Well my truck is acting up again. Long story short. on way home from work, it started sputtering and like holding back, acting like it's starved for fuel, but it never would die. Automatically I thoguht I had ran outta gas, stopped got gas, and continued home. Still sputtering around mid throttle, low end 0-2000-2500 RPM's it was great, past 4000 RPM's it was great, but it was just sputtering under load. It took me a day or 2 to trace it down, after new plugs, wires, cap, button, check.... recheck... retrace...replace every single vacuum line. Still "holding back/sputtering" under load, and only when in gear. So then I started troubleeshooting Emissions systems, Egr/Bpt/Ab etc.. Everythign checked out ok, EGR diaphram was ok, or at least I thought it did. I was 1 day away from carb rebuild/weber replace. I was really thinking clogged injectors/jet. Luckily late one night, I was surfing for solutions and similar problems, and I can't find the page, but basically he disconnect the egr vacuum line, plugged it, and the sputter went away. So he's left it like that. So I tried the same thing and like magic it was gone. Great news..... right. Very next day it over heated on way home from work. I of course was watching and listening closely to anything unusual. After a quick cool down in 2 degree weather here in East TN. antifreeze/water, and made it home. Ended up having cracked radiator, and SEVERELY rusted interior of the original radiator, and was leaking pretty good. Replaced radiator, and all is well now. Except for fact that EGR is bypassed. My ? is I know the EGR has to have certain conditions met inorder to open/close one of which being the engine temp. reaching 122 degrees, on my model controlled by TVV valve, which I know is working., gas presure from exhuast manifold has to be great enough to close BPT valve,(BPT on 85 model) and throttle at mid-range. Could the VVT valve not have been functioning at the time I was working on it because of the coolant issues??? And as far as manifold pressure, after putting brand new plugs in, and running and checking and troubleshooting things the vehicle prob ran for 30-45 min on new plugs. I took all plugs back out, rechecked gap, checked compressions. everything was good, but, on the #4 exhaust plug.... it looked brand new. compared to the skin colored brown/tan of the other 7 plugs, this 1 plug was nearly spotless. could I have a valve issue on #4 cylinder??? And 1 more thing. My 1 owner truck has never had any type of seal leak or anything. around the same time things went awry that night on way home. I developed a oil leak around the "baffle" plate that screws in the block, PCV system. Round cylinder thing under exhaust manifold, with metal line around back of engine just under EGR metal line. Could all these things be telling me i've got a blown head gasket?? Anyway thanks for reading. Sorry for long post. Any help, suggestions, ideas, thought appreciated. Truck is running fine now, but it has a ever so slight "hiccup", and has a lil' less power. Not sure if it's cause EGR is unhooked, or from me tinkering with card.

A lot of questions in there for one easy response, but yes, the TVV could have misfunctioned. The cylinder/valve issue with the clean spark plug has me a little lost. Is the truck still running right now? I don't think you mentioned your mileage, but on an older one of these trucks with their aluminum heads, the overheating alone might have caused a warped head/headgasket failure. Definitely worth looking into.

OK I'm still having the same issue. It has progressiv Ely gotten worse. Only tuning in last post I said my exhaust plug was clean. It was my intake and exhaust plug. Intake plug is sparkling white. Looks brand new even after a month. I got inline spark tester. And everything is good. Only problem with spark is exhaust side is really weak. Not sure if its normalbut its ddef weak. I swapped the coils. And no matter which coil is used the one that doesn't have the brown wire has a weaker spark going to all plugs on that coil. I've already got a carb kit to rebuild it. I know gas to carb is good. So hopefully its gas to 4 cylinder. Could a dropped valve cause no fuel to 4 cylinder? As always any help appreciated.

Oh BTW. Truck has 185k. One owner-b4 me. 85 720 only 2 wheel drive though.

Well i'm still stuck. I've done everything except rebuild the carb. If this helps anyone figure anything out. Since I've unplugged the vac. advance, it runs like it use to. Everynow and then I can feel a slight shudder, but very rarely. So what does this mean? I know I'm getting spark on intake side, and very weak spark on exhaust side. As for fuel to all 4 cylinders, I'm going to check it now.

Anyone know what would cause me to have weak spark on 1 coil? and i've swapped wires to the 2 coils, it's the wires coming in that are giving me issues. when I swap out the wires, the weak spark follows the wires. Since it sat behind a guys house for 5 years, I'm sure there are some wiring issues. Does anyone know where the wires on the coils come from? My wires aren't like my Haynes book say. 1 coil, my intake side, is maybe a 10 gauge, while exhaust is maybe a 16-18 gauge. The smaller ones are giving me little spark.?? and my wire colors aren't the same as the book.

So, first thing. Because the engine is carbureted, that means that unless your head is totally boned, #4 is getting fuel if it's getting air. Three possibilities come to mind:
(1) Exhaust valve never closes, so the gas goes straight out of the tailpipe during compression and no significant ignition happens in #4
(2) Intake valve never opens, so no air or fuel gets into #4 at all.
(3) #4 rings are boned, and so there's no compression and fuel goes straight into the block (which could be related to your PCV issue)

One easy test: disconnect wires from all spark plugs. Pull one of the plugs from #4. Crank the engine. Does it smell like fuel? If so, #4 is getting fuel, which implicates the exhaust valve or rings. If not, there's no fuel, which implicates the intake valve.

You can repeat the test with a known good cylinder just to see what it's supposed to be like.


Alternately, if you have a buddy with a compression tester, that'll tell you right quick if the valves aren't sealing.

Number two, given that you had a leak develop right after the overheat, that seems to suggest pretty strongly that the head warped. :o/

That said, the sputtering until you disable the EGR suggests that the secondary plugs may not be doing their job. Looking at the wiring schematic in my FSM, there is a fuse that handles _only the exhaust side plugs_. That's the first thing to check. datzenmike has the layout of the fuse box here:
http://720world.com/forum/topics/pic-of-fuse-box-cover

So, I'm trying to make sense of my wiring diagram. First off, it doesn't seem to indicate wire gauges, so I dunno if the signal wires are supposed to have the same gauges on the two sides. My guess is that they should, and so that lighter-gauge wire could also be causing a voltage drop to the input of the exhaust coil, but that's just a guess. First things first, hit up that fuse.

Okay, colors.
Here's a wiring diagram. It's not as useful as the one in the '86 FSM (EL-37 and EL-38 are the ticket), but it's online:
http://nissannut.com/projects/z24i_fuel ... wiring.jpg (from http://nissannut.com/projects/z24i_fuel_injection/ )

Note that this is my first time reading an auto wiring diagram, but I'm pretty familiar with electronics from other contexts. That said, the wire colors are kind of confusing:
1) Brown is the source of power to the intake coil. At some point, Brown is connected to White/Blue, which connects to the ignition and to the top side of the ignition section of the fuse block (aka fuses #1-#5).
2) There is a White/Blue wire on the trigger side of the intake coil. _This is a different wire than White/Blue from #1_. This wire goes to the distributor for the trigger signal on the intake side
3) Black/White is the power source to the exhaust coil. This connects to the bottom side of Fuse #1 (10A). As such, it should be at the same voltage as Brown (aka wire #1), assuming that wiring is all in good shape, and the fuse is in good shape.
4) Red is the trigger signal for the exhaust coil. It connects directly to the distributor with no detours.

Note that there are some other connections. Wire indices match above:
1) Brown also connects to "Condenser", which is basically a cap. Presumably, it helps to compensate for voltage drops due to the coils charging.
2) White/Blue also connects to a resistor, the other side of which goes to the Tach as the tach input signal
3) Black/White connects to "Condenser" as well. It has a distinct cap from #1, although both caps share a ground.
5) The shared ground from "Condenser" is a Black wire that connects directly to the grounded body of the distributor. The schematic shows it going through a "Plain connector."
6) There is a Brown wire on the bottom side of Fuse #2 (15A). This is _not_ related to the Brown wire in #1. The power supply page (EL-5) shows that this wire powers "Inhibitor switch, Engine control system (Auto choke heater, Fuel cut solenoid, Detonation control unit)

So, just to reiterate:
— Brown from intake coil hot side is the same wire as White/Blue at the top side of the Fuse Block.
— White/Blue on the ground side of the intake coil is the trigger signal, and serves as the tach input signal as well
— Brown from the bottom side of Fuse #2 is different from Brown on the power side of the intake coil, but they are actually connected through Fuse #2

Thank you for your informative reply. The truck has never leaked a drop of oil, since i've had it.(after replacing sending unit) The night it started missing, I got home popped the hood, exhaust side of block, under ex. manifold was wet from oil. After watching it closely for last few weeks, it appears to be coming from that litle canister(3" tall, 1" around) thing below ex manifold, other side of PCV valve. I'm not sure if this this screw into the block, or maybe the baffle plate is stuck... I've already checked the valve, it was clicking, I did not however check the vacuum. Will do in next few days.

I've also taken the valve cover off, checked all the valves, all looked good, all within specs. I've yet to check the wet plug on #4, which I will be doing in the next few days. It really makes me think its a ex valve sticking open.... piston comes up to create compression, compression goes into crankcase.

Wiring problem, I've checked my fuses, all good. On my weak side wires, I've got a red wire, and a black with white stripe, and on the ignition side, i've got a larger gauge wire, 1 brown, and one white/blue. I've got the diagram, but I can't find that condenser thing. I've replaced the ignition module, no change. I've checked many things with multimeter from haynes. I don't have my book in front of me right now, but I'll let you knwo exactly which test my module failed. I've had a battery light on for years now, but haven't been able to track it down. I've had alternator checked/recheck. batt checked/recheck. Gotta be a wire somewhere chewed into.
I'll get back to you in a day or 2. thank you for helping me spitball, and giving me some ideas.

GOT IT!!! Finally... Just like almost all 720's it's been a real b**** to diagnose. But I happen to read a post on a similar issue, and how it ended up being his timing. I broke out the timing light and low and behold, my timing was prob between 30-40 BTDC. I had no idea it would even run that far off. I know my 97' struggles to run past 8 Degrees either way. So I've apparently jumped a tooth. Time for a chain, which will be coming in the next few weeks, Since it's made it to 190K, and I'm pretty sure it's still the OEM chain.. I can't complain. However, I do have one more question.. During my diagnosis I've been pulling these little metal things outta my vac. lines. I'll be posting pics of them. I'm not sure what they are nor have I ever seen any of these. Little tiny, look like air flow restrictors maybe,?.? thanks for any input

They are air flow restrictors, yes. I actually did a mini writeup about replacing them:

So, quick tip for moving those restrictors over:

First off, there are three of them, and two sizes. One with a larger opening, and two with smaller openings. IIRC, the two smaller ones come off of the TVV, and the one larger one comes out of the carb base and goes to the EGR control line. That all kind of makes sense, since those are the three controlled vacuum leaks in the system.

To remove: just use a sharp knife/razor to cut the old vacuum hose lengthwise down the side, and go easy when you're passing over the restrictors, as they're pretty soft (look like brass). Make sure to clean them out with carb cleaner on both sides, and air-dry with compressed air if you got it.

To install: spray a little bit of WD-40 on the end of the new vacuum hose, then gently push the restrictor into the hose. I either used my hands or a pair of needle-nose pliers. After that, you need something long and skinny to actually seat it 1-2cm down from the hose end. I used a roll pin punch of appropriate size and it worked out great. You could probably also use a toothpick (the wood wouldn't damage the inner surfaces).

(From: http://community.ratsun.net/topic/60975 ... try1060474 )

Well it was too good to be true. It seemed to run better after adjusting the timing, but it only lasted a day. Then it reared it's ugly head once again. Timing good. still hesitating. however. I've been adjusting on the carb, to get the secondary barrel to kick in, once it kicks in, it can really move once does kick in. I'm thinking I had my throttle adjus screw backed off so far, that the secondary chamber only kicked in when the primary butterfly was prob 90%+, nows it's closer to 50%. Once it kicks in it's good, but from 0 to 50%, it struggles. Some other thing I noticed, the flat above my exhaust manifold, thats vacuum controlled, and lets a constant flow of hot air into my breather, it stays shut, no matter what. I can unplug the vacuum line, and it open up, and runs a little better. but i thought it was suppose to stay closed only with the engine cold, and open once it warms up.?? I do hear a new, buzzing that is coming from that temp control valve in my breather.. I'm guessing it's not working correctly. I'll try replace it this weekend and get you guys an update then.

I've replaced the Air temp control valve that controls that flap in breather. It was bad. And staying shut even after warmi g up. My vacuum control valve was bad, the one that advances timing. I've replaced those 2 and will continue in the morning. Hopes its better

I think my suggestion at this point would be a carb rebuild. If the fuel inlets are partially clogged on the primary side, that could potentially explain what you're experiencing (doesn't get enough fuel until the secondary opens up).

One thing to possibly try before that is to replace the fuel filter. It should be integral with the fuel pump, mounted _inside_ the bottom.

That said, do you still have the weak spark? Are you still getting no fire out of the #4 cylinder?

I've ended up removing all vacuum lines, only leaving my Dist Vac. advance. And the hesitation has completely gone away. I used a vacuum pump and found that my VAcuum control valve was bad, little white thing that has 2 ports front of engine, pass side. It was bad, replaced it, and My charcoal canister is bad as well.. And according to the Haynes book, and Autozone. my EGR valve after applying vacuum. it should stay open after applying vacuum for at least 30 seconds. Can anyone confirm this? My does not. It closes withing 5-10 seconds. Which would explain the slight sputter while holding throttle steady. During acceleration EGR opens and feels great, but when I'm holing it steady. Egr starts to close, hence the sputter. My next days off I'm gonna try replace Vac systems, one at a time. And see what happens. I also left my brake booster hooked up. When I removed my EGR to check for cleaning and stuff, I had to push down the tube, and it ended up cracking on the exhaust side. now I've got a exhaust leak on the manifold side. Luckily i've got a spare in the garage, i've just gotta figure out how to get that freaking nut loose. I've been spraying(PB) and steel brushing since last night. As far as spark, I've still got weak spark on exhaust side plugs, I think that is a wiring issues, hopefully i'll be able to get a new harness soon. Oh and look what i just bought!!!!! http://www.ebay.com/itm/1986-Nissan-Fac ... true&rt=nc

Hopefully u can seen it. 86' FSM for 30 bucks!!!

Nice catch, with the FSM. That's exactly the one I've got (and I've also got an '85 truck).

As for the EGR, I read the 30 seconds thing also, and that's not my experience. I have a brand new (aftermarket) EGR and it closes after 5-10 seconds as well.

As for the nut on the manifold side of that EGR tube, I all I can suggest is a wrench with some wide jaws and a lot of leverage. Hitting the nut with a torch might help as well. I have a wrench that's ~4mm thick, and when I tried to loosen that side, I started putting an indentation on the nut. That's when I decided that I didn't _really_ need to pull that nut off

Hey what happened......talk about a cliffhanger. ... I been doing all the same things. I'd like too hear a happy ending. ...

Well ive Never gotten rid of the tiny flat spot(hesatation). I did pull card off and rebuild which made a HUGE difference. But the sputter is so small now u cant even notice, my buddies make fun of me cause they cant feel it, but i feel it and it drives ME F#&>&>' NUTS!! LOL still drives like a champ.

Well glad to hear it mostly worked out. I been feeling really frustrated, but gonna keep at guess when I can get time....think I depending on what compression comes out at ,think I better suckit up and get another carb.....