Engine stutters and maxes out below 2k rpm

[Wertbe]

Hey y'all, new to the forum. I've been having a frustrating issue with my '98 SE lately, which really came out of nowhere and so suddenly. I was driving on the highway one day (70 mph cruising if it matters) and noticed it started to stutter slightly every once in a while, something I've never noticed before. A couple days later on that same highway, it went from a slight stutter to very apparent misfiring very quickly. The max rpm I could get the engine to progressively shrank as time went on, eventually getting to the point where it wouldn't even start.

After doing what I could in a remote area, I noticed there wasn't a spark when I did the old screwdriver-stuck-in-spark-plug-wire trick. Naturally, I replaced the distributor cap/rotor and an ignition coil (they were cheap). After replacing the ignition coil, it seemed to have fixed the issue, running and revving like normal while parked. However, when I tried driving it around, the same thing started happening within minutes, and I barely was able to limp it back home. While diagnosing fuel pressure, I noticed that the engine will sometimes 'snap out of it' and idle perfectly smooth at 1k rpm, and when I rev, it goes wild again.

I don't think it's a fuel issue because 1: the missing spark I mentioned earlier, 2: a new ignition coil seemed to help, 3: using a fuel pressure tester reveals the pump is giving a steady 35-40 psi. I've only been able to take out the right bank of spark plugs (the ones not covered by the intake manifold), and they look due for replacement, with very apparent wear patterns. But with what I mentioned about the periodic smooth running, it makes me think there is a sensor issue somewhere. There hasn't been any check engine light to indicate a faulty sensor though.

TLDR: Engine doesn't run smooth, rpm maxes out way too low. New ignition coil temporarily fixed it, but quickly reverted back to rough running. No check engine light, and steady fuel pressure, my instincts tell me it's an issue somewhere in the ignition circuit.

I tried recording what is happening. Sorry for the shorts format, youtube formatted it like that.
https://youtube.com/shorts/OvFNfK1ecIw

This one is where I discovered where it sometimes will run smooth at 1k rpm, you can hear my confused "what?" 
https://youtu.be/pndj0Tl-8nA

As I usually am when I come to forums for help, I have no idea what to do next.

 

 

[Slartibartfast]

 

Sounds like the bearing in the distributor. Here's a writeup for rebuilding it.

[Strato_54]

2 hours ago, Slartibartfast said:

 

Sounds like the bearing in the distributor. Here's a writeup for rebuilding it.

link doesnt work

[Strato_54]

I believe this to be forum page Slart was referencing though.

 

 

https://www.clubfrontier.org/threads/distributor-rebuild-on-the-cheap-for-1st-gen-nissan-frontier-xterra.350719/

[Slartibartfast]

^Yep, that's the one! Not sure how the link got screwed up, sorry about that.

[Wertbe]

On 2/23/2024 at 2:12 PM, Slartibartfast said:

 

Sounds like the bearing in the distributor. Here's a writeup for rebuilding it.

Didn't see this until now, but I came to the same conclusion. When I first opened up the distributor completely, there was dust and metal shavings everywhere, and a single exploded bearing. I'm guessing the debris got the ICM sensor dirty and sent faulty signals. I don't know how thoroughly I was able to clean it, but I took a duster can and sprayed it in the slot for a few seconds, after also changing 5/6 spark plugs (I wasn't able to get to the 6th one) and spark plug wires. It seems to be running good, for now.

 

Have you seen issues related to that bearing before? Your response denotes past experience with this exact issue.

[Slartibartfast]

Not on my own, but I've seen it come up a few times on here. Good to hear you figured it out. I'm not sure if it's the debris covering the slots in the wheel or the shaft flopping around in the dead bearing that does it.

 

And yeah, that #6 plug can be a real piece of work. The right combo of extensions and a U joint can get it, as can the socket in the factory tool kit (assuming the R50 had the same tool kit as the WD21).

 

When I went through mine, I had a reason to pull the intake off anyway, so I went ahead and did the plugs while I was in there. They're much easier to replace when you can see them!

[Strato_54]

18 hours ago, Slartibartfast said:

The right combo of extensions and a U joint can get it, as can the socket in the factory tool kit (assuming the R50 had the same tool kit as the WD21).

The look on my dads face when I showed him the tool bag with the #6 tool was priceless. Had it out and replaced in 5 minutes, and any other R50 owner that hasn't used it is missing out!