severe top-end sputter

[D-Con]

I just installed a o/r x-pipe and FR-500 exhaust in my otherwise all-stock hardware Cobra.

Before I did the exhaust I had downloaded one of the standard programmed Predator tunes for mildly modified stocker, or whatever they call it, and also turned the rear o2 sensors off. It seemed to work fine with the stock exhaust on it.

Now I have a bad sputter at the top of 1 and 2 gear (didn't try for 3). It doesn't seem to have a problem if I just mash the throttle in a higher gear but I didn't try to run it all the way out like that. :shrug: I cant tell if it's fuel or spark, but my guess is fuel.

I just remembered I should have unhooked the battery to let the computer re-learn, but haven't tested it yet. Could that be all of it?

I'm a newb to Cobra tuning...help?

 

[Posi]

Get that thing on a dyno and have everything checked.

 

[04CobraMatt]

Canned tunes suck. I would put back the stock tune (dont worry about the SES light) and try it out again.

If it goes away and you dont plan on a custom dyno tune anytime soon, get some MIL eliminators and be done with it.

 

[S.V.T.]

dude that canned tune is CRAP.
my buddy used one after an xpipe and catback install (only mods) and the car kept stalling out.
get a custom tune, or leave it on the stock tune.

 

[01cobravortech]

Generic canned tunes can suck the big one at times.

 

[D-Con]

Boy you guys are right. Put the "HP stock tune" , (meaning user adjustable stock tune) back in with the rear o2 stuff turned off and no other changes; problem solved.

I Let off as soon as sputter started. :shrug: Now I just hope I didn't hurt it :nonono: :mj: Didn't think just exhaust would lean it that much with stock pulleys and intake. I'm an idiot.

I wanted to try the exhaust and see how it sounded inside the car. I am going to be swapping the Whipple on this weekend I think and already have a tune ordered from Amazon.

I learned a valuable(hopefully not costly) lesson, NEVER change anything without having the WBO2 on it to verify everything OK afterward. I'd love to get a dyno-tune, but there's nobody within 500-miles of Salmon, ID that I know of.

I pulled a plug (#7 on a GM) and the piston top looks nice and black and the plug was clean but didn't look overheated. I am going to guess the factory wide gap platinum plugs blew out before I could hurt it. I'll have to compression test or leak-down to be sure.

Thanks for all of the advice, you guys were right-on.

 

[D-Con]

I'm replacing the original plugs and am going to verify everything is OK with a compression test. It looks like others are getting around 150 psi? I'm at 4000 ft so expect a little less than that, though I'm not sure how much lower. As long as they are all the same I'll assume I'm in decent shape.

Also, how do you disable the ignition? Just unplug the COP's, or is there a fuse or relay that can be pulled?