and Driving Impressions
As set up and intended, the ignition and Atomic EFI function
separately. Performance synchronizes as well or better than a factory BBD carburetor and this conventional
Motorcraft ignition distributor.
MSD indicates that a
smoother idle might be possible when using the Atomic EFI spark timing control functions. Another plus is the
ability to change the spark timing curve with a hand-held electronic programmer. Timing changes can include
total degrees of advance at a specific rpm and what rpm the spark advance begins—all done
without touching the distributor!
Unfettered by a
plethora of performance-inhibiting OEM vacuum and switching devices, or an OEM Jeep microprocessor that interferes
with spark timing, the Motorcraft
distributor actually works well. The ignition is stable and responsive. Some of this, of course,
is the result of using an MSD 6A box and Blaster 2 coil upgrade.
We left the stock
distributor vacuum canister and mechanical (centrifugal) spark advance mechanisms in place—and did not tamper
with the OEM spark advance curve. Our only adjustment was base timing.
Our tests revealed optimal tune at 10-12 degrees base spark timing advance with the distributor vacuum canister
hose temporarily disconnected and taped off; we had the engine idling while setting base spark
This is an AMC/Jeep 2.5L or 4.2L
timing mark at the crankshaft pulley. Base timing at idle, vacuum line temporarily disconnected and taped, is
typically 2- to 10-degrees before TDC for a stock engine (depending upon transmission type, fuel grade and
altitude). Atomic EFI allowed us 12-degrees without ping, using 91 octane fuel.
The vacuum advance
unit now receives a clean, ported signal via the CTO, which simply regulates cold engine spark timing advance and
EGR function. ”Out of the box”, Atomic EFI produced exceptional performance and excellent fuel efficiency without
any "ping" (detonation) under load. Testing ran from near sea level to 7,000 feet elevation.
Note: Use of lower octane fuel may require
slight retarding of the base spark timing. Emission results may require air/fuel ratio adjustments.
Any MSD software
fuel map changes could affect spark timing needs. If so, base timing may require
Even without a four-gas analyzer, we were able to see an immediate difference in tailpipe coloration. EFI
air/fuel ratios constantly respond to the oxygen sensor findings. AFR adjustment is in milliseconds, and the
result can be a cleaner tailpipe, less emissions and far better engine performance.
installation intentionally took a minimalist approach. We wanted a true sense for what the Atomic EFI system, by
itself, can achieve. The engine's spark plugs were not cleaned or changed.
After Sierra Trek rock crawling in low range, we removed the spark plugs (see
above). They read a nice light tan, uniformly, and carbon soot from the carburetor days has
burned away, a continuing process.
Atomic EFI, an MSD 6A digital box and the MSD Blaster 2 coil each play a role here. EFI is clearly an engine
saver, preventing enriched fuel cycles and flooding. Concise and consistent air/fuel ratios help a 4x4
survive on the rocks!
Our installation produced excellent drivability and a dramatic increase in performance. Although we did not
dyne this chassis/engine before and after the MSD Atomic EFI installation, real world driving response
supports a conservative 30%-35% horsepower gain. This would be typical for a 4.2L AMC/Jeep inline
six-cylinder engine after a quality EFI/TBI retrofit.
Stock power for the later emission era 4.2L Jeep inline sixes was in the paltry 110 to 116 horsepower range.
Our power gain estimate reflects two decades of driving Mopar EFI retrofits, earlier Electromotive TBI,
Howell TBI 4.2L sixes and the 1987-up Jeep OEM 4.0L MPI models. The Atomic EFI retrofit produced the
characteristic 'seat of the pants' torque boost found with TBI.
An immediate fuel efficiency increase of 18%-plus validated our projections over the BBD carburetor. This is
likely to improve yet, as the engine has only preliminary tuning—and the tests included grades under
Acceleration is instant, with throttle stability markedly improved. Off-pavement, the EFI can hold a fixed,
preset idle speed regardless of the altitude or vehicle’s angle—under any reasonable engine load. This is a
major safety benefit when rock crawling, where a BBD carburetor is notorious for flooding, surging and
stalling the engine at the most inopportune times and places!
Last year, the project 1989 Jeep YJ Wrangler 4.2L six-cylinder engine stumbled and
stalled its way over the Rubicon Trail with carburetion. Above, owner Dan Hiney (co-organizer of the 2011
Wheelers for the Wounded Rubicon Super Event) takes vets over this trail. A reliable, safe
Jeep 4x4 is essential! Dan Hiney brought the Wrangler back in 2012 equipped with MSD's Atomic EFI—see the Jeep
being tested with MSD Atomic EFI in place of
Our YJ Wrangler
prototype vehicle, with only initial tuning, headed off to the 2012 Sierra Trek event. A true 4WD challenge, Sierra
Trek attracts hardcore four-wheelers to test their driving ability on the notorious Fordyce Trail in the Sierra
The 4.2L inline
six-cylinder YJ Wrangler's performance, best summed up by owner Dan Hiney, suggests a bright future for MSD’s
Atomic EFI. Here is the driver's seat report from a hard trail, Jeep 4x4 rock
the owner of this 1989 Jeep YJ Wrangler, I have struggled with the performance of the carbureted 4.2 liter engine
for over nine years. The carburetor just could not keep up with altitude changes, steep incline and decline angles,
and off-camber situations common to our sport of rock crawling. With the BBD carburetor, the engine often stalled
or flooded in these situations. The engine was so difficult to manage that it took away from the overall experience
and satisfaction of running trails like the Rubicon…
co-organizer of the ‘Wheelers for the Wounded Rubicon Super Event’, it is imperative that I have a dependable, safe
vehicle to use. Each year since 2009, we have shared with our Nation’s Heroes the trails that they have fought
for...MSD shares my vision to support these warriors and has partnered with me by making the newly developed Atomic
EFI kit available.
"With help from Moses Ludel, the publisher of 4WD Mechanix Magazine online
at www.4WDmechanix.com, I installed the
kit on the Jeep YJ’s 4.2L inline six-cylinder engine. To complete the installation, MSD provided their digital 6A
ignition module, a Blaster 2 coil upgrade option and the MSD Tach Adapter.
“The installation just complete, I tested the kit at the famed Fordyce trail during the 2012 Sierra Trek. Just
getting to the trail proved to be a drastic improvement. The noticeable horsepower gains were felt immediately
while pulling steep grades from 200’ elevation to 6,000’ elevation. Previously the Jeep fuel economy was right at
11.5 mpg—with the Jeep fully loaded for five days on the trail and pulling steep grades, we achieved 13.5 mpg! That
is an 18% improvement despite these steep grade conditions, which is truly exceptional.
“The trail performance was drastically
improved. Electronically controlled EFI maintained a steady idle through a variety of rock obstacles, and it
was an absolute pleasure to drive the Jeep! I simply put the transfer case in low range and let the Atomic EFI do
the rest. It was rock crawling at its finest as the Atomic EFI accounted for a variety of changes and the Jeep
crawled from one obstacle to the next. Performance was seamless, and I could tell right away that MSD has done
its homework in the development of this system…
"I could not be happier, and
I now have confidence that I can show our veterans the experience that they deserve during our WFTW events. Thanks,
Note: On the weekend of September 8th and 9th, the magazine covered
the "2012 Wheelers for the Wounded Rubicon Super Event" in HD video...Dan Hiney drove while I filmed the YJ
Wrangler—on the same rocks where the Jeep stumbled and stalled last year...See the trail HD video and hear Dan Hiney's comments about
the MSD Atomic EFI under the hood!—Moses Ludel
For more MSD
Atomic EFI information from the
official MSD Atomic EFI website, click
here! For access to the MSD website Home Page and catalogs,