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Exhaust pops

Started by Bighook8, May 26, 2014, 08:38:38 AM

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Bighook8

my 68 Deville exhaust pops...seems to be mostly at the muffler when the car is cold and in fast idle. 

1968 DeVille drop top

The Tassie Devil(le)

The indication is of an extremely rich fuel/air mixture.

The unburnt gas is still burning after it leaves the cylinders.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Bighook8

Wouldn't it happen all the time then...?  Only noticeable when cold. 
1968 DeVille drop top

Jon S

Richer mixture when cold as choke is on.  Try kicking choke off after 10 seconds of starting and see if popping stops.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

Bighook8

So I should check the fuel air mixture when it is warmed up and choke off as it sounds like running rich, and when choke is on and cold...really really rich.
1968 DeVille drop top

Gene Beaird

The coil on the choke gets weak with age, so they'll be a little weak, and not open as fast as they used to.  You may just need to open the choke a little bit.  When the car is cold, I'd go take the air cleaner lid off of the air cleaner, then go start the car as you normally would.  With the car running with the choke on, try to open the choke butterfly just a bit to see if the idle goes up some, and/or the popping stops, or gets less.  If so, you may need to:
1. verify the choke isn't sticking due to dirt, and if not,
2. open the choke a bit by gently, and ever so slightly straightening the linkage to the choke butterfly. 

It is also possible that the popping is due to you getting a little more air into the exhaust via a small leak, causing unburnt fuel (no matter how well tuned the car is, there will be some unburnt fuel when the car is cold) to burn.  I'd also get under the car and look for misaligned or cracked exhaust pipe, or small pinholes due to rust. 

If the car is otherwise running well when warmed, there should be no need to adjust anything when it's warm. 

Gene Beaird,
1968 Calais
1979 Seville
Pearland, Texas
CLC Member No. 29873

Scot Minesinger

Yes, agree popping is unburned gas igniting in hot exhaust pipes.  Likely cause is too rich of air/fuel or miss-firing.  Pursuing choke issues as suggested in this thread is the way I would go first too.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

Alan Harris CLC#1513

Did 1968 have the Air Injector Reactor system? I can't remember.

My 1969 had it and it often made small popping sounds at the exhaust.

TJ Hopland

I believe most 68's had the AIR (smog) system.    I don't think they were too fancy.   I think the only time they did not inject air was when you first let off the throttle.  I think they operated at idle.   Maybe they had some sort of thermal switch that kept them from working at idle?   May be worth checking a vacuum diagram for a 68.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

SixDucks

Hi all,
Just a heads up. All of the previous replies are correct. However this can also be the initial signs of an exhaust valve not seating correctly due to age and normal wear. If all other corrective measures fail to yield adequate results it may prove worthwhile to due a compression test or even better yet, perform a cylinder leak down test.
Hope this helps.
Terry
Current:
1941 coupe
1962 Fleetwood
1988 Brougham
Previous:
1956 Series 62 Sedan
1963 Fleetwood
1975 Fleetwood Brougham D'Elegance
1989 Brougham