# 86.5 Z24i Engine cutout SOLVED!!



## saudade (Apr 10, 2010)

Some of you may have been following the saga in another thread.

Recapping, my Z24i has been cutting out around 2500 rpms. It ran fine up to that rpm "limit". I'll spare you the parts I've replaced, time and money I've spent. Turns out the issue was with a buried splice connector in the main harness that feeds power to the 2 injectors. For some unimaginable reason, Nissan engineers spliced the 2 power wires (one for each injector) down to one wire, then about 8 inches later, spliced it back to 2 wires. This second splice was completely corroded and came apart with the slightest tug. I clipped, stripped and crimped them back together and problem solved.

Here's a pic of the bad splice.











Here's a pic of the other splice (sorry for the fuzziness).


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## saudade (Apr 10, 2010)

Thanks to all of you who've followed the thread, made suggestions and hung in there. A very special thanks to Nissanpartsdept for providing the "silver bullet" that led to the final solution.


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## CMax03 (Jan 17, 2009)

Done alot of that guys!


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## zanegrey (Dec 5, 2005)

very glad you are back on the road...

thanks for the progress report..


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## saudade (Apr 10, 2010)

Thanks Zane! It even passed smog test today !!


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## saudade (Apr 10, 2010)

Due to a request for some details, I've decided to add to this a bit.

First, the harness in question comes through the firewall on the passenger side then splits. One split runs down the inner fender then splits again into several branches. The pic below shows the harness with a red line. The 2 red circles indicate the approx location of the splices.












Next, there's more than one spice at the location on the right. When I fixed it originally, I only looked at the injector splice. A week later I sliced it up again to check the other splices. You can see what they looked like.










So if you're going in there. Take the time to check them all out!


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## NissanPartsDept (Mar 31, 2010)

Saudade, I am so glad I was able to shed some light on your problem. I guess sometimes us old farts can remember a few helpful tips lol.

Glad to see you posted the pics for the future. Wish I had had some when I was explaining it to you.


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## saudade (Apr 10, 2010)

NissanPartsDept said:


> Saudade, I am so glad I was able to shed some light on your problem. I guess sometimes us old farts can remember a few helpful tips lol.


As one old fart to another, I too occasionally have moments of genius that always surprises my teenage sons.  



> Glad to see you posted the pics for the future. Wish I had had some when I was explaining it to you.


I knew right where you were talking about. Hopefully the pics will help others.

Again, many thanks!!


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## burvis (Jul 15, 2012)

This is exactly what my truck is doing! I just got my truck, and it ran fine for a couple of months. A local mechanic confirmed that fuel is cutting out above a certain rev range. I bet this is going to solve it. Thanks in advance....


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## saudade (Apr 10, 2010)

Good luck! Hope this works.


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## smj999smj (Jan 1, 2006)

I hate those splice connectors! Best thing you can do is break out the soldering gun and solder all of those splice connectors for a better and more permanant repair!


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## saudade (Apr 10, 2010)

smj999smj said:


> I hate those splice connectors! Best thing you can do is break out the soldering gun and solder all of those splice connectors for a better and more permanant repair!


Yep. I cut and re-spliced all of them with solder and heat shrink tubing.

You can see by the dates, this was over 2 years ago. Truck hasn't skipped a beat since.


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## burvis (Jul 15, 2012)

Ok, today I had some time to look at if, finally. I can't find any loose wires anywhere, all the plastic connection blocks look fine. Are the splice connectors inside the harness itself? In other words, do I need to slice open all the bundled wires to find them? I also found a few vacuum hoses that are missing in the area behind the throttle body.

To recap, the engine cuts out very suddenly and completely over a certain rev range. All cylinders stop firing as though the ignition was switched off. When the revs drop, the engine resumes. Revving in neutral, it sounds like you're gunning the engine. Under load the truck bucks.

I took it to a shop, and they confirmed I have spark throughout the rev range, and that it's fuel that is being cut off. THey were stumped, and replaced the fuel filter, which did not fix the problem. 

When I found this thread, it seems to describe my symptoms exactly. But I'm a bit stuck. I have attached a few pics. Any ideas welcome.


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## burvis (Jul 15, 2012)

Havent figured out the photos yet... Here are links

IMG_2482 | Flickr - Photo Sharing!
IMG_2483 | Flickr - Photo Sharing!
IMG_2485 | Flickr - Photo Sharing!


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## saudade (Apr 10, 2010)

Yes, you have to cut open the bundle. Not sure why I don't see it on yours though. Is yours a D21 "HardBody"? 

Someone did hack it up. I'd redo those splices.

Follow the harness out of the TB with the red,green white wires showing and see where it goes.


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## saudade (Apr 10, 2010)

If it cuts off, how did they verify spark across the "entire" rev range? Another cause of the same symptoms is a bad Intake ignition coil. Both intake and exhaust fire until about 2500rpm, then the exh cuts off and only the intake fires. If your int coil is bad, then it shuts off completely until the RPMs drop.

I had this happen too once before. Both coils are the same so you can swap them to see if that's it.


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## burvis (Jul 15, 2012)

Thanks Saudade, looks like we have the same truck...

Not sure how they verified the spark, not too impressed with the shop overall, won't go back. Here's the update. I sliced open the bundle coming off the throttle body, there were no splices. I found one splice nearer the firewall, but it was intact. I opened the plastic block junction that connects the wires that run to the injectors. I tugged on all the wires going into both sides of the block and they all seemed firm. I noticed there was a lot of engine oil inside the block. Weird, but it's close to a vent hose for the rocker cover on the passenger side, and that hose is cracked. That's the only way I can figure that oil might have gotten inside the connector block (?!?). Anyway, I wiped out as much of it as I could, put it all back together, and guess what? It's running great. I think it's probably a coincidence, and I bet this problem comes up again until I find the real solution. Maybe it was the oil, who knows? Running good now....


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## jumpin1 (Jul 4, 2011)

Nice job finding your problem, I have the same problem with my HB. I would like to read the other thread where can i find it.


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## saudade (Apr 10, 2010)

This was started by someone else but I joined in.

http://www.nissanforums.com/hb-truck/159160-87-hb-z24i-jerking-high-rpm.html


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## jumpin1 (Jul 4, 2011)

checked the harness, no splices. Anyone think it could be the ascd switch at the top of the clutch pedal?


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## saudade (Apr 10, 2010)

I don't see how it would. 

You going to have to go back to basics. You first need to establish if you're loosing spark or fuel.


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## jumpin1 (Jul 4, 2011)

I bought the truck 6 months ago and had the bucking problem. I thought that the problem was fixed. recently I replaced the trans, clutch, slave and master clylinder. went to put the thing back on the road and all the bucking problems re apeared. the only thing i can tie together with the tranny is the ascd switch at the top of the pedal. I read up on it and it turns out to be a rev limiter type thing ????????


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## burvis (Jul 15, 2012)

OK, I have now pulled apart and resoldered a few places. But still have the intermittent bucking/surging/rev cutout problem. I have learned that if the coutout problem shows up, I can simply shift into neutral, cut the ingition and restart and the problem vanishes. I'm forming the superstitious opinion that some kind of IC chip somewhere is failing. Does anyone know of a circuit that changes the voltage to the injectors over a certain rev limit. Is it possible that over a certain rev range, some IC chip sends a signal that cranks up the voltage to the injectors, sort of the way an old four barrel carb's two second chambers would open up at higher revs?


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## saudade (Apr 10, 2010)

Well, it doesn't work quite like that. The ECU determines the length of the fuel pulse to adjust the F/A ratio for any given condition. So it sprays for longer or shorter times, not more or less pressure/flow rate. The injectors themselves are either on (open), or off (closed).

Having said that, intermittent still certainly implies an electrical issue. So we need to determine if the electrical problem is affecting the fuel delivery or ignition. You mentioned earlier someone checked and said it's fuel. So let's verify.

Assuming when this happens, it also happens in neutral so you can rev the engine up by hand and get the surging. If so, get a can a started fluid. Remove the top of the aircleaner. Rev the engine until it surges. Spray some starter fluid (short bursts at first) down the throttle body. If it now revs up, you know it's a fuel issue. (Mine did this). If not, then it's likely an ignition issue.

Let the engine idle for a minute, and try again to see if it repeats. Don't go too crazy with the spray.


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## ozarkian (Dec 9, 2011)

*94 v-6 with same problem @ 2400 rpms*

I am going to highjack or perhaps just join in on this thread.
I have a 94 v-6 4x4 doing the exact same thing. 

It did this last year at this same time of year (weird). Last year I thought it was dirty injectors and ran a few cans of fuel treatment through it at it cleared up. I was under the hood poking and proding all day as well. I could have jiggled the harness and "fixed" the problem temporarily.

Regardless it is back with a vengence and no amount of fuel treatment is making it better.

Do you boys think it is a problem with splices like your 86 ? Or maybe something else you have discussed? 

What I have done up to this point is: Fuel filter
Throttle position sensor
checked codes. 14, and 34, and 51
Don't freak!! They were old codes and I cleared them and drove thetruck and redid the codes and only got the knock sensor.

Please help me fix my baby

thanks in advance

crystal


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## burvis (Jul 15, 2012)

HI Crystal, 
Reading through everything I could find on this problem, it seems there are a couple of things that can cause the same symptoms - bucking while under load or cutting out over a certain rev range, making it sound like you are rapidly gunning the engine in neutral.

First, figure if it is spark or fuel. Saudade gave me an easy test, take off the air cleaner cover and get a can of starter fluid. Start the engine and rev up to where the cutout starts happening, and spray starter fluid in the intake. If it smooths out and revs normally, you have a fuel problem. That's what I have.

Some folks have said a bad coil will cause the same symptoms. But that would kill your spark, and I haven't investigated it because my spark is OK.

In my case it was happening because something was cutting off power to the injectors. I wish I could say I have found a definitive answer as to why it is happening, but I can't. I have split open the harness, looking for bad splices, and resoldered a couple connections just to try something, but the problem kept returning.

It sounds dumb, but the last couple times it happened, I killed the ignition just as it started bucking, and restarted the engine. Since doing that a couple times, the problem went away and hasn't come back. Who knows why. It has been running great for months. I have a feeling I'm not done with this adventure though. Good luck!


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## ozarkian (Dec 9, 2011)

Thanks for the input Burvis.


Let me try to clear up what is going on.

When driving, and only when driving. Each time you change gears and the RPM's drop to below 2500, as you try to come back up the truck will "bog down or lug" Not so much as to stop you, just enough to make the engine vibrate and shake.

I picked this thread because after an exhaustive search of this site this is the thread that most closely resembled my particular problem.

I understand that this was a TBI engine and mine us multi-port and a few years newer.


The fact that the problem sound so similar gives me hope.



It is almost impossible to tell any difference in the engine while it is in the shop and just sitting in nuetral even though I rev it up to the 2500 mark. It only seems to happen if the truck is under a load. I live in a very mountainous area so the loads are worse going uphill, which we seem to do alot LOL.

MY fuel economy has fallen off and of course the performance stinks. This problem is driving me nuts!! :wtf:



PLEASE HELP!!:waving:


I know you guys have the answer I need.

crystal


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## saudade (Apr 10, 2010)

Well a few words/questions then.

Is is consistent or intermittent? Have you moved the injector harness around to see if it clears?

Go up a long hill with a spark plug wrench and let it bog/lug. Then stop, let it cool a bit and pull the plugs and check their color.

Check your fuel pressure.

Check your compression.

Also, I think you'd be better off in a separate thread. My title is aimed specifically at owners with the same engine as mine. Given it's age, I'd bet it gets overlooked by others with same engine as you.

Lastly, I had a similar problem with my Cherokee. Occasionally, it would run rough and even backfire a bit under load. Then it would miraculously clear up before I could check it out. Turns out it was a break in an injector circuit inside the main harness along the valve cover. I can only guess that the torque under load caused the engine harness to flex ever so slightly but enough to make or break the circuit.


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## ozarkian (Dec 9, 2011)

thanks anyway. i will try a new thread.


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## yellowrosefarm (Dec 11, 2011)

I picked the wire harness apart on my 86.5 and found the splices just as described. They were not corroded but I soldered them anyway since I was right there. Then I moved over to the 88 and picked that harness apart. No splices all the way to the firewall. So Nissan, in the spirit of continuous process improvement must have deleted the troublesome splices some time before 88.


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## yellowrosefarm (Dec 11, 2011)

My 88 is fixed. The cutting in and out at wide open throttle was a bad intake coil module. End of story on that one, now back to the 86.5.


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## Skinny G (May 9, 2002)

yellowrosefarm said:


> So Nissan, in the spirit of continuous process improvement must have deleted the troublesome splices some time before 88.


No - they moved them to behind the valvecover, in the firewall harness that comes down and feeds the injectors. You will find two in there that need to be re-soldered.

I wrote up my repair (on my '94) here: Hideous Quirks « Mr. Wellwood's Tech Ed Site


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## vjquan (Jun 4, 2009)

Does anybody know if this applies to the V6 motor?


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## PittBull (Jun 5, 2013)

This is exactly the problem I'm having with my 86 1/2 HB Z24.
I'm going to check my harness today.


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## PittBull (Jun 5, 2013)

I don't have either of the wiring splices. I also swapped out the coils.
No change. I may go the junkyard and see if the coils are still in another truck I saw months ago. Try swapping the coil "modules", I'm assuming that's the electric block the coils plug into. Gotta be cheaper than a new one. If still there I'll pull both coils.


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## PittBull (Jun 5, 2013)

Coils that were at the junk yard months ago are gone.
I'm going to try an intake coil module.
Looking at the front of the truck, which coil is intake and which is exhaust?
I unhooked the one on the drivers side and truck will start. Unhooking the coil toward the passenger side the truck will start. Drops rpm at 2500.
I'm thinking the intake coil is not working. Having swapped coils the other day, both are good.
Intake coil "module" is what I believe is bad. 
Correct?


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## saudade (Apr 10, 2010)

The coils swap as you noted. The ignition modules don't. 

Running only on the exhaust, the engine will cut out about 2500. The first time mine did this, it was the intake coil. When I discovered the coils are the same, I swapped them to run my truck. I did eventually replace the bad coil.

Does yours do it in neutral? Mine did. If so, spray some starter fluid down the TB while it's breaking up and see if that helps. If it does, it would suggest your problem is fuel related. If not, it's likely electrical.

If electrical since your coils are good, I'd suspect the ign module. However, take your dist cap off and have a look inside.


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## PittBull (Jun 5, 2013)

yellowrosefarm said:


> My 88 is fixed. The cutting in and out at wide open throttle was a bad intake coil module. End of story on that one, now back to the 86.5.


This has solved my problem with my '86 D21 also.:jump:

I swapped out the dist cap and rotor with a pair that were like new I found at junk yard while looking for the coils that are now gone.

thanks again for everyones' help.


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## Randal1 (Aug 9, 2013)

*help throttle body wiring*

hey im new to the forum but i just got the 1986.5 d21 with the tbi. It was running when i got it but when i "floorboarded" the gas it would have a slight hesitation and then pick back up. It didnt keep it from driving though. So i looked at my wires coming from the throttle body and someone has put prongs on each wire and plugged them into the harness so it doesnt clip together like most harnesses. Anyway i accidently unplugged the wires and now i dont know how to plug them back in. I mean I cant figured out the order that they plug in. I can add a picture if that would help explain. I just need some help!


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## TheRepairMan (Jun 30, 2009)

Randal1 said:


> hey im new to the forum but i just got the 1986.5 d21 with the tbi. It was running when i got it but when i "floorboarded" the gas it would have a slight hesitation and then pick back up. It didnt keep it from driving though. So i looked at my wires coming from the throttle body and someone has put prongs on each wire and plugged them into the harness so it doesn't clip together like most harnesses. Anyway i accidentally unplugged the wires and now i dont know how to plug them back in. I mean I cant figured out the order that they plug in. I can add a picture if that would help explain. I just need some help!


You should post pictures, but it sounds like you nee to start a new thread instead of doing it here in this one. Also, someone might be able to send you a wiring diagram with connector information.

-R


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## Stvsmth8 (Apr 15, 2020)

Im running into this problem even now in 2020. anyway those pictures still exist?


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## saudade (Apr 10, 2010)

Sorry 'bout that. They were all in Photobucket. All gone now but I'll report what I have.

I circled the location on the splices. For some reason, 2 leads come from the firewall, get sliced into one, then later splices back into 2 that feed the injectors. Not even soldered, just crimped. one leg corroded and was intermittent. A quick snip, strip, and crimp (with solder) fixed it.

Good luck!


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## saudade (Apr 10, 2010)

Here's a pick of the actual splices before repair. You should clean them all up while you have the harness apart.

Good Luck Again!!


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## Stvsmth8 (Apr 15, 2020)

HOLY CRAP! Thank you so much, I thought this was totally going to be a shot in the dark adding this comment. I’ll be sure to update once the car is out of the shop tomorrow but here is where we’re at now

I have a 1986.5 Nissan D21 hardbody 4x4 5 speed.
I Bought it this way, the truck ran absolutely fantastic other than a shitty idle, but if you went over 2800 rpm it would buck in limp mode. Since then I have bought a brand new throttle body with oem replacement fuel pressure regulator, injectors, wiring, connections, maf sensor, tps sensor, everything on it. I have also replaced the fuel filter and fuel pump. And cleaned the egr valve. It’s all getting put back together in the morning for the first startup since. So I suspect with the codes being cleared in the ecu already. If this truck doesn’t run right after everything I suspect the problem HAS to be the wiring harness fault or the ecu has gone bad. Thanks again


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## saudade (Apr 10, 2010)

Sadly, I had to get rid of mine a while back. We had it since new. There are a few other "quirky" things about it.

So there are both intake and exhaust spark plugs. Each run off separate coils. Both sets of plugs fire at low rpms to help promote better combustion. One stops firing (exhaust I think) around 2500 rpms. One time I had an issue with it cutting out around that rpm. Turned out one coil was bad. I swapped the coils so it would run until I got a replacement. 

I had the same issue later on, but this time was not the coil. I deduced it was a fuel issue. Turns out the 2 injectors in the TB work in a similar way. Both injectors fire at low rpms, one shuts off around 2500 rpms. This was the issue in this post. 

Hopefully, yours will run great once you get it back.


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## Stvsmth8 (Apr 15, 2020)

I’ve cut apart the entire wiring harness and those splices you have pictured are nowhere to be found. On mine it’s 4 wires all the way from firewall to end I’ll attach a picture in the morning. After everything I’ve replaced it either has to be just a bad ground. Or that the injector control module inside of the distributor has gone bad. I’ve replaced the one that’s outside.


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## Dycen11d (Jul 26, 2021)

ozarkian said:


> Thanks for the input Burvis.
> 
> 
> Let me try to clear up what is going on.
> ...


I have this same problem. Only way around it that I’ve done was disconnected my battery and reconnect it and it would last about a week and then start doing the bucking phase again


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