Engine running to rich


Asked by Aug 25, 2009 at 10:42 PM

Question type: Car Customization

92 toyota truneo with 20 valve black top with oversized pistions. It runs 2 rich when full open throttle any suggestions how to fix it because I just did a 100 % rebuild on it. New everything

12 Answers


engine is too powerful for a trueno...oversized pistons give a lot of throttle but also strains the car too much...if u have a stock intake it wouldnt be too much of a problem with gas...other than the engine what else is new?


i heard a couple of possibilities.. 1 fuel pressure to high engines needs 33 psi the fuel pump of a ae92 gives out 38 - 44 psi. 2) O2 sensor of a 16v not 20v. 3) the map sensor does not have the right serial number of the BLACK TOP.....


I guess my first question is how have you ascertained that the engine is running too rich at wide open? Is it bogging? Has it been checked with a wideband? If it truly is running over rich check what your fuel pressure is, if it is receiving too much pressure you may have to install an adjustable regualtor to tune it down. The O2 sensor is unlikely if it hooks in to the harness you should be good all narrowband O2 sensors operate in 0-1v range. Proper functionality of the sensor would be the only thing that would come into question here. An improper serial MAP sensor can also be a good chance. Couple other questions I have are; does the vehicle have the proper ECU for the engine so it can interpret the sensor data corectly and were the injectors changed out for larger ones? I had over rich fueling issues in an old 325is I had when I went to larger injectors and a chip that was corrected when I went up a size on the mass air meter. A little more info my shed some more light on the right direction to go.


i do have a low idle after a while of driving it.. no wideband.. o2 had to get mod chaged the conector... and no the injectors are the same...but she is fun to drive and redining at 9000 rpm is fun to hear but not on regular basies


There's should be a screw on the throttle body that you can usually turn in to bump up idle a little. But, it it's around 500 rpm currently you should be more than fine. As far as modding the harness as long as the O2 sensor is matched to what the ECU requires you should be fine. Meaning if it was supposed to be heated you used one that is heated and vice versa if it required a nonheated you used a nonheated. A little rich at WOT is normal, it provides a safety margin and if it has no issues operating in and transitioning from part throttle to wide open I'd say everything is stellar and to not worry about it.


Thanks for the info. My concern is when driving in fifth gear at 100k an hour and down shift to third gear and go full open throttle I get black smoke out of exhaust amd exhaust tip is black any ideas?


oil change already? if not, do so...carb engines have that problem so u have to clean the filter every now and then......oh and sometimes low quality fuel leaves a lot of excess and it turns into black residue and smoke...or...get a catalytic converter if u havent installed any...


Really no worries to be had. The black smoke is just from the initial enrichment command by the computer when it sees the throttle open rapidly it injects extra fuel to compensate for what will be the on rush of more air. This in turn is what creates the short burst of black smoke. If it is more extended than the intial burst then some additional tuning may be required but I wouldn't worry a lot about. Many factory ECUs run overly cautious fuel mapping, getting it in to a tuning shop they can get it up on the dyno hook in a wide band see how everything is operating. I'm not familiar enough with the older Toyota ECUs to know what's available to tune the factory ECU, but most likely the shop would use some form of piggy back to tune in open loop operations. I guess over all I wouldn't be concerned if it were my car, my 04 Subaru does about the same thing under WOT if that's any consolation to you.


i guess is hould start looking for a wie band cause its not just a short burst its untill i let go of the pedal or easy off...... and the engine and ecu is 98 toyota trueno...


the engine doesn't have carbs..... 4 throttle bodies....


Individual throttle bodies? Man that's neat.


There might be some open source tuning available for the ECU. Getting a solid tune on it is probably the next step, it most likely is setup very conservatively from the factory and could have some fuel pulled from it. I know from looking at mapping on my buddies 350z Nissan enrichened the top end severely cutting power output up top leaning it out made a world of difference in power output on the top end of that car.

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