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Old 06-30-2019, 09:15 AM   #1 (permalink)
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Needing some insight on OBD-2

Hello again everyone.

I've posted on here a few times about a fuel injector swap for my Ranger. Finding a different injector like what I want is proving difficult. The flow rates are always higher than stock. I was hoping the ECU (by way of the O2 sensors) could make the proper adjustments to the pulse width (I think Ford calls it the duty-cycle ?) to bring the AFR back in line. I asked on a Ranger website and even though I believe the response I got, I'm looking for either a second opinion or confirmation. The OBD systems are a bit above my pay grade.

Long story short......stock 2003 Ranger injectors are 4 hole, 18# flow rate. I have found "plug and play" 12 hole injectors but they flow at 23#. Nearly a 20% increase. The info from the other site goes like this.......new injectors will run rich. Downstreram O2 will read rich and ECU will throw a CEL and then make adjustments. If the ECU has the room in it's stock programming to make the adjustments to bring the AFR back in line it will do so, but still throw the CEL because it knows it shouldn't have had to make the adjustment in the first place. AFR may be in line but the light stays on.

My questions are this......

1) If the ECU makes the adjustment and the downstream O2 sensor reads OK, wouldn't the CEL go off? The ECU is smart but it isn't AI. It's more of an if then statement isn't is? If O2 is bad then CEL. If O2 is good then no CEL. Right?

2) and maybe not answerable.....Is a 20% increase to much for the ECU to handle by itself without having to pay for a custom tuner.

The 12 hole injector may not lead to much if any MPG increase, but might lead to a cleaner burn, unless it runs to rich. Wouldn't that help with emissions (we don't have testing here) and smooth out the idle some? I can get the injectors for about $50 but the time involved in removing the intake to install them is daunting. If they were easily accessible, I'd just go for it and report back on how it all worked out.

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Old 06-30-2019, 12:48 PM   #2 (permalink)
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I don’t have much Ford specific experience, mainly Gm. A lot of vehicles seem to be able to adjust the long term fuel trim +/- 25% and short term +/- 25%. Problem is I think most will set a rich or lean code once the long term is off 20-24%. So the vehicle may be able to correct 50%, you may be stuck with a check engine light if you’re holding over 20%. It may be fine, aside from the light, while in closed loop, but I’d guess you’d be dumping extra fuel whenever you’re in open loop. Making the change for mileage, I’d be scared of going to a higher flow.
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Old 06-30-2019, 02:49 PM   #3 (permalink)
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Thanks 2000mc. Interestingly enough we looked at an injector for a GM engine. I think it was an LE-8 (?) Had the correct flow (or possibly 19#) but for some reason we ruled it out. For the life of me I can't remember why.
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Old 06-30-2019, 03:20 PM   #4 (permalink)
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Agree with 2000mc. Despite adjusting fuel trim, the ecu will still know the fueling is out of spec and "broken" and so the CEL will stay lit. Check your Illinois smog test rules. If like Cali, then a CEL is an automatic fail.
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Old 06-30-2019, 06:11 PM   #5 (permalink)
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No worries on the smog testing California98Civic. No testing in Illinois. Maybe for commercial vehicles but I'm not even sure about that. We did find an injector that was about as perfect as it could be, but was shorter. Not sure I could adapt the fuel rail to mount to something solid and I'm not comfortable with is just "floating" only on top of the injectors.

Ford did make a California only 12 hole injector for the mid 2000's Focus with the ztech engine but they also flowed at 23# from what we can find. Bosch and Denso and the like are really tight lipped on their injector specs.
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Old 07-01-2019, 04:59 AM   #6 (permalink)
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If the ECU doesn't make a long-term fuel trim adjustment (or the adjustment isn't quite enough), every time you change throttle position it will swing rich until the O2 sensor has a chance to correct.

It's possible that even if it does make the correction, it will need to relearn it every time you start the truck.

Ideally you'd get aftermarket engine management and correct for the larger injectors.
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Old 07-01-2019, 06:32 AM   #7 (permalink)
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Thanks everyone.

So it's beginning to sound like if I want to pursue this I need to either find an injector with the same specs (flow rate along with the obvious other specs) or go with a larger one and pay someone to make some changes in the ECU to accommodate them. Finding such a low flow rate has been rather difficult and a "tune" will probably never return on the investment.

Maybe it's been a bit of a pipe dream?
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Old 07-01-2019, 08:58 AM   #8 (permalink)
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Do you know the fuel rail pressures that those flow rates are set at? If your ranger is flowing 18#/hr of fuel at maybe 40psig while the 12 hole injectors are flowing 23#/hr at 60psig, then they're not necessarily a larger injector.

It's used a lot in tuning if you need more fuel you bump up the fuel pressure to make up for smaller injectors.

Conversely, if you need less fuel you turn down the fuel pressure
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Old 07-06-2019, 12:44 AM   #9 (permalink)
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Quote:
Originally Posted by hat_man View Post
Thanks everyone.

So it's beginning to sound like if I want to pursue this I need to either find an injector with the same specs (flow rate along with the obvious other specs) or go with a larger one and pay someone to make some changes in the ECU to accommodate them. Finding such a low flow rate has been rather difficult and a "tune" will probably never return on the investment.

Maybe it's been a bit of a pipe dream?
A tune would work wonders on your truck. Not only for correcting the fuel tables for the 12 hole injectors, but for allowing a clutch fan delete and altering fuel/timing to give better mileage...
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Old 07-06-2019, 10:07 AM   #10 (permalink)
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Thanks KSA. I knew about the fuel pressure stuff already though. The 2000+ Rangers run about 55-60 psi on the fuel rail already. The stock injectors are rated at 18# at 43 psi/3 bar so yes they do flow more than 18#. 43 psi seems to be some sort of standard rating benchmark so even if I did the math to find out what they actually flow I couldn't use that number to find the new ones. Most everything is listed/rated at 43 psi. I need to hold somewhat true to the 18# rating.

Thanks bonestock. I would love to do a tune but I've heard they are rather expensive. I'm sure it would help quite a bit though. I have no clue as to how it's done anyhow or where I would have to go. I'm sure they would need the truck to read the computer and see what it has "learned" as to how I drive, and then make adjustments from there. I would love to drop the mechanical fan and just use the electric one. And I'm pretty sure Ford left some mileage on the table with a rather conservative stock tune.

If anyone has any more insight on the "tuning" process I'm all ears. There probably isn't much out here in Cornfield County Illinois for work like that though.

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