86 720: Runs but dies, won't restart until some time late : PICS

[Got_rwd?]

Good evening, long time lurker but now I've researched as much as I could have to figure this out . Now asking for your help please .

 

 

Background:

Bought a 86 Nissan 720 4x4 5speed .It's a California model emission

 

Issue:

Truck will struggle to start and randomly will start right up and run perfectly fine. Will run for a few minutes and then just turn off like if the key was turned , no dieseling or studder. I will try and restart it and pump the gas pedal, she will start and run like crap while I pump the pedal but will die if I stop.

 

I can return hours later and the truck will restart and run fine , but will die and continue the process mentioned above.

 

Parts replaced/rebuilt:

 

Rebuilt the carb

 

Redid all vacuum lines

 

Replaced the "ecc relay" by the battery

 

Replaced 1 ignition coil and checked wiring with what I found online

 

Replaced dizzy cap and rotor (checked the ignition module thing and it looks near new)

OLD STUFF

 

Checked ignition wiring (removed aftermarket alarm)

 

Ok so that's a sum of what I've done, now here's what driving me nuts

 

Here's the sight glass on the carb when the truck won't restart , it's 3/4 full

 

When I rebuilt the carb, the little metal ball and the bottom under the spring was either nowhere to be found or stuck inside , I left it alone and DID NOT use the one in the rebuild kit

 

The computer under the drivers seat has 1 wire pulled out (black/white) from the black plug

 

And how the hell do I use this multimeter ?! Lol

 

 

I'm stuck guys and don't know what else to look at

[Charlie69]

Here is what I hope will help you.  The White with Black stripe (WB) wire goes to terminal # 6 in the ECU Plug  I highlighted in red.

 

[datzenmike]

I would start with the obvious White/Black strip wire and get it connected up. The throttle switch tels the ECU that you are

 

A... at idle

B... at full wide open throttle

C... not A or B and presumably driving down the road.

 

Without this info the ECU can't properly tell what is expected of it as far as performance or emissions.

[Charlie69]

Great info Mike.  I was hoping you would help out.

 

If you click on the image I posted above it will take you to my photo bucket where you can click on the picture again to enlarge it or you can download the image to your computer for future reference.

 

I have my photo bucket unlocked so feel free to download anything you like.

[Got_rwd?]

Thanks guys, I was hoping for either one of you to reply since most of the threads I read included your replies lol

 

Thanks I will look into the wiring . I'll take a video to further illustrate my issue

[datzenmike]

Also take note that 720 owners often have problems with the feedback carburetor wiring. It's the short length of the carb wires to that round plug. They have been known to break internally under the insulation from flexing. There is a throttle position switch, idle cut, choke heater, mixture solenoid wire (and maybe more I can't remember) and all this info is fed to or from the carb and must be working. The problems are usually intermittent and hard to find. Wiggling the wires may produce a change in idle that points to a problem.

[Got_rwd?]

I have a feeling I have a bad carb, my choke stays open and feels like the spring is just floppy .

 

I need a good working carb , anyone selling one ready to drop in ?

 

I found some online new reman for $190

 

For those who went weber, is it difficult to wire up the electrics since I have a comp controlled carb ?

[datzenmike]

Easier and cheaper to fix what you have.

[DISLEXICDIME]

Are you sure it is not the black relay box that controls the fuel pump that is located at the top of the right kick panel? The relay go's bad and causes these kind of issues. THe solder joints go bad and you need to re solder them .next time it won't start check voltage at the fuel pump

[xsdg]

OP: slow down, slow down.  First and foremost, you mention that "the spring feels floppy" for the automatic choke.  That sounds a lot like it wasn't reassembled properly at some point.  The end of the spring needs to fit into a certain spot for it to actually transmit force to the choke flap.

 

Second, your carb fuel bowl is overly full.  How precisely did you check the float settings?  Did you make sure that the tiny retaining spring fit in the right spot on the needle?  Have you double-checked that your fuel return line is working properly, and isn't partially blocked or anything?

 

How familiar are you with carburetors?  Did you follow any particular guide for the rebuild?  I swear by fastboatman's awesome rebuild instructions — they kept me straight when I was just figuring stuff out and I managed to get it right the first time around (how exactly?  I really don't know :o)

http://forums.nicoclub.com/z24-carb-rebuild-diy-1984-86-t537596.html

[datzenmike]

Can't tell about the fuel level... figured parallax view. Thing is, the level should be at the dot. YOU check it and see and adjust if needed. Too full could easily overfill, flood and stall.

[Got_rwd?]

Update:

 

So I purchased a reman carb from national carb . My old carb had a broken bracket and vacuum pot for the choke. Didn't want to fiddle with it so I bought a reman carb to start fresh .

 

 

Installed new carb and the truck fired right up and ran fine for 20 mins . I gave it gas, rev up and then came down and died like if someone turned the key. It hesitated to turn back on . I let it sit for a couple hours and then restarted with same results as before . They only way I could get it fire back up once warn is pulsing the pedal or playing with the choke flap . Could it be that the choke is constantly being "hot" and not having a correct ground signal from ecu of harness ? The carb is new so I doubt anything is wrong there (pre-tested at 3.5psi). What position is my choke supposed to be in on a warm restart ? Do any relays control the choke ?

 

[Got_rwd?]

For fucks sake, ALL MY VAC LINES WERE WRONG !

 

Took the previous owners word that it ran good so I didn't check routing , I just replaced the old lines following the same route . Thank god for the nico forum write up showing the correct routes .

 

It's 1am , so I'll crank the truck over tomorrow to see if this fixes it . Matched all my lines to oem routes . Wish me luck guys

[Charlie69]

Well did it help.

[datzenmike]

Choke should be open in about 8-10 min. depending on how cold it is outside. Choke on will cause the fast idle to be on.

 

Not much on those feedback carbs that can be adjusted (like idle mixture)

[Got_rwd?]

Update:

 

Still same issues but she tries to stay running now when I go to restart . Always runs great when cold and I let it sit .

 

I took off the fuel pump relay and this is what I found:

 

Guessing I need a new relay :(

[Tinman]

Probably not.  All looks fine on that side of the relay.  The crud is just flux residue.

 

You can jump the power to the pump with a wire to see if the problem persists, and ONLY replace the relay if it doesn't.

[datzenmike]

I have a feeling I have a bad carb, my choke stays open and feels like the spring is just floppy .

 

I need a good working carb , anyone selling one ready to drop in ?

 

I found some online new reman for $190

 

For those who went weber, is it difficult to wire up the electrics since I have a comp controlled carb ?

 

 

Easier and cheaper to fix what you have.

 

 

Update:

 

So I purchased a reman carb from national carb . My old carb had a broken bracket and vacuum pot for the choke. Didn't want to fiddle with it so I bought a reman carb to start fresh .

 

 

Installed new carb and the truck fired right up and ran fine for 20 mins . I gave it gas, rev up and then came down and died like if someone turned the key. It hesitated to turn back on . I let it sit for a couple hours and then restarted with same results as before . They only way I could get it fire back up once warn is pulsing the pedal or playing with the choke flap . Could it be that the choke is constantly being "hot" and not having a correct ground signal from ecu of harness ? The carb is new so I doubt anything is wrong there (pre-tested at 3.5psi). What position is my choke supposed to be in on a warm restart ? Do any relays control the choke ?

 

This is an expensive way to rule out causes of problems.

 

 

Did you ever fix that loose wire from the ECU???

 

Where exactly does that White/Black stripe wire belong on the ECU???

 

 

Does the choke close when cold and open fully when warmed up???

 

 

 

 

 

 

 

 

 

You can jump the power to the pump with a wire to see if the problem persists, and ONLY replace the relay if it doesn't.

 

Make a small jumper from the White wire to the White/Black wire. This will force the fuel pump to be on at all times when the ignition is on. Do this and drive it. If the problem goes away then there is something wrong with ...

 

a/ the relay or..

b/ one of the inputs that keeps the pump on when needed.

 

 

This is not a fix only a way to narrow down what wrong, IF there is something wrong with it.

[Got_rwd?]

Hey Mike ,

 

I know what you mean on the expensive fix but I compared buying the replacement parts online and even went to the local junkyard to pull a spare datsun carb without the feedback ($20 bucks) . I just said screw it and turned in both carbs for core ($60) and bought the new one.

 

I did fix the wire . I couldn't find a way to unpin it so I recrimpped it .

 

I will jump the wire tonight and see if that works . I think the relay is bad because the residue was sort of wet/sticky (the carpet was wet when I bought the truck)

[Got_rwd?]

Here's a video I took a couple days ago of the carb . Anything weird ?

 

 

[Got_rwd?]

So I jumped the relay. No change .

 

I believe that not enough pressure is being sent by the fuel pump. I see the "idle jet" pumping gas but when I open the throttle , I do not see anymore gas being pump in thru any other "jet".

 

What is the stock fuel pressure ?

[Tinman]

Here's a video I took a couple days ago of the carb . Anything weird ?

 

 

Not really.  The secondary barrel won't even open unless under high load, so that's normal.  The primary is a little sputtery but it is metering fuel.

You have to check the fuel level in the sight glass in front with the engine running.  it should be right at the black dot.

 

Many issues with this carb are due to improper adjustments and vacuum leaks.  Hell, ANY vacuum leak makes these truck run like crap!

 

I'm not a fan of shop rebuilt carburetors, they rarely actually work right.  After 5 or 6, I learned to do my own.

 

You DID change the fuel filters?  If you have the stock pump, there is also one in the bottom of the pump as well as the one in line.

[datzenmike]

So I jumped the relay. No change .

 

I believe that not enough pressure is being sent by the fuel pump. I see the "idle jet" pumping gas but when I open the throttle , I do not see anymore gas being pump in thru any other "jet".

 

What is the stock fuel pressure ?

 

Stock pressure is 2.8-3.4 PSI and that is only enough to keep the carb full of gas. As long as the float chamber is full to the line on the glass the pump is doing it's job. It's not the idle jet that squirts fuel it's the accelerator pump. The accelerator pump helps enrich the mixture to transition from idle circuit to primary circuit when the mixture would normally go lean. Other than the accelerator pump there is no other fuel 'pumped' into the the engine. It is all done by vacuum generated by the venturi in the primary barrel. You may only see fuel sucked into the venturi only when well revved up.

[xsdg]

Got_rwd: Agreed with DatsunMike here: slow down, stop trying to fix the thing by throwing parts at it, and instead, try to figure out what's actually wrong.

 

From the sounds of it, you have a new carb and vacuum lines, but very similar symptoms as you had originally.  Is the new carb a feedback carb or not?

 

Looking at the video, it sounds like the idle is going up and down and up and down at the beginning of the video.  Is that accurate?  Do you have air conditioning?  Was it on while you recorded that video?

 

Quoting from your original message, "Here's the sight glass on the carb when the truck won't restart , it's 3/4 full".  Is that still the case?

 

 

Thinking about the parts of the truck that are temperature-sensitive, there's the Thermal Vacuum Valve (which enables and disables the EGR and vacuum advance), and there's the O2 sensor, which only functions once it's up to 600 degF or so.  Given that the truck starts fine _cold_, it sounds like the base carb tuning should be reasonable.  That said, if you've got a vacuum leak (for instance, in the notorious EGR tube), that could cause a problem.  You could try unplugging the bottom two ports from the TVV and leaving them open to the air, which will disable EGR and vacuum advance, and will make the truck behave like it's cold in that particular way.