Fired up the new coils (from Sultans of Spark, Performance Distributors) today. Started right up, like normal. It will take a bit of driving now to determine if performance has improved. Will follow up after a tank or so.

Noticed the HV posts are a bit smaller diameter than OEM, so the boots on the wires don't seal to the coils. Otherwise the quality of construction appears very good, especially the core lamination joint and paint and epoxy.

 

Update for new aftermarket coils on GEMs engine. One of the new coils malfunctioned while driving, so was driving on 6 cylinders, flashing CEL, very rough, smelled gas out the pipe (PO busted the innards out of the cats), codes P1313 and 1314 misfire catalyst damage banks 1 and 2. Figured it was likely a coil. Found the bad coil using an ohmeter (low ohms between HV terminals). That coil showed a small chip of plastic and epoxy shipping damage that I thought was superficial, looks like maybe it wasn't. So, I popped a known good old coil in it's place, rather than replace the lot.

Will keep driving for the experiment, now with the 3 new coils, plus a used coil that is not original Land Rover, rather made in Japan, with ohms that align pretty well with the new ones. The original LR coils have a bit lower ohms (-1 or 2K) between HV terminals, perhaps indicating fewer windings and lower voltage output. Truck runs great now!

 

This is interesting. I have a a 95 D1 with the 14cux system but run it on a Gems engine from a 96. I run my plug gap around .045 and have been running NGK's. I've been thinking about getting a hotter coil and opening up the gap more, so this is good info.

Also, i have a mitsubishi lancer Evo that runs a waste spark setup. I converted it to coil on plug but the wiring is still stock so it still fires it in waste spark, but each cylinder has it's own coil. If i had a GEMS engine with waste spark that's what i would do, 8 Coil on plug and open the gap up to like .055. Probably an increase in power and fuel economy.

 

Update aftermarket coils: Running on all four coil packs using the new coils. The vendor sent a new coil at no cost and quickly. Downside is one of the laminations was misaligned, slightly bent. Was able to swap it into the 2 & 3 position without removing the whole coil assembly. Plugs gapped to 0.055 inch. Starts right up, idles smooth.

So, if I had it to do over again, I would stick with stock coils, or a top brand from Rock Auto (e.g. Delphi) with welded laminations. I researched Coil-on-Plug and Coil-near-Plug options, but did not find any quality options that gave bang for bucks (they want more than I paid for the truck ), so stock configuration is OK by me. Probably better for resale when time comes, as well.

 

Another update: Another aftermarket coil failed a couple weeks ago, different cylinders this time, less than 100 miles or so. Swapped original coils back in, running great. Failure rate for the aftermarket coils was nearly 50%, so Coil Experiment is over. Still using increased gap on spark plugs.

 

I think youd need to be able to increase the dwell to take advantage of different coils, and thats deeper into GEMS tuning than I think anyone has gone

 

Technically, more turns of the secondary winding will produce higher voltage with a more powerful spark, given the same dwell and primary winding. Reducing the primary resistance or number of turns has a similar effect of increased spark power. The downside of higher voltage is greater risk of shorts or insulation failures. Suspect that's what did in my coils. By the way, the aftermarket coil supplier provided me a return authorization and promised a refund when the coils are received.

There's a company in England who made or makes chip upgrades for GEMs ECUs. The fuel mapping is changed, but not sure about dwell.

For my CUX truck, there are aftermarket mechanical distributors that increase dwell and spark power. I really like the one I installed.