GageBrand

there is a thumping noise coming from my exhaust and a significant loss of power. the engine isnt making any irregular noises. I was driving all day today and the car was fine, then I took it home for about an hour and when i was driving it started doing this, any reason why or what could be causing the misfire, I just replaced spark plugs, cap and rotor about 3,000 miles ago but not spark plug wires.

mcrandrz

Thats a backfire. Probably a clogged cat. If you have access to a pressure gauge I would remove the o2 sensor and test pressure. 1-2 psi is a clogged cat.

The easy way. Smack the cat with a hammer. ( not extremely hard but enough to shake it a little bit) any rattling inside? If so its failing and probably clogged.



Other thing. Check the gasket on your egr. I've had one break on me before and out caused this


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GageBrand

There is no cat, and my egr valve hasn't worked since I have owned the car but I have never had a misfire. This is a carburated model by the way. I replaced cap, rotar and plug wires today, Could a intake leak cause a misfire?

mcrandrz

So the egr is stuck closed or you have a piece of metal blocking it?

Now this "misfire" does it only happen at idle?

An intake leak would be a vacuum leak which would cause a surging idle.

What your describing sounds like an exhaust leak from the manifold. Test this way. Get a can of seafoam. Start your car and dump it straight into the carb see where the smoke comes from. There should be none coming from the engine bay.


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GageBrand

It is only a slight misfire and it happens when im accelerating and a little at idle, its a slight thumping noise coming from the exhaust but the car has a significant loss in power. I think my timing is off but im not sure how to reset the timing.

GageBrand

As for the EGR im not sure, I tried replacing it and it didnt like the new one and the one that is on there now is a discontinued part.. the weird thing is when I ran the codes myself before the misfire I got a code 32 and 34 EGR and MAP sensor but when I unplug the map sensor the check engine light would go away?