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Fuel trim readings got me chasin my tail

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Fuel trim readings got me chasin my tail

Old 06-13-2018, 11:25 AM
  #31  
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I can agree (almost) with @BareBonesXL. But the issue still screams for more INFO. It is very true that HIGH FLOW impact of dirty fuel injectors.

Fuel injector nozzles are intricate components (small holes - either three or four designed for a specific 'spray pattern'). Tiny droplets of fuel on the nozzle on engine shutdown sit there in the extreme heat and evaporate THOUSANDS of times over 200K miles. One hole plugged up, or with contaminates altering the spray pattern can effect efficiency of combustion - and this the amount of Oxygen seen by the O2 sensor. /// REMEMBER, the amount of oxygen being seen by the O2 sensor is the SOLE factor that drives STFT, an STFT migrates into LTFT as the 'primary' fuel-air correction factor ///

I am actually an advocate of replacing injectors every 150 - 200 k miles anyway. Partly because they are so hard to test - EVEN for proper flow let alone spray pattern. @BareBonesXL's suggestion, while good, would require controlling the source liquid pressure at the Injector's rated pressure in order to correctly collect the volume delivered.

Unfortunately - I don't even know what the LB/hr rating for the OP's 1998 4.6 injectors. I looked around on RockAuto and find that the OP's truck apparently has an FICM (fuel injection control module). I hate throwing parts at one SO BAD, but either the FICM, (new) Fuel Pressure Regulator, OR the injectors could be the problem.

I do not think you would regret 'biting the bullet' and replacing injectors at your mileage. Consider how many times they have 'slapped' open and shut in 200+k miles. My '04 5.4L idles 'UNBELIEVABLY' smooth - and fuel trims are within 0-5% across the whole range with the new Standard SIFJ66 injectors. But they set me back 65 bucks apiece - and I would not recommend using refurbished or remanufactured.

I do not have any good suggestions how to challenge sensors (my preferred method for diagnostics) or running good diagnostics to narrow things between FICM, Regulator, or injectors. Was your fuel pressure reading obtained from OBDII, or with a mechanical gauge? (there could be a difference there.)?
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Old 06-13-2018, 12:45 PM
  #32  
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Originally Posted by F150Torqued View Post
I am actually an advocate of replacing injectors every 150 - 200 k miles anyway. Partly because they are so hard to test - EVEN for proper flow let alone spray pattern. @BareBonesXL's suggestion, while good, would require controlling the source liquid pressure at the Injector's rated pressure in order to correctly collect the volume delivered.
This, below, is from Steve83's pinpoint test list. Apparently Ford has a machine. You can wire the injectors up in series and use an old fuel pump and a spare battery to do a crude wide open test. It can be very dangerous. This situation does lend itself to the pinpoint test protocol. You have to decide how much time you want to spend on trying to think your way to a solution.

From Post #7 -

H60 FLOW TEST FUEL INJECTOR(S)

  • Use the Rotunda Injector Tester, SBDSŪ Injector Tester or equivalent to flow test the fuel injectors according to the instructions for the fuel injector tester.
Is the leakage and flow within specification?YesNoDTCs P0171, P0174:

GO to H62 .
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Old 06-13-2018, 01:07 PM
  #33  
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In my life, and all the vehicles I've worked on at home, at a dealership, or at an independent shop - I've never encountered a failed, leaking, or clogged injector (even on Land Rovers & GMs). That includes both sets in the two 4.9L engines I've owned that were stuck shut (different from clogged) due to the engines sitting for several years. I cooked both sets to melt the congealed gas in them, and both engines are still driving on those injectors MANY years & HUNDREDS of thousands of miles later, without any additional service, other than some occasional pour-in fuel cleaner.

I still recommend you go back to post #6, start at H41, and follow the instructions to the letter.
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Old 06-13-2018, 03:32 PM
  #34  
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Originally Posted by BareBonesXL View Post
...
You can wire the injectors up in series and use an old fuel pump and a spare battery ...
????? Whuttt? That ain't gonna work BareBonesXL. unless you got a 96 volt battery.

Plus, I've acquired, collected, bought, stolen quiet a few tools in my short 72 years, and I'll be damned if I can find my Rotunda Injector Tester, SBDSŪ Injector Tester, OR even the instructions for either.

I don't know, but one might be able to use a high pressure electric fuel pump (with adjustable PSI output ???). If it wouldn't burn out running 100% duty cycle. But still --- I don't even know the Lb/hr that his injectors are rated.

@Steve83 --- It ain't based on nothing scientific, but I've seen grey-whitish residue on too many things from evaporated gas. And I know every drive cycle there is some fuel on the injector tip that dries before the next startup. Maybe they don't 'FAIL' that often. But in all those instances you talk about, could there have been some that deliver 10% more or less than they should. THAT rate would definitely throw fuel trims way off (by much more than 10% - OF A SPECED PULSE WIDTH, which is what we are dealing with here).

JUST SAYIN'
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Old 06-13-2018, 04:09 PM
  #35  
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Probably right, I forgot that I had been working with older 2.5 ohm injectors, not these high impedance units. Two batteries in series would probably do it. One might even do the job. They don't need to snap open quickly, just open fully. They're just small solenoids. Anyway, it just takes the urge and some know-how.

All it takes is some water in the fuel to cause some rust in the lines or the filter or the injectors themselves and you can screw them up. Steve83 is working both sides of the diagnostic procedure. The one he posted says that contaminated injectors are a potential cause. So it is a thing.
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Old 06-13-2018, 06:36 PM
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Originally Posted by F150Torqued View Post
I've seen grey-whitish residue on too many things from evaporated gas.
This is what I assume was on those 4.9L injectors:


(phone app link)


I never removed, cleaned, or flow-tested any of them. I just applied 12V across each bank for a few minutes at a time until I heard all 3 click open. Then I applied fuel pressure (with my makeshift fuel pump system & some Berryman's B12) and repeated it momentarily to push the slime out. Then I started the engine and let it run until it warmed up & smoothed out. That was roughly 700Kmi ago for my Bronco's engine, and probably 250Kmi ago for the one in that album.

So whatever residue might accumulate on a running engine's injectors, I don't think it would EVER build up to a degree that's beyond what Ford engineers designed the EEC/PCM to be able to adapt to.
Originally Posted by F150Torqued View Post
...could there have been some that deliver 10% more or less than they should.
Well, buildup on the outer surface of the nozzles certainly wouldn't cause the injectors to flow MORE. As to how much LESS they might flow - I doubt it's enough for anyone to measure; even with lab equipment. Certainly nowhere near 10%. Ford has specified deposit-resistant injectors (DRIs) since ~1990, and I doubt they went back to deposit-susceptible injectors for the OP's 1998 truck. Read the informational TSB in this caption:


(phone app link)


Originally Posted by F150Torqued View Post
THAT rate would definitely throw fuel trims way off (by much more than 10% - OF A SPECED PULSE WIDTH...
IDK where you're coming up with your numbers or conclusions, but I don't see anything there I can agree with.
Originally Posted by BareBonesXL View Post
All it takes is some water in the fuel to cause some rust in the lines or the filter or the injectors....
That would be noteworthy since the fuel lines & filters are stainless steel, except where they're plastic & paper. So it would take quite a bit of water & time for anything in them to rust.


(phone app link)



(phone app link)


Most of the metal in the injectors is stainless & brass (filter screen), so they're not a likely source of rust, either.


(phone app link)
Originally Posted by BareBonesXL View Post
Steve83 is working both sides of the diagnostic procedure..
I'm discussing the injectors because there appears to be some interest in & conjecture about them. But I've never suspected or suggested that the OP's injectors have any problem contributing to his symptoms.
Originally Posted by BareBonesXL View Post
The one he posted says that contaminated injectors are a potential cause. So it is a thing.
But not from rust, or from fuel deposits. Fuel injectors are VERY susceptible to contamination by silicone grease (for example), which some uninformed mechanics apply to fuel system fittings. So there are reasons for the Ford procedure to mention that possibility. But that doesn't make it a LIKELIHOOD.

Last edited by Steve83; 06-13-2018 at 06:52 PM.
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Old 06-14-2018, 12:13 AM
  #37  
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Hey guys sorry i havent been answering just not enough time on a 24 hour clock.
So to answer a few questions you guys had;

* The fuel pressure tester is a brand new Innova mechanical fuel injection pressure tester.
* No I have never changed o2 sensors.
* My obd11 scanner is one I bought online called BlueDriver bluetooth scan tool.

F150Torqued I believe it was you that mentioned my concern with STFT being positive and LTFT being negative at the same time which wasnt the case. I was concerned with (or dont understand) why both STFT and LTFT were negative at the same time @ idle, and both positive at the same time under load. So that being said it tells me that at idle its taking fuel away and under load adding fuel which is part of the reason im chasing my tail lol.

Steve83 as soon as i possibly can i will be starting on the diagnosis that you posted previously. I have a lot on my plate right now ( long story) and have been unable to work on the truck but still need to get it figured out.

Thanks again all you guys for your help, you have no idea what this means to me.

Goinwheelin
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Old 06-14-2018, 01:15 PM
  #38  
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Thank you @Goinwheelin

I hate spending so much time explaining what I don't know - but I'm not familiar with Bluedriver's capability and cursory online search didn't completely cure that problem.

But, a monitoring fuel trims while doing a simple hypothetical test can help understand the relationship between STFT & LTFT. (STFT can be likened to a weather vane - shows which direction LTFT is going to be moving if conditions stay as they are.) ie: is the problem still present (at CURRENT RPM / LOAD conditions). The fuel trim 'table' in the PCM is multi-dimensional (at least two dimensions) based on engine RPM & LOAD). /// IF STFT & LTFT were at ZERO, at idle, and you 'create' a small vacuum leak (SAY unhook PCV valve hose)./// STFT will go 'positive' to compensate for the 'unmetered' air being ingested into the combustion process (note this ~number). If you leave it this way for a few minutes, LTFT will grow to be equal to the initial STFT number noted as STFT gradually declines back down to ~ZERO. Along the way - you will have LTFT positive, AND STFT some less positive.

Now if you plug the vacuum line back on, LTFT will still be ~'positive', but STFT will go negative the SAME amount --- sum total being ~ZERO. But LTFT will be positive while STFT is negative, and after a while they will BOTH be ~zero again.

You can verify this with Bluedriver. I emphasized RPM & LOAD because it adds yet another layer to consider. The fuel trim tables are multi-dimensional (at least two dimensions) consisting of fuel trim values at various RPM and LOAD conditions. (It looks something like a Rubics Cube.) A problem CAN be occurring at ONLY certain range of RPMs or LOAD. And Mass Air Flow is a component part of LOAD calculations!!! (more to keep in mind!)

------------------

But, I alo read up on the Innova fuel pressure tester and - from what I see, it's reading is "RELATIVE" to 'atmospheric' pressure. Your injector nozzle is at the valve port (I think, like my '04) and is at 'MINUS' IM vacuum relative to 'atmospheric' so vacuum amount (21 in-hg = 10.3 psi) must be added to your readings. I went back to post # six and I note that your fuel pressure readings look pretty OK: The fuel pressure regulator AND FICM must be working OK.

Originally Posted by goinwheelin View Post
Thanks everyone for you help on this. I did a couple more tests today, vacuum and fuel pressure so here's the results;

Vacuum
@ idle 21 in-Hg steady
Snap throttle. Vacuum peaked or zeroed, then went to 26 in-Hg for a couple seconds and then went back to 21 in-Hg steady.

Fuel pressure
Key on engine off. 36 psi
@ idle. 30 psi
Vacuum disconected @ fuel pressure reg. 40 psi
@2000 rpm. 30 psi
Pressure after 5 min. shutdown 36 psi.

I did these tests 3 times each but on the 2nd fuel test the pressure after shutdown bled of to10 psi in about 1 or 2 min. That doesn't sound right.
What could cause that?
Is this something that would cause lean codes?

Thanks again everyone.
Goinwheelin
I'm guessing your injectors are probably rated at 39 or 40 psi (as my '04) and the system seems to be maintaining that across RPM (& Load??) range.

--------------------

I know @Steve83 po-po's the idea of that 'injectors' can get curded up --- (but if the Fuel Rail, fuel lines, fuel filter has been off / opened up and ANY junk gets in there - it AINT GONNA pass through them little bitty holes in the injectors. And the result of that would certainly show up quick in the fuel trims. (More at higher RPM --- IDK, maybe). The only other thing that strikes me is O2 sensors. (I recommend you replace them -ANYWAY). I believe clogged CATS would exhibit the opposite effect and drive fuel trims negative (because trapped inert gasses in the exhaust makes exhaust more oxygen deficient, making O2 sensor voltage outputs higher - shortening fuel trims at higher RPMs.... IMO.)

Just my 2cents for you to ponder.
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Old 06-14-2018, 11:00 PM
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Have you considered replacing your gas tank cap? We just recently went through a check engine event on our 2007 F150 5.4 and thankfully that was the solution. In between figuring it out, the truck ran badly and we were chasing poor idle with a/c max. After some research, went to Ford dealer and got a new gas tank cap for grins. . Everything is better, truck running normal, no more check engine light. The guys at Ford parts counter chuckled when I bought the gas cap - bet you got a check engine light! This is literally the first problem we ever had with this truck, it has about 155,000 miles on it. Lives in the country, bounces every other day on a long dirt road - the gasket on that gas cap was dried out to the point of shooting trouble codes. Worth a try for $20.
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Old 06-14-2018, 11:25 PM
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Originally Posted by fang2015 View Post
Have you considered replacing your gas tank cap? We just recently went through a check engine event on our 2007 F150 5.4 and thankfully that was the solution. In between figuring it out, the truck ran badly and we were chasing poor idle with a/c max. After some research, went to Ford dealer and got a new gas tank cap for grins. . Everything is better, truck running normal, no more check engine light. The guys at Ford parts counter chuckled when I bought the gas cap - bet you got a check engine light! This is literally the first problem we ever had with this truck, it has about 155,000 miles on it. Lives in the country, bounces every other day on a long dirt road - the gasket on that gas cap was dried out to the point of shooting trouble codes. Worth a try for $20.
Thanks for the input fang2015, I kinda chuckled as well when i read your post cause i had the same thing with another vehicle lol.
I do believe that would be a code to do with the evap system which is a little different codes than what im getting. But I will check it out just cause its a nice easy thing to do.

Thanks again
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