nosebleedZ Posted July 6, 2007 Share Posted July 6, 2007 I tried to post this earlier but my computer did something funny. Anyway, I have a 79 zx that I have been working on the past year-majorly overhauled everything-body/ paint, engine/ tranny, interior, etc. I have the car 95% complete but I have an engine miss/ lean condition from 1500 to 2500 rpm. The car idles fine, revs good past this point, has steady vacuum (18"), everything is pretty much new. The A/F guage goes to about 16:1 or less at this rpm under load or revving from an idle and when it smooths out an revs it is still on the lean side of stoich. I have built and modded Z cars for about the last ten years & was a dealer tech on Nissan vehicles prior to that. In my experience with these cars, I've never had one with a gremlin that I couldn't find in a few days, so I'm stumped & a little embarrassed. The mods to the engine are as follows from current rebuild be me: F54 block-Ross 2.8 forged pistons/ chrome rings/ stock rods & crank/ trimetal bearings, MN47 head- port polish/ seals/ springs/ Msa turbo cam/ chain & gears/ Cometic gasket 1 MM, SDS additional injector computer w/ 750 cc injectors, 270cc injectors on rail, Garrett GT3271R ball bearing turbo, 4" thick vertical core I/C, N/A dizzy, N/A ECU, new ECU harness, new sensors-all, except Turbo MAF w/ N/A guts, narrow band O2 w/ A/F guage, RRFPR, FD3S BOV/ bypass valves, Walbro 255 lph pump, 60mm TBI upgrade, 2.5" DP/ exhaust. All tune up & engine parts are new-not joking. The tests I have run include FSM EFI checklist, EFI component checks, injector pulse tests/ dizzy input, fuel pressure-36 psi @idle/ 58 psi @ WOT, stethoscoped entire engine bay for vacuum leaks, reclocked dizzy/ oil pump 5 times-returned to original setting because it made it worse, FSM EFI relay checks, leaned & richened by MAF gear position-made worse. Swapped ECU's 3 times, MAF once, & cleaned/ greased/ reconnected all harness plugs. Base timing is 5* BTDC & 18* w/ advance connected. Oh yeah some other oddities: the plugs are sooty black (rich look), car can take 5 seconds to crank before starting when cold-intermittently, & tailpipe smoke is non existant, even on cold start? With all the knowledge on this site, I need someone to point me in a direction I have not been. Thanks, NosebleedZ Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted July 6, 2007 Share Posted July 6, 2007 I would suspect cam timing. I have had similar problems with my '81 and it has become almost unnoticeable but I have messed around with so much stuff on it that I'm not really sure what helped it. I do know for sure the cam was off and may still be a little. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 6, 2007 Share Posted July 6, 2007 http://forums.hybridz.org/showthread.php?t=123582 Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted July 11, 2007 Share Posted July 11, 2007 I read that link and played around a little with my AFM, didn't really do anything but while I was messing with it I noticed my BCDD (boost controlled decelleration device, on the bottom of the intake, looks like a water filter you would find on an air line.... anyway) kept making noises on and off at say 1500rpm, I noticed it would make my afm move when it would make noise. Basically, it was letting air in when it shouldn't be. So I disconnected the hose going to it and plugged it. Now my low rpm seems to be more powerful and smooth. Quote Link to comment Share on other sites More sharing options...
monsterz Posted March 3, 2010 Share Posted March 3, 2010 u can open the afm cover and lose the screw inside and turn the white gear that hold the spring turn it tight. u can see less smoke and boost fast. Quote Link to comment Share on other sites More sharing options...
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