Shaky Idle

[OB1214]

Hello all! Hope You are having a great day. I was hoping you guys could potentially help with a slight dilemma I have. I have a 1996 k3500 with a Vortec 454. Ever since I bought my truck back in August I've had a slight shake in my idle nothing serious just something that annoys me when I'm at a red light. It has never stalled on me when driving or taking off from a red light, and never had an issue starting when the motor is up to temp. Many of my sensors on the vehicle were shot since it was sitting for 5 years. The things I have changed include:
- New Injectors
- Fuel Pump Assembly
- Fuel Pressure Regulator
- Upper and Lower Intake Gaskets
- Fuel Filter
- MAP Sensor
- Idle Air Control Valve
- Temp senders
- Distributor
- Cap
- Rotor
- Ignition Control Module
- Coil
- 02 Sensors
- Exhaust Manifold Down Pipe Gaskets (Donuts)
- Oil Pressure Sender

I hooked a manual vacuum gauge on the intake and had 20 inHg.

I should also inform you guys that my long-term fuel trim is at 6-7% more fuel on bank 1, and 3-4% more fuel on bank 2. I think that these rough idle and the fuel trim are linked together, but I could be wrong.

I pulled the coil wire off, took the valve covers off, and cranked the motor to see if I had a rounded cam lobe. (I do not) and I also checked valve lash, everything checks out.

I don't know if this is an issue but I replaced my EVAP solenoid with a NAPA branded and it was quiet for a couple of weeks, and then it started to make a loud clicking sound heard from inside the cabin with windows rolled up. I swapped it out for another one, and same story. Quiet for a couple of weeks, and now it's clacking again.

Please let me know what you think, and any possible solutions.
Thank you,
OB1214

 

[Nick_R_23]

Do a compression test.

 

[Schurkey]

Connect a scan tool. Verify ALL sensors, and computer outputs. Check the misfire counters.

Verify fuel pressure.

 

[OB1214]

Do a compression test.

Connect a scan tool. Verify ALL sensors, and computer outputs. Check the misfire counters.

Verify fuel pressure.

I will verify fuel pressure tomorrow afternoon, I have that with me at school. Left my compression tester at home, ill see if the school maintenance garage will let me borrow theirs. I have an Autel AutoLink AL539B as well as an Autel MaxiLink ML629 with me at school. They both are capable of on-board monitor testing. However, I recall not being able to use them because of a CAN issue, or something of that nature. I'll verify this tomorrow, and keep you guys posted thank you for the help and input.
OB1214

 

[OB1214]

Using both Autel units for onboard monitor test. I receive the prompt that the selected mode is not supported. However, for my I/M readiness test which checks all systems, the MIS test was checked meaning no misfires. I hooked up my fuel pressure gauge and have the key on not running I had 55 psi. In park, at an idle, I have 47 psi and 2k 46.5psi. In gear, at an idle, I have 48 psi, power brake at 2k I had 54 psi. Still haven't had a chance to run a compression test.
OB1214

 

[Schurkey]

1. What is fuel pressure spec? Seems to me it's higher than what you're saying you have.

2. Is the gauge accurate? Easy for "diagnostic tools" to give false readings because they haven't been maintained or verified for accuracy. Then you chase your tail because the tool didn't give you correct info.

 

[OB1214]

Looked through the manual can couldn't get a definite answer on the spec but I looked through the forums and many said that the pressure should be 58 to 62 psi for a Vortec 454. The gauge is good used it on other vehicles and is within spec.
I took some pics from my scanner of all the live data today my truck was saying it was running +12.5% long term bank 1 and +7.8% long term bank 2.
Heres the rest of the data

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[Nick_R_23]

Fuel pressure isn’t going to cause shaky idle. That’s due to individual cylinders not performing combustion cycles like the others. This is most commonly caused by a misfire or low compression not allowing a complete fuel burn…which is most likely allowing fuel from an incomplete/inefficient burn to exit the cylinder and enter the exhaust and giving you false readings.

Since you‘ve already replaced just about every part possible, if you’re confident that your ignition system is working properly and using high quality components, at this point you should be performing a compression test to isolate the cylinder that’s operating out of sync from the rest and causing your shake. I‘ll bet you have a low cylinder due to a sticking/damaged valve or stuck rings - especially if this engine has been sitting for 5 years.

 

[OB1214]

Replaced every sensor on the vehicle with Delphi, Dorman, Delco. The ignition system consists of standard (wires and cap), standard blue streak (rotor), NAPA (Distributor, all they had in stock when my original one sh** the bed. and msd (coil).
Im at school at the moment and do not have my compression tester with me, and found a MAC tool compression tester deluxe CT115 for 44 dollars plus shipping. should be here next week. will keep you posted on what the compression is when I get my tester in the mail.

 

[stutaeng]

The bank one LT fuel trim seems a bit high. Ideally it should be less than 10%...but 2-3% is better.

Question: what happens to the fuel trims if you increase the RPM? Say at 1k, 2k, 3k RPM? Stay the same? Decrease?

Your static fuel pressure does seem low, but that would lead to a lean condition, and you have slightly rich condition...

Need more testing.

The EVAP purge solenoid could be stuck open, causing higher fuel trims. Find a way to temporarily plug it and see if there are any changes.