I was wondering if anyone knew whether the Z's ECU has cylinder-specific fuel maps, per cylinder offsets to the base map, or just the exact same delivery for all cylinders?

The reason I ask, is that flow bench tests allegedly show a significant disparity in air flow between the front and rear cylinders. If so, it seems reasonable that Nissan engineers would have compensated for this by delivering differing amounts of fuel to each cylinder.

Finally, if that's the case then wouldn't aftermarket plenums that effectively balance air flow between cylinders cause the front cylinders to run a bit lean?

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Jeff

 

Now you know why I haven't bought a plenum... I agree with you, just because your car pulls hard or makes 20whp with a plenum doesn't mean its safe... It could be running lean, actually many people don't know that running lean makes more power. Just don't trust those plenums being manufactured right now... they look to HOME MADE.. Kinetix looks the best IMO but even then I have to see some charts to finalize my decesion...

 

I haven't bought one either, and have also wondered if the measured horsepower is coming from leaning out the front cylinders. I think you'd need a MAF sensor per cylinder, O2 sensor per cylinder, and/or exhaust temp sensor per cylinder in order to make sure it's safe. Otherwise, the other cylinders will skew the results (especially in the case of single O2 or exhaust temp values).

That said, I haven't heard of anyone damaging their engine from a plenum yet. So if it is a problem, it takes a while for the damage to build up. I also imagine we'd hear reports of spark plug damage in the front cylinders if they're running too lean.

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Jeff

 

The damages wont come right away... Keep in mind, they will come when you push the car hard and the weather conditions are horrible... Time will tell

 

Can you explain the logic behind this. I was under the impression that the plenum just redistributes the air more evenly to the front two cylinders, which would actually be safer than stock if using FI, and have no detrimental effects at all on a N/A engine. If you are making your assumptions just on looks itself, please don't respond, as I am looking for your technical knowledge.

 

First, note that this entire thread is based off an assumption. Then, know that they are saying that if their assumption is correct, that the ECU provides less fuel to the front cylinders due to the stock plenum design, installing an aftermarket plenum will cause the front cylinders to run lean as they are now receiving more air than the ECU thinks and are not getting enough fuel to balance the mixture out. This is a good point if the assumption is correct.

However, my AF, while measured at the cat area (all cylinders), is just like a stock Z. I do not think that the ECU obtains separate AF ratios for each cylinder as the ECU is able to adjust the AF accordingly and it is measured stock after the collecters in the exhaust. This is from the factory. There is nothing telling the ECU at the cylinder what to make the AF ratio.

Or is there? I would certainly be surprised. My best guess is that everything is just fine.

 

Yes, this is definitely just a theory and in fact all injectors could be receiving the same signal for open duration, all other things held equal (MAF reading, RPM, throttle, O2, etc.).

I think the best way to confirm or deny this potential problem would be to measure the duration of the signal sent to each individual injector while holding RPM as steady as possible. An OBD2 scan tool might give enough information to figure this out. However, splicing into the wires going to the injectors would probably be the most accurate.

I do think it's still possible to have a reasonably good AF ratio measurement from 3 cylinders with the fronts being lean to some degree. Whether that would be a dangerous amount, I don't know.
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Jeff