The Definitive Injector Swap HOW-TO
DISCLAIMER: This swap ONLY applies to the 1993 thru 1998 Jeep Grand Cherokee "ZJ". Although many other vehicles have included the 4.0 and 5.2/5.9; there is NO guarantee that this swap will benefit or even work on a different vehicle; because there have been many different varying injector sizes, connectors, and engine/fuel management systems on vehicles with these engines. Do your research on your particular vehicle, paying close attention to stock injector specs vs new injector specs, before you attempt this on a different vehicle.
So I think its time there was a write-up that defeated all the misconceptions, conflicting information, and myths about the infamous injector swap mod. I will try to do it as completely and accurately as possible, please comment so I can correct the post :)
There are two sets of steps, one for the 4.0, and one for the 5.2/5.9 found below courtesy of 1SASjeepster.
The injectors used for the swap are the EV6 injector design as opposed to the stock EV1 injector design. The 4-hole pintle of the EV6 leads to better atomization of fuel, thus a more complete burn, with the same flow rate as the stock 1-hole EV1 design. You can see this easily in this video:
The performance/economy advantages are:
-Engine idle becomes smoother
-Small increase in throttle response
-Small increase in fuel economy
The injectors you need depend on the year and engine of your ZJ You will need an injector with the proper Jetronic/Minitimer connector or an adapter that will plug into your ZJ’s harness. I have collected information from Jeepers that have done this swap to determine the best injectors for each model year. You can use the information below to select the best injector for your jeep
Stock Model numbers & Pressures:
Stock 4.0 Injector (93-95): Siemens 53030343; 22.4lb/hr @ 39psi
Stock 4.0 Injector (96-98): Siemens 53030778; 23.7lb/hr @ 49psi
Stock 5.2 Injector (93-94): Siemens 53007809; 18.4lb/hr @ 39psi
Stock 5.2 Injector (95onl): Siemens 53030262; 24.6lb/hr @ 39psi
Stock 5.2 Injector (96-98): Siemens 53030778; 23.7lb/hr @ 49psi
Stock 5.9 Injector (98onl): Siemens 53030778; 23.7lb/hr @ 49psi
Bosch 0280155703; 21.8lb/hr @ 39psi & 24.4lb/hr @ 49psi
Bosch 0280155710; 17.3lb/hr @ 39psi & 19.4lb/hr @ 49psi
Alternates, as reported by a few people in other posts. These injectors have been reported with mixed results, you can read for yourself in the thread. I have posted their specs here for easy reference:
Bosch 0280155784; 20.2lb/hr @ 39psi & 22.6lb/hr @ 49psi (slightly less flow than the 703s. You will need a Jetronic/Minitimer adapter for the electrical connector.)
Bosch 0280155789; 19.9lb/hr @ 39psi & 22.3lb/hr @ 49psi (slightly less flow than the 703s. Also needs a Jetronic/Minitimer adapter for the electrical connector.)
Bosch 0280155715; 21.3lb/hr @ 39psi & 23.8lb/hr @ 49psi (very close to the 703s flow. Users have reported mixed results with new/tested injectors. No adapter needed)
93-95 4.0 w/703s: CONFIRMED (zander21510, 93zjbums, ahoyt653)
96-98 4.0 w/703s: CONFIRMED (MaintMech, melk, moggie99, johnt671, torchd, DickDickle)
93-94 5.2 w/710s: CONFIRMED (General_Jeep, soopaghetto, ozzy_2_me, Proph2010)
1995 5.2 w/ 703s: CONFIRMED (extrememarine, dnuccio, jetjr91)
96-98 5.2 w/703s: CONFIRMED (1SASjeepster, zturn13,Mity White 96)
1998 5.9 w/ 703s: CONFIRMED (nickszj, NYCXJ90, hm_dart)
*Please help me improve this post by posting your success so that I can add your data!
The root of most problems people have had with this swap is leaky, old injectors untested from the junkyard. Exposed to the elements, these injectors are highly prone to decay. If you find your Jeep to be spewing white smoke or running rough, or if you just want to take the precautions and test the injectors first, here is an easy way to do it:
Cars where the injectors can be found:
Tools & supplies needed:
-Ratchet kit to unbolt fuel rail
-Pie pan or small, shallow container to catch fuel
-A little clean motor oil or lubricant oil
Steps: This was performed on a 95 ZJ with a 4.0. I used 703 injectors. (5.2 and 5.9 procedure click HERE)
1. First, if you have used injectors, perform the rebuild. Be very careful not to damage the pintle on the injectors. If you have extra parts, they are extra, don’t try to add them to the injectors. You can remove the old filters by using a screw, screwing it into the old filter, and pulling out with pliers. The old pintle cap can be removed by carefully using a blade to cut the cap down the side and pull off. (I stabbed myself when i did this...not fun...cut AWAY from yourself...)Install all the new stuff!
2. Disconnect the battery. DON'T IGNORE! Not just because of the safety aspect, but as you are working it will reset the PCM and allow it to "learn" the new fuel trims needed to operate efficiently. The PCM will return to its factory values, and as you drive it will adjust the injector pulse rate to accommodate the different injector design. This is vital if you want to notice any benefits quickly. Also, if you have the equipment, blow some compressed air around the injectors prior to removal. This will prevent dust and pieces of who knows what from getting into the combustion chamber.
3. Relieve the pressure on your fuel rail. Take a rag and and unscrew the plastic cap near the front of the rail. Push the little button inside and fuel should first squirt out and then eventually dribble. Hold the rag under it and keep it there until it stops squirting. You can then screw the plastic cap back on so you don’t lose it.
4. Unplug the electric connectors from the fuel injectors. Pull them out of the way. It shouldn't be a problem, but if for some reason they are very loose or the wires aren't tied down, make sure you keep track of what plug goes to what injector.
4. There are 3 bolts to remove the fuel rail, and you need to remove the 3 throttle body cables and get them out of the way to make a clear path for the fuel rail to be pulled. You need to place the shallow container, or have a buddy hold the container, under the fuel rail, so that you can catch the excess fuel. Pull sharply on the rail in the direction of the injectors to remove. Usually the injectors will stay in the rail when you pull it from the intake. Remember you have a lot of fuel still in the rail.
5. Keep that container under the rail over as you remove each injector, because there is a lot of fuel in the rail (way more than you would think...).
6. Once you have everything disassembled, you can attach the new injectors to the fuel rail. Lube the O-rings with some motor oil or lubricating oil to make them easily slide into the fuel rail openings. Make sure they are oriented properly, the pintle holes should go into the intake. You can spin them when everything is attached to a point, but it might help if they are oriented with the connectors pointed up so you can connect the electrical connectors easily.
7. Lube the other ends of the injectors, and evenly push them into the holes in the intake manifold. You know they are in when you can line the fuel rail holes with the bolt holes.
8. Bolt everything up and reconnect the electric connectors.
9. If you made a mess with all the fuel, soak as much up as you can and give it an hour or so for it all to evaporate so you don't start a fire. Just in case, have a fire extinguisher handy (the C type).
9. Start her up! It may take 2 or 3 more seconds to turn over, the fuel rail has to regain pressure and squirt fuel into the cylinders.
10. Enjoy! There are a few pictures below for reference taken from the older threads courtesy of melk.
Old injectors vs the 703 injectors with new O-rings, filter, and pintle caps:
Fuel rail with old injectors:
Fuel rail with new injectors installed:
Great technical work! I recommend this for sticky. I dont want to come off as a critic, but the only thing I see that is missing is to disconnect the battery and use compressed air to clean around the injectors prior to removal. The battery disconnect is not only for safety, but to also learn the new injector pulsing.
Very nice job! Well thought out with good pics.
As a side note: When I did mine I didn't pull the fuel line off, just moved the rail out of the way. Had to pull each injector one at a time. Didn't pull the trans/throttle cables, just unbolted the bracket to have some more room. As I pulled each injector I had my shop vac running and kept it on the injector to suck the crud. Also when cleaning before installing the new ones had the vac running to keep it clean.
2X on lubing the O-rings, I tore one doing it dry and had to hit NAPA for new ones. I used white lithium spray grease on my finger then applied to the O-rings.
Used a rubber mallet (lightly on the rail!) to firmly seat the new injectors, I was surprised how loose they were even with the rail bolted up.
The only really noticeable change for me was how much more responsive it was under light throttle.
Watch the clips on the rail/injectors! My Jeep was hungry and ate the one from #6. Had to run to pick a part for replacements!
'96 GC 4.0
lol nice pics :)
Great Job Man !!!!
Thanks A Lot
I found more info after you directed me
Disconnecting the battery isn't going to make the computer "learn" the new injectors, fuel injection doesn't work like that.
The PCM has static values calibrated into it called injector data. This houses data regarding the injector size, pulse widths, minimum pulse width, and flow values based on voltage and vacuum change.
Happy Ho Ho
Something I am curious about is the different resistances listed... 12 ohm and 14 ohm... Wouldn't it be prudent to use injectors that match the factory resistance?
(could be impedance as well, but not sure.)
+1 for sticky. Thanks Zander for making this how to, I've been wanting to swap the injectors for a while, but haven't seen a decent write up on it til now.
Stealing your idea with painting the fuel rail, just btw.
One last thing, where'd you get the k&n filter for your valve cover?
On OBD-2 vehicles this data is always being recorded and stored. Resetting the PCM is an option for it to relearn quicker but it is by no means necessary. If you just driving around it will eventually get to the same point as it did if you disconnected you battery and started over.
With all that said, there is no way for the PCM to learn an injector size. The only way for that to be done is to reflash it with more proper parameters. The point of resetting the PCM is so that it resets the fuel TRIMS. The reason these injectors work is because they are already close to the proper size and they are a much better design.
Also, it's incorrect to say the O2 sensors are adjusting to a 14.7 to 1 air fuel ratio. O2 sensors don't read air/fuel, they read in lambda. O2 sensors are always trying to adjust to 1.0 lambda, which for pump gas is 14.68:1, assuming no ethanol content. With E10, it's more like 14.13:1. If you put E85 in the tank, they injectors would still shoot for 1.0 lambda which is something like 9.7:1 AFR.
Yes these injectors are a worthy upgrade, no the PCM does not NEED to be reset.
Dude thank you! This is so much more to the point and has all the information we need. I gave up searching through the other thread....
Vote for sticky!!
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