Exhaust popping.

[Rickerbucks]

I was given to belief that exhaust popping was from a rich condition with unburnt fuel popping though the exhaust.

This happens to me at light cruise so it happens a lot and is embarrassing.

My AFR seems fine at about 11.5 - 12.5 whilst this is happening. Is timing a factor? I have it at about 37 degrees.

It seems to have got worse since I changed my timing trim numbers to zero.

Any thoughts.

 

[55Belair]

I am pretty sure that a rich pop will come back through the intake. If it pops through the exhaust, I think that is indicative of a lean condition.

 

[Rickerbucks]

Sorry. Typo. Yes the pop is a lean condition, but the afr does not seem to be lean.

 

[Craig Smith]

Actually, rich comes out the pipe and lean goes through the TB typically. Of course anything is possible, but whenever I see a car popping through the pipes the problem is solved by removing fuel.

Here's my take on this. If you are coasting, the TB is alomst all the way shut. Therefore, with almost no air going through the engine, you need almost no fuel. If you have enough fuel going through this thing to actually register an AFR richer than 15.94:1 during decel, it is my opinion that you are over-fueling the engine there.

 

[Rickerbucks]

AHHHHHHHH

So to MUCH fuel will cause the popping. Candidly I'm getting myself confused.

So 15.94 on decel IS OK?

I DO have a very rich condition on decel. It is like 9 - 10:1 when I take my foot off the gas. BUT the popping does NOT happen on decel per se, it happens as holding a cruise speed. ie 5th gear, 1700 rpms holding at that, afr 12:1 or so and pop pop pop.

I think row 2 and 3 from the bottom of the VE map are about 75 and the cell that this occurs in is the fourth row from the bottom and the number in the cell is 47.

HOWEVER, it seems to me that I cut the VE numbers in row 2 - 3 to about 20 - 30 before and the popping was a lot WORSE. I INCREASED these cells to 75 to reduce it. Maybe I put in SOOOOO much fuel the poppng went away because it was affectively flooded.

I'll play with it.