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Discussion Starter #1
Ok, here's the deal:

I have a '99 Cougar 2.5L V6 5 Speed with ~105,000 miles on it. Bought it from a used dealership at 94,000 miles, and some things have gone bad. Most I already know.

Needs: New Oil pan gasket, front right wheel bearing, and a new ICV. There are a few other problems that I am not able to narrow down.

My car hesitates under 3400 RPMs. It feels like I am driving against a wall of air. But once it hits 3400RPMs, BOOM, it blasts off full acceleration no problem. I have read that it could possibly be the IMRC (leaving the secondary butterfly valves open). But the CEL code makes me think it might be a clogged or bad cat. Would a clogged cat also throw this symptom? I have already replaced all 4 O2 Sensors btw.

Another thought is that I might have a vacuum leak causing the P0420 code. Could that also be causing the hesitation? From what I've read on this site it sounds like the IMRC but the mechanic at the Ford Dealership told me that the butterfly valves were opening. I'm not sure how much I trust that opinion though because he did not take more than a 30-second look at the butterfly valves and the engine was running cold.
 

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No, the P0420 code is most definately a clogged cat issue. I'm not sure which one as these cars have 3; one in both headers (pre-cats) and the main cat. I'm thinking one of the pre-cats.
 

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Discussion Starter #3
Yes mine has 2 pre-cats and 1 main cat. How would you recommend I go about unclogging it and making sure it doesn't get clogged again (at least for a while)?

And is that the reason for the hesitation under 3400RPMs? By hesitation I mean if I floor the pedal it shakes, bucks, whatever you wanna call it, until it hits 3400RPMs and then like clock work takes off.
 

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Discussion Starter #5
Sounds good but before I do I want to know if the clogged cat is the reason I am having the hesitation symptoms.
 

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It could be something as simple as a Dirty or malfunctioning cat monitor.

Before you start throwing any money at it, switch the front and rear lower cat monitors (oxygen sensors). The front is below the oil filter, the rear is in the Y-pipe behind the oil drain plug. Clear the codes, and see if it comes back. If the same code comes back, it's a problem with the cat; if a different code comes back, it's a problem with the sensor.
 

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Discussion Starter #7
I have already replaced all 4 O2 sensors as I did have the P0171 CEL code before. This is the only code that came back. Guess it's time to replace a pre-cat :facepalm:.
 

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Discussion Starter #8

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The Low Coolant sensor is not the same as the Coolant Temp Sensor. The level sensor is in the overflow tank, while the temp sensor is in the coolant crossover.
 

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Good thread. I am sure you don't want to hear it but there are a lot of posts on here about hesitation problems. There has been a lot of products and parts purchased for the hesitation problem but there is no conclusion on what causes it.

I have the same problem right now. I just bought a new fuel pump and fuel filter. Guess I'll try that?.? I have tried quite a few other things also but can't solve it. Good luck and let me know if something works!
 

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The problem is that there are about a dozen different things that COULD be causing it. None are really much more rare than the others, so it's a delicate process of elimination.
 

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some one needs to make a post i guess of a list of what can cause the bucking or hes, of the cougar, parts from spark plugs to the butterfly valve sticky, just a list or so instead of reading all the different post of the different solutions.
 

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I got this same code 2 weeks ago. My car has been sluggish about 3 months after ive got it. So far I replaced my EGR valve and DPFE sensor. Ive also gotten all of the EGR passage ways cleaned out. After I had that fixed this code poped for me... I still have yet to swap out my sensors to see what the problem is. The light went off about 4 days ago. It would be sweet if my problem was magically solved because i hate throwing money at the same damn problem.
 

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thats what i dont want to do is keep blowing the money that aint doing a thing, i want to do it the first time !
 

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i had the P0420 CEL and when i got my dual flowmasters put on the CEL went off and hasnt come back on since
 

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i am having the same problem with everything. i dont have to money to keep throwing stuff at it. i hope someone can figure out what causes the problems. the car ran great when i had it in hawaii but i shipped it to philly and it sat for a year while deployed. its been to two mechanics and no answer.
 

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New coil pack killed the 0420?

I have both 0420 and 0430 codes though... think I have to deal with gutting.
 
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