Back fire damage???

[graham]

Following my recent ignition troubles, for those who are unaware see Ignition, Part Time? (http://www.ifsja.org/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=2;t=014187#000018)
During this troubled time, there has been a series of massive exhaust back fires, every time the ignition cut out. To the extent that the un-baffled muffler has been ripped wide open and what was a small maniflod leak is now a raging torrent.
Now when the motor runs, the valve train on the left (passengers side) seems very rattly. sounds like loose tappets. This is the same side as the leaky manifold.

What damage can be done to the engine by a exhaust back fire?
What would I be looking for?

:confused:

[Lindel]

You've probably seen the extent of it, in blown seals, but if it's bad enough, it's possible that pushrods could be bent, or perhaps a collapsed lifter, but I don't think that would happen.

[Serious Johnson]

Graham:

It's not likely that an exhaust backfire would do much to the motor. As I guess you know, it's just unburnt downstream fuel from when the ignition was off-duty exploding after the power comes back and heat is made. It's possible that a really big one could send a reversion pulse strong enough to overcome the flow at the exhaust valves, but hey, the li'l buggers deal with that all the time, just in the other direction. Maybe some pipe crap could lodge between a valve and seat, but I doubt it. And its POSSIBLE that an enormous reversion pulse could attempt to slam the intake valves shut as they're trying to open, hammering the valves, rockers, pushrods, lifters, cam, chain -- you see where I'm going. This would be similar to spark knock in it's effect. But my experience is that it's completely useless to try diagnosing any noise until the manifold leaks are fixed. It's amazing how exhaust leaks, at the manifold especially, can telegraph in a way that makes them sound like something else. I've seen stethescope diagnosis fooled by it.
Please post again once the leaks are gone, and let us know in the interest of science how things are. Goood luck.

:-

[dnixon]

oh my my auto shop teacher gave me a little tip if you really want to wake up pedestrians walking down the street... *First if you like your exhaust system DON'T do this... I have never tried it but supposedly you will have to get a new exahust system... and who knows what else.. well if you have a carborated engine.. as you are driving you need to shut off the motor and then start it back up again... ITS SUPPOSE to give a HUGE backfire and possibly send you exhaust system towards the ground.. But i have never wanted to try it on my vehicle... but maybe it works... I don't know how this helps your problem but I just wanted to share my story on backfires.. I have an 83 and on the driver side exhaust heat riser it has a valve mechanism with a vaccum hose attatched... well when my vaccum was messed up this valve wasn't opening during the release of the throttle.. well this situation is supposedly ideal for some grumbling and some minor back fires and occasionly some big back fires.. I dont' know if you have fixed your backfiring issue but i fixed the vaccum and that fixed my backfires... maybe that helps...

[mdill]

I don't think a backfire could hurt the engine, it may trash the EGR valve, and blow out
the AIR tube check valves, which may take out the diverter valve also, but don't see it
hurting the exhaust valves or lifters ...

Mike D.

[Al Johnson]

Oh, yeah, you can make a big ol' shotgun blast by shutting off the ignition, coasting a second, and turning it back on. Most exhaust systems will put up with a few of these, but a weak one will blow right out. Fun when you're a teenager in the country with nothing to do.

[dnixon]

Originally posted by Al Johnson:
Oh, yeah, you can make a big ol' shotgun blast by shutting off the ignition, coasting a second, and turning it back on. Most exhaust systems will put up with a few of these, but a weak one will blow right out. Fun when you're a teenager in the country with nothing to do.nice so my shop teacher didn't lie... man he was the best... some advice from him.. don't try to use jet fuel in your lawn mower... it just doesn't work.. haha

[andy d]

i had a bad coil that was mis- diagnosed as a carb trouble due to the rich running. the backfire split the seam on a brand new muffler :eek: twice :eek: :eek: melted the core on a brand new cat too. replaced the coil and engine was fine. have you found out what the trouble was Graham?

[Glenn_tx]

Hell yeah! We spent the better part of high school scaring the Bejesus out of people on sidewalks. My buddy had a 78 Chevy truck and I had a 74 AMX. Neither of us had any problems from it as far as I know. Try it, it's fun to watch people running for cover. Just cut the ignition as you driving, pump the gas a few times, and turn the ignition back on.

[HeepofaJeep]

We do it in my friends Ford work truck all the time. Works great--especially in a 460!

[graham]

Originally posted by Serious Johnson:
Graham:
It's not likely that an exhaust backfire would do much to the motor. As I guess you know, it's just unburnt downstream fuel from when the ignition was off-duty exploding after the power comes back and heat is made. It's possible that a really big one could send a reversion pulse strong enough to overcome the flow at the exhaust valves, but hey, the li'l buggers deal with that all the time, just in the other direction. Maybe some pipe crap could lodge between a valve and seat, but I doubt it. And its POSSIBLE that an enormous reversion pulse could attempt to slam the intake valves shut as they're trying to open, hammering the valves, rockers, pushrods, lifters, cam, chain -- you see where I'm going. This would be similar to spark knock in it's effect. But my experience is that it's completely useless to try diagnosing any noise until the manifold leaks are fixed. It's amazing how exhaust leaks, at the manifold especially, can telegraph in a way that makes them sound like something else. I've seen stethescope diagnosis fooled by it.
Please post again once the leaks are gone, and let us know in the interest of science how things are. Goood luck. :-Well SJ, in the interest of science.........
I fixed the exhaust manifold leaks last weekend, took quiet some time. I post a story about that later!!!
Went for a test run this arvo, no valve train noise and runs great. Not sure whats exactly improved the performance. Ultimately it was the pick up coil in the distributor that was dickie, only cost $104. But having changed the coil, ignition module, positive battery lead and #4 spark plug plus the numerous back fires that may have loosened some gunk, it's never run better.
Should not have said.......hope the blessed Jeep Gods are'nt listening/reading.... :(

[ November 15, 2002, 06:20 AM: Message edited by: graham ]