EFI Options for the AMC 6-258 Engine

From: Mark Shipman <marko@endoimage.com>

I bought my Jeep five years ago, and it never would quite run right. I soon discovered that perched on top to the intake is a devil contraption called the Carter BBD. This combined with the 10 miles of vacuum hoses, (if one lined up all the hoses end to end, a Carter BBD equipped Jeep would use ten gallons of gas to get from one end to the other, if it stays running long enough) solenoids, delay valves and switches, combined to make my Jeep run like I was feeding it low grade Mexican gasoline. I had the thing checked out many times and even had the carb rebuilt by my Jeep dealer (by the way, my dealer could not check the computer that controls the carb. They said it was too old). Still no improvement. After about 35 seconds of soul searching, I decided to go EFI. I knew that the system I wanted was going to be not only a closed loop system with feedback from an O2 sensor, but one that also integrated the ignition system. At the time there were only two systems like this. One was from Mopar and the one I chose was from Electromotive. Here is a basic breakdown of the two systems:


This is a sequential port injection system with a manifold similar to the Wrangler with the injectors close to the intake ports on the head. It has a computer controlled distributor that replaces the stock vacuum advance unit, a number of sensors for such things as coolant temp, throttle position, manifold air pressure, exhaust O2 and crankshaft position. These feed into an engine control computer similar to the computer found on a 4.0 Wrangler. The installation of this kit is involved and is said to take one to two days out of the do it yourselfer's life. One gentleman told me he installed his in 12 hours. I know, that among other things, you must replace the harmonic balancer located on the front of the engine and the intake manifold. Both these tasks on a 4.2 require quite a bit of work. The people who answer the phone at Mopar probably won't tell you this but you will need a new washer reservoir and bracket as the computer mounts where the old reservoir is. In addition, the factory tach won't work with the new computer. Both points are covered in the instructions. This kit was just re-introduced with a CARB EO number, which makes it 50 state legal. I have not personally seen one on a Jeep, but I hear that the results are quite satisfactory with an increase in power, mileage and drivability. I have heard that mileage gains should be in the 5MPG range. And because the stock distributor has been replaced, the engine will rev easily over 4500. Mopar used to sell this for around $2000, but it goes for about $1500 through secondary sources. Add another $300 or so for the reservoir and new tach. I have heard only one complaint about the system. Evidently the K&N style air cleaner is totally exposed to splashing. Some kind of a splash guard may need to be fabricated to avoid drowning the engine.

I can't speak much of the reliability of the Mopar kit. I know that they have worked out the problems they had with it earlier. It is claimed to be made mostly of late model (pre OBD II) parts and can be serviced and installed at your local Jeep dealer. (I wouldn't trust my local dealer to change my spark plugs.) But long term service and support should not be a problem. In addition, you can use a code scanner on it to diagnose any problems.

The Mopar system is available through any Jeep dealer. Mopar carries it in its performance catalog. If your dealer's parts man gives you a blank stare, smack him upside the head and contact Mopar direct.

Electromotive JFI (Jeep Fuel Injection) Kit:

I chose this kit at the time because of early problems with the Mopar kit and because it was at the time the only one (the first) with CARB certification. It is a simpler kit, using a throttle body to replace the stock carb. But, like the Mopar, it is a feedback system that uses an engine control computer and sensors such as crankshaft position, coolant temp, throttle position, mass airflow and 02 for control of timing and fuel delivery. Its mass airflow design seems to be slightly more tolerant of engine mods, but is very susceptible to vacuum leaks. In addition it has an advanced distributorless ignition system that uses three coil packs instead of the distributor used in the Mopar kit. Before installation, or even buying a kit, check out the internal condition of your engine. A leak down compression test is recommended. Neither kit will work well on a tired engine. As for the JFI, installation is strait forward and took me the better part of a Saturday. The install goes something like this:

  1. Rip out all the old junk, such as the carb, its computers, the associated wiring, all the emissions vacuum lines, the distributor, plugs, plug wires, air cleaner, and the pulse air tubes if so equipped.
  2. Replace the distributor with their trigger assembly. This gives the computer info on crankshaft position.
  3. Replace the coolant temp sender and 02 sender (the JFI uses a four wire heated sensor for lower emissions at startup). Add the throttle body and hook up the associated vacuum lines and wires.
  4. Bolt the Mass Airflow sensor to the inner fender well, run the 3" dia. hose that connects the MAF to the TBI and install the K&N looking air filter.
  5. Bolt the computer to the valve cover and install the new wires and plugs. (I find that Bosch Platinums work the best.)
  6. Hook up the power wiring, check engine light, and tach.
  7. Install the electric fuel pump, filter and lines. This is an assembly that bolts on to the mechanical pump. Both the electrical pump and the mechanical pump prevent vapor lock and provide the necessary fuel pressure for the EFI.
  8. The only thing I had to fabricate was the throttle linkage. The TBI requires that the top hole in the stock linkage rod be drilled through. However, the stock linkage is hardened and will crack before you can drill through it with a press. I bought a piece of steel rod of the same diameter, cut it to length and drilled the necessary holes.
  9. Set the timing, crank her up and off you go.

As to cost, I paid $1660.00 for this kit in 1995.


I have had my Electromotive kit for just over three years now and for the most part it has been trouble free. The biggest problem has been vacuum leaks associated with the strange intake/exhaust manifold combination that Jeep used on the 4.2. In addition, a leaky valve cover, which is a common problem with the plastic ones found on 4.2's, can cause problems. A vacuum leak will show up as a mass airflow sensor error.

I have had failures of the magnetic pickup for the crankshaft position sensor, which takes the place of the stock distributor. The magnetic pickup is the most trouble prone part of the system. I am on my fourth one now but they are easy to replace and relatively cheap ($40). You should keep a spare in your Jeep. I have had two other strange problems. First, the wiring that goes to the computer (the computer, combined with the ignition coils mounts to the valve cover) which is held in to connectors by set screws, had started to corrode and come loose after a year and a half. Electromotive advised me to apply solder to the wires and re-install them. Problem solved. Secondly, the system is not tolerant of less than 9V from the battery while cranking. I was finding on cold mornings that although the engine would crank easily, the engine would not start. The solution is a new, healthier battery, preferably one that is not as effected by low temps. (Gel cells, spiral cells such as the Optima and dry cells such as the Predator fit the bill). I installed an Optima. Problem solved. An advantage of the Electromotive unit is that the designers were nice enough to include a check engine light that will flash trouble codes when asked. No code scanner is necessary.

Overall, my opinion of the Electromotive unit is positive. Customer support was very friendly and helpful. The unit has functioned well too. But with either of these systems, it is important that your engine and exhaust systems be in top shape. My engine had 36,000 miles at installation and now sports a Borla exhaust. But keep in mind, unless your engine is running poorly to begin with, you will not see a dramatic increase in horsepower. The Mopar should give you a slight edge over the Electromotive unit, but most gains will show up in torque at low RPM's and mileage. My Jeep will get 18 MPG on the highway (highway speed means 70 MPH in my home state of Texas) and up to 20 MPG with a tailwind. My Jeep will now top 80 MPH without breaking a sweat.

The best way to get power out of a 4.2 is to swap camshafts and have some porting and polishing done on the head. Neither of these kits will work well with this type of performance tweaking if you overdo it. They are both designed to work with stock components and anything that greatly increases volumetric efficiency such as hi lift cams will screw things up. Additionally, this sort of work will move peak torque up on the power band, which is not good for off roading. However, Electromotive offers a version of their kit, which is not CARB certified that includes a programmable engine computer. With a bit of luck and expert help, it is possible to get that system to work with mods to the engine and even with a supercharger, but you would be charting unknown territory.

In addition, with the Electromotive unit, I can vouch for the fact that that it will run with quite a few sensors defeated. Before I soldered the connections, as mentioned earlier, I did not have a throttle position sensor or an O2 sensor and it still managed to run. It ran rich and stumbled when cold, but it didn't let me down. Evidently, the only two sensors that will kill the engine if they expire are the MAF and crankshaft position sensors. However, with only those two sensors and more than 9VDC power, it seems to get along just fine.

Even with major vacuum leaks downstream of the MAF it still runs. The smoothness of operation is, though, inversely proportional to size of the leak.

I've even heard of one ingesting water on a creek crossing. With water over the hood, the MAF took a gulp and the engine stopped quickly. It did not completely hydro (to hydro is to ingest water to the point that the engine locks and bends all manner of internal components such as connecting rods.) With the Jeep out of the water, and the plugs out of the head, cranking the engine pumped out the H20. A little drying time for the plugs and MAF and off it went. Keep in mind that the computer and almost everything else on the Jeep was under water for quite some time. Electromotive claims the computer and coils are waterproof. I estimate that on my Jeep you could run it up to the headlights before water hits the MAF. The computer would still be dry. I have yet to try that.

When there is a problem, the computer stores trouble codes and will alert you with a check engine light. This can be wired into your existing check engine circuit after you rip the pathetic OEM computers out and forward them, along with the Carter carb, pulse tubes and 9/10's of the wiring and vacuum lines, to the home of the director of the California Air Resources Board (Send them COD).

The JFI is not nearly a sophisticated as a newish OBDII system, or even as the Mopar system, but its simplicity makes it easy to understand and work with.

The only times it has quit cold on me has been:

  1. After being rammed from the side at the left rear wheel by an old lady, (what a good excuse to get those one piece rear axles that I had been wanting, on her insurance) the main power line came loose. It seems EFI's love and need direct current. It was a bad splice on my part (Solder all connections!).
  2. Several months after playing around on a wet salt flat, enough corrosion had formed on the leads to the electric fuel pump to cause it to stop. A little scraping and bending on the connector and she's good as new. (The JFI system uses the mechanical and an aux. electric fuel pump. The mechanical pump pulls gasoline from the tank, the electric boosts it to 35PSI. Without an electric pump in the tank, the mechanical one is the only thing keeping the system from vapor locking. Electromotive must have learned this the hard way, as the fuel pump setup was included as an addendum to the installation instructions. This type of setup seems a little bizarre, but it's easier than installing an electric pump in the tank.)
  3. It wouldn't start when the magnetic pickup on the Crankshaft position sensor went south on a cool Colorado morning. I don't know if it was out of adjustment or what, but it ran so long as heat was applied to it. I tried matches and a candle but it wasn't until I broke out the hair dryer on an extension cord that I could keep it running. Eat your heart out McGuyver. Once warm it was OK. It got me the 950 miles back home like that. I now have a new sensor.

(Since this was written, I have gone through two more sensors. The one I replaced after Colorado died of natural causes. It started exhibiting problems by causing the engine to miss occasionally. It eventually would not let the engine start. The next one I killed. When I installed it, I did not tighten it up enough and it slipped into the teeth on the sensor wheel. It worked for a while after I fixed it but it eventually quit for good while on a highway exit ramp. When these sensors die, the tach reads zero no matter what. It's rather odd going down the highway with the Jeep in gear and the tach reading zero.)

One more cool thing about the JFI. It has an electronic output for a tach. It'll drive any newer tach although a factory tach takes a little more work. I installed a tiny SunPro tach a'la hot rod style on my steering column. It's a must for a manual transmission yoked to an engine that will probably grenade if taken over five grand. (Although I think I was told that the JFI incorporates a rev limiter, I have yet to test it.)

When there have been problems, Electromotive has been helpful and knowledgeable. In addition they have a web site at www.electromotive-inc.com. The JFI is not mentioned by name, but follow the links to the TEC-II section.

A few notes on the Howell system:

I have not seen one of these systems in action, but I hear they work well. They are based on the two-barrel throttle body that GM used to place upon the top of the 4.3 V6's. Once again, it replaces all the emissions junk and related hoses (air injection too) and uses 02, coolant temp and Manifold air pressure sensors for feedback to the computer. All of the parts are GM and are as common as TBI'ed 4.3 L V6's (There is no problem finding replacements). It differs from both the Electromotive and Mopar systems in that it does not include an ignition system. Like the Electromotive unit, it is a throttle body and it is easy to install. I have been told it installs in less than 8 hours.

Included Parts:

Parts not included:

Installation is quite straight forward with half a dozen connections into the Jeep wiring harness. Fuses and relays mount up high next to the battery and the fuel pump mounts on the frame rail next to the tank. The computer goes behind the glove box under the dash.

Among the recommendations are sealant between the TBI, gasket and manifold. This limits vacuum leaks. Also replace the plugs at the time of installation. The old ones living downstream of the BBD are going to be fouled out anyway.

Mileage gains are in line with the other units (18-20) MPG, power is probably a little less because of the stock distributor.

As the system uses proven parts, reliability should be no problem. Trouble can be tracked down with a GM code scanner. Unique to the Howell unit are the wiring harness and E-prom for the computer. Howell can do custom E-proms as well.

The system is 49 state legal and should be CARB certified by the end of summer.

I have been told that customer service at Howell is top notch with helpful and courteous people.

The cost is around $1000.00.

Since this writing I have found that some Howell owners were experiencing these problems:

Dave C wrote:

I have to say, about this whole thing, Howell has been an excellent company to work with. They are polite and always willing to help. I would give them an overall rating of 7. The problem is in the particular chip or prom they are using. It has some kind of known defect, according to every GM mechanic I've spoken to. When the system is put on the computer it reads all wrong. The engine is doing one thing but the ECM ignores this and tells the TBI to do another. I am getting it back tomorrow and will drive it for 400 - 500 miles then have the system checked again. Howell is working with me on possible credit for the work related to their systems failure.

C B Wrote:

Howell has been very good to me they even sent out some replacement wiring at no cost because the system was reporting bad O2 wiring (it didn't fix the problem). They are good guys. It sounds like this is a GM problem not Howell. Keep up informed as to your problems / solutions.

What are your symptoms? Both Bill and I are looking at several hundred dollar repairs if the Howell system is not causing our problems. I am having the following problems ....

1. Cold missing / rare stalling. Mixture seems overly lean.

2. Flat spots in acceleration at times (overly lean again it seems)

3. Shortened plug life because of excessive temperature (too lean)

4. Random error 13 code (O2 wiring bad) after warm restart, sometimes with a code 15. Field test shows system working normally (lean flashes and rich flashes and closed loop indications at the right times). I ignore the code 13 errors now. A shutdown / restart clears the error and it doesn't reoccur until the next warm restart.

Other than #4 it seems like all these problems could be the result of a bad intake manifold / gasket or some other kind of intake leak. It would be nice to know if this is the case or if the Howell kit is to blame.


A few note on all systems:

As these all are EFI, they run at higher fuel pressures than the old BBD gas dripper. Each uses an electric pump to raise the pressure. The use of the electric pump may lead to vapor lock problems in the fuel line under some conditions. Electric pumps are better at pushing not pulling. This is why most OEM installations will have at least one electric pump submerged in the tank. Electromotive's idea of adding the electric fuel pump after the mechanical seems a good solution to limiting this problem. If vapor lock becomes a problem, this kit can be ordered from Electromotive and should fix it.

Vacuum leaks become a much more important issue. All of these systems rely on some sensor to measure the amount of air being pulled into the engine. Any leak down stream of the sensor will result in a rich mixture. This includes leaks in the vacuum advance system, EGR system, EVS system and especially at the manifold. The Electromotive kit also requires a good seal at the valve cover.

If your Jeep doesn't have an O2 sensor, all these kits require the addition of one. This means removing and welding one on to the exhaust. This is not a fun task.

If your Jeep has pulse air tubes, they will no longer be needed. If you strip out all the tubing, you will be left with a stub on the downpipe and at the catalytic converter. These can be plugged, but if you replace the exhaust, you can order replacements without these stubs.

In Conclusion:

You can see that all these kit work well and are of top quality construction. Each gives a good boost in economy and drivability. But don't expect any of them to turn the old Jeep into a dragster. The kit you choose will depend on budget and how much time you want to spend putting it in. The bottom line is you won't go wrong with any of them.

If you do purchase one of these kits, or already have one, keep me informed on you experiences. As you can tell, the only system that I have any long-term experiences with is the Electromotive unit. As these kits start becoming more common, I would like to keep up with them. Also feel free to e-mail me corrections on any errors or omissions.

Keep Jeepin',

'85 CJ-7

Mark Shipman
President, EndoImage
1602 Rock Prairie Road, Suite 140
College Station, Texas 77840
fax 409-731-8048