popping and stuttering

[TylerMartinDelCampo]

so i have a 97 gst and when i bought it it had a 3 inch turbo back exhaust with no cat. now that i have it i had to put a cat on. since then when i punch it at low rpm it spools up to bout 11-13 psi and then it pops and stutters. then it will stay at bout 12psi and the popping and stuttering will go away once i hit like 4500 rpm? i know this is a bit vague and its a pretty noobish question but its bugging me so bad! anyone have a remedy other than just putting the straight pipe back on? i kinda wanna stay a little bit legal :roll:

[Jason Gilbert]

Did anything else get changed when you put the cat on? (Intake pipes/wiring/o2 sensors)?

[TylerMartinDelCampo]

no he said he just swapped out the pipe and then he had to raise the idle cuz it idled kinda low after he put it on. seemed like routine deal but now it doesnt run well at all when i try to rip. normal driving its fine. only when its WOT or close to it.

[John Hartman]

the idle should not have changed due to a cat install.

I'd look for boost leaks in the intercooler piping.  I'd also do all your regular maintainance.  It might just be coincidence that this started now.

I'd also check your rear O2 sensor as its near that area and may cause some sort of drivability issues.

Was the cat good?  If it is plugged, it will put excessive back pressure in the exhaust system.

Does it do this at low-no boost? Take it to the same RPM, but keep the boost down and see if it still does it.

PS, I'm going to move this to the garage, so more people can have access to it.  This is a more advanced topic possibly.

[Jason Gilbert]

So 3 things were changed during this process:
1.idle was adjusted.
2.Cat was added.
3. 2nd O2 sensor (??)

The problem is a little vague, but those 3 things are the only items affected. You would probably want to concentrate (or inform a reputable DSM mechanic) on those areas.

I dont know where to go from here.

[TylerMartinDelCampo]

yah it only does it when boosting. when i pull up the rpm and im not boosting it wont do it. no the rear o2 sensor wasnt chaged. i dont know what condition its in so ill have a look. and he said it idled lower with the cat in so that was his reason for raising it, i dont agree. the cat is good , brand new but im not sure if its high flow or not, he said it was hard to find one that size and this is what he got. how can i tell from looking at the inside of it if it is ? some one on dsmtuners said i could be running rich? any thoughts on that? its wierd, only at WOT from lower rpm ( 2000 and up til bout 4500) anything else, like if i ease onto the gas and bring rpm up slow and then get to Wot at about 4000 it wont do it and will boost fine. i think i have a boost leak tho, i spike to 15 were my mbc is set to and then i taper to 12. well thanks for the input, any other shots at it will help me out, im jsut a noob getting whipped by my turbo dsm.

[TylerMartinDelCampo]

oh and i have a off topic question, hope i dont get in trouble for it. what happend to "L & R"? i heard about them so much before on this site and now i hear they are gone?

[John Hartman]

probably knocking like a bastard if you are flooring it at 2000rpm.

What octane fuel are you using?

[Ritchie Hui]

oh and i have a off topic question, hope i dont get in trouble for it. what happend to "L & R"? i heard about them so much before on this site and now i hear they are gone?

Lowell closed his shop on kingsway due to private reasons... and openned up else where... but he doesn't do the hardcore stuff anymore.

[TylerMartinDelCampo]

94 octane everytime. knocking like a bastard eh , damn. is it ok to floor it like that? i kinda ease it down i dont literally stomp on it.  i always remember when i first got the car i could punch it anywere and it would pick up so nice and keep on pulling right to 6500 or so. maybe i need driving tips ?  :oops:

[John Hartman]

well, in 1st its probably ok because the load is alot less, but in say 3rd or 4th, that low is lugging the engine badly.  Its not a V8    it needs to rev.

If it was fine before, you probably do have a problem however.

[Kevin Jones]

Is it the spark plugs maybe? I'd check them out anyway. When my plugs are worn, and overgapped as a result, the car stutters under boost. It's worth a look.  

[John Hartman]

Good call Kevin, especially if he put in some sorta fancy ass plugs.  Just NGK BPR6ES and gapped to 0.28"  Seriously.  Tons of people post that their car is running like a bag of turds, and then it comes out that they used some sort of super fancy rare earth touched by the pope plugs.  And the rest have over gapped em, thinking that 0.28" is like a points ignition system gap.  I did that when I first bought my car.  I promptly put em back to correct spec.

I suggest doing all the regular maint items such as filters, check all your hoses and do a boost leak test.

[TylerMartinDelCampo]

sorry for not posting this earlier, but since putting in new bpr6es's and new wires my car has been unreal ! i also did a boost leak test and had a bad one at the bov flange. fixed the leak and omg. now i am running 14 psi and everytime i hit the gas it nails 14 psi and the car takes off. its so crazy, im tempted to say this is how its supposed to run.  
regular maintenance provails once again.