LBZ: Engine Knocking

[dsauka]

Just bought truck and haven't even gone thru a tank of diesel yet. I came up this hill and thought I'd floor it just to feel the power. Then all of the sudden a large knock developed in the engine. Knocks at idle and during accleration. The only time it doesn't knock is when you coast down hill (no gas).

I thought it was something major like a spun bearing in the engine so I did and oil change and took the filter apart but saw no sign of metal bits.

I'm thinking maybe an injector stuck open but no white smoke? Would an injector stuck closed make a knocking sound? What else can I check?

 

[RENODMAX]

Compression test, balance rates. Also change your fuel filter if compression is ok. Do you have white smoke out of the oil fill neck?

 

[dsauka]

fuel filter already changed. I'll check for white smoke out of filler neck.

 

[MACKIN]

Might be the opposite stuck close or part way stuck. Check balance rates

Mine knocked like crazy on the plus side! If it was stuck open besides white smoke you could possibly have fuel in your oil,do a wick test,and possibly heading towards a hydrolock if you keep driving amongst other things.

 

[dsauka]

fuel filter already changed. I'll check for white smoke out of filler neck.

No white smoke out the filler neck.

 

[MACKIN]

Did you check your balance rates yet?

 

[LWATSON]

Make sure you balancer isn't wobbling.

 

[redws6rocket]

Check your fuel to see if it has water in it

 

[JD4440]

Watch to see if the harmonic balancer is wobbling like Watson said

 

[dsauka]

Well I took it to a diesel speciality shop and they checked the balance rates. They told me it should be +-1 for normal balance rates. From what I read it's +-4. Anyway, they told me all my injectors need replacing. The worst one was at 4.1 on plus side. Would a 4.1 really be bad enough to produce that aweful knocking sound? Well they said they would have the truck back to me tomorrow. If it does solve the knocking issue then I guess they are right. But, if they just replaced all the injectors ($5400 bucks) and it still knocks then I"ll have to refuse to pay because I ask them to investigate the source of the knock and they said it was the injectors.

I'm just stumped as just a hair out of spec (if I"m right on the +-4) it would produce such a bad knock.

 

[dsauka]

My balance rates

 

[LWATSON]

I'm sure someone that knows better than me will chime in, but is it + or - 4. or .4 that is acceptable? I was thinking it was .4 but im just guessing.

 

[x MadMAX DIESEL]

You should have takin it somewhere else. They are dead wrong, those are perfectly acceptable balance rates. Sorry

 

[LWATSON]

The more I think about it I'm pretty sure its + or - 4.0, so your balance rates arent terrible.

 

[LWATSON]

MadMax treed me.

 

[Bako_Dmax]

I just had something very similar happen to my LBZ yesterday, except mine sounded like an exhaust leak. Could barely hear it at idle but under a load it was very load, coasting didnt make a sound. After hrs of checking exhaust, up pipes turbos etc it turned out to be my number 8 injector hold down bolt had come loose allowing air to blow past it.. Anyways I tightened it down and the knock went away... Something to check :thumb:

 

[dsauka]

mine is pretty loud even at idle...especially when the engine is cold.

I just feel bad replacing all the injectors if they didn't need it.

 

[Sledhead]

I just feel bad replacing all the injectors if they didn't need it.

The shop should be feeling bad, get your argument for reimbursement together;

Bad diagnosis
Better Business Bureau
LBZ's are not notorious for injectors
$5400 is way too much for LBZ injectors IMO
you may still have a serious $$$ problem

Just trying to help a fellow BC'er :hug:

Keep us updated.

 

[dsauka]

Well they told me that the parameters for the injectors are -+1.0 They sent me an e-mail stating that. If the parameters are really 4.0 then they screwed me over. I'm going to ask for documentation stating the +-1.0 before I pay. I wish I could fine documentation showing the -+4.0 but I can only find it on forum talk.

 

[BHoward6.6]

Fuel Injector Balance Test with Tech 2 (Automatic Transmission)FUEL INJECTOR BALANCE TEST WITH TECH 2 (AUTOMATIC TRANSMISSION)

DIAGNOSTIC FAULT INFORMATION


CIRCUIT/SYSTEM DESCRIPTION
The fuel injector balance test is performed when a misfire, knock, excessive smoke, or rough running condition exists with no electrical DTCs. This test uses the Balance Rate and Cylinder Power Balance test to identify cylinders that are not producing the designed power output. The balance rate adjustments are utilized by the engine control module (ECM) only at idle. The balance rates are the fuel adjustments for each individual cylinder based on the variations in engine crankshaft speed. The balance rates will change depending on if the transmission is in Neutral or Drive. During the Cylinder Power Balance portion of the test, the ECM turns OFF individual injectors while the engine is running. The ECM adjusts for the drop in engine RPM during cancellation and may not change on the scan tool display. The lack of power at the cancelled cylinder will feel like a misfiring cylinder or vibration. If a fuel injector is turned OFF and there is a no difference felt when compared to the other cylinders, that cylinder is identified with the concern. If the customer concern occurs during idle or during off-idle tip in acceleration, the balance rates are used to identify the cylinder with a fault related to the fuel injector or engine compression.

DIAGNOSTIC AIDS

• The Cylinder Power Balance Test may be performed at any engine speed or load from idle to wide open throttle (WOT). There is a 5-minute time limit for each test.

CIRCUIT/SYSTEM VERIFICATION
Observe the Balancing Rate parameters with a scan tool. Normal reading should be between +4 cu.mm and -4 cu.mm in Neutral or Park and between +6 cu.mm and - 6 cu.mm in drive. With the engine running at idle the Actual Pressure should be close to the Desired Fuel Rail Pressure.

CIRCUIT/SYSTEM TESTING

IMPORTANT: If any DTCs other than DTC P0300-P0308 are set, refer to Diagnostic Trouble Code (DTC)

1. Start and run the engine until the engine coolant temperature (ECT) is more than 82°C (180°F) .
2. Turn OFF all accessories.
3. Perform the fuel pressure regulator test, refer to Fuel Pressure Regulator Diagnosis.

• • If the fuel pressure regulator graph was not normal, replace the fuel pressure regulator.

1. Apply the parking brake and place the transmission in Drive.
2. Hold the brake pedal in the fully applied position. A hiss will be noticeable when the brake is fully applied.
3. Idle the engine for more than 30 seconds .
4. Observe the Balancing Rate parameters with a scan tool and record the values for Cylinders 1-8.
5. Repeat steps 4-7 with the transmission in Neutral.

• • Balance Rates should be between +4 cu.mm and -4 cu.mm in Neutral or Park and between +6 cu.mm and -6 cu.mm in Drive. Perform the Cylinder Power Balance Test in Special Functions if not within the specifications.

1. Record any cylinders that indicate a different cylinder power contribution and compare the Balance Rates previously recorded with the Cylinder Power Balance results.

• • If the Balance Rates were not high or the Cylinder Power Balance test did not indicated a cylinder with a different power contribution, refer to Diagnostic Aids.

1. Perform the engine compression test. Refer to Engine Compression Test.

• • If the compression test indicated any of the cylinder had low compression, refer to Symptoms - Engine.

1. If the engine did not have low compression on any of the cylinders, replace the fuel injectors on the cylinders that had poor cylinder power contribution, high balance rates, or a noise/smoke change during cancellation.

IMPORTANT:

• Failure to correctly identify the cylinder positions may result in the replacement of the wrong fuel injector.
• During replacement of the injectors, inspect the inlet and outlet fittings for corrosion or contamination. Refer to Contaminants-in-Fuel Diagnosis.

1. Operate the vehicle under the conditions in which the concern occurred.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• Fuel Pressure Regulator Replacement
• Fuel Injector Replacement (Left) Fuel Injector Replacement (Right)