Exhaust backfire after EGR delete

[matrophy]

Replaced exhaust manifold during transmission rebuild process and decided to delete the EGR and cap it off mainly to save me the trouble and expense of trying to replace the rusted-together tubes in the EGR system. I understood that deleting the EGR where one doesn't need a smog test to be an OK thing to do.

 

 I have slight backfires at deceleration that sound like they come from the exhaust - although I have only driven the truck for a few miles since reinstalling rebuilt 5-speed

so I'm not 100% certain it's in the exhaust. Haynes manual lists 'EGR malfunction' first when I look up 'backfire on deceleration'.

 

I gather that I may be running richer now?

 

Is a slight pop of a backfire worth worrying about?

 

Edit: I also replaced the thermostat and did a flush and fill of coolant and the engine never got to mid-way on the gauge today after significant time of idling and then driving. Now I'm wondering if the new thermostat is stuck open making the mixture richer. What would piss me off is that I tested the thermostat in hot water to make sure it would open and close like it is supposed to because the first thermostat I bought wouldn't open.

 

Edit #2: Thermostat was cocked in the housing rendering it the same as being open all the time. Once I fixed it the problem of backfiring went away. Couldn’t delete this thread.

Edited July 26, 2020 by matrophy

[Stinky]

Still illegal to delete egr, even w.o the smog check.

 

Backfire....often a sign that your exhaust is sucking air...you may have leak.  Usually it is will be at a joint in the pipe.

 

If you have none, then I suppose that it might be caused by the egr.  

 

What sort of muffler do you have?

 

A slight backfire, it sounds good to me

 

[matrophy]

2 hours ago, Stinky said:

Still illegal to delete egr, even w.o the smog check.

 

Backfire....often a sign that your exhaust is sucking air...you may have leak.  Usually it is will be at a joint in the pipe.

 

If you have none, then I suppose that it might be caused by the egr.  

 

What sort of muffler do you have?

 

A slight backfire, it sounds good to me

 

Stock muffler. Exhaust past manifold is solid. I had it all apart to pull engine and replaced exhaust manifold while I was at it so I'll check and see if maybe something's leaking. I can't hear anything obvious but I'll look more closely. I thought that installing the thermostat correctly stopped the backfires but they are back. Not loud - just little poops when downshifting on a hill.

[Charlie69]

All the tuner cars do this!  LOL

[datzenmike]

Backfire on deceleration is usually lean mixture, which is normal on a carb engine. Cylinder randomly fails to fire and is set off in the manifold by the ones that do.

 

You could try adjusting the BCDD (boost controlled deceleration device) who's job is to add a small amount of gas and air to prevent this. Adjust the screw clockwise it increase the sensitivity. Keep track so you can return to where you started if it doesn't help. Under extreme deceleration there is a fuel shut off system. There is a vacuum switch that turnd off the idle cut solenoid to shut off fuel to the idle circuit.