• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Injectors. How to rebuild oem vs "upgradeing"

B

Benthos

NAXJA Forum User
Location
Northern CA
99 xj, 230k miles.

Researching injectors and CAN'T BELIEVE in the forums there seems to be no real consensus.

50% of the posts about bosch remanufactured 4 hole "upgrades" are from upset people who bought them from reccomended rebuilders like Precision or K-suspension and had nothing but problems. They range from leaks, being DOA, or just severely worse performance. The china knockoffs run jeeps, but on the bench tests they are all over the place.

The only actual reliable source for any reaxy to go injector I could find is the new Siemens, at around 350 for a set. It's listed as OEM but is noted to be 4 hole.

https://www.fiveomotorsport.com/bosch-jeep-fuel-injectors-xf2e/

1) Did the 99 xj come with a 4 hole injector as oem?

2) Am I better of testing and cleaning my current injectors? If so do they have pintles and micro screens? If so where does one get those parts?

3) Send them out for a rebuild?

4) Are the issues with the reman bosch 4 holes smoothed out and I should just go with them from k-suspension or the like?

I am interested in 4 hole only for the reported smoothing of the idle. I fear if not oem they may clog easier, fail sooner, or while they work the ecm will just never play as well with them as oem.

I'm doing the exhaust manifold crack and since I have a slight otermitant vibration at low idke figure I might as do the injectors and 02 sensor while there. I've been running it with a huge split in the manifold for prob 150k miles so I suspect that's my problem.

But while there I want to do the injectors right.

Any thoughts are appreciated.

Thx
 
Wondering why you think the injectors need anything ? My 1998 has +284,000 miles and runs fine with the original injectors. One was cracked, and I replaced it with a used one from the junkyard.

4 hole injectors are pretty much a fad, and as you have discovered don't really upgrade anything, and often are faulty and a waste of money. The Jeep in-line 6 cylinder has never been known for its smooth idle, you should sit in my CJ-7 while it is idling if you think your XJ has a lumpy idle.

I would soak them in injector cleaner if necessary, gently brush with a nylon brush, and re-install them. Any money you are thinking of spending on injectors would be better spent on a header, catback exhaust, or other true performance upgrades.
 
Last edited:
running a bottle of fuel additive injector cleaner can help if dirt in injector is the issue. It has worked for me, (i.e. made unmistakable improvement in cold idle) but takes time, you got to burn thru the tank with additive. I know run a bottle of cleaner thru my cars once a year as a preventative measure. On other cars I have used rebuild services, and that has worked for me. on other cars, I just run them with no problem. I got stock jeep injectors in the XJ.
I doubt a four hole is hugely better than stock, yeah, in theory they maybe better, and heck if you replace an old bad set of stock injectors, where maybe one of them is wonkey, you replace them with a new set of four holes you paid good money for, well of course the jeep will run MUCH better, ( and you may tell the world that four holes are designed by God on every jeep forum, they cured all your running problems!) But truth is the Jeep would probably run just as good had that one clogged injector been replaced with a stock injector, rather than all six injectors with new four hole injectors!
I dont think jeep screwed up on the stock injector so horribly, that a "better" four hole design is going to make much difference. There is a limit on how improved an improved injector can improve a cars running.

Trends oft influence after market component selection more than technical reasons, just saying....
 
I'd be curious were you got your info from, K-Fab injectors are known to be junk chinese injectors!
 
Ps you can flow rate test and spray pattern test your injectors if you wish. If I planned on doing that, Id run the injector cleaner thru the system first, since that is easy and might eliminate a flow or pattern issue.
Some injector rebuilders/cleaners provide both before and after test data. price them, then price new stock injectors, Stock injectors can be pretty cheap, maybe less than the cleaning service? I was getting pricey classic european car injectors cleaned, but for them, the new price was many times the cleaning service price.

With stock jeep, it may not be economical to not buy new ones?

Amyway, keep it simple
 
Tim_MN said:
Wondering why you think the injectors need anything ? My 1998 has +284,000 miles and runs fine with the original injectors. One was cracked, and I replaced it with a used one from the junkyard.

4 hole injectors are pretty much a fad, and as you have discovered don't really upgrade anything, and often are faulty and a waste of money. The Jeep in-line 6 cylinder has never been known for its smooth idle, you should sit in my CJ-7 while it is idling if you think your XJ has a lumpy idle.

I would soak them in injector cleaner if necessary, gently brush with a nylon brush, and re-install them. Any money you are thinking of spending on injectors would be better spent on a header, catback exhaust, or other true performance upgrades.
Click to expand...

I plan to charge the fuel rail with them out and look for leaks and then visually check the spray pattern on each one through the fuel rail first.

Do I only need to clean them with the various methods or are there other parts in the injector that should be replaced like the screens and if so where does one obtain them?
 
Unless there are noticeable signs of clogged fuel injectors (such as a rough idle, stalling, poor acceleration, or high emissions levels), I doubt any service is necessary.

If you can find somewhere local that has an injector bench test machine, you could have them flow rate and spray pattern tested, and cleaned at the same time.

Other than doing that, some injector cleaner in the tank once every 6 months is all that is necessary.
 
Swapping to 4-hole injectors is more complicated than matching flow rate.

The notion of the factory single hole injectors is that a good fraction of the fuel atomization is accomplished by shooting the fuel at the back of the hot intake valve. The multi-hole injectors produce more of fog as shown in that video. While this looks appealing, the fog coats the ports and produces a transient AFR behavior. When the walls are dry and the injectors start cycling, the fuel sticks to the walls and the correct amount of fuel doesn't enter the cylinders until the walls reach their steady state coverage. When going to an injector off scenario, the opposite happens with a temporarily rich AFR occurring. I explained this using extreme example of a no-throttle condition compared to an on-throttle condition, but the steady state coverage of fuel on the ports will change with the pulse width and the frequency of pulsing (i.e., engine RPM). This is a known behavior, and modern ECUs that utilize a fog injector have algorithms to adjust the injector pulse width to account for this. My guess would be that the XJ ECU does not have an algorithm for this, and even if it does, it would need to be tuned for the 4-hole injectors.

A more obvious issue that occurs is that injector opening latency will affect idle AFR, and the 4-hole injectors will most likely have a non-trivial difference in latency compared to the factory injectors. ECUs can automatically compensate for this through the idle long term fuel trim, but its not a desirable approach to handling it because it can cause hesitation when coming off throttle. The better approach it to input the correct latency values into the ECU which I'm sure can be done by someone who knows the XJ ECU.

When I bought my XJ this past summer, I gave a fair bit of consideration to an injector swap, but I ultimately decided that without access to the ECU tables, its better to stay with the factory XJ injectors.

If you are looking to improve idle, I recommend looking at ignition upgrades. My experience is that a higher energy coil (or coil pack) and good plugs have a much more pronounced improvement in idle quality and light throttle responsiveness.
 
Benthos said:
99 xj, 230k miles.

Researching injectors and CAN'T BELIEVE in the forums there seems to be no real consensus.

50% of the posts about bosch remanufactured 4 hole "upgrades" are from upset people who bought them from reccomended rebuilders like Precision or K-suspension and had nothing but problems. They range from leaks, being DOA, or just severely worse performance. The china knockoffs run jeeps, but on the bench tests they are all over the place.
Click to expand...

The places selling cheap new injectors are giving you the crappy chinese knockoffs. Most of the people bitching got theirs from eBay, Amazon, or K-sus. Either get a local shop to clean and flow test yours, or find some who actually refurbishes and tests the bosch 4-holes and you won't have a problem.

I got a set of 4-hole bosch from jhc7399 over on cherokeeforum.com a while back and they work just fine. No change in power or mileage, aside from a slightly smoother idle from having clean injectors. My old ones had rusted up and were leaking.
 
maxbraketorque said:
Swapping to 4-hole injectors is more complicated than matching flow rate.

The notion of the factory single hole injectors is that a good fraction of the fuel atomization is accomplished by shooting the fuel at the back of the hot intake valve. The multi-hole injectors produce more of fog as shown in that video. While this looks appealing, the fog coats the ports and produces a transient AFR behavior. When the walls are dry and the injectors start cycling, the fuel sticks to the walls and the correct amount of fuel doesn't enter the cylinders until the walls reach their steady state coverage. When going to an injector off scenario, the opposite happens with a temporarily rich AFR occurring. I explained this using extreme example of a no-throttle condition compared to an on-throttle condition, but the steady state coverage of fuel on the ports will change with the pulse width and the frequency of pulsing (i.e., engine RPM). This is a known behavior, and modern ECUs that utilize a fog injector have algorithms to adjust the injector pulse width to account for this. My guess would be that the XJ ECU does not have an algorithm for this, and even if it does, it would need to be tuned for the 4-hole injectors.

A more obvious issue that occurs is that injector opening latency will affect idle AFR, and the 4-hole injectors will most likely have a non-trivial difference in latency compared to the factory injectors. ECUs can automatically compensate for this through the idle long term fuel trim, but its not a desirable approach to handling it because it can cause hesitation when coming off throttle. The better approach it to input the correct latency values into the ECU which I'm sure can be done by someone who knows the XJ ECU.

When I bought my XJ this past summer, I gave a fair bit of consideration to an injector swap, but I ultimately decided that without access to the ECU tables, its better to stay with the factory XJ injectors.

If you are looking to improve idle, I recommend looking at ignition upgrades. My experience is that a higher energy coil (or coil pack) and good plugs have a much more pronounced improvement in idle quality and light throttle responsiveness.
Click to expand...


This is a really excellent viewpoint. I also heard that the single-stream coming out of the OEM injector is designed to help keep the valve clean somehow...

I'm guessing that they were designed with them for a reason.

I think I will stay oem and get them tested.

I doubt they are the cause of my slight miss at idle. I bought a OBD2 reader that works with torque. But I'm unsure how to use that to help me with Diagnostics. I'm basically going to go for the problem that I know exist and I have heard that running a cracked manifold for a long time can mess up the oxygen sensor which can also cause the problem.
 
Benthos said:
This is a really excellent viewpoint. I also heard that the single-stream coming out of the OEM injector is designed to help keep the valve clean somehow...
Click to expand...

You don't want a stream of fuel piddling on your valves. That's a classic sympomt of a dirty injector. You want a mist with good atomization coming out at an appropriate angle. Also keep in mind that different injector can have different patterns regardless of the number of holes. Most of the videos you see on youtube comparing the chinese knockoffs show they have poor pattern and inconsistent flow rates compared to the genuine ones.
 
I got a set of the Bosch 703s for my '92 off eBay several years back.

It wasn't a totally smooth experience - one or more were overfueling, but the vendor did work with me to send me a properly working set (there was a mis-ship in there too where he sent me a set of yellow ones that weren't compatible). Ultimately, I have a set that seems to work at least as well as the OEMs for me.

I only had about 230K when I did this, but I'd read on here about someone who had an OEM injector fail and wash out a cylinder at 305K miles, necesitating a rebuilt engine swapped in. I figured that since I wasn't daily-driving my jeep at that point, a "fresh" set would be reasonable insurance against such a failure, and the 703s were at that time described here as a "drop-in" and slight upgrade.

I can't say I've seen any "improvement" over the original injectors (which leads me to suspect mine weren't having issues to begin with), but that wasn't the goal in my case - I mainly wanted to reset the clock on 20-odd years and 230K miles of accumulated wear/use on the injectors, and in that I've achieved my goal.
 
You must log in or register to reply here.

Similar threads

O
2000 XJ Failed Colorado Emissions high CO
2
Replies
27
Views
2K
Ken M
K
B
Rear leaf springs
Replies
15
Views
3K
Woodswanderer
W
my2monkeys
aw4, is this the original pan seal?
Replies
4
Views
86
kjc1972
K
M
Automatic Trasmission Rebuild - What to Replace?
Replies
6
Views
2K
mhead
M
8
OEM motor mounts for 4.0
Replies
5
Views
2K
maxbraketorque
M
Back
Top