MBredestege

I recently did a complete rebuild on my ‘00 Sport 4.0 after a 0331 head crack at 52,000 miles. During the build I put 784 injectors in I got from a member here and it has been running really well.
i reset the PCM after the build and again after the 30 minute cam break-in so the PCM wouldn’t have unusual data to set the fuel trim by.
Ive got about 200 miles on it now and put my OBD-IIII reader on it to look at timing, trims.
My short term trim is good, +/- 3% consistently. My long term trim sits around negative 23%. Is this something I should expect with the 784 4 port injectors since they have a higher flow rate? It’s running well so I’m assuming the PCM is doing it’s job and handling fuel trims properly but should it be that far off zero?
Could injector timing being off cause this or add to it? Im going to the Jeep dealer Monday to get the injector timing set, I’m sure it’s close but I have a friend that works there so it will be a “no charge” adjustment.
Mostly want some opinions on whether the 784 injectors would cause this and whether I should look into it further.
Thanks in advance,
Michael

00t444e

Injection timing is done by the computer and doesn't need to be set. What kind of fuel mileage are you getting with the new injectors? That's the best way to tell if something is off.

dave1123

The computer adjusts fuel trims by varying injector "on" times. It really doesn't matter how much the flow rate of the injectors are unless they are less than required, then it will run lean. The point of a 4-hole injector is to make the fuel droplets smaller so they burn easier. Like a spray nozzle as opposed to a squirt gun.

97grand4.0

No your trims are not acceptable. Your mileage will be terrible and you are running way too rich. This is exactly what happens when you go outside the box with flow rates. You have to keep flow rates to what the original injectors were. -23 LTFT is WAY out and typical of too high a flow rate. Your absolute values of the two trim rates should not add to more than 14. Ideally they should be 0.0-... So 23 plus 3, = 26 you're WAY off. Your PCM is struggling to control the fuel. I am surprised you haven't thrown a code yet. Also, if you check your emission monitor for CAT will show INCOMPLETE. This could prevent you passing inspection, but it's showing you the back O2 sensor is reporting that your cat is not working right. Meaning it's being fouled. The back O2 sensor is reporting that it's running too rich. Your cat will suffer and may be permanently damaged.
With your 2001, do you have Bank 1 and Bank 2? Are the readings similar both banks?

Not sure about the 784 injectors (I assume you went with Bosch and not the knock offs on Ebay ..which are seldom the flow rate they say they are..one size fits all) and I am not a buff on injectors and numbers, but, just because it's a 4 hole, doesn't mean it has a higher flow rate. A higher flow rate means more fuel than the OE intended, and the pcm and cat and exhaust are designed for.. I do think you can get 4 hole injectors with the OE flow rate. So maybe someone who knows can fill us in on that. If you do have the correct flow rate injectors, 4 holes would not make it "flow" more; only more efficiently, and that would not be the cause of your trims being so far out (at least that's my theory because I still run the OE 200k injectors with 0+/- 2% having tried the knock offs). Dave1123 had a link to an excellent site for injectors which listed stock flow rates and injector numbers.
Hope some of this helps.

Cummins93

If the long term is stable at -23 and the short term is +/- 5 then the ecu has effectively remapped the base map. It should take higher fuel trims to trip a code. Fuel efficiency and cat performance should be within factory spec.

97grand4.0

I think that the trims are supposed to be around 0.0 is well established fact. The PCM (Not ecu) is only trying to achieve a 14:1 air fuel ratio based on what the front O2 sensor tells it, if it has to subtract 23% fuel, well, that speaks for itself, in my experience, the numbers don't improve with time but this am not too sure of. Mine did not after 2 months. Going back to the oe injectors did improve them immediately and the monitor completed within a day or so.
I guess we could tell if the cat was performing within factory spec if we knew whether the 'catalyst monitor' was INCL or not. Simple enough to find that out if the OP would look at his scanner.
I have heard the code will set around 25%,

Cummins93

Yes if I disagree with what was said I will argue. If you want to discuss your opinions PM.

jordan96xj

MBredestege,

The first 3 responses to your post were pretty on point. I'm not sure what your dealer friend was going to help with, but there is no fuel injector timing to be set. Perhaps there is a procedure to re-baseline what "normal" is so that your long term will be represented as 0% (or close) again. Though I've never heard of such a thing.

-23-26% means your PCM is using almost its entire range of fine tuning ability to keep your air/fuel ratio in the correct range. You may be able to run with that much trim indefinitely, provided the true air content reaching the catalytic converter is not damaging it.

It's not quite accurate to say that the motor is running rich (mentioned in one of the posts). But most people would say it that way. It is more accurate to say that if the PCM was not heavily reducing fuel delivery to the combustion chamber, the motor -would- be running rich. Because the trim is between 23-26 that implies that it has reached a point where the PCM is on top of it. But without a lot of wiggle room. If it couldn't get it under control, the fuel trim would max all the way out and be pegged (usually something like 35% - and would eventually set an check engine code for lean/rich running condition).

Your PCM's general fuel delivery decision making is based on some assumptions:
1. Fuel pressure is right around 49.5%
2. Fuel injectors deliver X amount of fuel per unit of dwell time (ON time) based on the assumption in #1

If either of these two things are not true - the computer will have to constantly trim against them. For example, I recently installed a new fuel pump/regulator and the pressure was slightly higher than the one being replaced. So where I used to have a near 0% longer term fuel trim, I now have about -3%. Which is fine, and well withing normal parameters. But it illustrates how if either of the items above are manipulated - the trims will have to change to account for it.

I wouldn't want to leave my PCM trimming long-term at 23% (or more). I would prefer OEM spec injectors with normal fuel trims. That is just me. Because fuel trims are so useful for troubleshooting various issues, your trims might cause some heartache later when you need them for trouble shooting (like a bad O2 sensor, or bad MAF sensor, or small air leak, etc).

Btw, big props for checking your fuel trims and including that information in your initial post!

MBredestege

When I got to the dealer today, Matt explained what the cam position sensor does.

The CPS sets the timing of the fuel injector pulse with the position of the valve train so the injectors fire at the optimal time for the intake stroke/intake valve position to make the most efficient air fuel intake. That’s all it does, it has no effect on timing, trim, pulse width or any other function other than its position and confirmation to the PCM that the cam is turning. Since it is just pulsing fuel into the intake, it is not a critically timed function and can be quite far off center with no ill affects. The FSM explains in detail how to assemble and set them manually and is correct 99 times out of 100 after this procedure.

Mine scanned at “zero”.

However, if you want to check it to make sure it’s at center, you need a DRB-II Chrysler code reader. In the SET-SYNC setting in closed loop mode it will display a Zero or a +/- number for how far off zero it is. Loosen the ½ inch bolt holding the oil pump drive/CPS clamp and adjust to zero, (the same way and the same place we would adjust ignition timing back in the day) then tighten down. Takes 3 minutes.
Yes, this is a real thing.

As far as the -23% LT fuel trim goes, he was getting it at -18% after saturation. ST fuel trims +/- 2 or less. The PCM was maintaining the trims correctly and the O2 sensor oscillated beautifully between .2 and .8 volts so it is not running “rich” because it is corrected by the PCM. The All systems report OK, no pending, stored or permanent codes.
Functioning as intended.

The 4 port injectors I installed (BOSCH 028-0155-784’s) are very close to originals on paper and very popular with the Jeep community for an upgrade. Due to the LT fuel trims it is obvious that they throw quite a bit more fuel than the stock Chrysler 04854181 injectors that were in there.

We also discussed the possibility of a leaking injector dumping fuel in the intake but eliminated that possibility due to fuel pressure leakdown still being over 20 pounds after 30 minutes. Operating fuel pressure of 49 pounds. (Love the rail mounted fuel pressure gage I installed)

Conclusion?
The higher volume injectors are being compensated for by the PCM as they should be.
Will it hurt? Nope, but as stated in the above post, it could cause diagnosis issues should something else need troubleshooting in the future.

I will be looking for another set of more appropriate injectors to get my LT fuel trim where it should be.

Thanks for the input guys,

Michael

Cummins93

I've had my fuel trims max at +32 before and pull the AFR below 10:1 with 36lbs injectors. I still didnt get a code so I'm not sure if it needs to happen for a certain duration of time. To clarify yes long term fuel trims should not be excessive +/-10 but I have seen how far the ECU can adjust fueling. The JTEC even seems to adjust open loop fueling in start up and hot open loop based on the first and last o2 signals reported.

jordan96xj

Yes, it does have to see the max trim for a certain amount of time before it throws the code. I'm not certain how long it takes (I'm not even certain if it based only on time). While I have the FSM, unfortunately, it doesn't have specific code setting criteria. Maybe someone here with Mitchell, or All Data could find the criteria.

Speaking of fuel trims!

For the first time in 4 years (and 60k miles). My Jeep left me "hoofing it" this morning. Drove through floods yesterday, and the ground connection to my fuel pump gave up the ghost. I have the aftermarket fuel pump assembly from Crown, and the ground connection on that assembly is designed very poorly. I actually carry a fuel pressure gauge, and knew it was the fuel pump before the tow truck arrived. I knew it was electrical, and had already checked the relay. I even jumped underneath in my work clothes and took a wire brush to the ground connection. I was so close to fixing it. I just couldn't clean it up enough with the worn out wire brush I had on board.

MBredestege

With all this said, (I’m going to regret asking this cause I don’t want an endless debate) what is the best injector for a stock, fresh 2000 4.0?
Single ports do give a rough idle, multi port do improve this, so, which one is closest to stock and could achieve zero or near zero LT fuel trims?

jordan96xj

I won't pretend to have experience in this area (recommending various type of injectors). But I do have factory original injectors in my 96, and the idle is not rough. Isn't it possible that the rough idle is coming from something else? One of the opinions I've seen on this matter is that folks might be having problems with their original injectors, and then put 4-hole injectors in, and swear the swap was an effective "upgrade". But with no way to rule out that just replacing the problematic injectors might have brought a similar improvement.

Full disclosure: I have a 6 pack of 4-hole injectors I bought some time ago from the fellow on this forum that used to put together sets of them. They look like they are in good shape, but I'm very hesitant to install them now that I understand this issue a little better. I keep them as emergency spares for now. Kind of a "if it ain't broke...don't fix it" type of situation.