Nigel Posted August 26, 2002 Share Posted August 26, 2002 Hi Guys! I have a turbo 240Z with an SDS EM-3F EFI system. I recently enabled the FUELCUT BELOW TP feature. As a reminder, this cuts fuel when the throttle is closed and rpms are > 2000. The thing is that this causes lots of loud crackling and poping on decelleration. I'm not sure why it would be doing this if there's no fuel? Perhaps more importantly, I'm worried about what all those pops might be doing to the turbo? Is anybody else using this feature? Could this be damaging. Thank's all! Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted August 27, 2002 Share Posted August 27, 2002 Hmmm,the fuel cut is suppose to supress the popping you have. I have mine turned on and I don't have that problem. Are you sure you have the TP number set up correctly? I read my TP number with the throttle closed on the display and entered a value one number higher. My mixture meter goes completely blank when I let off the throttle over 2K RPM. Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 27, 2002 Author Share Posted August 27, 2002 Hmmm... I guess it shouldn't be poping then. I'll try entering a number one over what my TP shows with the throttle closed. I suppose I could have a leaky injector or injectors, but I took the fuel rail off and fired up the pump - nothing leaked. Oh yeah, my mixture meter also goes blank, but there still could be fuel there. It's just not sensitive enough to read it. And just to claify, this is happening when I'm decellerating with the car in gear (high vacuum). Unfortunately, I won't get to run the car again till Wednesday. Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted August 27, 2002 Share Posted August 27, 2002 Nigel,no I don't have my PCV hooked up. I have a breather on the valve cover and on the block vent I have a hose that extends down near the bottom of the oil pan with a breather on the end of it. I got oil accumulating in the intake with PCV and decided to bypass it. Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 27, 2002 Share Posted August 27, 2002 I don't use the SDS, but this problem is generic enough that I think I can comment. Most likely what is going on in your case is that you are running rich (probably too rich) immediately before you let off the throttle. The resulting unburnt fuel in the exhaust by itself will not cause any popping, because if you are running rich that by definition means that you have used up all of the available oxygen, and still have fuel left over. Now, when you drop the throttle and the fuel gets cut off, suddenly you are dumping a bunch of air into the exhaust. The newly available air allows the unburnt fuel in the exhaust to burn, and you get your backfire, or popping sounds. The solution for this is to either fix the rich condition that exists before you drop the throttle (requires some tuning expertise), or disable the fuel cut function. Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 27, 2002 Author Share Posted August 27, 2002 Interesting theory Tim. I've been working on leaning out the mixture under cruisng conditions, but it still runs rich in a bunch of places. I'll try to do some comparisons. Nigel Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 28, 2002 Author Share Posted August 28, 2002 Hey Tom: Do you have your PCV system hooked up? I do, and I was just thinking that maybe oil vapours from the PCV system are what is igniting when the car is decellerating. Just a thought... Nigel Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 29, 2002 Author Share Posted August 29, 2002 Well, it turned out to be the throttle position setting. 12 is what Gauge Mode was showing as closed and that's what I set the FUELCUT to. So, I tried 13 and that seems to have done it. No more poping on decelleration. The strange thing is that I also had 1's entered in MAN PRES around the manifold pressure that it sees under those conditions and that by itself should have also cut fuel according the the manual. But the manual also says that it determines pulse width by multiplying the RPM FUEL values by the MAN PRES values. If this is true then if you enter a 1 for MAN PRES then it will still generate a small pulse width based on the RPM FUEL value (1 X RPM FUEL = RPM FUEL vs. 0 X RPM FUEL = 0). I was also able to start the car with an RPM FUEL value of 1 at 500 rpm which acording to the manual should prevent the engine from being started. Hmmm... Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
Ron240zxt Posted August 29, 2002 Share Posted August 29, 2002 In comment to I was under the impression at idle or closed throttle, in gauge mode the TPS sensor, should be reading <0> this way the vehicle doesnt inject extra fuel into to the cyl. I know mine is seating at <0> with no problems. As for setting the sec section. you have to have 1's in 3-4 sections 500-750-1000-1250 Good Luck Ron Try the forum for SDS at www.sdsefi.com Quote Link to comment Share on other sites More sharing options...
Guest Tom Scala Posted August 29, 2002 Share Posted August 29, 2002 I think as long as you are using the map sensor I don't think you have to have the TPS close completely. As long as it has enough travel in it to go from closed to full throttle it can start anywhere. Quote Link to comment Share on other sites More sharing options...
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