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smoking after rebuild


81280zx

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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!

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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…

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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?

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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.

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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?

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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,

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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

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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. beatin.gif 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. gh.gif

 

 

Hope this helps,

 

Paul

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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.

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