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Engine Stumbles Intermittently

 
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GWilliamT



Joined: 15 Mar 2004
Posts: 8
Location: Walla Walla Washington

PostPosted: Sat Dec 29, 2012 8:12 pm    Post subject: Engine Stumbles Intermittently Reply with quote

BMW325e 1985, 5 spd, 293k
I need some suggestions about where to look for an itermittent engine problem.
Last summer I replaced my engine (thrown rod cap and holes in sump), with a used engine that came with the wiring harness, and manifolds. Engine runs well most of the time.
Occasionally, the engine will stumble, falter, and sometimes die. Waiting a short while, it regains its feet and is again running fine. Usually happens when slowing, as in approaching an intersection. This behavior is sometimes exhibited at start up, rough misfiring, then eventually smoothes out.
The misfiring, stumbling, does not seem cyclical.
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dt325ic



Joined: 24 Aug 2004
Posts: 307
Location: Atlanta, GA

PostPosted: Sun Dec 30, 2012 10:17 pm    Post subject: Reply with quote

I would check for any vacuum or intake leaks. My '88 had something similar a while back, and the intake boot between the air filter housing and the intake had cracks (on the bottom side, so it wasn't evident until removed). It was letting in unmetered air and causing my car to run rough, particularly when cold.

How do your spark plugs look? Any evidence of running lean or rich?


Last edited by dt325ic on Mon Jan 07, 2013 4:24 pm; edited 1 time in total
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idanity



Joined: 21 May 2005
Posts: 3097
Location: N.W.U.S.A.

PostPosted: Fri Jan 04, 2013 2:46 am    Post subject: Reply with quote

wow, 8 years and on your 3rd post.

i had a similar issue, like a hiccup, or loss of power. resolution was during a few things

AMS
c191 plug (which you don't have in a 85 eta, unless you got a newer i engine.
intake leaks (manifold gaskets)
ground (possible, but unlikely in my case)


as above, yours sounds like a vacuum leak, as in the air intake boot (big elbow) is prone to cracking on the ribs....squeeze it, if you see any cracks, just replace it.

but not discarding the cap/rotor too, i have seen similar issues with a loose rotor before.
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GWilliamT



Joined: 15 Mar 2004
Posts: 8
Location: Walla Walla Washington

PostPosted: Sat Jan 05, 2013 2:52 am    Post subject: Reply with quote

Thank you idanity et al. The vacuum is something I've considered. Seems remote given the infrequency of the problem. I've also considered the cap/rotor, which seems a littler more likely.

It is so intermittent it is hard to trouble shoot. May just start replacing likely parts.

I actually dropped back to an 84 m20 when I changed engines (not by design, it just came out that way).
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idanity



Joined: 21 May 2005
Posts: 3097
Location: N.W.U.S.A.

PostPosted: Sat Jan 05, 2013 7:23 pm    Post subject: Reply with quote

actually the intake boot does go through a lot of change during driving

cold, its hard, and warm its soft, plus your engine may have soft mounts, and the intake (on mine) is mounted on the car, so if the eng pulls away, it could be stretching the boot, opening the cracks, etc.

could also be injectors, but i would start with the cheap stuff, and regular maintenance.
i know they are temperamental at times...(think we all know that Smile )
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