81280zx Posted March 19, 2007 Share Posted March 19, 2007 hey all i have a 81 zx and i just rebuilt it and she is now running but she is also smoking at the same time. It is idleing rough with a slight miss to it. The stuff i did was put new rings on it and position them the way the chiltons book says. Put a n42 or 47 head on it that has all new seals new bearings and cleaned the pistons off. It also have a n47 intake mani with a 60mm t/b and im trying to adjust the afm to the new t/b cause when u hit the gas real quick it has a knock sound so i think it may be running rich or to lean. before i put the new t/b on and the head and mani it ran good but the rings were gone and smoked under power. Any suggestions would help alot or if anyone has had this problem before. Also when u slowly accelarate it it doesnt knok at all it goes throuhgt the power band nicely. Thanks all for the help! Quote Link to comment Share on other sites More sharing options...
Clifton Posted March 19, 2007 Share Posted March 19, 2007 Did you hone it or have it honed? Can you do a leak down? Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 19, 2007 Author Share Posted March 19, 2007 i honed the cylinders on it and they came out very nice. also i swaped the cam from my stock head to the n42 head could that cause a problem? Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 19, 2007 Administrators Share Posted March 19, 2007 When you installed the rings, generally speaking most top rings are barrel faced so they can be installed either way. The second rings are generally a scraper ring and as such are VERY specific as to how they are installed, (the ring just under the top ring). If you install the second rings upside down, the engine essentially becomes an “oil pump” and will burn oil. Without any more specifics, there could be several other things causing this such as bad PCV valve, scored cylinder walls, improper ring end gaps, valve stem seals worn, improperly installed stem seals or one or more of the valve stem seals popped off the guide, etc… Just swapping in a cam shouldn’t cause the oil burning problem. Let us know if you find the issue… Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 19, 2007 Author Share Posted March 19, 2007 all of the rings had markings on them to indicate which side was upwards. i know the pcv valve is in good conditon but i can change it to make sure and i will also check the valve steam seals to see if the poped off or not. Would anyone know what the knocking sound would be when u hit the gas real quick? Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted March 19, 2007 Share Posted March 19, 2007 IMO and "overhaul" equals disaster. IMO you should always check bores with a dial bore gauge and bore a block not hone and re-ring. Just my experience and my opinion. I'd rather do it once right than wrong first, then right. Cheaper IMO. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted March 19, 2007 Share Posted March 19, 2007 The knock could be detonation, possibly caused by a vacuum leak. Try backing off on the timing or switching to premuim gas to see if that helps. Not a fix but will help diagnois the problem. I have read that oil in the intake can cause detonation also. Could you have a leaky head gasket? Vacuum leak also comes to mind for a rough idle. Check all your hoses and get some starter fuild and/or propane to check for the vacuum leaks. Like BRAAP said, could be 100 other things too. Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 20, 2007 Author Share Posted March 20, 2007 i think it might be detonation caused buy a vacume leak cause i messed with the timing and it really didnt do much with the knocking but did calm it down then it was stumbling if u hit the gas hard. Im woundering if it could my my 60mm t/b Quote Link to comment Share on other sites More sharing options...
Clifton Posted March 20, 2007 Share Posted March 20, 2007 What is your total timing? Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 20, 2007 Author Share Posted March 20, 2007 right now its set at 8 btdc like the book says but it still runs like crap at that timing. was also considering it could be that i went to the 60 mm tb. Im getting really confused on this rebuild Quote Link to comment Share on other sites More sharing options...
z-ya Posted March 20, 2007 Share Posted March 20, 2007 What color is the smoke? Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 20, 2007 Author Share Posted March 20, 2007 the smoke seems to be whitish but really cant tell Quote Link to comment Share on other sites More sharing options...
JSM Posted March 20, 2007 Share Posted March 20, 2007 You put a different head on then what you had before? Did you do any head work to it? Mill the head, check it for straightness? White is usually water. Blueish is oil. Does it smell oily? How are your plugs looking? Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 21, 2007 Author Share Posted March 21, 2007 ok here's the update i rechecked the timing and of course i was looking at the wrong mark it was way off so i took out the screw that only ltes u go so far and played around and i saw a thick line come around and bam! the car idled smooth then i also replaced the tps and the smoking went away but there is just a wierd smell coming from the muffler but im thinking that it's cause its a fresh rebuild on it. I wanted to thank everyone that has helped me on this to get it right and that got me thinking more and foucousing more on this car. I will keep u guys updated on how it goes as i put everything back together and i will try to post up some pics of the motor, Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 21, 2007 Administrators Share Posted March 21, 2007 Good to hear that you were able to solve your smoking issues and misfire. Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 22, 2007 Author Share Posted March 22, 2007 thanks braap so far its running good so now i have to button things up and then i will take pics and post up to show u guys how it went Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 24, 2007 Author Share Posted March 24, 2007 ok today i took it out for a drive and under normal throttle it runs good but once u go and do a wot pull on it the motor cuts out at 4k or a little bit before. I already checked the timming on it and its set at 9btdc without vacume advance on. I tried richening it up thinking it was running lean and then it just stubles sooner. The car is acting like it has a rev limiter under wot. So now i was woundering how some of u are running the 60mm with the afm still on if u had to richen it or lean it out alot. I was thinking it wasnt getting enough fuel but under no load it will rev past 4k. So right now im stumped on this one. If any of u could help me with this problem i would apreciate it. And sorry for asking if this has already been disscused before. Thanks Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 24, 2007 Administrators Share Posted March 24, 2007 Your bigger throttle valve shouldn’t be causing any issues to this degree in regards to mixture. In fact, the only issue the 60 mm throttle valve would induce as far as drivability is concerned, is that it is a little harder to modulate off idle engine response, i.e. it will be harder to take off from a stop due to the fact the bigger throttle valve is letting more air in the engine for a given throttle position compared to the OE throttle body. What Throttle Position Sensor are you using? You have to us the Datsun TPS from your old Throttle Valve as it is a switch, not a potentiometer like comes on the factory Nissan 60mm Throttle bodies, (even though the plug may be the same?) Make positively sure that the TPS on your car is a factory EFI 280Z/280ZX, TPS, not from another newer vehicle. Just a quick run down of how the factory ECU interprets that TPS… The ECU needs that WOT signal which fattens the mixture for WOT power. Also, the OE TPS has a closed throttle switch which tells the ECU when the throttle is closed and if the engine is above 3200 RPM with the throttle closed, (i.e. decelerating from high RPM), the ECU will turn OFF the injectors, and then turn them back on at 2800 RPM. What happens quite commonly is when people wash the engine of their factory EFI Z cars, water will get into that connector and this shorts the "closed throttle" circuit. No damage is done other than the engine has a very violent rev limiter that comes on at 3200 RPM and disengages at 2800 RPM and the viscous cycle repeats rapidly. If this happens, you just have to blow out the water and all is well again. You may also have a plugged fuel filter. If the engine will rev higher at part throttle than it does at full throttle, that is a classic tale tell that that the fuel filter or fuel pump inlet screen is clogging. Over time, the RPM that the engine cuts out at, will become lower and lower till this taken care of. Also, you might try bumping your initial ignition timing up to between 12 and 15 degrees. You’ll immediately notice nice bump in power every where in the rev range and mileage increase as well. Hope this helps, Paul Quote Link to comment Share on other sites More sharing options...
81280zx Posted March 24, 2007 Author Share Posted March 24, 2007 Thanks braap for explaining that about the tps i didnt know u had to use the stock one cause i have seen people using the tps that came with the 60mm tb. I will put my stocker back on and adjust the timming to what u said 12-15. And do i keep the advance unpluged or just leave it hooked up? I also found that the vacume line from the canister came undone from the t/b to. Thanks again for taking time to explain that to me. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 24, 2007 Administrators Share Posted March 24, 2007 Set your initial timing with the vacuum advance unplugged, but don’t forget to plug it back in after your done setting the timing. Let us know how it goes… Quote Link to comment Share on other sites More sharing options...
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