I have ID725 primaries and I have been running into the dreaded minimum pulse width problem that the PFC has. Under high vacuum, just when you want to lean it out as much as possible the car goes from 15 AFR to 12s. I know this is because of the pulse width floor that the PFC has. The car used to go into the 11s at higher than 18 or 19 inches of vacuum but I have since started to add negative lag and been able to lean out those areas as well as idle.

My question, can I keep added negative lag and richening the rest of the map proportionately until I can get to 14s or 15 AFR or would excessive negative lag present some sort of problem unforeseen by me?


Thanks for any input.

Jimmy

 

I have seen tip-in hesitations occur.

 

Raymond,

He should be able to help any lag induced hesitation with your trick of modifying the
Inj vs TPS table.

Jimmy,

What is your base fuel pressure?

 

I wouldn't suggest hunting to lean out that very light throttle much beyond 12 AFR. You will run into hesitation issues in my experience.

thewird

 

You guys are right. Even with negative timing split I can't get it to run smoothly leaner than mid to high 14s between 2000 and 3000rpm. At higher revs it will run into the 16s with negative split but I always run into that injector minimum pulse width wall at very small throttle openings. I give up. Rather have a smooth running engine than that last 2 or 3 mpg.

 

I don't know about 2 or 3 mpg...

remember that a stock vehicle would run an airpump...

 

Does the airpump really affect gas mileage though? I thoughts its purpose was to dilute the exhaust for emissions purposes and to keep the cat happy. If I had everything stock wouldn't the 02 sensor read leaner because of the airpump but the actual engine itself would be using the same amount of fuel, right? Anyway, I'm pretty happy so far because now I can drive to work all week and only use about half a tank of gas.

Negative split helps alot, but the biggest gains to be made are on the highway because over 3000 rpm the engine can be run really lean without misfiring. Unfortunately I only live 6 miles from work.

 

I don't have brake specific fuel consumption figures for you for with airpump vs without airpump. Nor do I have any real-world figures for you. What I do know, based on extensive study of basically every relevant thing published in English by Mazda about the rotary engine, is that some of the port air actually flows back into the engine due to the high overlap.

We know for sure that the port air extends the misfire limit at low rpm/idle, going all the way back to the 1st gen Rx-7 with 12A engine:



There's a bunch of secondary air injection control diagrams in the FD service highlights document. Again, I can't present to you BSFC figures, drive cycle figures, etc, but it has at least some effect in engine operating areas. Other areas (like higher speed highway cruising) it doesn't affect so much.

 

That explains a lot. I actually lower my base fuel pressure from 40 to 38 and leaned out high vacuum areas and was able to achieve my target of around 14afr at 18 19 inches of vacuum.

I guess the lack of additional air injection is why I have a slight misfire sometimes around 2000 rpm. I thought it was fueling or timing but have played with both and can't completely eliminate it. I have the excessive LIM and all emissions removed so I guess I always have to deal with that. Car runs extremely well besides that.

 

I was having a smilar problem except I'm using stock injectors with a peak and hold driver and I was going get terribly rich at very low throttle/high vacuum and also at idle.



My original response was in this thread:https://www.rx7club.com/single-turbo.../#post11495166

Also you've probably seen this page but they list injector dead time for your injectors Injector Dynamics - ID725