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Topic: All of the sudden the engine started backfiring

in Forum: C3 Engines


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All of the sudden the engine started backfiring (1/17)
 6/4/24 9:53pm
RedwingvetteLifetime Member
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Waterford, MI - USA

Vette(s):
1973 Red coupe


Joined: 9/13/2002
Posts: 1741

Driving along at 70 mph on a highway and this happens. Had to be something simple but standing on the side of the road without any tools means call for a flatbed.

got it home, pop the hood, check the cap and rotor and what did I find?

one of the screws worked itself out and started bouncing around inside the cap

Next time put a drop of lock-tite on the screws



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Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

Dewitt radiator and dual electric fans
Borgeson Steering box
 


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Re: All of the sudden the engine started backfiring (2/17)
 6/5/24 8:22am
NorskyLifetime Member
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Burke, VT - USA

Vette(s):
SOLD - "The Toy" - '70 Convertible
SOLD - "The Beast" - '90 ZR-1 (#682)
SOLD - "Betty" - '28 Ford Model A Tudor
Still have - "BLKBRRD" - '78 Pontiac Trans Am


Joined: 1/23/2002
Posts: 7212

Nice sleuthing Sherlock...!!!  Glad that the issue was something simple to remedy.

And thanks for sharing...!!!



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Jim Olson 

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Re: All of the sudden the engine started backfiring (3/17)
 6/5/24 10:36am
Adams' AppleLifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
Posts: 20144

I have seen that happen before....never at a good time, either. Harmonic vibrations can cause those screws to loosen. Crankshaft/oil pump/flywheel vibrations can be transferred from the cam to the distributor thru the timing chain. Of course, the screws could have just been left a little loose, too. Glad it wasn't any worse than it was!



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Joel Adams
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Re: All of the sudden the engine started backfiring (4/17)
 6/5/24 7:29pm
BillHanna
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Cana, VA - USA

Vette(s):
1975 Stingray 71 350 engine Flat top pistons Sniper fuel injection Hyperspark ignition Vintage Air air conditioning Borgeson power steering box


Joined: 7/3/2016
Posts: 329

Last year I was on a ride with our Corvette club and all of a sudden the engine was backfiring back up through the throttle body.  It would barely run, so after getting home on a rollback and pulling the valve covers, I found that one of the exhaust rocker arms had broken.  So that cylinder would fire, and with no place for the hot gasses to go, they blew back into the intake when the intake valve opened.  If it had been an intake valve it would have just been a misfire. I replaced all the pushrods and the rocker arms with roller rocker arms -- I didn't want to go through that again!

One issue with the roller rocker arms is that they are taller, and required tall valve covers, which meant modifying the mounts and belts for the air conditioner compressor and alternator.



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Re: All of the sudden the engine started backfiring (5/17)
 6/6/24 5:14am
Kentvetteuk
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, - France

Vette(s):
1978 L48 Auto. Red with Oyster Leather interior. Owned since 1990.


Joined: 8/21/2002
Posts: 98

Pleased that it was something simple.

Last year our '78 suddenly refused to "pull", having done a 70 mile drive to an event venue without any issues.   Then when we left to drive to our hotel it would hardly run.     We had taken only a limited selection of tools, but I did manage to remove the distributor cap and check that all out, to no avail!

It turned out that the coil was the culprit, but I didn't settle on that diagnosis until it was too late in the day to order a replacement.  So, a day wasted at the hotel and a  VERY expensive ride home on a flat bed ensued.  (We discovered that the breakdown assistance here in France is woeful compared to the excellent service in the UK!)   I ordered a coil from the parts chap I have to use here now, over in Alsace, and it arrived the next morning.  If I had realised, I could have had it sent to the hotel and swapped it in the car park!

The episode has taught me to keep a few more spares in the car at all times and, carry a more decent set of tools! 😄    



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Stephen J Irons
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Re: All of the sudden the engine started backfiring (6/17)
 6/6/24 1:55pm
blu72
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Pasadena, MD - USA

Vette(s):
72 Coupe L48 4 sp Air Tilt Leather


Joined: 6/16/2004
Posts: 295

Similar problem 15 years ago when I first got the Vette running. On the way home from a party, showing off my new toy, the car starting bucking half way home. Maybe 50 miles on it at the time. Definitely an ignition problem I said to myself, but wait!! All the parts were new from spark plug/wires/coil and distributor.  Made it home but scared the wife into not riding in the car again. To this day even.....

Turned out the ignition parts inside the distributor were not good ones, a second set of points/condensor did the same thing after changing them AGAIN after 100 miles.

Change them 3rd time, now using original OEM GM parts. Problem solved. I believe the problem was the condensor only, breaking down under load. Name brand part but really auto part store junk.  😁

 

 



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Bruce
72 Coupe L48 4sp
Custom Blue/Silver/Pearl

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Re: All of the sudden the engine started backfiring (7/17)
 6/6/24 2:43pm
BillHanna
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Cana, VA - USA

Vette(s):
1975 Stingray 71 350 engine Flat top pistons Sniper fuel injection Hyperspark ignition Vintage Air air conditioning Borgeson power steering box


Joined: 7/3/2016
Posts: 329

Not specifically a Vette issue, but years ago my father in law had me drive a Mustang he had worked on.  About 5 miles from the house it shut off like the key was turned off.  I pulled the distributor cap and everything looked normal.  I hitched a ride home and later he got the car home and fixed it.  I asked what the issue was; all he did was replace the rotor.  The old one looked fine, no cracks or anything that we could see, but there was a gremlin in that part somewhere.

 



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Re: All of the sudden the engine started backfiring (8/17)
 6/6/24 8:06pm
RedwingvetteLifetime Member
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Waterford, MI - USA

Vette(s):
1973 Red coupe


Joined: 9/13/2002
Posts: 1741

Hit it back together this morning with a new cap, rotor, and points. I put a though of lock-tight on the threads so hopefully that won’t happen again.

i can’t remember the last time I changed the points but I do check the dwell every spring. They didn’t look bad but was time anyway. 



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Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

Dewitt radiator and dual electric fans
Borgeson Steering box
 


Re: All of the sudden the engine started backfiring (9/17)
 6/7/24 12:15pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1420

What about eliminating the points and convert to a Pertronics or MSD ignition?



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Re: All of the sudden the engine started backfiring (10/17)
 6/7/24 9:34pm
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 2403

AMEN! Did it many years ago. Best decision for ignition in my book. Can't beat it. Starts first time, every time. 



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Re: All of the sudden the engine started backfiring (11/17)
 6/7/24 10:36pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1420

MSD distributor and 6A spark box for me. 



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Re: All of the sudden the engine started backfiring (12/17)
 6/8/24 7:19am
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 2403

I did Pertronics. A superb electronic device. Also used the larger coil to enhance the effect. Points are a pain. 



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Re: All of the sudden the engine started backfiring (13/17)
 6/8/24 10:51am
BillHanna
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Cana, VA - USA

Vette(s):
1975 Stingray 71 350 engine Flat top pistons Sniper fuel injection Hyperspark ignition Vintage Air air conditioning Borgeson power steering box


Joined: 7/3/2016
Posts: 329

Remember when every 3000 miles you had to replace points & plugs, and an oil change?  Now its 10,000 miles between oil changes and 100,000 for plugs.  And they say cars are not built the way they used to be -- good thing!



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Re: All of the sudden the engine started backfiring (14/17)
 Yesterday 11:11am
gapl1953
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Springbrook, WI - USA

Vette(s):
1974 L82 coupe, 1990 ZR-1


Joined: 10/18/2020
Posts: 34

I've been having a problem with  my 74 L82 developing a misfire at higher rpm and progress down the rpm range. I replaced the condencer and it was good for about 400 miles and then it returned. I did this three times with the milage between the misfire developing getting shorter. Found the coil to be bad and replaced it along with the condenser. Problem solved for about 400 miles and it returned. After checking on how to test ignition componets it a old repair manual I found that both the new coil and condenser tested bad. Also read that if the coil doesn't have the correct resistance the condenser will go bad. I checked The diffrent points of resistance in the ignition system and found the 9" coil wire had 13,500 ohm resistance. Since resistance in the plug and coil wire should be 5,000 to 7,000 ohm per foot this coil wire was bad. I made a new coil wire and it tested out at 3200 ohm. I replaced the wire along with a new coil and condenser and so far so good it runs great. I hope the problem is now solved, but time will tell since I only have a little over 400 miles since the repair.

Re: All of the sudden the engine started backfiring (15/17)
 Yesterday 9:49pm
spinalman
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Lancaster, PA - USA

Vette(s):
1970 Green Convertible


Joined: 8/24/2008
Posts: 24

You guys have hit on similar experiences with my 72 Cutlass. I've been chasing a problem where the engine stops just like turning the key off. However, I have tried to restart with the ignition may work or no go. I have popped the clutch for a compression start, which sometimes works or no go. The last time it started on the 3rd compression attempt then accumulated gas in the exhaust pipe exploding with a bang.  The problem goes away or may only miss like it's going to stop, but I catch it and continue on. I have been plagued with this for almost 40 years. I can run for months without a hint of a problem. Garages simply replace points but that does not solve the problem but momentarily. I have replaced ignition run and start wires, ignition switch, coil and whatever. I'm not stupid and I've own the car since new. It has 309,000 miles on it and the engine has never been apart. I would appreciate input.

Jan Gerhart

Re: All of the sudden the engine started backfiring (16/17)
 Today 7:18am
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 2403

Jan, Your intermittent problem sounds a bit like one I had with a Park Avenue. It ended up being a wire that had been rubbing on metal through vibration. We located it in a dark garage at night, and saw the arc when the problem manifested itself. What a hair pulling frustration.



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Re: All of the sudden the engine started backfiring (17/17)
 Today 8:51pm
spinalman
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Lancaster, PA - USA

Vette(s):
1970 Green Convertible


Joined: 8/24/2008
Posts: 24

Thanks for the info. What I can't get my mind around is the infrequency. Like I mentioned in my note, I may go a year, then it occurs maybe without a complete shutdown. Other times it feels like a miss. Sometimes I just turn the key and it starts. I've pulled on the distributor wires, jiggled the ignition switch to make it happen. No resolution.

Thanks for your comments. Any info helps.

Jan

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