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Discussion Starter #1
Hi all,
This is my daily driver and I may even need to call in "sick" from work today since I can't get there.

'81 Bronco, 300 six.

Over the past month or so, I've had an odd misfire while driving around, like the engine was going too lean.

I have a Wideband O2 sensor on my engine, so I always know what the AFR is and I know it wasn't. It was just behaving like it.

Yesterday, I went out to start it and it wouldn't start. It just sputtered and backfired. I fought it all day long, pulling the carburetor apart and cleaning it, thinking that it might have gotten plugged. Reset the timing, put in new spark plugs, just trying a handful of different things.


I finally got it to start and it runs now, but it surges constantly.
At idle, it sounds like a helicopter with the exhaust sputtering.

I took it for a test drive and it surges at ALL speeds. When I was cruising, it surged, when I accelerated, it surged, when I let off the gas and coasted down in speed, it was still surging.

I did a compression test and I have 150psi in all cylinders. My engine vacuum is about 18 at idle and the needle is nice and still. Also, my AFR behaved perfectly normal while driving, so the carburetor is functioning as it should. The engine felt "healthy" behind all the surging.

I swapped the ignition module for the one in my wife's '84 Bronco (with a 300) and it made no difference.

Any ideas? I'm going to go out and start pulling more things apart, but I don't really have any direction.

Thanks for any ideas.
 

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Fuel pump? Vacuum leak?
 

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Discussion Starter #3
I checked for vacuum leaks, but even then I don't think that'd be causing the symptoms I have.

I wish I had a fuel pressure gauge, but I don't. However, I have a clear fuel filter and fuel seems to be flowing just fine. I think if it was the fuel pump, I'd be showing really lean on the O2 meter.
 

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Discussion Starter #4
Are there any kind of valve issues that wouldn't show up on a vacuum gauge? I would think that any valve issues would cause some kind of needle wobble or something, right?
 

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Discussion Starter #5
Looks like I sheared a distributor pin. It must've been a slow death due to how it'd been running poorly, and then finally decided to just let go.
 
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