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My next 720 resto


720inOlyWa

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EDITORS NOTE:

This thread begins with my search for a 720 4x4. I began posting when I was sure I had a deal for truck below. Fortunately, that all went south, because a much better truck presented itself... and I bought it. This thread is actually about the rehab of that truck, my 86 4x4 King Cab. If you are interested in skipping the missed opportunity and want to get to the truck I am working on, that story begins on page 2...

 

 

Well I went and did it... again. I couldn’t resist, actually. I nabbed another 720 to play with. This one is off of Craig’s list and I am sure I am not the only Ratsunite to check it out. After some arm wrestling, well she is mine.

 

While 2wd drive is pretty straightforward, I know little about dealing with 4wd trucks and their issues. I did read the shop service manual before I went for it and it seems like it is all fairly fathomable to me.

 

My question is, are these 720 4wd trucks as good as the 2wd versions? What should I be concerned with / look out for as I drag this thing home to resto? And 720 4wd owners, feel free to chime in and let me know what I am up against. Thanks!

 

It comes with the 2.4 fuel injected motor, which is also a mystery to me right now. Are the fi engines great, or not? It also comes with the original NAPZ 2.4 motor in the bed, presumably needing a head gasket/rebuild. If worse comes to worse, I will rebuild that one and put it back in.  

 

Any comments / advice on the 2.4 fi motor or 4wd 720 trucks would be helpful too.

 

 

NEW7204x4_zps3e0014b9.jpg

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From what I understand, it is a 2.4i motor, so I just supposed that it was a factory option. I hadn’t heard of it before. He said “it runs, but is not drivable. You have to flutter the gas pedal to keep it running.” Who knows what the heck that means. I got it for price where if I thought I had no option but to rebuild the regular 2.4Z back in the bed, I’d still be just fine. Hah- we shall see. 

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Wayno there are TBI (Throttle Body Injection) 720 and the engines are referred to as Z24I.  I have one.

 

There are a few 4x4 that were TBI from the factory in the states.  There is a special edition Factory Service Manual that covers the 720 TBI.  I have personally come across 2 of these 4x4 trucks.  I have also read that a limited # of 2 wheel drives were also shipped to the US but I have not personally found any.

 

This one just sold on ebay.

 

$_57.JPG

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I certainly will, Charlie... stay tuned.

 

My understanding is that it was originally carburated, and this is a replacement motor. Now I am pretty much scared shitless...

 

If, in the worst case scenario, it was originally a FI vehicle (which I doubt), exactly what is involved in making it a carb version? Fuel delivery? Wiring? (gulp)...

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I would be tempted to research the FI motor and see if it is an original one for the year, but build the z motor so she can run well first. Then tackle the FI one.  Sounds like a real find if the price was worth the learning curve.  Good looking truck too.  Planning a paint job and such down the way?

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Hey Charlie, I hope all is good with you.

I hope I didn't scare you on that one thread when I asked who drug you into this, that wasn't my intention, I just wanted to use the word drug and you left an opening.

 

I worded my response carefully when I responded, I used the word "true", as I don't consider throttle body injection a true fuel injection even though it does actually inject the fuel, so it is fuel injection, it just looks like a carb, most will think of the EFI manifolds when fuel injection is mentioned, that is what came to mind when he said it had fuel injection, although I have no idea what type it has, as no photos were posted of it.

Wayno there are TBI (Throttle Body Injection) 720 and the engines are referred to as Z24I.  I have one.

 

There are a few 4x4 that were TBI from the factory in the states.  There is a special edition Factory Service Manual that covers the 720 TBI.  I have personally come across 2 of these 4x4 trucks.  I have also read that a limited # of 2 wheel drives were also shipped to the US but I have not personally found any.

 

This one just sold on ebay.

 

$_57.JPG

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So thankful for the advice here. Once I can come out of a fetal position, I will let you know what I find out, regardless of how bad the news might be. Geeze, my little carb cab is looking good to me right now...

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Okay, brain dump follows:

 

The thing to understand about fuel-injected vehicles (which I don't understand for TBI vehicles, but do understand it for multipoint fuel injection systems) is how the feedback systems work.

 

One feedback system is the one that provides more fuel when the mixture is running lean, and less fuel when the mixture is running rich.  Most carbureted vehicles can't do this, so if they're set up to run rich, they just run rich.  If they're set up to run lean, they just run lean.  The Cali Z24 trucks ('85 and '86) _did_ do some feedback, by virtue of using a solenoid inside of the carb (which was basically a half-step ahead of the TBI on the Z24i).

 

For the Cali trucks and fuel-injected vehicles, they have an O2 sensor in the exhaust manifold.  The O2 sensor measures oxygen levels in the exhaust, and the ECU maps those O2 levels to Air/Fuel ratios (AFR).  The ideal AFR is 14.7:1 (14.7 parts air to 1 part fuel).  If the ECU sees a high AFR (so too much air; running lean), it adds fuel to the mixture.  If it sees a low AFR (too much fuel; running rich), it takes fuel away from the mixture.

 

Okay, let's jump to multi-point fuel injection, because that's what I understand.  To be clear, this is _not_ how the Z24i behaves.  For multipoint, you have one fuel injector for each cylinder, and generally, the fuel injector is pointed at the back of the intake valve(s) for that cylinder.  The ECU has a crank angle sensor and a cam angle sensor.  It uses those to determine (1) which cylinder has the intake stroke coming up next, and (2) for that cylinder, when is the intake valve starting to open, and when is it done closing?  _While the intake valve is open_, it triggers the injector to spray a specific amount of fuel into that particular cylinder.  It's not spraying full bore the entire time, mind you, but just a certain amount for a certain period of time.  Then the compression stroke, power stroke, and exhaust stroke happen like you'd expect.

 

But that's not all.  The ECU also keeps track of how much air is coming into the engine.  Most modern vehicles use a MAF (Mass Air Flow) sensor, but there are other kinds.  See http://en.wikipedia.org/wiki/Mass_flow_sensor and http://en.wikipedia.org/wiki/MAP_sensor .  So when the ECU detects lots of air coming into the engine, it automatically changes the injector duty cycles to add more fuel.  When it detects very little air coming into the engine (like at idle), it cuts the injector duty cycles to add less fuel.  At the same time, it's continually checking the output of the O2 sensor to to "trim" the fuel level and keep things running well.

 

 

 

That said, the main thing I don't know about TBI is whether (at constant throttle / at idle) the fuel injector has distinct pulses, or whether it's generally spraying the entire time.  By "distinct pulses" I mean "adds fuel when an intake valve is open, and shuts off fuel when the intake valves are all closed."

Judging by http://nissannut.com/projects/z24i_fuel_injection/ , it looks like the Z24i _only_ has a crank angle sensor and does not have a cam angle sensor.  That suggests that it doesn't know when valves open and close, and thus, that it just sprays fuel all the time.

 

Presumably, it will still have a MAF to determine whether it should be spraying lots of fuel or not very much fuel.

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Okay, so let's assume my TBI hypothesis is correct.  If you have to hold the gas pedal down to keep it from stalling, a couple things come to mind:

1) The MAF isn't properly adjusted, needs to be cleaned, or is just plain worn out or broken.

2) The O2 sensor isn't working properly, or doesn't have a proper ground.

3) The idle isn't set properly

4) Vacuum leaks

5) The ECU isn't working properly

 

Thankfully, the Z24i ECU has some diagnostic functionality (unlike the Cali Z24 ECU, grrr...).  See here:

http://www.infamousnissan.com/forum/showthread.php?s=ff4ac30d3354bd66ad875b6c7cf9af50&t=20905

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Hey Charlie, I hope all is good with you.

I hope I didn't scare you on that one thread when I asked who drug you into this, that wasn't my intention, I just wanted to use the word drug and you left an opening.

 

I worded my response carefully when I responded, I used the word "true", as I don't consider throttle body injection a true fuel injection even though it does actually inject the fuel, so it is fuel injection, it just looks like a carb, most will think of the EFI manifolds when fuel injection is mentioned, that is what came to mind when he said it had fuel injection, although I have no idea what type it has, as no photos were posted of it.

No worries Wayno you did not scare me off.  I was joking with Mike. 

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I want a new drug.

 

The electro-injection was introduced on 720s built from April '85 and on. A quick check of the air filter will show two wing nuts holding it on and not one as with a carb. 

 

If this was originally a carb engine converting to an EFI engine replacement would be a crazy amount of work. It would be simpler to take the EFI stuff off and swap the carb, intake, and distributor... basically just swap the block and head.

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XSDG great information and understanding thank you.

 

720inOlyWa.  First need to determine if the Z24I engine was stock to the truck.  Take pictures of the the engine and what is mounted on both fender wells.  I can tell from the pictures if you have all the correct parts.  Also need to check fuel pressure as the Z24I needs approximately 45 PSI where the carbed Z24 requires about 5 PSI.

 

If the original motor was A Z24I then all the components should be there.  Check the vacuum diagram under the hood this may give you an idea what engine was original to the truck.  The VIN is no help as both the Z24 & the Z24I were designated as "N" in the VIN.

 

To swap the Z24I engine into a stock carbed truck would take a lot of work as the ECU and wiring are different.  The coils are different as is the distributor. 

 

This is what I am doing on my stock carbed 86 King Cab.  I a also making this swap harder buy including the automatic 4 speed transmission.

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I want a new drug.

 

The electro-injection was introduced on 720s built from April '85 and on. A quick check of the air filter will show two wing nuts holding it on and not one as with a carb. 

 

If this was originally a carb engine converting to an EFI engine replacement would be a crazy amount of work. It would be simpler to take the EFI stuff off and swap the carb, intake, and distributor... basically just swap the block and head.

I here you on the new drug Mike!  After researching this Z24I swap into my 86 I am thinking of just doing either a KA or VG swap instead.  I am also going to go carbed on the Z24I motor I have. 

 

Mike are the distributor interchangeable between the Z24I and the Z24?

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I will take and post pictures when I can, probably in the next week or so. Man, I sure appreciate the input from everyone.

 

So let me get this straight- if this was a TBI vehicle to begin with, I will need to replace the engine, the fuel delivery system, the coils, and the wiring harness to convert it back to carb type? Anything else?

 

Thanks!

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If it was a TBI truck originally I would keep it a TBI truck.

 

Most of the emission parts are different.  I have one of the manuals that I posted the picture of. If it has been converted to TBI I doubt it was done properly because of the amount of work and parts involved.

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Thanks, Charlie. It will be interesting to discover what’s what. I may do a recon mission tomorrow, just to deliver a pipe bumper that I will bolt on there to tow it home, and to take a bunch of pictures .The price was good enough that I said yes, sight unseen. Now I get to deal with it.

 

If it is not too daunting, and does require either welding or steel fabrication- which I cannot do at this point- I will probably return it to a straight carb setup. The reason being that I love the straightforwardness of these little trucks. They oooze it. I am not really into this to learn about the esoteric or fancy-schmancy possibilities. I understand carbs. I get ‘em- mostly. I know that a Weber on a NAPZ motor is straight-up, straightforward stuff. It is in my comfort zone. I have no idea what language you are using when you begin talking TBI. Holy cow!

 

Now the labor- well, I don’t care much about how hard things are to do. I will take my time and figure it out as I go. Mike and wayno will hip me up if I am screwing things up. So will you, Charlie. And I am so appreciative for it, too. So if I have to pull and replace the wiring harness, somehow that feels a lot easier to me than figuring out the feedback loops in a throttle body injection system. It just does.

 

Now I can also see a time in the distant future when another generation of Nissan truck freaks comes across my truck and ponders what kind of asshole would have converted the most rare and sought after model back to a straight carb setup?!? I have actually been that guy before. So hypocracy is available to me here, too. Thing is, by the time someone has a problem with my shortcomings as a mechanic, I will be long dead.

 

I build and work on guitars for fun, too. It is great stuff and I love it. Very challenging work. When I rehab a fine old guitar with a worn out top, I replace that top with a brand new one. Fuck the collectibility impact, the top was worn out- it didn’t do its job anymore. Now it works to its fullest potential because it has a good top on there. Go make music already and don’t bug me about collectibility or originality. Make your own damn history with a new top.

 

I look forward to making tis truck nice again, one way or another.

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  • 4 weeks later...

Well, that deal went south in the most peculiar way. No point getting too far into it, but I was disappointed. I kinda had my mind all set on a sunroof... I’ve never had a sunroof before...

 

Oh well, this one fell into my lap instead. I already posted the particulars. With this 4x4, I am playing with ‘house money’. I traded in a way that made it, essentially, a free truck, plus $300. So was I going to say no?

 

The body is really pretty straight and good, so that is a huge plus. Not much rust at all. The previous owner said it has a blown head gasket, but I am not so sure. I think it may be leaking coolant at the intake manifold. No matter, it has 150k and will get the head gasket / timing chain treatment in any case.

 

This truck has been poorly cared for, poorly maintained. I have two days into it just getting some of the grime, oil, and shit of of it. In that respect, it is a real mess.  The previous owner wanted to keep the battery, so we negotiated that. But when he removed the battery, he removed the terminals as well! Ugh. No problem, I will get new ones when I get around to replacing the battery. Yesterday, I gave the battery tray the full POR 15 treatment as a first step in her rust rehab. I have a space heater running in the cab for the second straight day, trying to dry out the floor and seats because the previous owner left thedoor open for two rainy days before the tow truck came for it. Brilliant, kind hearted.

 

Under the hood was unbelievably filthy. It has a Weber, but everything seems jury rigged and cobbled together. The choke wire is’t even hooked up. Bunches of the hood blanket had fallen away and found their way into nooks and crannies. It was bad, I tell ya!. But much better today, and in a few weeks, it will be running great again and all immaculate in the engine room.

 

I had the good fortune of driving an 85 King cab 4x4 last week, a really nice one. And the owner gave me the rundown on the transfer case and we did a little four wheelin’. I’ve got to say, it was really fun! So now I am psyched to do a little of that with this truck in the near future. My plan is to fix it up and sell it to a friend who raises goats on Vashon Island. She wanted my 2x 720 truck immediately and almost offered enough to buy it right there on the spot, but I stuck to my guns and kept it. But I told her I would find another, fix it up for her, and sell it to her at a fair price. Time will tell which truck she actually ends up with, but de-funking this 4x4 version makes me appreciate what I cream puff ‘The Fudgecicle‘ was when I got it!

 

Now for a couple more ‘before’ photos.

 

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34RIGHTSIDE_zps4de502ee.jpg

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