TwinTurbo.NET: Nissan 300ZX forum - VR38 coils in the factory location. Part deux.
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Subject VR38 coils in the factory location. Part deux.
Posted by Zeus on May 10, 2021 at 9:50 AM
  This message has been viewed 489 times.
Message For some historical context, read this post first on how we got here: Click here

tl;dr: Not quite done yet, but it works!

Here's the progress.

The good news:

Got the coils / PTU bypass harness / updated dwell chip installed this weekend and got her running with this setup.

Admittedly, I had an issue at first where I could hear a loud ticking sound from a couple of the coils (3 & 5, specifically). Turned out to be the springs not making contact with the spark plug and so they were internally arcing (user-error on my part). Realized the issue, fixed that and the car ran perfectly. Smooth idle, no misfires.

You'll notice in the pics below I made sub-harnesses for each coil. I wanted this testing period to be reversible, so those just make this a plug & play situation until I decide whether to move forward with something permanent, but I'm not there yet.

Quick note about the sub-harnesses: the VG30 and VR38 coil connector pin-outs are different. Essentially power and ground are swapped. Signal is the same.

The meh news:

I struggled a bit with a couple of things. The spring would sometimes fall out of the stalk removing them from the car; which is more annoying than anything, but the real issue is that losing the spring causes the small resistor to also fall out of the coil. This is the real problem as losing that in the engine bay could easily ruin your day. The resistor is the little white nib in the pic below. I guess that's +1 for the OEM stalks as they don't have this problem.

Contacted PRP about that and they referred me to a video they made about how to handle this situation (embed further down).

I tried their "bend the spring a little" trick to keep it from falling out and that definitely seemed to help keep things in place. Still not really thrilled about that solution, so I offered feedback about adding a lip inside the stalk for the spring to grab onto. Hopefully that makes it into future design iterations.

I also had to slightly modify the spark-plug-end of their springs so as to not grab the head of the spark plug itself. Not a big deal there, just something to know. Otherwise, that's another reason for the spring / resistor to fall out.

Overall, I'd say their stalks are good, but these quirks just mean some finagling is required; which will certainly turn some people off. It's worth mentioning.

The OEM VG coils seal around the spark tubes. This is to keep water out. Obviously, in order to get the R35 coils to sit higher up, the universal stalks also need to be at full-length (ie: not trimmed down). I haven't decided yet whether this is something to be overly concerned about since I don't ever drive in the rain and have my splash-guards under the engine, but again, worth mentioning.

Lastly, you'll have noticed that none of the coils are actually secured to the plenum. I had worked with a local machine shop on fabricating a way to re-use the OEM VG coil brackets, but really wasn't happy with their solution. I've been in touch with someone else (Z community-specific) to get a better solution figured out. Hopefully more to come on that soon.

In the meantime, I just wanted to prove-out that this works and I've since reverted the car back to the OEM setup until a proper mounting solution to the plenum is sorted out.

Thanks for reading!


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