When you own a Jeep, there are all kinds of fancy aftermarket parts you can buy to upgrade your ride. But sometimes you can find yourself some performance gains just by grabbing OEM parts from another make or model. Like a Dodge Neon!
Jeep adopted fuel injection in 1987 with a system codeveloped by a joint venture between Renault and supplier Bendix. Called the portmanteaux “RENIX,” this fuel injection tech was replaced by Chrysler fuel injection in 1991, right when carburetors were breathing their death rattle in the last American carbureted 4×4, the Jeep Grand Wagoneer. Chrysler fuel injection was perfectly able at its task; it was simple and fairly unsophisticated. In the decade that followed, injector technology advanced by leaps and bounds. Jeep stuck with what it had in its legendary 4.0 all the way through 2006, because it did the job just fine, even though better parts were out there.
This decision ended up creating a grand opportunity. From the late 1990s onwards, it became possible to snag some nice modern injectors from a junker Dodge Neon, and slot them straight into your Jeep engine for a plug-and-play upgrade. Owners swore by it, saying a smoother-running, more economical engine could be yours—you just needed to swap the parts!
Swap ‘Em Out
The “upgrade” all comes down to injector spray patterns. When Jeep built its famous 4.0-liter engines starting for the 1987 model year, it used fuel injectors from Siemens which had a single hole in the spray tip. These worked just fine, but technology would soon move on. By the mid-1990s, Chrysler was using four-hole injectors across much of its product line, including the popular Dodge Neon. These injectors seemingly did a better job of creating a fine atomized spray of fuel, allowing it to mix better with the air for more complete and efficient combustion.
It just so happens that the injectors fitted to the Dodge Neon were not dissimilar from those that Jeep was using on the 4.0-liter engine. The size and general dimensions were the same, and flow rates were close, if not identical. Thus, all one had to do to “upgrade” the Jeep engine was to pop out the one-hole injectors and swap in a set from a Neon. Or, one-and-a-half Neons, given Dodge’s compact only had four-cylinder engines.
The swap is popular for a simple reason—people think it’s an improvement. Owners typically claim easier starting, smoother running, and better throttle response as anecdotal benefits. Some owners report improved fuel economy, too, on the order of 1 to 2 mpg. That’s notable for vehicles that routinely get less than 20 mpg in regular driving. However, one must also note that it can be difficult to quantify the benefit of such a swap. For example, if you’re swapping newer, cleaner injectors on to a vehicle with a 30-year-old fuel system, it’s hard to tell what was improved by the four-hole injector nozzles, and what was improved by the injectors being less clogged by years of fuel deposits.
[Ed Note: I did this “upgrade” in a parking lot just before my wedding. It was quite easy; you take a few bolts off that hold on the fuel rail, then you yank the fuel rail really hard so that it pops out of the intake ports, then you take off a few clips and swap out the injectors. 
My Jeep definitely ran better afterward, though I made a number of other changes simultaneously (including a new O2 sensor), and my ports and injectors looked pretty gunky:
So the jury is out on if the 4-hole injectors helped over the singles. I bought the four-holes because they were cheap. -DT]
Unfortunately, there are no dyno charts out there proving that the swap nets a real power increase of any sort. That’s perhaps understandable, given those that pursue low-buck upgrades are unlikely to spend money on dyno runs for proof. Big power gains wouldn’t really be expected, regardless, as the injector swap doesn’t get more air into the engine, nor does it add more fuel. It just allows the air and fuel entering the engine to (theoretically) mix better for more efficient combustion.
The difference in spray pattern is readily visible on a simple benchtop tester.
The Right Stuff
If you’ve come across this swap before, you’ve probably heard talk of people swapping in “703s.” This refers to a Bosch part number—0 280 155 703. This is the injector used in the 1995 to 1997 Dodge Neon. Since it’s physically and electrically compatible with the older Siemens injectors used across the Jeep range, it quickly became a popular cheap upgrade. As explained by guides from the Jeep community, these injectors can be swapped into an XJ Jeep Cherokee built from 1987 to 1998. The swap also works for a range of other 4.0-liter Jeeps from this time period, like YJ and TJ Wranglers, and so many others besides. Whatever you’ve got, it’s worth doing the research on the forums to find the right stuff.
The fact that Dodge Neons were plentiful in junkyards helped, but you needn’t limit your search to the bug-eyed compact. Beyond the 1995 to 1997 Neon, you can also find 703s in a wide range of other vehicles that use Chrysler’s 2.4- and 2.0-liter engines of that era. You can often find a set of these injectors lurking inside the Dodge Stratus or Caravan, the Plymouth Breeze, or the Chrysler Cirrus or Sebring. The easiest way to tell you’ve found the right parts is to verify the number printed on the injectors—you’re looking for 0 280 155 703. You’ll need to grab parts from multiple cars if you’re doing a swap into a 4.0-liter, since you’ll need six injectors and the 2.4- and 2.0- only have four.
As with any popular swap, opinion differs in the Jeep community about what works and what doesn’t. Some forum posters believe the 703 injectors aren’t suitable for early 4.0-liter engines built from 1987 to 1990 with the Renix ECU. The suggestion is that these engines may run rich with 703s, and that the Bosch 0 280 155 746 is a better choice. These can be a little harder to come by in the junkyard, having appeared primarily on the Alfa Romeo 164, and the Volvo 850, S70, and S90.
You will need slightly different injectors again if you have a later model Jeep. This is because earlier models with the 4.0-liter engine used a different connector style to later models. The 703s used the “EV1” style connector, with Jeep later switching to the “EV6” (newer) style in later years. These connectors are also known as Jetronic (EV1) and USCAR (EV6), respectively.
Thus, if you’re driving a 4.0 Jeep built from 1999 to 2004, you’ll probably be looking for the Bosch 0 280 155 784 instead. The “784” injectors have the EV6-style connector, and are found in the 1998 to 2001 Dodge Caravan with the 2.4-liter engine. You’ll also find them in the Dodge Neon and Stratus from the same time period, as well as the Plymouth Voyager and Breeze. (2005 and 2006 — the final years for the 4.0 — seem to require a different style, as well). Ultimately, whichever car you’re yanking parts from in the junkyard, it pays to verify the part number on the injector before you pay up and take them home.
In some cases, too, you can actually put the newer EV6-style injectors on an older engine. You can buy adapters to convert between the two connector styles if the injectors are otherwise physically compatible with the engine and fuel rail. In this case, you’ll want to research carefully to ensure you’re getting the right parts. The fun isn’t just limited to 4.0 owners, either. It’s possible to do similar upgrades to the old Jeep 2.5-liter four-cylinder engines, as well as some of the V8s (i.e. the 5.2 and 5.9) —just make sure you figure out what’s going to work for your specific engine before you lay out cash for parts.
Installation
Installing the new injectors is not a particularly demanding task, with many great guides out there breaking it down to a bolt-by-bolt level. It’s a little fiddly if you haven’t done it before, but it’s otherwise straightforward. Normally, the fuel rail is unbolted from the intake, and each injector can then be unclipped from the wiring harness and removed from the rail. It’s all plug-and-play if you’re doing it right.
The trick to a good install lies in gently wiggling the injectors to free them from the rail, rather than yanking or twisting them out. The same is even more important on reinstallation to ensure the o-rings are not damaged. These are crucial for sealing the fuel system and avoiding leaks which could lead to an engine fire. Often, a little lubrication is used during installation to allow them to seat tidily. Feeling them pop into place is quite satisfying if you’ve done it right.
Once everything is put back together, it should be as simple as putting in the key, letting the fuel system prime, and turning the engine over. Some guides recommend following a procedure to reset the ECU’s adaptive memory to clear any changes it may have made to injector trims over time. This could help the ECU better hit the proper fuel/air targets once it’s operating with new injectors, but it isn’t always necessary. It’s usually achieved with some combination of turning the ignition on and off and playing with the headlight switches, or disconnecting the battery. It tells the ECU to go back to factory defaults for the fuel map so it doesn’t have any preconceived notions about how to operate from its time with the old injectors.
Other Paths
It’s also worth noting that the Dodge Neon injectors aren’t the only way to go if you’re looking for a straightforward “upgrade.” Certain injector types used on Ford’s 4.6-liter and 5.0-liter V8s in the late 1990s and early 2000s can also serve as a drop-in swap, though it can be a little harder to find exactly the right type to suit your application. As per popular guides on the swap, you’re typically looking for “19#” injectors which have the right flow rate to suit the Jeep engine application.
You also don’t have to go to the junkyard and hunt for parts. Any number of parts stores will sell you brand new injectors, with many Jeep suppliers specifically selling “four hole” upgrade kits for older models. You can still buy older single-hole injectors, but many owners elect to upgrade when it comes time to replace tired stock parts these days.
If you’re feeling really flush with cash, you can get even more advanced injectors with more holes in them. Companies like K Suspension Fab sell kits to upgrade older Jeeps to 12-hole injectors from Bosch or Denso. In theory, these have an even greater ability to atomize the fuel and help the engine run smoother. Whether that’s borne out in practice depends on who you talk to. Reports from Reddit are mixed. Sadly, dyno graphs or other hard data are hard to come by. [Ed Note: I used the four-hole ones from K Suspension Fab; they work great. -DT].
There’s something fundamentally compelling about OEM parts swaps like these. It feels like you’re getting away with something—that you’ve identified some little secret that the automakers didn’t want you to know, and you’re getting more performance on the sly. Or perhaps it’s just because you can snag your “upgrade” parts so cheap from the junkyard.
Whether you’re swapping out injectors, hunting for Volvo diffs, or trying to snag parts for a lift kit, it’s all the same. Jeeps have always been a platform that welcomes a good junkyard upgrade or three. Bit by bit, piece by piece, you can assemble yourself a better off-roader from the parts you come by along the way.
Of course, always double- and triple-check with forums and read the guides from people who have done it before to confirm the swap will work for your specific model.
Image credits: Jeep, via YouTube screenshot
I did a similar swap when I had my Dakota R/T. It had a Vortec V1 supercharger and most of the forum dwellers at the time swore that swapping the single hole injectors that came on the 5.9 with Ford EV1 4 hole injectors made a huge difference in boosted applications.
Unfortunately I didn’t notice a difference. And soon after I sent most of a piston to the promised land and I never actually found out.
I get up to 30 mpg with even bigger injectors with 12 holes
While 4 hole 19lb injectors make the right flow rate for the stock exhaust and intake to make a good idle , these computers are variable and they can adjust the time that the injector opens to match a target exhaust gas temp. If you add an exhaust that adds extra flow rate you can add more horsepower to your injectors… Instead of running four whole 19 lb injectors what I run is 24 lb 12 hole injectors , and what I noticed is that not only is it more horsepower it’s also better fuel mileage at idle, with the brake specific fuel consumption of 51 lb hour per horsepower you can also make 48 horsepower per cylinder , but having 12 holes allows the computer to shorten the injector pulse at idle and also at full throttle there’s more adjustment because of the spray pattern allows more horsepower… But at idle it will also run smoother because the 12 holes are smaller holes and you can spray less fuel through them to mix more air with the fuel…
Was this just an attempt to call your boss a genius? Sounds like there’s a lot of geniuses out there, and it’s fairly easy and cheap to become one.
A lot of stuff makes sense if you look at it the right way. Years ago I assumed that a Bosch Lambda sensor was a Bosch Lambda sensor. They just had different connectors and wire length. Well, as long as they are similar types (heated 3-wire vs 4-wire vs single wire, etc). I used a 20$ Mustang sensor instead of the 200$ Audi sensor and just spliced the harnesses. Someone tried to argue that there were tiny differences in the sensor that would cause problems. Now imagine that Bosch would make hundreds of different sensors when software could compensate for anything they’d need to compensate for.
Later I assumed an aftermarket exhaust (and probably the OE) for my Audi S8 was the same as the S6 and S7 (just a bit longer). The part numbers were the same except for the last letter. Someone told me they were completely different as the rear track on the cars were different and there was no way it would fit. Imagine Audi would stamp out three completely different width exhausts that are almost identical but not quite to compensate for the 1.3 inch difference in width. Now maybe there were some internal baffles that were different but I doubt that too. The difference is accommodated in the rear valance. Result: Perfect fit.
Occam’s razor.