I’ve got a 1984 733i that I’ve been nursing back to some shadow of dignity for the past couple years. Recently it’s had trouble getting throttle. What’s confusing is that it seems completely random. I’ll start the car, it’ll idle okay, then idle rough, then idle okay. I’ll start accelerating, it’ll pick up alright, then lose 90% of its power for about 15 seconds, then all of a sudden boom, I’m getting normal throttle. My spark plugs are relatively new, and I recently replaced the fuel filter. It’s getting good enough air intake that intake shouldn’t be a cause. Anyone else experienced this and have any insight? Bad fuel pump maybe? Thanks.
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How much fun is in the tank?
1983 BMW 733i My current project (or at least one of them)
2003 Volvo V70 5 Speed Current Daily Driver
1993 300TE 4Matic Project wagon -sold
1997 E290 Turbo Diesel Wagon -traded for above, an amazingly comfortable car to drive, great drivetrain, but the rust, oh my god the rust
1992 BMW 525i -traded in
1990 Silver 300TE -Sold Loved the wagon, hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold
Try wiggling the harness at the afm when it's running rough.
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My 84 733i just started doing this last night after thousands of miles of perfect running. Wiggling the AFM harness seems to be the culprit. The engine is coming out for a turbo swap tomorrow so I am probably not going to fix it but I just wanted to chime in that motohunter's idea is right on. What is the fix for this and where does the bad connection end up being?
Steve H.
I cleaned mine with contact cleaner and put some dielectric grease in the connector.
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Just an update here y’all: I replaced my injectors and got a valve adjustment and it runs way better. Much less misfire when cold. However, I still have this problem where I get random misfiring after driving for about 30 minutes. It feels like it loses half its power and I start crawling at a very slow pace even with the pedal to the floor. I’m thinking this could be maybe a fuel mixture problem where maybe it isn’t adjusting fuel mixture when the engine is warm. That’s the best guess I got. Anyone else have any insight? This seems to be a problem with a few others on here. Running low on hope on my end.
Edit: just saw the AFM harness posts. I read those a while ago but I thought it was something else at the time. Will investigate that.
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Last edited by richmond92; 09-21-2019 at 12:19 PM.
It sounds like your high pressure fuel pump is on its way out
When your enemy is making a mistake, do not interrupt him.
Also check your charging system. My 1984 733i also had a problem where the charging system warning bulb in the cluster would intermittently lose contact in its socket. Because the bulb is in series with the field excitation wire, the bulb not working made the car stop charging. When it would stop charging, it would run terribly, misfiring and making so little power you could barely drive it. Verify that your charging system warning lamp illuminates when you have the ignition on and engine off. If it's not on, check if the bulb is burned out or wiggle it to see if you can regain continuity.
Steve H.
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