2003 Ta’Hoe—Fuel issues

[Jonesy92]

Hey all!
I’ve scanned over a few fuel issue threads, none have applied to mine.
Working on my 2003 Tahoe, 5.3 Gen 3 V8. Had a double lean code for each side, changed intake gaskets, knock sensors, and ran a secondary ground from the back ground strap as a precautionary. No nodes, but now she likes to bog out after coming down from high Rpms.
I’ve done a smoke test on the intake, as it’s aftermarket(I cut the old ducts off, installed clear heavy plastic see though), and I have no leaks. I should mention, the intake is a straight tube now, smooth inside.
Now comes my question, I’ve purchased a fitting for the fuel rail, and a guage. Removed the valve interior, and tightened the fitting, and then secured the gauge. (It is upside down). I started the truck, after noticing nothing on the gauge after “key-on” position. Started the truck up, and still nothing.
Am I missing something? It revs up but sounds like she’s starving for fuel. Slow increase in Rpms has no effect, but a quick push to the floor results in bogging, and a shudder, and it shuts off. Unless, I catch the Rpms and tap the gas less and less to Let it down easy.
Any ideas? Going to be picking up a fuel filter as it most likely needs changed. I just replaced the original starter on the truck with 238k miles on it.

 

[PNWYukon]

Are there any codes for fuel pump etc?

fuel filter would have to be seriously plugged for that to happen

if there is no pressure you could try fuel pressure regulator, but probably fuel pump.

 

[Fless]

Recommend renting a fuel pressure gauge from a nearby auto parts store. Many times they do that for a refundable deposit so if it's returned within the allotted time it's free. Then put the Schrader valve back in the fuel rail and do the standard key on, engine off ("KOEO") test.

You must have some fuel pressure if it runs, so something is wrong with the current test setup. If your truck is Flex Fuel the KOEO pressure specs are somewhat different from non-Flex. What's the 8th character of your VIN?

 

[Jonesy92]

No codes for fuel pump, replace filter as a preventative. It was a few years old.
My fuel pressure regulator is rusted, and I had a broken rubber elbow in the line going to. Replaced the line, not the reg. Will be changing it this week.
It is not the flex fuel V8.
I do however have a strange set of codes. Same code, twice.
P1516- Manufacturer Control Malfunction.
I used to have a double bank lean condition, but after new intake gaskets, and inspection of the knock sensors, those codes have been gone.
Any clues?

 

[Fless]

Didn't know they put fuel filters on the non-Flex trucks in 2003.

The P1516 code is manufacturer-specific and points to the throttle body, and to the actuator on the TB. Probably flaky or lost communication. Follow the wires from the TB back a foot or so to see if the wires have been compromised under the insulation. They are prone to flex and break there near the TV.

 

[Jonesy92]

I guess I should have mentioned I have updated the pigtails on the throttle body through the Gm dealership. I have also traced the wires, and reloomed them afterwards ensuring they were all intact. Volt meter helped provide continuity through each. I have also given it the old shake the hell out of it test. Neither of which reproduces the issue. Only way to reproduce, is to put it into gear with foot on break, and hold the gas at 2k exactly, for 5 seconds.
Lately, I can’t even get it to do that. As of now it’s just the two codes.

And yes, the fuel filter was behind the drivers side Frame rail, at an angle.
I am however, was of 20 minutes ago after driving from work. Idle to 1k rpm will almost give a backfire. After that, t continues up in the range, and runs fine. UNLESS, you’re at a stop, and need to hop out into traffic. Then you’ll get a backfire through the intake.

 

[Jonesy92]

I can also note that I have heard my throttle body doing what sounds like levers, constantly until I turn the truck to “key on” position. If I get it up to temp, shut it off, and turn to “key on” , no sounds. I do know my TB has the coolant flow line.
Spark plugs are also next on the to-do. Drove for a while with blown intake gaskets, and can only imagine my plugs are begging to be changed. Which could also, in theory, smooth out the acceleration in the low rpm ranges.

 

[Fless]

Has the MAF been cleaned?

 

[Jonesy92]

That has not been done. But. I did install K&N 4” intake kit, (without shield, but intend to put together one that will fit a little more to the truck).
Which means that the MAF was removed, and installed, but I was careful. Maybe not careful enough. After the intake install, I did a smoke test (best tool I’ve gotten so far at harbor freight!), and had now signs of leaking through the intake, tube, post MAF.
No experience in the MAF cleaning area. Simple pull off, spray around, not directly? Air dry? Figured my TB could probably use a nice cleaning also. Would you happen to know if the TB is just the simple 4bolts?

 

[Rocket Man]

Make sure to use MAF cleaner only and follow the directions. For the TB, use TB cleaner specifically also. You can do it without removing it. There’s several threads and YT videos on it.

 

[Jonesy92]

Awesome. I’ll do these, and report back.

 

[Fless]

Non-OE intakes and filters can dirty the MAF, more than the OE setup.

 

[Jonesy92]

As expected. I have not however, tested fuel pressure on the rail. My Original starter from 03 just went out this year. Completely rusted through, you could see the internals. Hell of a starter.
I am waiting on my pressure gauge to arrive.
Hopefully that MAF cleaning along with the TB will clear it up.

 

[OR VietVet]

When you check the fuel pressure, with the new gauge, I always like to have the longer line on it that allows you to bring out the back of the hood and tape to w/s to watch. Hopefully the MAF clean and TB clean will fix it.

I did replace my throttle body recently, just because. I still was not happy with the throttle response very slight lag. Ran fine but I am picky. I replaced this Accelerator Pedal Position Sensor and the lag is gone.

Without adjustable pedals: https://www.rockauto.com/en/moreinf...7DAc0taQ9e4s0mXPjcSUQdEJCYoqDprnPGgTpJBtagmDk

With adjustable pedals: https://www.rockauto.com/en/moreinf...7DAc0taQ9e4s0mXPjcSUQdEJCYoqDprnPGgTpJBtagmDk

 

[PNWYukon]

When you check the fuel pressure, with the new gauge, I always like to have the longer line on it that allows you to bring out the back of the hood and tape to w/s to watch. Hopefully the MAF clean and TB clean will fix it.

I did replace my throttle body recently, just because. I still was not happy with the throttle response very slight lag. Ran fine but I am picky. I replaced this Accelerator Pedal Position Sensor and the lag is gone.

In retrospect, do you think the problem was only the APP sensor?

 

[OR VietVet]

Very well could have been that but this was during the time that I was replacing parts, right and left, just so I could get my rig to as close as possible to completely dependable and I had no CEL. My tech friend, at the shop that I was doing most of the work at, suggested the APPS and that was an easy fix that did work. I was gonna replace the throttle body anyway, even if I did the APPS first and the lag went away.

 

[Jonesy92]

Reporting back today. Maf and
TB have been cleaned, tediously. Runs great now. But on cold start, under 40*, instantly kicks into REP mode. Clear the code(which is 4 codes. Bank 1 lean 3 times, and manufacture control malfunction). Started it today, and got Bank 1 lean 4 times. The same code repeated. I’ve checked fuel trim on both long and short term, and they’re in range with specs from GM. Any ideas?
I did also finally get the correct fuel pressure rail gauge, and have 53pounds at key on, and 56/55 at idle. Hard acceleration shows 64/65 pounds.

 

[Jonesy92]

If I remember correctly back when I bought this truck, I had a code for that. Something about accelerator pedal performance? I guess I’ll look into the APPS

 

[Fless]

Fuel pressure seems high when running. I think these like to run in the low 40s -- 43, 44 or so. Fuel pressure that's too high can cause issues, maybe not these, but...

KOEO specs for NBS V8 engines:
Non-Flex: 55 to 62 psi
Flex: 48 to 54 psi

 

[Jonesy92]

I would figure that specs would give or take a few psi into the mix given where it’s driven, etc. would that be correct?