[saudade]

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).

 

[saudade]

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.

 

[saudade]

Thanks Zane! It even passed smog test today !!

 

[saudade]

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!

 

[saudade]

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!!

 

[saudade]

Good luck! Hope this works.

 

[saudade]

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.

 

[saudade]

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.

 

[saudade]

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.

 

[saudade]

This was started by someone else but I joined in.

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

 

[saudade]

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.

 

[saudade]

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.

 

[saudade]

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.

 

[saudade]

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.

 

[saudade]

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!

 

[saudade]

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!!

 

[saudade]

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.