst of 4" in 90 minutes. I went over to pick up the BMW and drive it home, and even though the cover did its job, with rain and humidity there was a lot of moisture under the cover anyway.

I started it right away, and it ran like crap. Stumbling, sounding like it was missing, almost stalling, idle all over the place. When I would give it a little throttle sometimes it would respond, and sometimes the throttle input had no impact and it just kept stumbling, missing, almost stalling.

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Did that for 5 minutes or so, then settled down. I drove it home with no issues at all. At the time I thought maybe just the built up moisture trapped under the cover made the air filter moist, and it was pulling that into the engine, but didn’t really try to diagnose anything else.

Then it sat in my garage for almost two weeks over my business trip to Singapore.

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Last night I finally got back out to drive it for a quick trip to the grocery store. It started up just fine with no indications of the prior issue. I let it warm for a couple of minutes, then drove to the store with no problem. It was driving perfectly normal.

Came back out of the store about 15 minutes later, started it, and it was back to the same issue- stumbling, sounding like it was missing, erratic response to the throttle input, and this time it backfired a couple of times.

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I nursed it back home, but then had to spend some time with my 13 year old and a case of “I just don’t want to do my homework”. (That could be a whole other post...)

When I finally sat down to do some research on mye28.com, what I came up with was a couple of threads that seemed to indicate this can happen if the cat is starting to go.

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Since it is so erratic it makes some sense, I think. If a piece of the cat moves around and blocks it up I can definitely understand it running rough like it was, and even not responding to the throttle input. But if it is clear it should run just fine, which it was.

Other thoughts?

Another picture from my Singapore trip for your time. This is one of my favorite shots of Gardens by the Bay at night.

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