Testing Throttle Position Sensor (2005) - UPDATED (Injector?)

[nick0789]

2005 Tahoe, 5.3, gas, ~223k miles.

I’ve noticed recently (who knows how long it’s been going on) that when leaving for my daily commute that when pulling out of my neighborhood (wheel turned) that when I press the accelerator there’s usually a latent period between me pressing and the engine / transmission responding. It’s almost like I press the pedal, the engine hesitates just a hair. It doesn’t bog down or give indication that the transmission may be slipping, it just needs a second to realize what I’m telling it to do.

If I go easy on the pedal, I don’t really notice it.

Browsing around on the forum I’ve found the following usual suspects:

1. Fuel pump
2. TPS
3. Torque converter
(I may be missing more)

I have a bidirectional scan tool so I can read live data but I’m not really sure what I should be looking for from a data collection standpoint.

For the TPS and fuel pump can someone provide some input as to what I should be looking for (visual cues on the plot, voltage readings, etc)?
I can go rent a fuel pressure gauge and test the rail in the parking lot no problem, though the sending unit is relatively new (OE; replaced a few years back).

Thanks!

 

[rockola1971]

Id check that fuel pressure first and if it is within spec I would be looking to clean that throttle body real good (taken off the engine).

 

[nick0789]

fuel pressure test results:

KOEO: 49-50 psi. Held steady for the 5ish minutes I had it on while I was doing other stuff in the garage

Running at idle: 59-60 psi. No noticeable drop or rise in pressure when pressing on the accelerator pedal (both slow, steady pressure as well as “foot to the floor”)


I know the KOEO pressure for the non-flex should read 55-62 psi based on my research but I’m not sure how much that applies here since my running pressure is steady.

I replaced the fuel pump back at the end of 2021 while replacing the EVAP lines (thanks to a blown canister). I had the tank out so I didn’t want to drop it again. The part number is MU1639 (GM OE). I’d like to think I could get more than 40-50k out of a pump but the pump “seems” to be fine.


I’ll still remove the throttle body (also replaced early 2022 when I did the intake manifold gaskets; GM OE part 12679525) and clean it up and see how it rides tomorrow morning.

 

[rockola1971]

fuel pressure test results:

KOEO: 49-50 psi. Held steady for the 5ish minutes I had it on while I was doing other stuff in the garage

Running at idle: 59-60 psi. No noticeable drop or rise in pressure when pressing on the accelerator pedal (both slow, steady pressure as well as “foot to the floor”)


I know the KOEO pressure for the non-flex should read 55-62 psi based on my research but I’m not sure how much that applies here since my running pressure is steady.

I replaced the fuel pump back at the end of 2021 while replacing the EVAP lines (thanks to a blown canister). I had the tank out so I didn’t want to drop it again. The part number is MU1639 (GM OE). I’d like to think I could get more than 40-50k out of a pump but the pump “seems” to be fine.


I’ll still remove the throttle body (also replaced early 2022 when I did the intake manifold gaskets; GM OE part 12679525) and clean it up and see how it rides tomorrow morning.

Have the fuel filter on the drivers side chassis? Has it ever been replaced?

 

[nick0789]

Have the fuel filter on the drivers side chassis? Has it ever been replaced?

The fuel filter is integrated into the sending unit for my model year. I may go out in a bit and see if I can read live fuel data on my scanner and report back.

I did go back and look at my most recent oil analysis and trace fuel amounts were detected in the oil. I had 0.8% (under the 2.0% threshold), though had none in my oil in the change prior to this analysis. The lab indicated that the amount was relatively common so I don't know that I am too concerned about that number at this time. I may still look at the injectors if I can't isolate anything elsewhere.

 

[nick0789]

went and checked some live readings on my lunch break. I did notice that at the midway hashmark on the temp gauge (between 160 and 210) I was getting a loud tick / knock. This is not my video but it sounded just like this:

It was raining and I didn’t have a screwdriver or my stethoscope to see where it was coming from but I went and drove around the parking lot and the noise was gone by the time I was at full operating temp. Checked resistances of injectors when I got home and got the following:

Passenger front to back (ohms): 13.8; 14.2; 14.3; 14.1

Driver front to back (ohms): 14.1; 14.1; 14.2; 13.8

All are within spec technically but if curious to see what everyone else thinks (spec is 11-14 ohms). I would imagine the two at 13.8 ohms are outliers but I’m not more than 0.5 ohms difference across the eight.


Other live data is as follows:

TPS: 3.6%
MAP: 11 inHg
MAF: 0.76 lb/min
STFT B1: - 1.6%
LTFT B1: - 0.8%
STFT B2: - 2.3%
LTFT B2: 0.0%

 

[Fless]

Sounds to me like a small exhaust leak on the passenger side in that video (I know, not yours).

 

[nick0789]

update:

Was sitting in the drive thru last night and was hearing this:

I gave it some throttle and it cleared up and the idle went back to normal. This morning I went out and started the tahoe and let it idle while I was trying to get some other things in the back. By the time the engine was at operating temp, the sound came back. Pulled out the stethoscope and listened to the injectors and they all sounded similar. Put the stethoscope up to the spark plug heat shields and heated the “knocking”(?) on cylinder #4. Pulled it out into the street and got some speed and the sound went away.


Is this leaning towards an injector issue or something else? I checked the plug and it looked similar to cylinder #2 in front of it. I also checked the wire and coil and was getting spark there. No codes.

I also hooked up the fuel pressure gauge and checked it several times. Sometimes the pressure would hold, on occasion it would drop right away. Figured it was from not tightening the fitting enough so I got it as tight as I was comfortable and tried one more time. I got this (don’t mind the water trickle sound, I was draining the catch can at the same time):

This was right after I took the key out of the ignition so it was already a couple PSI lower.


Other than an injector issue, is there a way to test the fuel pump itself. Again, mine is relatively new but I’ve seen new things break quickly.