Part throttle stumble 00 LS1 - NJFBOA - Home of New Jersey's Camaros and Firebirds

Kat · 10-06-2009, 06:24 PM

Going into second gear about 3/8th throttle the car stumbles falls flat on its face, hits second gear and does that for a little bit. Then takes off and goes. Car does seem down on power from what it was when it was new. The stumble problem is itermittent also.

Things done..

Cleaned MAF
Cleaned IAC
New plugs, wires, front O2's, fuel filter, fuel pressure is dead nuts on 58 psi all the way through the RPM range.

The auto xray shows that everything is working aside from going a little bit lean.. Which I atest to factory programing.

Odd ball thing about is that it does throw the P0420 code for cat inefficeny (also P0137 and P0157). As far as I know those codes wont throw the car into limp home mode.. Then again I never looked into it either.

Mods done to the car are mostly suspension stuff, magnaflow cat back, SLP airlid and K&N.

Any ideas? Maybe it just might need the Amsoil mod...

JL8Jeff · 10-06-2009, 06:56 PM

Might be the rear 02 going bad and not giving a good signal. That might cause a false lean reading(more than 25% off) and going into limp mode.

Kat · 10-07-2009, 08:12 AM

Alright... sounds logical.. We'll see on friday when the car gets a "tune" to turn off the rear O2's..

Whiplash Performance · 10-07-2009, 09:41 AM

Quote:

Originally Posted by Kat

Alright... sounds logical.. We'll see on friday when the car gets a "tune" to turn off the rear O2's..

Does the car have headers?

Kat · 10-07-2009, 11:01 AM

Nope stock manifolds and ypipe.

GP99GT · 10-07-2009, 07:59 PM

rear O2 doesnt effect fuel trims it just tells if the cat is working properly or not...TPS? probe the TPS and see if it has a clean sweep of voltage from 0 throttle to full

JL8Jeff · 10-07-2009, 08:04 PM

Quote:

Originally Posted by GP99GT

rear O2 doesnt effect fuel trims it just tells if the cat is working properly or not...TPS? probe the TPS and see if it has a clean sweep of voltage from 0 throttle to full

That's what I was just thinking, the rear 02 shouldn't have an effect on performance. It would be the front O2 sensors showing a lean condition that could cause problems. Could be a cracked hose or air leak causing the lean blip and stumble.

KirkEvil · 10-07-2009, 09:35 PM

does it only do this going into 2nd?

Kat · 10-08-2009, 08:10 AM

Nope not always going into second and the last I checked the TPS was good. Which was a few days ago.

Kat · 10-12-2009, 06:35 PM

More to this. Borrowed a friends Snap-On Modis scanner.. Seems that the LTFT are hitting 25% at part throttle and the STFT are arround 60%. Under WOT the front O2's are reading way lean... Funny the FP is dead steady at 58 PSI.. Wonder that since it is almost a 10 year old pump that it can't keep up anymore.

Tomorrow's project.. Ohm out the injectors, change the fuel filter again and do a volume test on the pump... yay...

S.J.SLEEPER · 10-12-2009, 07:17 PM

bad cats? bad o2's? ........ or better yet a 5 volt reference issue?

JL8Jeff · 10-13-2009, 11:25 AM

Could be a vacuum leak somewhere with a cracked hose or something.

bobbyn362 · 10-13-2009, 01:22 PM

Is the mass Air stock?

GP99GT · 10-13-2009, 04:13 PM

a steady 58 PSI sounds fine to me, if not a little high (my mustang has 40ish psi at the rails). Check for vacuum leaks first before you go tearing apart your fuel system, clean your MAF, stuff like that.

Kat · 10-15-2009, 06:53 PM

The MAF is stock, the FP is correct for a LS1 car. Fords are rated much lower. Cleaned the MAF, the O2s are err 2-3 months old, as far as I can tell there is no vac leaks ( did the carb cleaner test)

Possiblities.. Cats clogged.. Im saying no, mostly cause when the car is seeing fuel through it, the fugger pulls quite nicely. Just seems to be part throttle like when you are gently trying to pass someone it just flutters, falls flat on it's face then slowly picks back up when the O2's see burnt fuel..

Other possiblity is that the O2's are just junk out of the box and should try some NTK's

Next one is that around where the EGR tube you can hear what is a vac leak (wasted a bit of the carb cleaner in that aera) could be that the EGR valve is stuck open.. But that would mean that it would run like crap all the time tho..

Time for a beer.

B4C · 10-15-2009, 07:35 PM

You can kill o2's really quickly if they get contaminated with certian types of RTV.

Kat · 10-15-2009, 07:47 PM

Good thing nothing was done to the car that required RTV

JL8Jeff · 10-15-2009, 08:43 PM

AC Delco O2's or some other brand? I had the heater circuit go bad in a brand new AC O2 so I had to pick up another one to get through inspection.

Kat · 10-16-2009, 08:07 AM

Nah not AC's good old Bosch. Im guess that Im one of the few that hasn't had a problem with them over the years. Then again with the luck that I have anymore I could have gotten the worse O2's of the group.. lol

SilverDropTop · 10-16-2009, 09:56 AM

Why not remove the egr system and plug it since your getting a tune anyway? No check engine lights when it flutters correct? No other codes?

Kat · 10-16-2009, 10:44 AM

Quote:

Originally Posted by SilverDropTop

Why not remove the egr system and plug it since your getting a tune anyway? No check engine lights when it flutters correct? No other codes?

EGR is turned off now.. Haven't gotten to take it out yet due to this lovely weather..

Nope no check engine lights at all. Figured that it would get a lean code but doesn't...

This is kinda odd for me to figure out. Usually Im on that **** like flies man.. lol

sweetbmxrider · 10-16-2009, 12:50 PM

if you still have access to a scan tool with data stream, look at the ltft at idle. if its high, rev it to 2500-3k rpm. if the ltft drops significantly, i would look for a vacuum leak. my thoughts....

GP99GT · 10-16-2009, 03:50 PM

ive never had a problem with bosch, had them in my last 2 mustangs...but who knows, could be a bad 02. could be lots of things. like sweetbmxrider said though, datastream is wonderous

Kat · 10-16-2009, 09:23 PM

Quote:

Originally Posted by sweetbmxrider

if you still have access to a scan tool with data stream, look at the ltft at idle. if its high, rev it to 2500-3k rpm. if the ltft drops significantly, i would look for a vacuum leak. my thoughts....

Will do tomorrow. Can do that with the auto x-ray..

If I can figure this out before Nov 1st for the shootout at Island I'll have the 2kZ28 there looking for low 13's.. I know the vvert wont be done by then.

S.J.SLEEPER · 10-16-2009, 09:41 PM

have you removed the egr & looked @ it? it is possible to be stuck slightly open by a piece of carbon between valve & seat.

stick car? auto?