Nismo280zEd Posted July 24, 2003 Share Posted July 24, 2003 ok... i took off just about everything emissions on my car... egr disable, fuel vapr recirculatory pump gone.. also the device that slows the rpms when decelerating is gone. my car runs about 15 deg advanc at idle if i retard it anymore it start to knock... but it will backfire when the rpms coast down.. there is a pop at 2,500, then 2,200 2,100 2,000 (three quick pops not as violent) my friend thinks it's excessive gas firing in the exhaust... in which case is there any way to fix this? -Ed Quote Link to comment Share on other sites More sharing options...
stagefumer11 Posted July 24, 2003 Share Posted July 24, 2003 what is this device for slowing down the revs? Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted July 24, 2003 Author Share Posted July 24, 2003 can't remember the exact name... but it's a big chunk of metal on the top of the intake manifold just to the left of the EGR valve and it has a device that comes out of it like a rod almost that attaches to the throttle linkage. Under vacum it basically holds the linkage from droping to low rpm suddenly. (annoying as crap) -78 280z Quote Link to comment Share on other sites More sharing options...
zcarnut Posted July 24, 2003 Share Posted July 24, 2003 Have you confirmed that the timing marks on the crankshaft damper and the timing indicator piece on the front cover are accurate? The harmonic damper is a two piece unit and I have seen slippage of the outer ring if the rubber insulator material has deteriorated. To be sure just locate TDC using the piston stop method. Quote Link to comment Share on other sites More sharing options...
stagefumer11 Posted July 24, 2003 Share Posted July 24, 2003 are you able to take a p ictue of th is valve? Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted July 25, 2003 Author Share Posted July 25, 2003 actually when i rebuilt the head i put a new harmonic balancer on it... brand new one... not used. and yes i've confirmed the marks w/ TDC, etc. like i said though even if the marks where wrong... if i retard it anymore it'll knock.. I just want to get ride of the backfiring noise cause w/ my exahust it's loud as hell and anoying Quote Link to comment Share on other sites More sharing options...
stagefumer11 Posted July 25, 2003 Share Posted July 25, 2003 souunds similar to what mine is doing, coming off the t hrottle it pops and burbles ect. could this be tim ing ? Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted July 26, 2003 Author Share Posted July 26, 2003 Well when i brought my car to Z guy here localally in Houston,TX... he claimed my car was running 40 deg too advanced... Yet somehow i ws get about 24-25mpg on the highway and almost 20 in the city. and pulled like a mother when you stomped on the gas. so i adjusted the timing to where the manual says... and it knocks.. so i advanced it enough to stop knocking but it still has that gargle at around 3k and pops when you let off the gas. Quote Link to comment Share on other sites More sharing options...
Clifton Posted July 26, 2003 Share Posted July 26, 2003 my car runs about 15 deg advanc at idle if i retard it anymore it start to knock... -Ed When you retard it more it knocks? I think you mean advance it more and it knocks. Are you talking light pops or gunshot sounding backfires ? Are you running aftermarket exhaust with low back pressure. If so then some light pops is not uncommon. I f I go from full throttle to closed throttle I can get a bang but from cruise to decel nothing. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted July 26, 2003 Author Share Posted July 26, 2003 Negative.. i mean retard.. when i try to get timing where the manual says it should be the engine knocks at low rpm. And i get a variety of pops actually... if i'm at like 4-5k and put in the clutch... and the rpms drop... no pops maybe a light muffled pop. but if i'm at 4-5k and just letting the revs drop... medium to loud gunshot pop at 3k then around 2-2,200 rpm i get the light muffled pops several of them. Yes i have aftermarket headers and 2 1/2" exhaust into a Magnaflow street series flow through muffler. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted August 1, 2003 Author Share Posted August 1, 2003 so no suggestions huh? -Ed Quote Link to comment Share on other sites More sharing options...
Clifton Posted August 1, 2003 Share Posted August 1, 2003 "The device that slows the rpms when decelerating is gone"I would put this back on. If you are not geting complete combustion on decel and are a little rich on decel, the throttle being slowly closed even for a brief second should allow enough air to enter to burn off the excess fuel. Try to hold the throttle open just a little for a second next time you decel and see if it still back fire. Most modern EFI cars have a fuel cut if the TPS is closed and above a certen rpm and or a dashpot to prevent the throttle from completely closing fore a second. I don't know what to say about the knock. Maybe rod bearings. You could try to isolate it by pulling plug wires, or just leave it advanced. As long as you don't get to far advanced (36*+ total, depending on temp)and knock from that. Quote Link to comment Share on other sites More sharing options...
DAW Posted August 1, 2003 Share Posted August 1, 2003 I think you should check your cam timing and make sure it isn't retarded. A chipped/bent valve can produce those symptoms. Most likely you are dumping in too much fuel when the throttle closes suddenly and it detonates in the hot cylinder or exhaust system. Is this a high compression engine or stock c.r.? It sounds paradoxical that it would ping MORE when timing is dropped back. Are you setting back up the idle when it's retarded? (probably a retarded question) It may be increasing the temp of the cylinder with the retarded timing, contributing to ping. Have you tried a colder plug? Are you running too rich (floats too high, needle/seat leaking, suction piston/needle sticking, etc)? I put together a high compression, f.i. engine that backfired on deceleration but it stopped doing it before I troubleshooted it. In my case I think it might have been carbon build up in the headers glowing and igniting too rich a deceleration charge and possibly too high an idle speed. DAW BTW, I doubt the garage guy meant 40 degrees too advanced (i.e., 60-70 degrees); I bet he meant total advance was 40 degrees, or advance was 40 degrees in addition to the initial advance. DAW Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted August 1, 2003 Author Share Posted August 1, 2003 I don't want to put the decel vacumn piece back on.. i'm trying to get ride of all that mess. Plus i like my rpms to just drop when i want them 2 and not hang. this piece has been disabled for many many years on my car. and always caused a couple muffled backfires... But ever since my head was rebuilt and new exhaust was put on... actually since 9-11 when i got my car running... it has had a big backfire at 3k. that is the one i want to get ride of. I was running high psi but it was set up on vacumn. so it wasn't much more than stock until you mashed the gas. Due to lack of MPG this piece is disabled at the moment and stock fuel pressure regulator is being used. Also i have a "hick-up" on low end when i'm starting off really slow barely applying gas... is that just my TS not adjusted right? when the head was rebuilt racing springs were put in too match the cam to keep from high end "floating" also i had the head shaved a little and only using a 1mm metal gasket.. i wouldn't call it high compression.. but it's higher than stock. Quote Link to comment Share on other sites More sharing options...
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