Ignition coils

lunchbox

Well-known member
Apr 20, 2004
2,043
108
49
St Louis, MO
What are people using these days? I usually buy whatever the local guy has in stock. I looked on Rock Auto. They have several brands now. Anyone have a preference or found "better" spark with some?

GEMS truck
 

Tugela

Well-known member
May 21, 2007
4,624
415
Seattle
I'm using genuine. Got a spare set for GEMS in good shape (used) if you are interested. Not entirely sure if I want to sell or hang onto it in case I need it in future for my own truck.
 

mearstrae

Well-known member
Mar 15, 2017
128
13
Pennsylvania
I'm trying the Davis Unified Ignition, SOS coils pack. Good price and performance voltage. They have them for both Disco 1's and 2's. And distributors for the pre '95 LR's as well.
 

robertf

Well-known member
Jan 22, 2006
4,609
242
-
Interesting
Is that $109 for a set of 4, or each?
Their site is lacking tech specs. You mind taking a resistance reading from each pin to the coil conductor?
 

lunchbox

Well-known member
Apr 20, 2004
2,043
108
49
St Louis, MO
The price listed is for the set, not one coil pack. I ordered a set and they will be here tomorrow. The website claims you can run a .055 gap. I'm at .040 now. I'll leave it there and see how they act. It's a claimed increase of 50% to 40,000 volts.
 

p m

Administrator
Staff member
Apr 19, 2004
15,231
557
57
La Jolla, CA
www.3rj.org
This makes me curious.
I found GEMS ignition circuit the most-reliable by far and large. In the total of close to 300k miles of use of GEMS trucks, I have replaced one coil - and I am not even sure it was needed.
Likewise, GEMS fuel control circuit rarely runs very rich, so the lifetime of spark plugs gets close to 100kmi or beyond. Why would I need to screw with opening the spark gaps and higher-than-stock-voltage-rated wires?
 

robertf

Well-known member
Jan 22, 2006
4,609
242
-
I agree. I've changed out one coil pack and it also wasn't the problem. GEMS has been reliable other than crankshaft sensor wiring. Only reason I'm interested in these coils is the higher compression I've got on mine with the 4.0 pistons/4.6 rotating assembly. Stock engine I wouldn't bother. Aftermarket "performance" ignition parts have been unreliable in my experience
 

mearstrae

Well-known member
Mar 15, 2017
128
13
Pennsylvania
The standard coils are adequate, I must confess. But, I've always found an improvement in mileage and performance with higher output coils. Same with the single spray stock Bosch injectors (tuner folks call them "Toilet Flush" injectors), but the Gen 3 four spray Bosch injectors also improve mileage and performance. And these performance items cost less than factory, the Gen 3 injectors cost per set what LR charges for one injector. Keep in mind that these vehicles weren't just built by engineers but also accountants.
 

p m

Administrator
Staff member
Apr 19, 2004
15,231
557
57
La Jolla, CA
www.3rj.org
But, I've always found an improvement in mileage and performance with higher output coils.
Does "always" include a CJ5 or specific to a GEMS (or any other OBD-2 close-loop fuel-injected vehicle)?

I would be blown away if anyone could offer quantitative measurements of mileage and performance improvements using non-stock coils on a D1. My own gas mileage varies easily by 1 mpg depending on how many lights I hit during a particular week or two.
Anecdotal evidences of the sort of "at the first fuel-up after the change, I put in three gallons less" are dismissed automatically.
 

lunchbox

Well-known member
Apr 20, 2004
2,043
108
49
St Louis, MO
Well. I'll have them on this weekend. I hit the 1/4 mile in about a week now. So maybe I'll get that down to 6 days. Last fill up, I got 5mpg. I'll cross my fingers for 6!
 

ERover82

Well-known member
Nov 26, 2011
3,729
328
Darien Gap
Might be easier
fuel_trailer_low.JPG
 

mearstrae

Well-known member
Mar 15, 2017
128
13
Pennsylvania
OK, on one project (a '95 R.R.C. Lwb) I was able to squeeze out on average about 20mpg on a vacation trip. Granted there were several modifications to allow this to happen. It was a trip from Pittsburgh to the Outer Banks and a week of touring around. I installed a 40,000v GM HEI dizzy and the Bosch Gen3 injectors. Also, a K&N filter and a custom free flow exhaust system. Highway miles crept up to 22mpg, on return the mileage still stayed above the average for these. So, I'm not just slapping on HP coils and driving around the block and saying, "Holly shit, that runs great and look at the mileage." I've started these same mods on my D2, so only time will tell if it works the same way. But, hey it's worth a try...
 

lunchbox

Well-known member
Apr 20, 2004
2,043
108
49
St Louis, MO
My only question now is, where to gap the plugs. They claim an increase over stock of 50%, or 40,000 volts. The website also claims you can open the gap to .055. I usually run the recommended .032 gap. Maybe I'll go 50% increase on that, or about .048
 

Tugela

Well-known member
May 21, 2007
4,624
415
Seattle
OK, on one project (a '95 R.R.C. Lwb) I was able to squeeze out on average about 20mpg on a vacation trip. Granted there were several modifications to allow this to happen.

If you could post a more detailed description of what you did it would be an interesting addition to the tech page here. I recently bought a 1993 SWB and it gets 12mpg if I'm lucky. Some of this is probably due to the sad state of neglect in which the previous owner kept it, so I hope things improve as I perform long overdue routine maintenance tasks. The RRC is a more comfortable vehicle than my D1 for longer trips, so an increase to even 16mpg would be a welcome change.
 

mearstrae

Well-known member
Mar 15, 2017
128
13
Pennsylvania
I'll try to remember the details of these mods. The R.R.C. engine was a 4.2 in good condition (good vacuum and good compression numbers). I used a Buick HEI coil in cap (for the 215 or 340 old style engines), with a long housing (there are short shaft/housing HEI dizzys that would be hard to fit, I tried...), this still required the power steering bracket to have a large chunk removed to clear the dizzy. I'm sure there are high voltage dizzys that use a more standard small cap with external coil. The Gen3 Bosch injectors were for a Ford Mustang 302cid and rated at 19# and matched (these were re-man units). The spark plugs were NGK and gapped at .050. K&N air filter was installed, I also removed the inlet horn from the air box (don't know if this had any effect) to lessen any restriction on that end. The exhaust system was custom with single free flow muffler, one pipe in and two 2 1/4" pipes out. But I think any free flow system would work, such as MagnaFlow. The timing was set to highest steady vacuum reading. I also replaced the clutch fan with an electric high CFM unit, so it had full cooling at idle and thermostat control. This being a 14CUX ECU it might have been more forgiving of such mods. To be sure I wasn't just causing an extremely lean condition to get the mileage, I checked with an exhaust analyzer to be sure it was in spec. I had thought of adding alcohol injection, but this proved to be a PITA and expensively complicated.
 
Last edited:

p m

Administrator
Staff member
Apr 19, 2004
15,231
557
57
La Jolla, CA
www.3rj.org
If you could post a more detailed description of what you did it would be an interesting addition to the tech page here. I recently bought a 1993 SWB and it gets 12mpg if I'm lucky. Some of this is probably due to the sad state of neglect in which the previous owner kept it, so I hope things improve as I perform long overdue routine maintenance tasks. The RRC is a more comfortable vehicle than my D1 for longer trips, so an increase to even 16mpg would be a welcome change.
Nick,

please disregard most high gas mileage reports from the East Coast. The road from P-burg to Outer Banks is as flat as they come. All it takes to get to 20 mpg in a Classic is to drive it under 55; I can't say anything about Penn part of the road, but N.C. fits the bill exactly.

My WAG - out of the slew of mods to the Classic, only the injectors came remotely close to affecting the mileage. All high-voltage coils is smoke and mirrors and snake oil. Been there, I have to admit, and done that.

Removing the inlet horn on the 95RRC/D1 airbox for the purpose of improving the airflow compliments high-voltage coil perfectly.

... and yes, I would happily run my engine rich rather than see the pistons melt from detonation (which 14CUX does not detect and cannot do anything about).