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Bucking and jerking, acting like it Either won't shift or it…

Customer Question
Bucking and jerking, acting...

Bucking and jerking, acting like it Either won't shift or it is not firing on all cylinders

Mechanic's Assistant: What is the make/model/year of your car?

Sorry, 2008 Chevy Equinox

Mechanic's Assistant: Are you fixing your Equinox yourself? What have you tried so far?

It has had a complete tune up, 2 new coil packs, oil changes on schedule

Mechanic's Assistant: When was your last oil change?

1000 miles ago. I still have 75% oil life left

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

One code keeps coming back with multimisfirings and another with general Exhaust system leak

Submitted: 8 months ago.Category: Chevy
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Answered in 3 hours by:
11/11/2017
Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago
Peter Bagley
Peter Bagley, Auto Service Technician
Category: Chevy
Satisfied Customers: 1,292
Experience: master tech
Verified

Hello and welcome to just answer, my name is ***** ***** master tech here to help. I cannot see or hear your vehicle so I rely on your patience and input to my questions so I can help you better.I have read your notes and have a question before we proceed.

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

Could you please forward any codes you have so we can proceed?

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Customer reply replied 8 months ago
The codes are 0488 and 02300? I know the former is correct, I know the latter said multiple misfiring, but was not specific about any one particular spark plug, just the coil pack which we have had replaced and it ran with out bucking for I week. When I had the time up, it ran without bucking for about 3 weeks. When the coil pack was replaced, we also changed spark plug number 1.
Customer reply replied 8 months ago
Tune up
Customer reply replied 8 months ago
I might add that it is a V-6 and ask who was the hair-brained engineer that designed the transmission dipstick where a layman can’t get to it to check it?
Customer reply replied 8 months ago
Sorry. I had the codes wrong. The 0488 was exhaust leak and the 2300 was the multiple misfirings.
Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

Thanx for that info, unfortunately I will be out this evening but can get back tomorrow morning with some further help if that's ok. If not I can opt out so another may help you faster or you can wait till then?

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

thank you for your patience, till then.

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Customer reply replied 8 months ago
It will not start now at all. I have juice, since the lights work, but when the key is turned the doors click and the ignition clicks and nothing happens.
Customer reply replied 8 months ago
Sorry.codes were p0300 and p0466
Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

Thanx for clarifying that for me . In the process of helping you I will use info sources from many different places , such as shop manuals , internet links and my personal experiences as I see fit to give you a fast and clear process to solve your issues. In doing so you may interact with questions and requests to clarify things on your end . So with that being said , lets start.

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

P0300 CHEVROLET - Cylinder Misfire Detected Random Cylinders;

Possible causes; Faulty spark plug (s) Faulty ignition coil (s) Clogged or faulty fuel injector (s) Intake air leak Fuel injectors harness is open or shorted Fuel Injectors circuit poor electrical connection Ignition coils harness is open or shorted Ignition coils circuit poor electrical connection Insufficient cylinders compression Incorrect fuel pressure

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

The P0300 code means that a cylinder(s) is misfiring or is randomly misfiring. Start by checking for intake leaks, intake gaskets are commonly caused of multi-cylinder misfiring. If no leak is found the next step is to replace the spark plugs. If the problem persists more tests needs to be done to diagnose the problem.

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

So as you see it is more of a miss rather then any transmission problem so you can breath easy . If you wish me to walk you through any test proceedures you need to do let me know. Now for the code p0466.

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

What Does P0446 Code Mean? OBD-II Code P0446 is defined as a Evaporative System Vent Control Circuit Malfunction

The evaporative control (EVAP) system captures any raw fuel evaporating from the fuel storage system (e.g. the fuel tank, filler neck, and fuel cap). Under precise operating conditions—dictated by engine temperature, speed, and load—the EVAP system stores and purges these captured fuel vapors back into the combustion process. The carbon canister, which stores the raw fuel vapors, utilizes a vent valve that allows fresh air to enter the EVAP system. This displaces the fuel vapor as it's purged into the combustion process. Common Problems That Trigger the P0446 Code;

  • Missing fuel cap
  • Defective Evaporative Vent Valve
  • Defective or damaged fuel cap
  • Distorted, damaged or cracked Fuel Tank Filler Neck
  • Torn or punctured Evaporative system hose(s)
  • Defective Fuel Tank Sending Unit gasket or seal
  • Split or damaged Carbon Canister
  • Defective or damaged fuel tank
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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

Want to Learn More?

The EVAP system is designed not only to capture, store, and purge any raw fuel vapors that leak from areas in the Fuel Storage system, but also to run a series of self-tests that confirm or deny the operational and vapor holding ability of the system. This is an important task because at least 20 percent of vehicle-produced air pollution originates from malfunctioning Vehicle Fuel Storage systems.

There are many ways to "leak test" the EVAP system, but most perform the leak test when the vehicle is sitting (like over night) or during the initial start-up after the vehicle has been sitting over night. The EVAP system's operational performance is also tracked by the Powertrain Computer by reading the change in the oxygen sensor voltages and short term fuel trim whenever the stored vapors are released or "purged" back into the combustion process. These values should indicate that fuel is being added to the system and that the overall mixture is getting richer. The purging process occurs when the vehicle is under acceleration, which is when most vehicles require additional fuel.

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

P0446 Diagnostic Theory for Shops and Technicians

Some PCMs will trigger this code if the the proper level of vacuum was not reached during a leak test and the EVAP system contains a bypass valve that isolates the fuel tank from the carbon canister-vent valve assembly. This vacuum is measured and monitored by the Fuel Tank Pressure Sensor. The vacuum can be too high and for too long (stuck closed vent valve) or it can be too little or non-existent ( stuck open vent valve, a leak in the system or a defective fuel tank pressure sensor).

Here is how the evaporative leak test is performed by the Powertrain Computer:

  1. When the leak test is performed, the vehicle must have been sitting for at least four to eight hours so that the engine temperature and outside air temperature are identical. There must also be between 15 and 85 percent fuel in the tank—this is to provide a baseline for the test since gasoline and diesel are volatile fluids that expand and vaporize easily with warm temperatures.
  2. When the leak test initiates, the Vapor Canister Vent Valve is closed to prevent any fresh air from entering the EVAP system.
  3. The Purge Valve is opened, which allows the engine to create a vacuum in the EVAP system.
  4. After a specified time interval—usually about ten seconds—the Purge Valve is shut off and the vacuum level in the system is measured by the Fuel Tank Pressure Sensor.
  5. Finally, a countdown initiates, which measures the rate at which the vacuum decays in the system. If the vacuum decays much faster than the specified rate or if no amount of vacuum is reached on two consecutive tests, then the Power-train Computer will fail the EVAP system and trigger a P0446 code.
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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

Common Tests for the Evaporative System

  • Retrieve the code and write down the freeze frame information to be used as a baseline to test and verify any repair.
  • Perform a careful and close visual inspection of all accessible hoses and components in the EVAP system for any signs of damage or degradation.
  • Using a scan tool, pay very close attention to the Fuel Tank Pressure readings. Does the Fuel Tank Pressure Sensor work properly? If it doesn't, the system will think that no pressure or vacuum is being created when the EVAP monitor is performed when, in fact, there is a pressure/vacuum being created that Fuel Tank Pressure Sensor is unable to read. The Fuel Tank Pressure Sensor is the primary feedback sensor that the Powertrain Computer relies on for the leak test data each time the EVAP monitor is run.
  • Inspect and test the fuel cap to determine how well it fits onto the Fuel Tank Filler Neck. Make sure the Fuel Cap Seal isn’t dry or cracked. If the cap will not seal or hold vacuum/pressure, then it can trigger the P0440 code.
  • Verify that the Purge Valve and the Vent Valve work properly and hold vacuum for a sustained amount of time—at least thirty to sixty seconds. If either one of these valves function improperly, the system will not develop and/or hold the proper amount of vacuum.
  • If all the components seem to function properly, then perform another smoke test of the entire EVAP system. This will usually root out any leaks that are hidden behind and/or under components of the vehicle. Pay close attention to the Fuel Tank Filler Neck, the Carbon Canister, and the Fuel Tank itself, especially where the Fuel Pump and Fuel Level Sending unit are located and sealed. Occasionally when a Fuel Pump is replaced, the seal isn't replaced or properly installed. This can cause small leaks in the system. You might have to remove the rear seats to further inspect and pinpoint the source of a Fuel Tank leak.
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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

I hope I m not overwhelming you with all this info as that is not my intentions, but to give you all the info available around this issue so you can better understand it.

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Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

I myself like to keep things simple and attack involved problems one step at a time and I;m sure you do too, It is quite possible both these codes are related as a vacuum leak! So as you stated you just had a complete tune up correct? Question--- did this just happen right after the tune up?

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Customer reply replied 8 months ago
No it did not happen after the tuneup it was intermittently him happening for months before that also yesterday I replace the battery as it wouldn’t even start could that be the ignition coil also when I drive I hear something like water under the hood of the engine or what sounds like the hood directly in front of me it’s either that or it is a lot of sparking going on what do you think Also the code was 0466 sorry about the confusion
Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

Easy way to think if you have sparking going on the engine get a spray bottle of water and start you vehicle at night, let it idle and spray a fine mist all over the wires and coils. If there is arcing or sparking it will light up like a Christmas tree and you will see where it is coming from. Let me know what you find. Also if you think you hear whater gurgling, take the rad cap off top coolant up to the top of the rad and run to operating temp and look for bubbles

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Customer reply replied 8 months ago
Will do this tonight and get back to you
Chevy Mechanic: Peter Bagley, Auto Service Technician replied 8 months ago

will check back on your notes

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