Noisy/Ragged engine
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Trailering
Joined: Apr 2019
Posts: 22
Likes: 1
Noisy/Ragged engine
79 Bronco with a 400 in it. All new pipes/muffler installed last year so they're in good shape. I noted a hairline crack in the exhaust manifold on one side so I pulled those off, replaced the manifolds and gaskets and it's a little better but still raggedy as all hell while accelerating.
Occasionally i'll get a backfire while driving (usually over 45-50 mph). Any ideas what to check next?
Occasionally i'll get a backfire while driving (usually over 45-50 mph). Any ideas what to check next?
Hotshot
Joined: Jul 2020
Posts: 10,529
Likes: 2,657
From: Near Salt Lake City
The firing order, the rate of timing advance and the cap for carbon arcing
A broken valve spring will cause it to backfire too
Backfire generally just means you are lean
But can be caused by numerous things (like an intake valve sticking and the cylinder firing while the valve is open)
Valve guide wear, and worn valve springs come to mind
I'd also use a vacuum gauge on the engine to check for leaky valves
A broken valve spring will cause it to backfire too
Backfire generally just means you are lean
But can be caused by numerous things (like an intake valve sticking and the cylinder firing while the valve is open)
Valve guide wear, and worn valve springs come to mind
I'd also use a vacuum gauge on the engine to check for leaky valves
FTE Community Team
Joined: Dec 2023
Posts: 8,855
Likes: 4,266
From: sussex county, nj
i'm with above, and add i would do a cylinder leak down test, that will aid in finding if you have a valve issue as manicmechanic noted, when the pressure of the tester is on. a leaky intake valve will be heard backing into the carb a leaking exhaust valve will be heard in the tail pipe
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