OT exploding 84 Chevette

fixerupper · Nov 21, 2009

It'll blow the muffler wide open if I let up on the gas too fast for the first five miles or so after a cold startup. What a bang! Lights up the countryside if it happens at night. Letting up on it slowly avoids the bang, but what gives? I've been scratching my head about this for several years and several mufflers too. I had a straight pipe on it for awhile to avoid the damage but got a fixit ticket for that stunt. It still did it with the straight pipe. Last night it lit up the countryside for my son but the muffler didn't open up this time.

It's obviously an over rich situation from the choke combined with a cool exhaust system allowing a buildup, but no other vehicle I've ever owned did this.The exhaust is tight with no air leaks around the manifold area, or anywhere, as far as that goes. The timing is right and it's not chugging from being over choked. The converter is not on it anymore. Could that be the reason for this? I have more invested in mufflers than the car is worth! Jim

ted regentin · Nov 21, 2009

I can't tell you for sure on a Shovit, but on some Chrysler products if the cat is gone backfires destroying a muffler is very common.
Hope this helps,

504-2 · Nov 21, 2009

A converter would burn the gas and not let it build up in the exhaust.( they are not expensive on the net.)I used to buy them on spechal for the shop for 40.00 each.(sold for 125.00)

Wesley Stephens · Nov 21, 2009

I had an 82 F-100 with a 3.8 V-6 (yes, that's right) and it would do the same thing. I eventually took the air pump off of it because of a bearing failure and it stopped. I was in high school at the time and had a local welder make a hollow muffler out of 16 ga. steel so it wouldn't bust. I had a lot of fun making that thing backfire. I had a manual choke on it and I'd make it flood so it would backfire and sometimes I'd switch it off and let it load up and switch it back on. I still do that sometimes with my 68 Ford, but it's not as much fun with glass packs because they don't hold the vapors very well.

big fred · Nov 21, 2009

Most carbureted emissions cars of that era had a dashpot on the carb linkage that would keep the throttle plate from closing too fast. After 25 years, it may have worn out and the throttle is simply slamming shut too fast. Should be an inexpensive fix.

Kris Golden · Nov 21, 2009

sounds like the timing is too far advanced. Back in high school I had a 78 Mustang II [171 V-6/4 speed manual] and it did the same thing. I was really impressed with the way it ran [it would pop a wheelie!!] and it would get 27 MPGs so I left it alone. The kid I sold it to blew the entire exhaust system off it in a matter of days and his dad set the timing back so it wouldn't do that any more.

S.Crum · Nov 21, 2009

Had that happen with Dad's 68' Chevy K-10 once. You'd thought I blew the whole truck up from the way he b***hed. I even put a new muffler on it.

RickieBlue · Nov 21, 2009

This vehicle had a pulse air injection system to burn off any escaping emissions in the exhaust manifold...I believe there is check valves on each manifold runner where the piping attaches..a slight leak will allow it to suck air into the exhaust when it should not be there....thus creating your problem....I believe they can be plugged off and then your problem will go away.

Allan in NE · Nov 22, 2009

Hey Pard,

Yer making me feel old again. :>)

Standard transmission with an air pump, right? Bad diverter valve or it's vacuum hose is off.

Allan

fixerupper · Nov 22, 2009

Well thanks for the ideas. I'm gonna have a little spare time today to check her over. One $50 muffler equals somewhere around 700 miles worth of gas at 35 mpg.

My son does most of his trucking in this area around my home but he lives 30 miles in the other direction so he parks the truck here at the farm and drives this car home. It's kind of a letdown to crawl out of and 18 wheeler and get into a Chevette. Jim

JDemaris · Nov 22, 2009

I remember doing that on purpose when I was much younger. While going down the highway fast, I'd turn the IGN key off for awhile, and then turn it back on - and get a loud bang. Sometimes the muffler would blow to pieces.

I had that same problem with several Chevettes that had two barrel carbs. Never had the problem with the one-barrel versions. I'm not sure what the problem was, but I had the air pump disconnected on them all.

I'm still driving two 1981 Chevettes, but they are both diesels. No such problems.

fixerupper · Nov 22, 2009

This is a 2bbl. Wish I had a diesel. I've told this story before, but I went to O'Reilleys for spark plugs for this car. I didn't have the plug number with me so the kid behind the counter looked it up in the book. He looked for awhile and then asked me " Is it a gas or a diesel". I politely told him it's a gas. I should have told his it's a diesel and let him search for awhile. Jim

JDemaris · Nov 22, 2009

Yeah, but he would of found something. Delco sells an AC 33G as a "spark plug" in some listings for the diesel Chevette. Actually, it's a glow plug, but who wants to mince words?

OT exploding 84 Chevette

fixerupper

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ted regentin

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504-2

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Wesley Stephens

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big fred

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Kris Golden

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S.Crum

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RickieBlue

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Allan in NE

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fixerupper

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JDemaris

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fixerupper

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JDemaris

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