Hi;

Im new here and im sorry for my bad english.

I have 1997 camaro z28.

During rough idle problem i noticed that if the engine is cold , bank 1 and bank 2 injector cycles are equal. but after warm up bank 1 injector cycle 1ms bigger than bank 2.

I changed HO2 sensor but nothing changed.

İs it related with Pcm or something else.

Do you have any idea ??

 

The pulse width for each bank is determined by a multiplier called the "long term fuel correction" (or "LTFT"), or BLM (block learn multiplier). The PCM makes a calculation of the fuel mass required, based on the mass air flow measured by the MAF sensor, divided by the air fuel ratio. It then sets the pulse width at the value required to deliver that mass of fuel. The O2 sensor tells the PCM if it made the correct calculation.

If there is a departure from the target A/F ratio (nominally, 14.7:1 on closed loop), and occurring over an extended period of time, the PCM will adjust the LTFT to correct the mass fuel calculation, and bring the A/F ratio back to 14.7:1, based on O2 sensor feedback.

Since each bank of the engine is controlled independently, there can be a difference in the injector pulse width, due to differences in the "learned" LTFT's. A small difference is common. A large difference indicates an imbalance in the operating conditions of the two banks of the engine.

This could be due to misfires, a vacuum leak on one bank, an exhaust leak before the O2 sensors, a stuck, leaking or dirty injector, uneven valve lash adjustment, a leaking fuel pressure regulator, a faulty O2 sensor or faulty O2 sensor wiring. Anything that can affect ONE bank of the engine can cause the difference.

In open loop (cold start) the PCM may ignore the LTFT's and simply use the standard calculation for both banks, resulting in identical pulse widths.

Under what conditions do you see a 1 mSec difference in pulse width? At idle, where you may only see 3 mSec pulse widths, a 1 mSec difference is significant. If you are at wide open throttle, maximum RPM, where you might see 20 mSec pulse widths, a 1 mSec difference is not so significant.

 

Thanks for your fast reply;

Im trying to solve this problem since ı bought the car.

I rebult engine 3 weeks ago and i have checked vacuum leaks , exhaust leaks,dirty injectors , valve lash adjustment and ho2 sensors but everything was normal.

Before rebuilt İ had same problem.


During idle, bank 2 cycle at 3ms but bank 1 at 4ms to 5ms

And one more thing I have LPG system on the vehicle , during operation with lpg ı face with same problem. So according to me its is not related with fuel system. Because during lpg , system cuts gasoline side.

I changed bank 2 HO2 sensor to bank 1

Im suspected to pcm but i dont know how to check.

İs there seperated injector ground for each bank at pcm?

One more thing, The pcm part number is 16214399 and knock module is 16214671. Is it normal ?

 

And i started car without HO2 sensors unplugged ( open loop) and still have diffrence when warmup ??????

Im confused. (

 

You need to clarify what you just posted.... you unplugged the O2 sensors. Did you reset the PCM to clear the LTFT's? Are we only looking at the engine idling, or are you actually driving it?

I told you how it works. If you don't agree, there's not much more I can say.

 

Thanks again.

İ didnt reset pcm. İll try it tomorrow.

 

How are you reading the pulse widths? The PCM does not make all calculations simultaneously. It steps through the calculations, meaning the left and right bank pulse widths are not calculated at the same instant in time. The pulse widths are also changing rapidly, up to 9 times per second. If you are reading this off a data log, post it so I can see it.