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Discussion Starter #1
Okay so i just swapped my 3.8L out for a 5.0L V8 in my 91 cougar. everything went well until i started it up and let it run for about 5 minutes, reving it up a bit then go look under the hood and the CAT's are about 4,000 degrees and bright RED. lol i dont know whats going on. i did just keep the stock exhaust from the v6 that was in the could this be why? what else could cause this?
 

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The only times I have heard of that happening is from clogged cats. I wouldn't leave the stock exhaust on there but it should be good enough to drive it around.
 

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Discussion Starter #4
okay well heres the thing it says 5.0L HO on the motor but when i used the 351/HO firing order it didnt start but when i changed it to the 5.0L firing order it started first try and runs great? i dont get it?
 

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That's a good thought about the timing. That could be it.

How is the car running in general? Can it idle on its own?
 

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The wrong firing order will dump fuel that isn't firing and cause the cats to glow.

The correct firing order for a 5.0 HO (302) is 1-3-7-2-6-5-4-8.
 

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Discussion Starter #8
it didnt run on the HO firing order but when i put it on the regular 5.0 firing order it runs perfect. mind you i had to play with the distributor a bit but other than that its perfect. runs on its own, sounds good at idle and when i rev it up it sounds nice. at first it was sluggish and backfired and popped a little but once i got the timing in the right spot its perfect. it has run in a year because i was rebuilding it so thats normal to backfire and pop a little on the first start right? i think im just going to go buy some aftermarket universal magnaflow cats and see if that helps if not i guess im going to have to try something else
 

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Stupid question, and don't take this the wrong way, but you are numbering the cylinders the ford way and not the chevy way, right? The cylinder numbers are 1234 down the passenger side and 5678 down the driver's side. Also the rotor spins counterclockwise. I suppose it is possible someone swapped in a cam for a standard output 302 into your engine, but I can't see why anyone would do that, especially since almost all aftermarket roller cams use the 351 firing order, so that you have it running with the firing order supposedly wrong makes me more inclined to believe you put something back together wrong.

One other question, the 3.8 that you pulled out, did it have blown head gaskets by chance? Cause that coolant in the cats can cause them to start glowing now that an engine that is running right is in front of them. Unless that was the case, I think you probably have something messed up with the firing order. In fact, I would say double check everything with the firing order before you mess with the cats, cause it seems highly unlikely that someone swapped a 302SO cam into an HO motor. Unless, I just thought of this, maybe someone just put an HO upper intake onto an SO motor. You know what, maybe pull the valve covers off and turn the engine over just to make sure.
 

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Discussion Starter #10
actually yes the 3.8 had blown head gaskets...lol....and it runs perfect now except for the cat problem....i think im just going to buy some aftermarket universal magnaflow cats and put them on and see what happens...i triple checked the wires and everytrhing and yes i used the ford cylinder numbering..lol...ill keep you guys posted to what happens im going to replace the cats on sat....thanks for the input!
 
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