bumble zee Posted September 10, 2002 Share Posted September 10, 2002 here is my setup, 76 280z with a 81zxt motor, stock turbo, straight out 2.5" exsaust, 76 280z intake manifold, volvo i/c... i have a problem.. i am running very lean under high rpms... i am at 10#'s of boost. i swapped out computers and it worked fine for a day, but then it starts leaning out again.. its like its learning something... any ideas of what could be wrong?? Quote Link to comment Share on other sites More sharing options...
Guest Cusp Posted September 10, 2002 Share Posted September 10, 2002 Your know it's lean from a a/f meter? or you think it's lean from hearing pinging? hmm... A few things I'd check are knock sensor, spark plugs, and (the longshot) your voltage at the fuel pump. I'm sure you're using premium gas, but because it's important, I thought I'd mention it anyway. Oh, and I know exactly what you mean about the car "learning" how to run crappy! My daily driver runs best right after reconnecting the battery, when it goes to factory defaults. This learning process is kinda like public education, the more you learn through it, the worse off you are. Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted September 10, 2002 Share Posted September 10, 2002 make sure the fuel pressure is up at high revs.i made a mechanical test gauge with a pressure gauge from a bearing supply house and some fittings from hardware store.this is dangerous in terms of possable leaks but i had to know pressure.i have a 77 with 81zxt power.at boost the pressure runs uo to 65 psi.if you have it cutting out after 1/2 throttle or so my problems have been cured by swapping ecm.been through 3 in 80,000 miles.if you got a used engine that wasnt run for a long time have the injectors flow tested & cleaned.i put in new injectors when i did my swap. Quote Link to comment Share on other sites More sharing options...
bumble zee Posted September 10, 2002 Author Share Posted September 10, 2002 i run premium all the time... i have a fp guage where i can see it all the time.. full boost im at 50# of fuel pressure. i also made my timeing back to stock.. no change. No i dont hear pinging.. watching my air fuel guage Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 10, 2002 Share Posted September 10, 2002 It's not easy, but you can try to check what the duty cycle is on your injectors. If you are getting close to 100% (I'm not sure what the max is on stock ECU), that could be the cause of the top end leaning out. Quote Link to comment Share on other sites More sharing options...
bumble zee Posted September 10, 2002 Author Share Posted September 10, 2002 it cant be the injectors.. could it?? cuz when the ecu is "fresh" when i swap em out.. the car runs fine.. basically perfect.. then over time, like 3 to 4 days it just starts slowly leaning out. there is something that it is learnign from that is making it dumber. I have replaced the o2 sensor also, no change, a/f guage runs cleaner Quote Link to comment Share on other sites More sharing options...
bumble zee Posted September 10, 2002 Author Share Posted September 10, 2002 also i am running a fuel regulator from a 300zxt. Quote Link to comment Share on other sites More sharing options...
Guest Cusp Posted September 10, 2002 Share Posted September 10, 2002 Maybe you've reached the flow limits of your fuel pump. Not in terms of pressure, but overall flow. Just a guess, you've troubleshot alot of different ideas already it seems. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 11, 2002 Share Posted September 11, 2002 Originally posted by Cusp:Maybe you've reached the flow limits of your fuel pump. Not in terms of pressure, but overall flow. Just a guess, you've troubleshot alot of different ideas already it seems. If the flow limits of the pump are reached, the result is a drop in fuel pressure Quote Link to comment Share on other sites More sharing options...
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