Guest bastaad525 Posted January 30, 2004 Share Posted January 30, 2004 http://hybridz.org/phpBB2/album_pic.php?pic_id=2553 that's my dyno run from a month or so ago. Been thinking alot about the fuel curve. Goes WAY rich between 3000-4000rpm. Also, still haven't completely eliminated my light misfire at idle and low revs.. thinking that might be caused by being overly rich also, since I've tried to adress the other causes I know of. Thinking of just reinstalling another MSD to cure the miss but would rather fix the problem than just bandaid it first. Obviously the dyno run is not an indicator of how rich-lean it's running during normal driving conditions so I'm not sure if I should go by this. I will say that this fuel curve seems pretty typical of the few other stock EFI'd '81-81 ZXT motors I've seen dyno sheets on. Should I crack open the AFM and tighten the spring? I dont think it would effect the 4-6k rev range much if at all so I'm not worried about over-leaning... should I be? I do run with my 02 sensor disconnected, when I hooked it back up it leaned out a bit, mostly in that super rich mid rpm where it went from 10:1 to 11:1 A/F ratio, however, the car runs much rougher with the 02 connected, and I dont think it's because my sensor is bad. Another member here, I believe szlash280 reported that when he installed a new 02 sensor his car still ran rough and then smoothed out when he disconnected it, so I'm hesitant to run out and pop $40 on one myself. What do you guys think? Quote Link to comment Share on other sites More sharing options...
Vintage-TechZ Posted January 31, 2004 Share Posted January 31, 2004 I remember when I was still using the stock turbo electronics on the ZX engines.about 60% of the glitches encountered were in the "FLAP" style throttle box.They were constantly posing "little gremlins" because of little things like grit build-up etc.It was constantly a reoccuring problem,and just replacing it only delayed it from the next go round. The next item a little more important in many directions was the flow rate of the injectors.(but that should go to another thread )If you havent taken them out and floed their CC's,and made sure their cleanliness is perfect and a really close flow rate ,it can kill any chance or good idle and acceleration no matter what else you replace. Perhaps you've already dialed that in,excuse me if I've missed you alresdy addressing that . Those problems were eventially what made me delve into using 3.0 mass air,harness,injectors etc. on my turbo 240-Z. (much better performance) .................Vince Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted January 31, 2004 Share Posted January 31, 2004 yeah that's one mod I would like to do, switch over to the 300zx ECU and harness and such. Money and knowledge are keeping me from doing that one so far. It's on my to-do list though... some day some day. You're not the first person to say it worked better though. You may be right about the injectors, I haven't had them flow balanced or CC'd or anything. Anyone know how much a service like that costs? That may also be out of my range right now, and I suspect I may fix that to no avail, I'm more with you on thinking it's AFM or other similar problems. Quote Link to comment Share on other sites More sharing options...
Sean73 Posted February 1, 2004 Share Posted February 1, 2004 By disconnecting the O2 sensor, the ECU has no way of calculating the proper fuel mixture in closed loop mode. That may explain your overly rich condition at mid RPMs. I think you have to get the stock fuel system to run right, with the stock components before tweaking things like the AFM. I would buy a half-way decent O2 sensor (Bosch, Nissan) then check the other EFI items. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted February 1, 2004 Share Posted February 1, 2004 Even with the 02 connected it runs really rich in the midrange, though it does lean out noticeably, at 11:1 instead of 10:1. Problem is with the 02 connected the car runs much more roughly throughout the rev range. And it's not just my 02 sensor, another member on these forums bought a new bosch sensor and installed it and right away noticed the same problem, car idled much more roughly with the new sensor, and much smoother when he disconnected it. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 1, 2004 Share Posted February 1, 2004 The O2 sensor whould not be in the loop at all during a dyno run as it's WOT, and the EGO circuit is disabled during such conditions. Only during partial throttle conditions, below 3500 rpm (or thereabouts) does the O2 Circuit have any effect on the mixture, and then it's only about a +/- 5% from the factory programmed hard-code. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted February 1, 2004 Share Posted February 1, 2004 Tony D, I always believed that as well, but again, there was a pretty big difference in the air/fuel ratio on the dyno between the runs I did with O2 disconnected and connected. Here is the dyno chart that shows my first and third runs, the only thing we changed for the third run was to connect the O2. http://hybridz.org/phpBB2/album_pic.php?pic_id=2554 I actually did two runs w/o the O2 (second run I dont have the graph for, was) and both runs w/o the O2 were pretty much identical at about 10:1 A/F ratio. With the O2 connected it leaned out to 11:1. Though I will say, I dont doubt that it may have been something else just getting 'tired' after the first two runs, maybe the fuel pump? I know dyno testing is hard on a car... shoulda done the one with the O2 second and re-disconnected it for the third... I'll try to remember to try this next time I dyno. Quote Link to comment Share on other sites More sharing options...
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