03 Ford 5.4 fuel pressure

marty79

marty79

Well-Known Member
Joined
Nov 24, 2013
Location
Newton, NC
Hey everyone, could someone please verify the proper fuel pressure for this 2003 Ford Expedition 5.4 L I'm getting mixed results on the web between 38psi and 65psi WTH? Mine is 55running, 58 when giving throttle. It's my last test to find this stumbling it has. It bucks/hesitates under light throttle or mostly notice in OD otherwise runs fine. Only codes are lean codes for both banks. Thank you.
 
Check the manual for it some vehicles show fuel psi for that model or all of em..?
 
Look elsewhere.

If it doesn't have any problems anywhere except part throttle, it's generally not going to be a fuel pressure issue. If it can supply fuel pressure under higher loads, it's got plenty of fuel pressure for part throttle.

If this is your last test, what else have you tested?

Because of your lean code on both banks, and the part throttle behavior, I'm going to say it's likely the MAF, or maybe a PCV leak. When was the MAF last cleaned, and have you done anything to test it?
Hmm. Maybe O2 sensor as well, if the ECM adjusts fuel trim for the entire engine (instead of just that cylinder bank) based on O2 feedback. I don't know enough about that engine to have any intuition about that.

Because it's already 16 years old and probably has pretty high mileage, could be a vacuum leak after the MAF too.

Could be a coil, but if it's not stumbling under anything other than part throttle than that is likely not the issue.
 
Screenshot_20180203-210240.png
 
Fabrik8 said:
Look elsewhere.

If it doesn't have any problems anywhere except part throttle, it's generally not going to be a fuel pressure issue. If it can supply fuel pressure under higher loads, it's got plenty of fuel pressure for part throttle.

If this is your last test, what else have you tested?

Because of your lean code on both banks, and the part throttle behavior, I'm going to say it's likely the MAF, or maybe a PCV leak. When was the MAF last cleaned, and have you done anything to test it?
Hmm. Maybe O2 sensor as well, if the ECM adjusts fuel trim for the entire engine (instead of just that cylinder bank) based on O2 feedback. I don't know enough about that engine to have any intuition about that.

Because it's already 16 years old and probably has pretty high mileage, could be a vacuum leak after the MAF too.

Could be a coil, but if it's not stumbling under anything other than part throttle than that is likely not the issue.
Click to expand...
Thank you sir. All new coils, plugs, vacuum hoses/fittings, sprayed carb cleaner everywhere and nothing.
All 4 O2 sensors show same voltage as the others (none of them are off reading from the others). Long term fuel trim 2 is way off, other readings are good.
I'll clean MAF sensor and look up how to test it, thank you very much
 
Replaced fuel filter last week also. New DPFE sensor and EGR system when I got it 4months ago too.
 
I've been looking into that just earlier, gets me little confused but I'm still researching the proper values
 
I'm not good with diagnosing computer/sensor issues lol
 
But what would make a post-cat sensor read the same as pre-cat sensor?
Think about it and explain how that could have an effect on fuel trim.
 
One reads pre-cat and one post-cat. Something is supposed to happen while in the cat that would change that voltage signal.
Why isn't that that voltage signal changing?
 
marty79 said:
Long term fuel trim 2 is way off, other readings are good.
Click to expand...

Oh really? That changes things a little. If it's a MAF or PCV problem, both long term trims should be pretty maxed out. This sounds more like something that is affecting one bank (because of the long term trim) but is making both banks lean, so that narrows the suspects a little. I'm going to think about that a little, but that's a good clue.

The O2 readings can be deceptive, because the readings when you're looking at values can be different than the readings when the condition is actually happening. You really need to check the O2 sensor response to certain conditions, not the readings when it's just sitting there idling and not stumbling. The post-cat O2 sensors should be fluctuating a lot though, unlike the pre-cat O2 sensors. The post-cat O2 sensors are usually a less accurate narrowband O2 sensor (the pre-cat are a wideband, which are used for air/fuel feedback) and have a different output voltage response because of that. The post-cat O2 are only used to detect a problem with the cat itself, as they are compared to the readings from the pre-cat O2. Narrowbands are cheaper, and they work just fine for that simple task after the cat.
 
Last edited:
I had cabbage for dinner and there's nothing on TV. Might as well cruise the tech forum while pooping.

I doubt the 4 O2 sensors having the same reading is causing a miss/stumble/hesitation. But it is interesting they all have the same value. The fuel trim and lean both bank codes tell me it's likely a MAF issue or a vacuum leak.

If you have a tip-in, light load misfire on a COP modular Ford engine, you can almost always bet on at least 1 failed coil, if not more.
 
Thank you guys, I'm overwhelmed with all this stuff on O2 sensors lol, I'm gonna have to try and get a freeze frame data when it comes back and study it again..maybe post it here. I'm reading so much but it's not going too well. I will also look at live data again tomorrow and make sure I'm not writing wrong readings
 
Jody Treadway said:
I doubt the 4 O2 sensors having the same reading is causing a miss/stumble/hesitation. But it is interesting they all have the same value. The fuel trim and lean both bank codes tell me it's likely a MAF issue or a vacuum leak.
Click to expand...

I'm not convinced of a MAF issue anymore, because only one bank has a long term fuel trim problem. They should both be maxed out if it was a MAF problem.
 
Jody Treadway said:
doubt the 4 O2 sensors having the same reading is causing a miss/stumble/hesitation. But it is interesting they all have the same value. The fuel trim and lean both bank codes tell me it's likely a MAF issue or a vacuum leak.
Click to expand...
Don't hold me to that yet, I need to double check this out but that's what I thought I remember seeing. I'm so flustered with this issue for 3weeks now. Doesn't do it all the time that's what ticks me off and hard to diagnose
 
Some days when engine cold runs like ass for first 15min other times crank up and go with hardly no stumbling.
 
marty79 said:
Thank you guys, I'm overwhelmed with all this stuff on O2 sensors lol, I'm gonna have to try and get a freeze frame data when it comes back and study it again..maybe post it here. I'm reading so much but it's not going too well. I will also look at live data again tomorrow and make sure I'm not writing wrong readings
Click to expand...

Don't get hung up on the O2 sensor stuff, I was just explaining why they shouldn't be reading the same under different conditions.
 
marty79 said:
Some days when engine cold runs like ass for first 15min other times crank up and go with hardly no stumbling.
Click to expand...

Also good information, and will help narrow things down.

So to clarify (for everyone thinking about this), when it runs like ass for 15 minutes, is it also idling like ass?
 
Fabrik8 said:
Also good information, and will help narrow things down.

So to clarify (for everyone thinking about this), when it runs like ass for 15 minutes, is it also idling like ass?
Click to expand...
No it always idles fine, only notice if I take off really easy or lite throttle in OD, otherwise don't act up 95% of time
 
Jody Treadway said:
I missed the bank 2 part. Thought it was 2 banks.
Like normal, you're on it!
Click to expand...
That much I do remember being right..all 3other fuel trims we're around similar but bank 2 long term fuel trim was like -45
 
Back
Top