Hey everyone,

I have a 1996 Vanden Plas, US spec AJ16 bwith California emissions. I've been having some issues with intermittent poor idle quality and multiple cylinder misfires at part throttle cruising. When I lay into the throttle everything cleans up nicely.

I plugged in a global obd2 data logger to see if i could pin point the problem but havent had much luck. The only red flag I've noticed is that bank one, cyls 1 2 3, switches out of closed loop and into open loop right as the intermittent issues start. The only codes i get are for multiple cylinder misfire and possible catalyst damage due to misfires.

What would cause bank 1 to go open loop while bank 2 stays in closed loop?

I know each bank has its own o2 sensors and knock sensors but beyond that everything else is shared correct?

 

I would suspect a cracked exhaust manifold or bad o2 sensors. Check the LTFT and STFT and see what you see.

 

The car does have a cracked manifold. The rear manifold has a crack over in between ports 4 and 5. The LTFT1&2 are both reading +6.2% The STFTs fluctuate a bit, 0 to +24.2% on bank one and -6.3 to +24.2 on bank two. They usually stay in the 20s. The B2S1 o2 sensor is dead, stays stuck at .005 all of the others read around 1.2 +/- .150 at idle.

Coolant temp seams to be reading correctly 209° F after a 10 mile drive in warm weather.

MAF reads .01 lb/min at idle. That seems low to me but i dont have any numbers to compare to.

When bank one goes into open loop mode it STFT goes to zero until it goes back into closed loop. Its o2 readings drop down to .550

It seems odd to me that bank two isnt the bank going into open loop as it has a bad o2 and a cracked manifold.

I'll get a new o2 sensor on order and see if theres an improvement.

Any thoughts on the rest of the numbers are appreciated.