240-Lsx

So first id like to say I have been dealing with trouble shooting this problem for a LONG time, and have tried everything.

Swapped Ls6 W/cam and ported heads into a nissan.

Car runs great at low rpm and has no issues at all, drives around 14.5-15.6 while cruzing.

At wot, as RPMS increase so does AFR. sometimes up to around 17.
But at 1/2 throttle car stays at 12.5-13.5 AFR and runs smooth to redline.

Here is what I have checked and changed trying to track down the problem, please, any input would be greatly appreciated at this point.


New:
Walboro 255lph
Benched and cleaned LS3 injectors
Fuel press. 61PSi and holds at WOT
Intake gaskets
no vacuum leaks at all
Grounds
Battery
TR6 Plugs
45% injector duty cycle
knock sensors and harness
valley cover gasket
throttle body gasket
valve cover gaskets
valve seals
RTV gasket on intake rocker arm bolts
No Knock or Detonation recorded
Map
Maf
TPS
Wide Band has been calibrated and is functioning properly


I turned up fuel pressure and it was rich until the same spot (5K) and it climbed high again.

Couple questions:

As of today i noticed the hotter the engine bay was, the lower the voltage output. started at 13.5v at cold start and was down to 12.6v within 20 mins of driving.

Can a cylinder that has no ignition be giving a lean reading on my Wide Band because of the O2 that has not been burned off?

joecar

May need to correct MAFand VE table and set PE table (and make sure PE enables).

In the meantime, you can hack the PE table.

Yes, misfires cause O2S to report lean due to unburnt oxygen.

fst100

iTrader: (5)

Have you checked the fuel filter?

240-Lsx

So a few things I forgot to mention.
Car was dyno tuned at 12.5 and was great for months and this happend out of no where. So I don't think it is a tuning issue. It also picked up a slight backfire in the exhaust every once and awhile, leading me to believe there is unspent fuel lingering.

Brand new fuel filter

And last night I changed the alternator and have the same results. I also checked the grounds and power cables too.

Next I am going to check my intake manifold and pressure check it for leaks.

One note, in 1st gear cruising at a steady 3-5k rpm, the car starts choking speraticly. Almost on a cycle of lean and normal. It will choke and go lean then return to normal, and happen again and again.

240-Lsx

Could bad O2 sensors affect the AFR after the tune where it won't run correctly at wot?

joecar

This means something broke or came loose.

240-Lsx

Well I figured as much, I just cannot track down what is malfunctioning.

Also, while idling there is a pretty strong vaccum coming from the valvecovers. Maybe I never noticed it before but is that normal? For example, I can remove the oil cap and a strong suction is holding it in place.

joecar

Do you have the fresh air hose connected from TB to valve cover...?

If you remove this hose does the level of vacuum under the oil cap change...?

jimmyblue

iTrader: (11)

Have you checked for signs of misfiring? Any of that will
spoof narrow and wideband sensors lean. Look at cylinder
mode misfires, each cylinder, as high in RPM and MAP as
you can get (this mode quits, rolling over to revolution
mode, midrange and then you lose the per-cylinder info).