Steve in Mesa AZ Posted February 6, 2012 Share Posted February 6, 2012 I began work this weekend to eliminate the exhaust leak on an 83 280zx. Two broken bolts allowed enough of a leak to be irritating. The engine has 290,000 on it and has never been apart. I bought it from the original owner at 285,000 or so and have only put a few thousand miles on it myself. When I removed the manifolds to replace the gasket and repair the broken fasteners I noted a difference in the color of the exhaust residue in the #4 exhaust port. All the others were a nice evenly burned white but the #4 port was almost completely black(note picture). Has anyone had enough experience with these to know what the difference may indicate? I'm anxious to get it back together and do a compression check. Other than that I am not sure how to proceed. The car has never been altered in any way. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted February 6, 2012 Share Posted February 6, 2012 Can you please resize your pic? I'm viewing on a 17" monitor and I can't even see the atypical exhaust port in full next to the typical one. Quote Link to comment Share on other sites More sharing options...
Steve in Mesa AZ Posted February 6, 2012 Author Share Posted February 6, 2012 Can you please resize your pic? I'm viewing on a 17" monitor and I can't even see the atypical exhaust port in full next to the typical one. Sorry -- I hope this image is a little more helpful! Quote Link to comment Share on other sites More sharing options...
dexter72 Posted February 6, 2012 Share Posted February 6, 2012 How was the engine runnning before you pulled the manifolds off?. Also make sure the exhaust manifold is not warped at the ends. #6 port on the manifold will usually warp, if that end exhaust manifold bolt breaks. If it has been driven for a while like that its best to check it with a straight edge. You may either have to shave the manifold down or replace it if its warped. Have you changed the fuel filter yet?. Usually white exhaust residue means the engine is running lean, The white residue on those ports does not look right. The #4 exhaust port actually looks brown to me and that looks normal. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted February 6, 2012 Share Posted February 6, 2012 The purpose of the exhaust liners are to burn off any remaining fuel that was not completely burned during the combustion process. The ones that are white are probably working as intended, but the black sooty one is definitely not getting hot enough to do its job. I would check out the injector on that cylinder to see if it is sticking open or if there's something else that would cause it to run rich. Someone with more knowledge of the stock EFI system might be able to chime in and give a more detailed explanation of why that cylinder might be running rich. How do the plugs look? Quote Link to comment Share on other sites More sharing options...
luseboy Posted February 6, 2012 Share Posted February 6, 2012 I'd almost say you're buring/leaking oil in #4, that looks kinda like how some of my exhaust runners do on my P79 after some oil leaked onto them during a re-build. Check your valve seals/cylinder bore, make sure you aren't getting oil into the cylinder. If you have that many miles on the engine, and the valve seals haven't been replaced... I'd assume they're bad and replace them with some viton ones. You can get a little look into your cylinder by pulling the spark plugs and looking in with a flashlight. Quote Link to comment Share on other sites More sharing options...
icice9 Posted February 6, 2012 Share Posted February 6, 2012 you might be burning oil in that cylinder.. most likely cause of this is a bad or warn valve seal allowing oil to come down the valve stem and into your combustion chamber... Quote Link to comment Share on other sites More sharing options...
Steve in Mesa AZ Posted February 7, 2012 Author Share Posted February 7, 2012 I will check the manifold for a warp - It did run several thousand miles with a broken bolt in the end of #6. Other than that irritating leak it really ran quite well. Vacuum leaks continually pop up - all the hoses are old and dry. Thanks for the info. Quote Link to comment Share on other sites More sharing options...
Steve in Mesa AZ Posted February 7, 2012 Author Share Posted February 7, 2012 The purpose of the exhaust liners are to burn off any remaining fuel that was not completely burned during the combustion process. The ones that are white are probably working as intended, but the black sooty one is definitely not getting hot enough to do its job. I would check out the injector on that cylinder to see if it is sticking open or if there's something else that would cause it to run rich. Someone with more knowledge of the stock EFI system might be able to chime in and give a more detailed explanation of why that cylinder might be running rich. How do the plugs look? I have not encountered exhaust liners before. Your description of their function sounds interesting-- I'll do some reading. The residue was black sooty like a bad fuel burn and not sticky like a bad oil burner. I will pop the rocker arm cover however and take a look at the valve seals. The cover needs a good cleaning anyway. Have not pulled plugs. Thank you again for added information Quote Link to comment Share on other sites More sharing options...
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