do I need to put back on my catylic converter

[turboreese415]

I took off my bad catylic converter from my 87 grand national and I replaced it with straight pipe I noticed since then it makes knocking or slapping noise when I drive the car for a while is this because I have no cats

 

[Raeban]

Nope. I'd be willing to bet the significant majority of members on this board have no cat. Just take a look under the car and make sure your exhaust hanger is attached or look for anything obvious that may be hitting.

 

[turboreese415]

Nope. I'd be willing to bet the significant majority of members on this board have no cat. Just take a look under the car and make sure your exhaust hanger is attached or look for anything obvious that may be hitting.

Nope. I'd be willing to bet the significant majority of members on this board have no cat. Just take a look under the car and make sure your exhaust hanger is attached or look for anything obvious that may be hitting.

 

[turboreese415]

What about my 02 sensors are they reading correct

 

[turboreese415]

Its running rich too

 

[fitz3820]

Will not change O2 readings, the sensor is upstream of the cat. What are you scanmaster/scan tool numbers?

 

[turboreese415]

Will not change O2 readings, the sensor is upstream of the cat. What are you scanmaster/scan tool numbers?

Don't know do I need to buy one the problem is after I drive it 40 about 20 mins u hear knocking from down below only when car is driven for a while not at start up

 

[gsgnnut]

Is it a rod knock? could be the oil is heating up and thinning out ? If its a stock motor you should be using 10-40. if you use 5-30 or similar light oil it likely will start to knock when it heats up. otherwise something with the exhaust is heating up and getting loose and banging around.

 

[turboreese415]

Is it a rod knock? could be the oil is heating up and thinning out ? If its a stock motor you should be using 10-40. if you use 5-30 or similar light oil it likely will start to knock when it heats up. otherwise something with the exhaust is heating up and getting loose and banging around.

Not a stock motor I'm using amsoil what weight should I use

 

[turboreese415]

If it was a rod knock it would knock on start up 2 right?

 

[gsgnnut]

10w-40 is what is normally used . It might not knock at start up. if you used too light an oil like a 5w-30 , at start up its cold and thick enough not to knock but when it heats up its way too thin and could start to knock . I had a GS with a real tired motor that didn't knock at start up but after it was fully heated up it would start to knock. thicker oil temporarily helped but it eventually it needed a rebuild.

 

[Boostrules]

Did you notice a change in performance with the straight pipe installed? I been thinking of swapping out my working cat for a straight pipe if it's a noticeable difference by the butt dyno. Hope you worked out your knock issue.

 

[ravege]

I went the other way, had a gutted cat and installed a working 3-way cat. I'd say yes, a little loss to the butt dyno, a little bit quieter, and what smelled like a very rich running engine to almost no gas smell at all.