Throttle by cable calibration basics

[RDF1]

I agree with Caudle, Fuel pressure gauge with a cold start, hot start and the intermediate temp starts.
Just cause the pump is new doesnt mean its good.

[weinerschizel]

I really hope isn't the check ball but think I can verify that when I get the pressure gauge. I was VERY careful to clean the tank as best as humanly possible. I used dish soap and foamed it up then ran water through it for a good 30 minutes. Then I went back through and got ALL the water out and lastly dried as best as humanly possible with clean microfiber towels and lastly let it set till completely dry.

Do you know of the tables for the tune? I've looked through a bunch but don't recall a cranking table that includes time since last run.

[TheMechanic]

I have replaced countless fuel pressure regulators for a ruptured diaphragm. Easy diag. Idle and disconnect fuel pressure regulator vac line. Wait for up to 30 seconds. If ANY fuel comes out it is bad.
Next as someone mentioned hook up a fuel pressure gauge. Ignition on will give full fuel pressure. It should hold that pressure. If it declines....
3

Important: Before you proceed with this diagnostic, inspect the fuel system for damage and for external leaks.

Turn OFF the ignition.
Turn OFF all accessories.
Caution: Wrap a shop towel around the fuel pressure connection in order to reduce the risk of fire and personal injury. The towel will absorb any fuel leakage that occurs during the connection of the fuel pressure gauge. Place the towel in an approved container when the connection of the fuel pressure gauge is complete.

Install the J 34730-1A Fuel Pressure Gauge.
Place the bleed house from the fuel pressure gauge into an approved gasoline container.
Turn ON the ignition, with the engine OFF.
Command the fuel pump ON with a scan tool.
Bleed the air from the fuel pressure gauge.
Important:

You may need to command the fuel pump ON several times, in order to obtain the highest possible fuel pressure.
Do NOT start the engine.
Command the fuel pump ON with a scan tool, and observe the fuel pressure gauge.
Is the fuel pressure within the specified value?

385?425 kPa

(55?62 psi) VIN: (V, T,U)

335?375 (48?54 psi) VIN: Z


Important: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize, then remain constant.

Monitor the fuel pressure gauge for 1 minute.

Does the fuel pressure drop more than the specified value?

34 kPa

(5 psi)


Relieve the fuel pressure to the first specified value.
Monitor the fuel pressure gauge for 1 minute.
Does the fuel pressure drop more than the second specified value?

69 kPa

(10 psi)

14 kPa

(2 psi)


Turn OFF the ignition for 15 seconds.
Turn ON the ignition, with the engine OFF.
Monitor the fuel pressure gauge.
Start the engine.
Does the fuel pressure drop the specified value when the engine is started?

21?69 kPa

(3?10 psi)

[weinerschizel]

Thanks @TheMechanic! I'm convinced is a fueling issue of some kind. Don't really know of anywhere in the Tune that would address such symptoms.

I suspect the injectors, or something on the rail. Pressure regulator was on my list of items to check but as I've not fiddled with injection fuel system in a good 15 years, your tips are greatly appreciated! I'll test the fuel pressure regulator as you mentioned.

[weinerschizel]

I performed the quick test for the pressure regulator. It passed.

Idled engine w/ vacuum line disconnected from it for a minute. No gas cam out of the pressure regulator vacuum port.

However, before testing the pressure regulator I pulled the intake off. Truck hadn't been started in two days. I opened the throttle blade and ran my finger in the intake. It's full of moist soot. Smells like gas too... I need to raise the injector rail, pressurize the injectors and see if any leak.

Still waiting on the pressure tester to arrive in the mail.

[weinerschizel]

I maybe onto something...

I lifted the rail and pressurized the system. Then I watched the injectors for drips. No drips. Nothing pooling on the top of the engine...

However, I ran my finger under each injector. EVERY single one was damp. Not sure if that's normal... I could wipe the injector, then do it again a few seconds later and would be damp again. I wonder if these injectors aren't closing all the way.

Video HERE

[Alvin]

That can definitely cause hard starts.

[DougO]

I'm having the same issue as you are. I've replaced the following.
1 New fuel pump
2 new OEM regulator
3 New gm flex injectors
4 new OEM TPS and IAC did the reset
Next is the OEM crank sensor

[weinerschizel]

Thanks @Alvin. Yeah, I'm looking for new injectors. I'd like to find some of the 8.1L injectors but may spring for a used OEM set to save a few $$ until I can get around to fully tuning my setup.

@DougO good luck with your diagnosis. I went down the crank / cam sensor route. Was VERY skeptical they would be issue at all. Especially the crank sensor. I have a new crank sensor here but never bothered installing it. I will at some point. Let us know what you find out.

[DougO]

I'll be putting it in this weekend and I'll report back, I'm leaning towards some tune issue.

[TheMechanic]

I maybe onto something...

I lifted the rail and pressurized the system. Then I watched the injectors for drips. No drips. Nothing pooling on the top of the engine...

However, I ran my finger under each injector. EVERY single one was damp. Not sure if that's normal... I could wipe the injector, then do it again a few seconds later and would be damp again. I wonder if these injectors aren't closing all the way.

Video HERE

Did you perform the KOEO fuel pressure? Did the pressure hold?
Slight oily residue on inside of throttle body is from the PCV system. Lots of hard driving can cause it when blowby starts to overcome the ability of the PCV valve to pull in crankcase vapors so those vapors are routed to the fresh air hose in front of the TB and behind the MAF. If it is excessive a check of the PCV for deposits and make sure you are running FULL synthetic motor oil and you should be good to go. Check the fresh air hose for accumulated oil also.