Cause of overheating exhaust?

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sdoan
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Joined: Sat Jun 23, 2007 2:02 pm
My tercel:: 1983 Tercel 4wd DLX 2nd owner (sold), 1984 SR5 3rd owner (sold), 1984 with 4A engine and factory sunroof SR5 3rd owner.
Location: Bellingham, WA

Cause of overheating exhaust?

Post by sdoan »

The exhaust system is running hot (roasting smells and touching tail pipe outlet burns the fingers). I suspect it is the catalytic converter overheating. Normally a cat overheats due to too much fuel, but car is running well (not misfiring), timing recently set to 10*, air filter is recent, float level is correct and choke opens completely. Is there anything else that would cause excess fuel in the exhaust?

1984 FED Tercel with stock carb and emissions.

Thanks,
Shawn
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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Cause of overheating exhaust?

Post by Petros »

Sounds like the AAP might be leaking fuel into the intake manifold through the TVSV. Pull the vac line from the AAP on the carb and see if it has fuel in it. A good temp fix is to just cap both ends, it is not needed for normal driving, only for cold start and driving. So it might be a bit baulky untill it warms up. Besides the timing, that is about the only thing that would cause a hot exhaust.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
User avatar
sdoan
Top Notch Member
Posts: 392
Joined: Sat Jun 23, 2007 2:02 pm
My tercel:: 1983 Tercel 4wd DLX 2nd owner (sold), 1984 SR5 3rd owner (sold), 1984 with 4A engine and factory sunroof SR5 3rd owner.
Location: Bellingham, WA

Re: Cause of overheating exhaust?

Post by sdoan »

Thanks Petros!

Checked the AAP and it was OK (no fuel in line). Did a minor carb rebuild (had a kit) and found the carb to manifold bolts were not tight (not loose, but nearly), passage for the powervalve piston was blocked by gasket material, the fast idle speed setting and throttle positioner settings were off. Everything else seemed OK.

Starts, idles and drives well but exhaust still gets hot.

The ceramic catalyst is broken into several large chunks (too large to drop out) but they do not seem to be restricting the exhaust. Any reason broken ceramic would run hotter?

Thanks!
Shawn
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Petros
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Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: Cause of overheating exhaust?

Post by Petros »

no, I doubt that would cause it to run hot. backed up cat usually results in cooler exhasut, and low power. check for other vac leaks in the system, that makes it run lean with hotter combustion. check the manifold bolts between head and intake manifold (easy to check with the carb off, with the carb on more difficult, need open end wrench to reach underside bolts).

Double check your timing, exhaust temp rises with less spark advance because fuel is still burning when exhuast valve opens so higher exhaust temps. Also check that mechanical advance is working properly (either remove dist cap and see if it moves freely, or check with timing light, should advance when you rev the engine). Usually lubricating mech advance with spray lube, and working it back and forth frees it up (sometimes you have to dismantle dist and clean parts of rust and gunk).
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)
User avatar
sdoan
Top Notch Member
Posts: 392
Joined: Sat Jun 23, 2007 2:02 pm
My tercel:: 1983 Tercel 4wd DLX 2nd owner (sold), 1984 SR5 3rd owner (sold), 1984 with 4A engine and factory sunroof SR5 3rd owner.
Location: Bellingham, WA

Re: Cause of overheating exhaust?

Post by sdoan »

Thanks Petros! Will check manifold bolts. Timing advances nicely.
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