1990 Jeep Wrangler Hot catalytic converter

Tiny
RPALOMAREZ
  • MEMBER
  • 1990 JEEP WRANGLER
  • 2.5L
  • 4 CYL
  • 4WD
  • MANUAL
  • 13,000 MILES
The catalytic converter smokes and gets red hot when it runs for a while. I've replace the converter with a new one, but it still does the same.
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Sunday, June 21st, 2015 AT 5:08 PM

3 Replies

Tiny
CARADIODOC
  • EXPERT
Catalytic converters get red hot because something else is causing it to. They don't do that on their own and you don't replace them for that unless they have already been damaged. They get hot from too much unburned fuel going into the exhaust system, typically due to a spark-related misfiring cylinder. On '96 and newer vehicles those misfires get detected by the Engine Computer and it will set a diagnostic fault code telling you which cylinder is at fault. On yours we only know at least one cylinder is misfiring. You should be able to feel that in the way the engine runs and idles, but you'll need to do a few tests to figure out which cylinder is responsible.

The best place to start is by replacing the spark plugs and wires, and the distributor cap and rotor if you haven't already.
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Sunday, June 21st, 2015 AT 6:54 PM
Tiny
RPALOMAREZ
  • MEMBER
I've replaced plugs, rotor, wires, and dist. Cap. If it is a cylinder misfiring, does that mean I need to overhaul, or replace value?
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Sunday, June 21st, 2015 AT 8:25 PM
Tiny
CARADIODOC
  • EXPERT
No. There's a whole bunch of things that will cause a misfire. You need to figure out why this is occurring. The only thing we can assume for now is it's not fuel-lacking-related because you're actually getting too much fuel into the exhaust system.

You need air, fuel, compression, spark, and correct timing. Timing is not the cause because for camshaft and valve timing to be late, as in a jumped timing belt or chain, all cylinders would be affected equally and the engine would be very hard to start, and then it would have very low power.

Loss of spark is the most common cause of a misfire, but if a lobe is worn down on the camshaft, you won't get enough air to flow freely into that cylinder. You'll need to remove the valve cover to watch how much each valve is moving to identify that.

Low compression on one cylinder will cause that one produce low power but it's unlikely you'd feel that as a misfire. Also, you'd still be getting the right amount of air and the right amount of fuel. The fuel / air mixture would burn properly and not allow excessive fuel to go into the exhaust system.

A leaking injector will allow too much fuel into one cylinder, but there's a quick test for this to start the diagnosis. Just attach a fuel pressure gauge, then watch what happens to fuel pressure right after you stop the engine. With a leaking injector, the pressure will drop very low within perhaps as much as half a minute, usually less.
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Sunday, June 21st, 2015 AT 8:46 PM

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