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Discussion Starter #1
ok guys here is the story, i thought i had a precat failure, so i removed the precats, and rebuilt entire engine

the engine has less than 10 miles on it, but it has poor acceleration and bogs down when i hit the throttle, all the o2 sensors are new, i am baffled as to what it could be

there is no check engine light, so im stumped, any ideas guys???


thanks a bunch from a guy with $2500 in a brand new motor and she still doesnt run right
 

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Do a Compression Check.. This will tell if One of the Cams are out ( It'd have to be the Exhaust.. as the Intake will toss a Cell )..

Need to know about the Intake.. Stock or Aftermarket..

Clean the Maf..

Can you Read the Fuel Trims from the OBD2 Port?..

Cap
 

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Discussion Starter #5
engine is a brand new rebuild....i replaced the manifold to delete precats, and no main cat is still there.....i did compression check all are normal
 

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To verify that, remove the main cat and shake it - some crap may come out. (But then again - maybe nothing will come out and it is still bad.) I would not trust that main cat at all. If you did have precat failure, T-bone (and Cap) are right as rain. You are lucky you asked us! A clogged main cat can ruin your brand new shiny engine.

We've just seen that before and it is vewy vewy baaad. You probably caught it in time (just 10 miles).
 

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It is very hard to understand how an owner could be familiar with this site and not know that in the event of PDS:

1. Replace engine
2. Replace manifold (or decat)
3. Replace muffler

This has been documented for almost 10 years.
 

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I am confused, too, by "and no main cat is still there". Is it "and no, main cat is still there" or "and no main cat is there (anymore)?

If the main cat is gone and it is a good rebuild, look for the basic things that might have happened wjhen replacing the engine like electrical connections, intake air leak, MAF installed backwards (it happens), and things that an OBD-II scanner might pick up. Did you do anything else when you replaced the engine?
 

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10 miles is not usually enough for a CEL -- at least many CELs take 1 or two complete "drive cycles" to appear (20 minutes above idle speed after a cold start).

Odds are great you have a MAF issue, or a wiring issue as others have said.

So, what was actually found wrong with the old engine? Cyl walls scored, bore out of round, rings gunked up?



your main cat is clogged it is full of your precats replace it and HOPE that not much of it was sucked into your new engine.
It would take a miracle of science for ceramic material to get sucked up the 2-3 feet through several bends and into the head during startup or valve overlap.... that or you'd have to put a shop vac on the throttle body and hold the throttle open while rotating the crank by hand. Hopefully the OP didn't do that.
 

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Discussion Starter #14
sorry guys i didnt mean to confuse any one

i blew the engine back in may and thought it was caused by the precats so i rebuilt the engine and eliminated the pre cats.....the new engine didnt run right so i pulled it out and sent it back to machine shop for round two, round two took care of the low compression after the first build....now it is in the car with no pre cats, and yes the main cat is still on the exhaust....

the car still bogs down, doesnt throw a check engine light, i m at a loss, monday i am cutting out the main cat and going from there
 

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Sounds like another case of why rebuilt engines suck. Go for round three.
 

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Discussion Starter #16
i just checked compression tonight, it is 180 across the board...i am pulling the cat tomorrow

now when i replaced the manifold with one that deleted the precats, one of the factory precats was already punched out, the other was pretty well melted together...

i didnt find any pieces of the precat in the exhaust system
 

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Replace the main cat. The pre-cat material didn't just disappear, its currently clogging your main cat and preparing to FUBAR your engine with excessive back pressure. Read the Precat death syndrome sticky.
 

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Discussion Starter #19
The engine now has a manifold with no precats....thanks for everyones help....and im pretty sure the engine is built good...everything but the cams crank block and head were new....I am pulling the cat tomorrow
 
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