97 Tahoe With P0300 Code

[cbaranski]

I'm new to this forum. Ok here is my situation. I got multible codes for misfireing. A good buddy who has the same truck but a year older. Told me that he had to replace the injection spider. So I did, I got the AC-Delco set up. got it all together and now I still have a P0300 code. I cant figure this out. I need some help.

[merlin5577]

I had this exact same problem on my Suburban. Stumped me for months! Turned out to be a sticking EGR valve. 30 minutes and a new valve, Problem solved. That would be the first thing I would check. Good luck. And welcome to the site.

[jrrod2004]

Welcome to the site, here are a few things that GM says that could throw that code...

 

 

 

Service Information

1997 Chevrolet Chevy C Pickup - 2WD | Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K) Service Manual | Document ID: 1765100 #02-06-05-004b: Info - Misfire DTCs P0300, P1380, P1381 and Catalytic Converter Damage Due to Installation of Alarm Systems - (Feb 14, 2006)

Subject:Misfire DTCs P0300, P1380, P1381 and Catalytic Converter Damage Due to Installation of Alarm Systems

 

 

Models:2006 and Prior GM Passenger Cars and Light Duty Trucks

 

 

2006 and Prior HUMMER H2, H3

 

 

2006 and Prior Isuzu Light Duty Trucks

 

 

This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 02-06-05-004A (Section 06 - Engine/Propulsion System).

 

General Motors Engineering, in an effort to determine the root cause of catalytic converter damage, has determined that aftermarket alarm systems incorrectly installed in vehicles have the potential to cause misfire codes and damage to the converter. These alarm systems use a circuit interrupt which utilizes the ignition circuit on the vehicles.

 

These alarm systems utilize mechanical relays and normal vehicle movement can trigger these relays to engage and disengage the ignition circuit while the vehicle is in motion. These disruptions of the ignition circuit, which occur in milliseconds, may cause more fuel to be commanded. Over time, this dumping of fuel on and off again can cause misfire codes and ultimately damage the converter assembly.

 

Important: Engineering could not identify any alarms that utilize solid state circuitry that would eliminate this concern. Because of this, it has been determined that all alarm systems must be routed through the starter circuit in order to avoid this condition.

 

Dealers must be aware of this issue and take note of the wiring on vehicles with alarm systems that come in for repair, particularly for catalytic converter damage that seem to have no known root cause.

 

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

 

 

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

 

 

© 2008 General Motors Corporation. All rights reserved.

[jrrod2004]

Service Information

 

1997 Chevrolet Chevy C Pickup - 2WD | Chevy Pickup, GMC Pickup, Suburban, Tahoe, Yukon (VIN C/K) Service Manual | Document ID: 65833 DTC P0300 Engine Misfire Detected

 

Circuit Description

The crankshaft position (CKP) sensor and the camshaft position (CMP) sensor are used in order to detect an engine misfire. The VCM monitors the speed of the crankshaft. The VCM detects a deceleration of the crankshaft that is not associated with a normal engine speed reduction. In order to determine if a misfire occurred, the VCM compares the deceleration information to the engine speed and the engine load. If a misfire event is determined, the VCM compares the crankshaft position to the cam sensor signal in order to determine which cylinder misfired. The VCM stores the information in separate accumulators for each cylinder. Upon completion (or failure) of the test, the VCM evaluates the number of misfires in each accumulator. If the accumulators are somewhat even or if 3 or more cylinders are misfiring, then this determines that a random misfire has occurred. The VCM also utilizes the input from the ABS wheel speed sensor in order to determine if a rough road condition exists which could cause a crankshaft acceleration and deceleration. If a rough road condition exists, the diagnostic will not run. This DTC is a type B DTC.

 

Conditions for Setting the DTC

 

• No TP sensor DTCs

 

 

• No MAF sensor DTCs

 

 

• No Crankshaft Position sensor DTCs

 

 

• No Camshaft Position sensor DTCs

 

 

• The ECT is greater than or equal to -7°C

 

 

• The engine speed between 600 RPM and 5600 RPM

 

 

• The system voltage between 9 volts and 14 volts

 

 

• The positive throttle position change is less than 4.9% for 100 msec.

 

 

• The negative throttle position change is less than 2.9% for 100 msec.

 

Action Taken When the DTC Sets

If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the malfunction indicator lamp (MIL) after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present.

 

Conditions for Clearing the MIL/DTC

The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

 

Diagnostic Aids

The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring.

 

Many different condition could cause an intermittent misfire.

 

Check for the following conditions:

 

 

1. Check the spark plug wires and the coil wire for the following conditions:

   • Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.

    

    

   • Check the wire routing in order to ensure that crossfiring is not occurring.

    

    

   • If the misfire occurs when the weather is damp, the problem could be due to worn plug wires.

    

    

   • In order to test for this condition, spray the wires with water and with the engine running, watch for spark to jump from the wires. If a spark is visible, replace the wires.

    

   
   

2. Check for contaminated and a low fuel level and the following conditions:

   • Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition.

    

    

   • If the fuel level is low, contaminants in the bottom of the fuel tank could enter into the fuel metering system.

    

   
   

 

[cbaranski]

My Tahoe cant even drive its so bad. At idle it has a miss, and then you put it in gear its totally undriveable. It pops a cuts out really bad.