ahardb0dy Posted October 23, 2017 Share Posted October 23, 2017 Trying to help someone on another forum. He has a Hardbody with the VG30I (88), seems like it has a misfire on number 5 cylinder. He has replaced the plugs, wires, cap and rotor, the number 5 plug has spark when it is removed and placed near the engine. Engine has good compression and timing is correct. When he removes the number 5 wire while running the RPM's do not change. Any thoughts on this? Thanks Link to comment Share on other sites More sharing options...
Slartibartfast Posted October 24, 2017 Share Posted October 24, 2017 Hmm. TBI, so it's not a dead injector. Assuming all tests so far are accurate, and all parts replaced are good, all I can think of is a restriction in the intake or exhaust runner for #5--like the air cleaner was off and a mouse crawled into it or something like that. (How's that for a long shot?) Could try positioning the engine with the intake valve open, spark plug out, and jam an air nozzle in the hole to see if anything blows out. 1 Link to comment Share on other sites More sharing options...
Citron Posted October 24, 2017 Share Posted October 24, 2017 Is he sure the intake valve is opening? I have never heard of issues with Nissan cams, but Chevy was notorious for cam lobes rounding off. The only thing that is missing is fuel, since he has spark, compression and correct timing. Link to comment Share on other sites More sharing options...
mluczaj22 Posted October 25, 2017 Share Posted October 25, 2017 codes? Link to comment Share on other sites More sharing options...
ahardb0dy Posted October 27, 2017 Author Share Posted October 27, 2017 I don't know if he checked for codes, it runs, but runs rough, he said it was backfiring on deceleration but than adjusted the timing and that stopped, His mechanic was saying it might be a stuck intake valve More info, engine has about 225K miles, has good power and doesn't burn oil. He said when he shuts it off it runs for a few seconds (dieseling??) Link to comment Share on other sites More sharing options...
Slartibartfast Posted October 28, 2017 Share Posted October 28, 2017 Stuck valve doesn't make much sense with the compression reading good. Dieseling sounds like an injector leak. Not sure how an injector leak would cause a single-cylinder misfire, though. Link to comment Share on other sites More sharing options...
ahardb0dy Posted October 28, 2017 Author Share Posted October 28, 2017 Weird that the plug has spark when pulled and held next to the engine but doesn't effect the idle when the plug wire is removed from the plug while running Link to comment Share on other sites More sharing options...
Citron Posted October 28, 2017 Share Posted October 28, 2017 (edited) I think he is missing fuel. So the plug would still be sparking away but no detonation. That's why I asked if the valve was opening, because that is about the only way to get a no fuel condition to a single cylinder on a tbi, a stuck closed valve. Especially considering that the compression is good so we know that the exhaust valve is closing completely. Does the plug look like it is lean? Edited October 28, 2017 by Citron Link to comment Share on other sites More sharing options...
ahardb0dy Posted October 29, 2017 Author Share Posted October 29, 2017 he said he pulled the valve cover today and everything is moving the way it should. Link to comment Share on other sites More sharing options...
Citron Posted October 29, 2017 Share Posted October 29, 2017 The other possibility is the new plug wire is leaking and when it is in the plug well it is arcing over to the head instead of sparking the plug. I have never heard of it with a new wire though. Is there any whitish discoloration anywhere on the wire to evidence arcing? Link to comment Share on other sites More sharing options...
adamzan Posted October 30, 2017 Share Posted October 30, 2017 Dumb I know, but is the plug wire seated on firmly? I swear every time I do plugs on my pathfinder I fire it up and it has a miss. Every time there was one wire that was not on securely. Easy to tell if its getting fuel and not firing, the plug should be soaked with gas. I say "should" as that has been my experience before. 2 Link to comment Share on other sites More sharing options...
ahardb0dy Posted October 31, 2017 Author Share Posted October 31, 2017 he said he doesn't remember what the old plug looked like. He also posted a video of doing the compression test on #5 cylinder. I told him to get a new gauge because there is no way the reading he is getting is correct, he is showing 210 PSI, The service manual shows a new engine should be at 173 PSI. Link to comment Share on other sites More sharing options...
Slartibartfast Posted October 31, 2017 Share Posted October 31, 2017 Crappy tools are always fun. But the plug that he's been trying to run it on should show fuel pretty much immediately if it's getting fuel but not burning it. I'd be inclined to stick a boreoscope down that hole and see if anything jumps out. I don't know how much carbon buildup you'd need to make a misfire (shrouding the plug?) but it's something else to check, anyway. Link to comment Share on other sites More sharing options...
ahardb0dy Posted November 3, 2017 Author Share Posted November 3, 2017 He said he figured it out and it no longer has a misfire. He said he pulled the TB and the gasket was all tore up 1 Link to comment Share on other sites More sharing options...
Slartibartfast Posted November 3, 2017 Share Posted November 3, 2017 Ah! That makes sense. Link to comment Share on other sites More sharing options...
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