nosebleedZ Posted July 5, 2007 Share Posted July 5, 2007 Hey guys, as stated in the title, I don't think I can see the trees because I'm standing in the forest! I have a '79 zx with the following mods: F-54 block stock bore( Ross forged w/ chrome rings, stock rods, tri-metal bearings, stock crank, etc.) MN-47 head with fresh port/ polish/ seals/ Cometic gasket, turbo cam, etc., Garrett GT3271R ball bearing turbo, Vertical core intercooler 4" thick, Walbro 255 lph fuel pump w/ filters, 270 cc injectors in the rail, 2 each 750 cc injectors fired by the SDS piggy back computer, 60 mm TB w/ Datsun TVS, zx turbo MAF w/ N/A guts, other sensors are stock (new though), narrow band 02 w/ guage, twin FD3S diverter valves, N/A 82 ECU w/ new replacement wiring harness, new cap, rotor, wires, NGK plugs, coil, condensor, N/A dizzy, EFI hoses, new starter, alternator. That is most of the engine mods that come to mind, other than "one off" spacers, adapters, etc. The engine has less than 25 miles on it with no leaks since I rebuilt it. The problem I am having is a lean miss from 1500-2500 rpms. The car idles fine and revs OK under load past the stutter. The base timing is set at 5* BTDC with advance unhooked. Noid light is giving good pulses that change with load & rpm. I have used the FSM to check all EFI curcuits, relays, etc, & passed. I have tried 3 different ECU's with the same result. Fuel pressure is 36 psi @ idle & 58 psi @ WOT (RRFPR controlled). Checked dizzy to injector pulse relation (3 fires: 1 pulse)-seems OK. Screwed with MAF wiper and resistance tested-OK. Readjusted valves, reclocked distributor/ oil pump 5 times-small changes for the worst usually, so reset it back. I have used a stethoscope to listen for vacuum leaks for hours with none found-boost guage hold steady at 18" of mercury. I am at a loss. The same system (minus the turbo & intercooler upgrades) ran flawlwssly for 2 years! I have rebuilt & modified datsuns for the last ten years, heck I even worked as a tech on Nissan vehicles for four years before that.....so I'm stumped, discouraged, tired, & a little embarrassed that I cannot find this gremlin. So please, masters of Hybrid Z's, yank me out of the forest! Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 6, 2007 Share Posted July 6, 2007 Have you tried tuning with a Wideband O2 sensor? That might reveal what's going on. Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 6, 2007 Author Share Posted July 6, 2007 No, I thought the n/a ECU had only provisions for narrow band width. I am using the stock sensor with stoich guage. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted July 6, 2007 Share Posted July 6, 2007 You can use a wideband to datalog AFR's to a computer and analyze it later. It doesnt necessarily have to tie into the factory ECU. The only problem is that you might not have any way to tune out the misfire. Maybe it's time for you to get a standalone fuel/spark system and ditch the factory EFI and AFM. By the way my turbo motor idles at 24° btdc and maxes out at 41° btdc by 3000 RPM. I decrease to 24°btdc max by 15psi boost. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 6, 2007 Share Posted July 6, 2007 This post has been removed to avoid confusion. I had misread the original and posted incorrect information for the equipment being used. Sorry to have interjected. Warren Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 6, 2007 Author Share Posted July 6, 2007 Thanks for the suggestions guys, it almost does seem to be timing related. And I know where you are coming from on the "factory " turbo timing on your cars. It is *20 BTDC w/ the ECCS system. On a non-turbo it is 5-10* BTDC with total advance at WOT of about 30-35 degrees BTDC. I have run the timing as an N/A with an inline one way valve to limit advance when boost comes on. The funny thing about this is that I ran this setup with no issue for two years! I will try to advance the dizzy some more & see if that helps/ or hinders matters. I'll post my results today and again, thanks guys for steering me in another (much needed) direction! -NosebleedZ Quote Link to comment Share on other sites More sharing options...
rags Posted July 6, 2007 Share Posted July 6, 2007 One other thing you didn't mention was the TPS. Is it coming off the idle circuit when you crack the throttle? Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 6, 2007 Author Share Posted July 6, 2007 Yes ,Rags, I verified it with the meter....continuity @ idle/ 35* throttle angle & it goes to infinite. In reverse the WOT switch checks OK too. Any other stabs at it....I'll take 'em! Thanks for your question. Quote Link to comment Share on other sites More sharing options...
sweetleaf Posted July 6, 2007 Share Posted July 6, 2007 With all those goodies in your motor. Why be held back by the stock system and not go to a standalone? Just curious? Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 7, 2007 Author Share Posted July 7, 2007 Well sweetleaf, that is a good question really. The SDS system has been wonderful since I've owned it. I can stay out of the throttle & literally get 21 to 24mpg and when I want it and the boost guage reads 1psi hundreds of additional horses gallop to life (at about 8-10 MPG LOL!) This system is actually a carry over from my first turbo build. I know the stock EFI is antiquated and if I do end up on a standalone it will probably be an SDS EM kit. I know alot of guys on here use MS controls, but there are so many posts I see with soldering this, retuning that, diagnosing this,....i honestly am a little leary of it. If some of you have hit a home run with MS, I might consider it if the wife won't divorce me. I have probably $25,000 in the car already with me doing absolutely everything. What is your experience with various standalones? Also any input on my lean condition? Quote Link to comment Share on other sites More sharing options...
sweetleaf Posted July 7, 2007 Share Posted July 7, 2007 I use an Electromotive TEC II . The biggest reason for this though, I got it pretty much when they first came out and there weren't that many other choices. It has proven to be a great unit though. Very durable and problem free. I still need to send it in for a prom update, so I can use the new win software. I still run the old PafZ Blend. If I was to buy another one today, I'd probably go with the MS or something else. Just because of the price, but the unit has worked pretty much flawlessly so it's proven it's worth. Do a lot of reading as there are a multitude of units out there today. There are some really good comparisons and writeups on here. Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 7, 2007 Author Share Posted July 7, 2007 Is the Tec 2 unit OBD-1 or 2 diagnoseable? I actually have a guy that I met in Knoxville that was running a F.A.S.T. ECU on his S30 turbo and the system was OBD-1 scanner compatable. The SDS unit I looked at, I think has OBD2 and an optional UEGO wideband setup for a grand or so. I would really like to upgrade,but I honestly don't think my problem is in the Datsun system currently. I need to pinpoint this gremlin & maybe go standalone afterward. I would hate to change everything & find the same issue. Based on my first post, ever have anything similar before or after EMS? Tomorrow I'm going to try some more timing adjustments as recommended by Warren & Cygnus. Quote Link to comment Share on other sites More sharing options...
Afshin Posted July 7, 2007 Share Posted July 7, 2007 Here are a few thoughts, if it’s running lean and missing, that it is less likely to be ignition related as poor ignition more often results in poor combustion and rich mixture. If it’s lean at low RPM and not high load, then it should not be fuel delivery, so fuel pump, injectors and pressure are likely OK. For low load lean mixture I think the likely players are faulty AFM or poor connector/wire. I know you checked the AFM per the manual, but that method may not be sensitive enough to pick up poor signal for part of the operating range. I would certainly go to the junkyard a get a cheap used AFM and see if it changes anything. Plugging and unplugging the connector and cleaning them can fix such gremlins quite often, but you probably have already tried that and it seems that you replaced the harness. Was this problem present before and after replacing the harness? I strongly recommend using a connector cleaner, if you have not used any since the problem started. If the problem persists, I would then pick up another distributor from the junkyard and see if it changes anything. This would not be my first guess, as you tested the distributor as well and it is running lean and not just misfiring, but you can never tell and you are somewhat stuck and you have gone thru all the basics. BTW is this truly RPM dependent or is it load dependent? Does the RPM at which it happens change when accelerating in first or second gear vs 5th on the highway? Does it do this when revving the car in neutral? Are you sure it is running lean and if so does it run lean first and then miss or is it simultaneous? Lastly at what point do the SDS additional injectors start kicking in? Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 7, 2007 Author Share Posted July 7, 2007 Afshin, I have recleaned all terminals & connectors several days ago & used dielectric grease to protect. I have performed a ohm check with no connections showing infinite on the new harness unless the sensor it is connected to is open with the engine off. Believe it or not I have tried one of the spare good AFM I have in my garage- slight change for the good but it just moves the stumble down the rpm band about 200 rpm. I believe this is due to the size difference in the turbo AFM housing & the N/a AFM. I could try a third one I guess. And yes, the miss/ lean condition is rpm dependant wether the car is driven or while in neutral. When revving the A/F guage will stay stoich range (14:1) until 1500, drop to way lean (17:1), miss almost simultaneously, then majically at 2500-take off & rev to 6800 or so. The real rub though is that it stays stoich the whole time. Before, it would even go slight rich (13:1) when revving in neutral. The SDS computer is set to fire the additional injectors at 0" vacuum & beyond (psi) and varies gain dependant on load input from the distributor negative lead (rpm) & by boost pressure (psi). It can be set for 10 to 80% injector (s) duty cycle by a gain knob. Any other ideas? This thing is gonna be the death of me! Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 7, 2007 Author Share Posted July 7, 2007 Guys, I have some updates on the car....I have checked the timing extensively-right on. The car starts by barely touching the key. I swapped TPS/ TVS- no change. Readjusted TPS- no bearing on the miss occurring. I actually motorvacced the fuel system thinking I had an injector clogged from sitting-a little smoother @ idle, but the miss is still there! WTF?!?!?! If an 02 sensor is bad it cause this? In my experience, the green light on the ECU will not pulse & the system goes into rich limp mode. The ohm test on the sensor was good, but what the hell? Any other ideas? Quote Link to comment Share on other sites More sharing options...
Clifton Posted July 7, 2007 Share Posted July 7, 2007 The base timing is set at 5* BTDC with advance unhooked. Just a stab in the dark here, but on a turbo car, start the base timing at 20 degrees BTDC and increase 1 degree per lb of boost up to a max of 30 degrees BTDC then level it out. Bet it runs better. Warren Sorry but that's the worst idea I've heard of for setting timing on a turbo engine. nosebleedZ. Does it miss at cruise, light load, and WOT at those revs? You said it was a little better with an n/a afm and it seems to be lean by your narrow band O2. I would try using one of your spare afm's and soften the spring up some. Just mark it before you start messing with the spring tension. You could also connect a voltmeter to the afm and measure the 0-5 v signal while driving. An analog one would be easier to read with the sweep. Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 7, 2007 Author Share Posted July 7, 2007 Clifton, that is a good idea on the AFM while driving. I think the voltage is acscending on Datsun EFI. I'll try that & see if I get the hiccup at a certain voltage. I was already a little ahead of you on the spring tension, I tried it loose (richer) & tight (leaner) on both meters. Either the engine would stall coming to an idle after revving or it would lean out and pop like Orville Redenbachers. Quote Link to comment Share on other sites More sharing options...
Warren Posted July 7, 2007 Share Posted July 7, 2007 Clifton, You're right. I just realized that he's not using an SDS ECU for TIMING, only for additional fuel injectors. Therefore the the information I was referring to is incorrect. I was getting the timing curve ideas from: http://forums.hybridz.org/showthread.php?t=78186 http://forums.hybridz.org/showthread.php?t=78960 http://forums.hybridz.org/showthread.php?t=92442 http://forums.hybridz.org/showthread.php?t=77085&highlight=SDS+Timing Sorry to have posted in this at all now. (Crawling back under my rock now) Warren Quote Link to comment Share on other sites More sharing options...
Clifton Posted July 7, 2007 Share Posted July 7, 2007 Clifton, You're right. I just realized that he's not using an SDS ECU for TIMING, only for additional fuel injectors. Therefore the the information I was referring to is incorrect. I was getting the timing curve ideas from: http://forums.hybridz.org/showthread.php?t=77085&highlight=SDS+Timing Sorry to have posted in this at all now. (Crawling back under my rock now) Warren I wouldn't go by what most people do for timing on this board. I've seen some of the worst timing maps on here. Scottie-GNZ's on your list link is a pretty good general safe one though. nosebleedZ, does it occur under cruise and load or just quick throttle openings? Quote Link to comment Share on other sites More sharing options...
nosebleedZ Posted July 7, 2007 Author Share Posted July 7, 2007 It happens at a steady throttle state, like cruising -to a lesser degree, & really hiccups bad when you stab the throttle. After 2500 it pulls easily to redline, although a little lean still at WOT (dances between 14 & 13:1). Quote Link to comment Share on other sites More sharing options...
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