Cut off cat and straight pipe ?

[IanRosean]

I have had my 00 Bonneville for about 8 months now and I have always had a cat code i think its like P0420, my fuel economy is terrible it seems like i get about 40-45 MPG per quarter tank of gas and even less on the highway, would it increase my MPG if i just cut the cat off and straight piped it ? I know the check engine light would always be on but that does not bother me and i don't plan on ever selling the car either.

[nos4blood70]

You could weld in a test pipe in place of the cat, however I would at least get an emulator from ZZP to get rid of the code. The PCM might be trying to test the cat which will make the car run rich, ergo lowering your fuel economy.

You could also get a Magnaflow cat welded in instead which could get rid of the CEL.

How's the other maintenance on the car? There may be more to the bad fuel economy problem than just the cat. Does the car feel alright? Steady power, etc?

[IanRosean]

thanks for the quick reply,
Everything else on the vehicle is running fine, it is about to hit 148k and I have had all the maintenance done on it EXCEPT the o2 sensors.
one thing it does after sitting cold overnight or while im at work when i first start the car it does blow out alot of white smoke out the tail pipe but it does not affect performance and the power seems pretty steady throughout the whole RPM range.

[IanRosean]

And when you say get an emulator what do you mean by that ? I am very interested in fixing this and gaining some MPG, can you shoot me a link to the ZZP site with what I need ? I have the 00 Bonneville SE

[nos4blood70]

Here's the link to the emulator:
http://shop.zzperformance.com/store/p/4 ... lator.aspx

That white smoke should just be steam which is normal. When the weather gets warmer that should stop.

[IanRosean]

The weather is warm I'm in florida lol, I read up a little more and seen something about it being oil leaking in somewhere but that it wouldn't really hurt the engine much, and I've noticed I have to change my oil pretty frequently but it doesn't leak onto the ground underneath the car.

[nos4blood70]

White smoke would be burning coolant, which is VERY bad. What's the state of the lower intake manifold gaskets as well as the upper intake? Have they ever been changed?

[IanRosean]

I have only had the car like 7 months the only thing I have done is a complete tune up with all premium plugs wires and filters, and one of the coils and the module underneath went out and the car was misfiring so I replaced the coil and the module. Are you sure its coolant? wouldn't my car be running hot then ? because it definitely does not run hot, but I am planning on re doing the heads sometime in the near future. My father in law told me it was most likely oil leaking through the valve seal or something like that.

[nos4blood70]

Don't do the heads, there's no point. 3800 head gaskets are bullet proof.

Check your coolant level. Sounds like the car might need a new UIM and LIM gaskets. How does the oil look?

[IanRosean]

The oil looks alright, I just checked coolant level in the reservoir and it was kinda low so I filled it, i'm guessing LIM and UIM is upper and lower intake manifold ? I have never done it before in my life but I'm sure they need to be changed, is there a tutorial somewhere ?

[nos4blood70]

You are correct. Here's a write up:
http://www.pontiacbonnevilleclub.com/fo ... c3591.html

If you take your time and pay attention to detail I think you could easily knock it out in 6 hours at the very most, even if it is your first time.