Injector replacement

[Cossed78]

I haven’t necessarily noticed an issue specifically with my injectors, but I’ve heard that many have noticed improvements when buying the “new” 4 hole injectors. I looked through some older posts and found a few people selling them by themselves for cheaper but wasn’t sure if those were still options. But I’ve found a couple options online

injector rehab - seems like best option, pretty sure they show a video on the improvements as well

eBay - only a little more expensive then injector rehab, comes from a Volvo and looks new, but worried about authenticity 

Ksuspension- seems similar to injector rehab but very long wait time.

 

will likely choose one of the first two but would prefer buying from a specific person. Any available? Thanks.

[Gojira94]

First, welcome to the forum!

Second, update your signature with year, engine, trans and trim level when you get a chance.

Third, add your VIN to the registry - https://comancheclub.com/forum/28-comanche-registry-vin-decoding/

 

And to your question- I've done an enormous amount of research on this subject for the 87-90 and 91-up 4.0. Much of it applies to the 2.5, though slightly smaller due to its shorter stroke/ smaller displacement per cylinder.

 

For an 87-90 ("Renix") era 4.0 I recommend an injector that has 4 characteristics:

1. 190-196cc/min flow rate as measured at 3 bar/ 43.5psi (approximately 18lbs./hr.)
2. Is a Bosch "long" style EV6 injector with a Jetronic injector harness connector, for a direct swap on length and connection to the wiring harness
3. 4-hole nozzle- sometimes description will include the term "conical spray" pattern, which is fine
4. Impedance/ resistance of 14-16 Ohms

For a 91-92 Comanche or 91-96 Cherokee 4.0, recommendation is as follows:

1. 196-208cc/min flow rate as measured at 3 bar/ 43.5psi (approximately 19lbs./hr.)
2. Again, is a Bosch "long" style EV6 injector with a Jetronic injector harness connector, for a direct swap on length and connection to the wiring harness
3. Again, a 4-hole nozzle- sometimes description will include the term "conical spray" pattern, which is fine
4. Impedance/ resistance of 14-16 Ohms

I use a number of sources for reference but the deepest library I've seen is at https://www.injectorplanet.com/. You can search part number and get specs for a specific injector. I like to sort by flow rate and see everything they've cataloged that matches the characteristics above. I've never bought from them but they have an Ebay store with 99.7% positive feedback.

 

I've encountered about 2 dozen great candidates, more if you include standard length, which you can use with an adapter. Also a good number that have the USCAR harness connector, with a Jetronic to USCAR adapter. I've done business with Injector Rehab, they're fine. Avoid anything that's been "rebuilt, with improved flow." Cleaned and rebuilt and flow-matched is what you want.

 

Bosch 0280155700 is an excellent injector for 87-90.

Bosch 0280155746 is an excellent injector for 91-96. It's the most talked about "Volvo" injector but its popularity has made it somewhat scarce.

 

Give us some specs on your MJ and we can make some recommendations of what/ where to get it without dealing with knock-offs.

[Cossed78]

Ahh yes I should’ve included that it’s an 87 4.0l. I’ll add that to my signature soon, and my truck is already on the registry. Hasn’t moved more then 1000 miles since then but has a few new parts and sold for the same price.

[Tactical Bacon]

The improvements people detect are either illusory or a result of replacing old, worn, and/or faulty injectors. Will the aftermarket 4/6/12 hole injectors work? Absolutely! Will you gain horsepower or fuel economy over stock? No. Possibly better throttle response.

 

That all being said, I would 100% recommend replacing the injectors on your Jeep if they're original. The Renix era injectors are known to split and leak fuel, potentially causing an engine fire. 

[AnotherOldJeepGuy]

For what its worth, I have replace 3 of my 6 injectors and all the o-rings to stop visible fuel leaks.  If it runs any differently with 3 new and 3 old I can't tell.

[Pete M]

I replaced all the orings on Breanne's 88 only to have one injector split and spray gas all over the place a few months later.  could have easily burned the truck down.  I swapped them all out for factory ford Expedition injectors from a junkyard and it runs great.    

[75sv1]

I have dome Ford 4 holes, and 12 holes. The engine seemed to run smoother with the Ford 4 holes. I did not notice and MPG or power increase. With the 12 holes, I originally noticed a power increase. Then with in a week it was back to stock power. ???? I do think the ECU corrects back to its 'normal' as best it can. Also, injectors are rated to a fuel flow rate and pressure. So, without tuning the ECU to the change, it is questionable as to any improvements or not.  There are some who have upped there Fuel regulator PSI, and had good results. 

[Gojira94]

I'm not trying to be an a$$/ 'that kid' but some clarification is in order...

 

In a nutshell, all we're trying to do is replace an old injector with a new one that acts electrically like the old one, very close to the effective flow rate of the old one and can be had reasonably easily. Better atomization from an updated spray pattern is just a post EFI stone age bonus. We're not looking for more power, that won't happen without more displacement, head airflow or both. Or altering the Renix calibration, which we can't do at this time.

 

To start, if the latency/ Ohms resistance of a chosen injector is too low, the injector flows fuel before the intake valve is open enough to ingest the fuel, and as much as 33% of the fuel puddles on the back of the intake valve. In response, the long term fuel trim goes up, asking for more fuel via a longer injector pulsewidth, wasting more fuel than it would with a vacuum leak, smelling rich and running erratically. Engineers who write the calibrations, including the Renault/ Bendix engineers, know exactly how the injector behaves and literally build the 'tune' around that. These days, we alter more modern cars' calibrations with characteristics of the chosen injector with things like HP Tuners, TunerPro RT, QuarterHorse, standalone systems, etc.

 

Ohms resistance determines how long it takes the injector to start to open and get fully open. The original Renix injector has a resistance of 16 Ohms +/- 5%. A 12 Ohm injector will start to open and get fully open in only 75% of the time it takes a 16 Ohm to do the same at a given voltage, delivering fuel too early in the 'suck' phase of the cycle for a Renix calibration. That's why, even before looking at the flow characteristics, we need to consider Ohms resistance. I did a huge amount of work some years ago with getting "Bosch for Ford" data from multiple injectors into GM calibrations so modified LT1 F, Y, B and D body cars could run better injectors (that have substantially more resistance/ latency) in place of the 12 Ohm Rochesters. For those cars I could easily modify the calibration ("tune") to change everything related to injector characterization. Since we can't modify the calibration for Renix computers, we have to use an injector that behaves electrically like the original and flows an appropriate amount of fuel, that the Renix computer can set a usable long term fuel trim for.

 

The original Renix single hole injector 53003956 has bench flowed as much as 240cc/min in the real world. But as it's used by the Renix computer, its pulsewidth/ on time (duty cycle) isn't very long except in power enrichment. So most of the time it acts like a much smaller injector (19lb/hr or so) and atomizes decently well for what it is, at lower pulsewidths. And it met the emissions standards of its day, when gas was about $1.30/gal, and wasting some portion of the fuel with first generation injector design wasn't a big deal.

 

Any injector swap that initially makes the engine happy or seem to pick up some power is because it's running rich, in the 12.5:1 - 13.4:1 AFR range where more power (and higher emissions) is expected. The computer sees that at the O2 sensor and tries to adjust the long term fuel trim to where short term fuel trim can yield 14.6-14.7:1 and it runs like it did before the swap (if the injector isn't too big to begin with). So shorter pulsewidths are the computer's solution to an injector that's too big, but just small enough to manage. Long term fuel trim will be below 128, maybe well below for an injector that's too big. And injector duty cycle will be very, very low. If it's too big to manage, the computer likely won't stay in closed loop. It smells rich, and fuel economy suffers accordingly (Neon injector 0280155703).

 

Now, to flow rate, number of holes and connector - we already have widely reported great results with the "Bosch for Ford" injector 0280155700 (14.2 Ohm - 191cc-192cc/min.) and "Bosch for Volvo" 0280155746 (15.9 Ohm - 208cc-209cc/min.). Both are 4 hole injectors with a plug and play Jetronic connector we already have in our Jeeps. Both of these injectors are manageable by the Renix and 91-95 Chrysler SBEC computers. They're more efficient at atomizing fuel, so more of each pulse is mixed and burned, and the computer gets to its target AFR with just a smidge less fuel than with the Renix 53003956 or 91-93 HO 33007127. The 0280155700's slightly shorter latency does mean that some fuel (12-13%) is delivered early, but the 'early' fuel is atomized/ suspended well enough to be almost entirely ingested as the intake valve gets above .100" lift.

 

12 hole injectors are almost 100% exclusively going to be equipped with USCAR connectors, which means an adapter is needed (though fairly cheap). But I don't see any substantial benefit with a 12 hole (yet) until everything good with 4 holes/ Jetronic connector becomes scarce. 12 hole does fully atomize the fuel a little closer to the injector nozzle than the 4 hole does, suitable for cars with the intake valve extremely close to the injector boss. I suppose the 4.0 does seem to fit that category...

 

Disclaimer: A fair amount of the fine detail data for Bosch injectors isn't available outside what Ford does for their performance injectors made by Bosch. Things like High Slope, Low Slope, Breakpoint, Minimum Pulsewidth, Battery voltage offset compensation, etc., the last 3 being the most important for idle stability/ idle AFR. Other car makers have this data and usually don't publish it, but they most certainly do use it to write their calibrations. Even the Renix calibrations are going to have a couple of offset and battery voltage compensation tables to handle adding some pulsewidth time at/ near idle based on the original Renault/Bendix characterization data for the 53003956. But that's a whole 'nother discussion.

 

IF you have an adjustable fuel pressure regulator, you can turn a smaller injector up a bit or turn a larger one down. IF you have a REM II, you can tweak pressure until your long term fuel trims are within a couple points of the median value of 128. Warning - too large an injector at lower pressure may lose its good atomization characteristics. Better to turn up a smaller one, but there is a point of diminishing returns there as well. If you don't have an adjustable FPR (most of us) you need to find out where fuel pressure is with a gauge as a starting point. Injector work needs to follow established healthy fuel delivery at expected (or manageable) pressures.

 

P.S. - Stay away from anything Bosch with a V-spray pattern. They're for 2 intake valve applications.