Super high fuel trims and P0171/0174

What Your MAF Numbers Mean:

• Idle: 3.4 g/s → Perfect. Normal idle range is 2–4 g/s. You're right on target.
  
  
• Under load (uphill): 63.4 g/s → Also excellent. At wide open throttle (WOT) or high load, you're typically looking for anything over 45–50 g/s, depending on engine displacement.

✅ What This Tells Us:
Your MAF sensor is likely working properly. It's reporting realistic airflow values under different conditions. So that moves the MAF way down the suspect list, assuming these readings are consistent and stable.

So What’s Next?
We’re circling back to:

1. Fuel Delivery Issues
   • Your fuel trims are super high (25–34%) except at WOT (where trims are ignored). That still screams fuel pump or fuel pressure regulator.
     
     
   • If pressure is low, ECU adds more fuel = high positive LTFTs.
     
     
   • Momentary surges in power = possible fuel pressure fluctuation.
2. Fuel Pressure Test
   • You need to confirm that your fuel pressure is in spec (around 44–55 psi depending on load).
     
     
   • See if it drops under load or during that “wake up” surge.
3. Vacuum Leaks (worth a second pass)
   • Even tiny leaks post-MAF can cause significant lean trims.
     
     
   • Smoke test is ideal if you can get access to one.
4. O2 Sensor Scan (Optional)
   • If you’re watching live data, check pre-cat O2 sensors.
     
     
   • They should be switching rapidly between ~0.1V and ~0.9V at idle.
     
     
   • Lazy or stuck sensors can cause the ECU to miscalculate fuel needs, though they’re rarely off on both banks.

You’re really narrowing this down well. If fuel pressure is low, this could be one of those classic “runs fine at WOT but lean at cruise” cases due to a weak or tired fuel pump.[/QUOTE]

 

I got close to 85, took a drive on lunch.

 

So it isn't a MAF or breathability issue.

My money is on low fuel pressure but we'll have to await the test results to know for sure.

 

is there a way to check if it's a fuel pump electrical issue prior to receiving the pressure gauge? or has that been ruled out?

 

You would have to access the fuel pump connector and load check the circuit with a high amp test light or other suitable load unless you had an oscilloscope and amp clamp to look at current ramps of the pump.

 

Fuel pump it is?

 

Worth driving it like this at all? Just to see? Or is the proof in the pudding,

 

Pressure is already low, no need to drive it.

You could jump out the fuel pump resistor and see if it impoves but in all likelihood it's the pump.

Only other verification test you can do is access the fuel pump connector and load test the circuit with a headlight bulb but that's likely gonna involve dropping the tank anyway.

 

Yupp, that's what I figured. Any advice on what route to go? I'm thinking suck it up and get one of the oem ones that are the full unit for like 380. Thought about the urd kit but being 20 years old I feel like I shoukd just put a whole new unit.

 

Which company did you send your instrument cluster to be repaired for the P0500. How fast was the turnaround.
Thanks

 

this is what I'm looking at grabbing, place is an hour from my house.

 

i used Automotive Circuit Solutions. Turn around was great. about 300 bucks all in all with shipping both ways.

~220 for repair
~30 for them to 2 day air it back (took 4 days because they completed repair on a Friday and don't ship till Monday, so i got it the following Tuesday)
~30 to ground ship there (my ups wanted 170 for 2 day air?)
~10 bucks of insurance to take it too 500 (waste for me)

i sent mine on a Monday, and received it back the next Tuesday (so 8 days in total)

seems fine so far

 

I'd go OEM, they typically last 200-300k. Unusual that yours failed at 75k but you said it had poor maintenance so maybe it got some crap in the tank.

 

Okay well glad I was already planning that.

Have you ever dropped one? Any tips or tricks, should I try to clean the tank with just, well more gas? Haha I've watched videos but no one talks about cleaning the tank or get this seal this clip etc. But I added to my cart everything I gathered I could need from random yt and forms.

Also just want to thank you and yotadust* both for chiming in. As an ME I appreciate any and all critical insight and testing methods. Top notch help lads.

 

I've done exactly one and it's been a few years but I recall it being pretty easy although we don't have to deal with rust here.
Seems like getting the cover off the top of the pump to unplug it was a bit of a chore though.

I will say mark your lines as they can be easily swapped if your not paying attention.

 

it had the frame recall done about 10 or so years ago, hoping that helps.

just ordered what i listed above, ill update back with how it goes, few weeks maybe.

thanks again

 

If you have a Regular Cab or Access Cab I believe you can get at it by pulling the bed but it's under the cab on Double Cabs.

Hopefully it's not too rusty, maybe crawl under it and hose everything down with your favorite flavor of penetrating spray.

 

double cab short bed TRD off road. so im SOL there, i have to drop.

Rust is pretty okay as the last 6 or so years of the trucks life it saw MAYBE 1k a year. so the frame is mint. the body has some rough spots but, 20 years old what can you do.

fun fact, when i asked my uncle about the rear diff locker he told me he NEVER pressed the button. So i took it on a dirt road to test and it still works, was surprised by that being un actuated for 20 years. lol

 

There's the Ole gal camping last fall.

 

I've never done this, but I would echo the 'crawl under it and hose down anything you have to remove with PB Blaster or the fluid of your choice'.
Also, as far as cleaning the tank, I'd give it a good look once you have the pump out and you'll know what you need to do.