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Observations and Driving Impressions

Atomic EFI fully installed and trail tested

     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.

  Note: 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 timing.

Typical Jeep/AMC inline four or six-cylinder timing cover and marks

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 adjustment.

Reading the tailpipe emissions

     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.


Reading the spark plugs

Our 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 load.


     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!


Dan Hiney at the WFTW Rubicon Super Event

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 carburetion!

  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 Nevada Range.

    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 crawler:

Dan Hiney on the Rubicon Trail with Vets

    “As 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…

WFTW Super Rubicon Event for vets

  “As the 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, 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, MSD!”

—Dan Hiney

   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, click here.


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