cygnusx1 Posted May 31, 2005 Share Posted May 31, 2005 Yesterday I went for a 150mile cruise. At one point on the highway, I downshifted to third and mashed the gas. After about 5200RPM I heard ping from the motor. I shifted into fourth and then heard ping again around the same RPM. This is the first time I have ever heard ping in my turbo Z. I have it setup pretty aggressively for the stock EFI. At what point would the knock sensor kick in and bring back timing? Was the knock sensor doing it's job? How much timing would the stock ZX ECCS system pull out? Stock L28ET long block, 14psi TO4B, 27deg adv base timing, 60psi fuel@boost, stock EFI with Walbro pump. I had it on the race track last year and never heard ping but I was keeping the RPM's below 5K. I know, I should upgrade the EFI soon...no preaching please. LOL. Quote Link to comment Share on other sites More sharing options...
fl327 Posted May 31, 2005 Share Posted May 31, 2005 My experience with the knock sensor is that it doesnt work very well. Whenever Ive had a ping, I never noticed any sudden timing retard, and Ive had it ping quite a few times. Quote Link to comment Share on other sites More sharing options...
Thumper Posted May 31, 2005 Share Posted May 31, 2005 Actually I don't think its entirely your efi problem. More like you injectors can't keep up. I had pinging at 13psi on ghettto beast intill I upgraded the injectors then I ran it up to 18-20 psi with no pinging on the stock efi. About the knock sensor I have ran with it disconnected. What ecu are you running. On a 82 ecu stock timing is 20 so 27 is kindof up there. I had a 83 ecu so when I ran 27 degrees it was only 3 advanced. Personally I would try to retard timing 3 degrees and then see if it fixes it. If not then upgrade the injectors. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 31, 2005 Author Share Posted May 31, 2005 Yes it's the 83 ECU so I am 3 degrees advanced from stock. I will try turning up the FMU (fuel pressure under boost) to see if I can tune out the lean up high without getting fat down low. Last I remember, the FMU would go too rich too soon if I fattened it up too much. I could very well be at the injectors limit... Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted June 1, 2005 Share Posted June 1, 2005 Stock knock sensor is also deactivated around 3500 rpms and up I believe. Mario Quote Link to comment Share on other sites More sharing options...
fl327 Posted June 1, 2005 Share Posted June 1, 2005 Stock knock sensor is also deactivated around 3500 rpms and up I believe. Mario I can believe that, since it doesnt work like it was supposed to do. Wonder what good a knock sensor could be 3500 and under?? Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted June 1, 2005 Share Posted June 1, 2005 the electronics technology was a little behind in 83-a lot of $10 or $20 toys have bigger processors than a 81-83 zxt ecm has in it.preignition will change from day to day.affected by gasoline and outside air temp-or a lean mixture. Quote Link to comment Share on other sites More sharing options...
wayne_in_KY Posted June 1, 2005 Share Posted June 1, 2005 So how do we find out if the knock sensor is disabled at 3,500 RPM? Is there someplace that explains the logic used by the ECU? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 2, 2005 Author Share Posted June 2, 2005 I had some free time tonight so I turned up the fuel pressure and went for a run. I definately lost a little bit of power with the added fuel. I got it going up a hill on the highway in 4th at 5400 RPM with the windows open and along a stone wall. I didn't get any audible ping at all. I probably lost about 5-10HP but got no ping. I saw a little more smoke in the exhaust also. I think I'll leave it like this for a while and see how it goes. The air temp tonight was about 10 degrees cooler also. Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted June 2, 2005 Share Posted June 2, 2005 I can't find it where it said about the knock sensor, but it would make sense to me because the stock ecu goes into a preprogrammed fuel map for anything above 3.5k rpms. I think it would do the same for timing, as these maps are for "max power" Mario Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted June 2, 2005 Author Share Posted June 2, 2005 That makes sense as Nissan built this motor much stronger than it needed to be for 7psi. I figure they designed the whole system to run it as lean as possible during cruise conditions as they had huge pressure from the gov to make it run clean and get high mileage. Fuels at the time were also changing. The knock sensor could let them get really close to the edge of "leanness" during normal highway cruise. It was probably intended more as a tuning device than a safety device. Up in the higher RPM's, like you stated, they probably turned off the knocksensor and just added a power-minded fuel curve. At 7psi even a bit of ping probably wouldn't hurt this motor much. Quote Link to comment Share on other sites More sharing options...
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