HELP Code PO300
Thread Starter
Cruising
Joined: Jun 2016
Posts: 11
Likes: 0
HELP Code PO300
I have a 2003 coupe automatic with 9997 miles. I've have had no problems with the car but we went out to dinner and pulled into parking spot and it stumbled (never had this before). It set diagnostic code PO300 and now continuously miss fires on #8 cylinder I cleared the code and it still miss fires and it resets code PO300. I checked each cylinder spark with a clamp-on timing light and I get no light on #8 but all other cylinders firing OK. I traded ignition coils #8 and #4 and still no spark on #8 but #4 is OK. I checked fuel rail pressure 59 psi. I checked ohms on injectors and got 14.2. I pulled spark plug and plug wires and they are OK.
Any suggestions will be helpful.
Any suggestions will be helpful.
Pro
Joined: Feb 2006
Posts: 718
Likes: 7
From: Jacksonville , NC
I have a 2003 coupe automatic with 9997 miles. I've have had no problems with the car but we went out to dinner and pulled into parking spot and it stumbled (never had this before). It set diagnostic code PO300 and now continuously miss fires on #8 cylinder I cleared the code and it still miss fires and it resets code PO300. I checked each cylinder spark with a clamp-on timing light and I get no light on #8 but all other cylinders firing OK. I traded ignition coils #8 and #4 and still no spark on #8 but #4 is OK. I checked fuel rail pressure 59 psi. I checked ohms on injectors and got 14.2. I pulled spark plug and plug wires and they are OK.
Any suggestions will be helpful.
Any suggestions will be helpful.
Only thing left is to swap plug wires and plugs
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
If the other cylinders are firing, it cant be a CRANK SENSOR.
Here is a schematic for the coil. You need to check coil POWER, Ground, signal hi and low. Don't guess,,,, Use a METER!
Also examine the connectors for the coil harness and the bank connector on the coil mount bracket. Look for damaged wires, female wire connectors ect. The harness that runs down the drivers side of the engine bends around a metal bracket. Look at that area for damaged wires/harness!
Here is a schematic for the coil. You need to check coil POWER, Ground, signal hi and low. Don't guess,,,, Use a METER!
Also examine the connectors for the coil harness and the bank connector on the coil mount bracket. Look for damaged wires, female wire connectors ect. The harness that runs down the drivers side of the engine bends around a metal bracket. Look at that area for damaged wires/harness!
Last edited by Bill Curlee; Jun 22, 2016 at 02:51 PM.
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Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Signal HI is the IGNITION CONTROLLED signal from the PCM that actually FIRES the coil! ... IF,,,,,,,,,,,,,,,, you have access to an old POINTS DWELL METER, you can actually read that signal! Or you can use an O Scope!
Just compare the readings from a known good working cylinder to #8 and the FAULT should jump right out!
NOTE! The ignition circuit wires are know to have damaged insulation!
Bill
Just compare the readings from a known good working cylinder to #8 and the FAULT should jump right out!
NOTE! The ignition circuit wires are know to have damaged insulation!
Bill
Melting Slicks
Joined: Nov 2014
Posts: 3,399
Likes: 1,339
From: Havre de Grace Maryland
[QUOTE=73Corvette;1592478648]I never knew anything about a crank sensor until my wife's 2004 Murano just quick running while she was driving. Luckily she was in the Right lane was able to pull over. After the car was dropped off by the tow truck to the repair shop, it started. The repair shop tried to get the car to duplicate the problem for 2 days. No luck. The internet suggested fuel pump OR crank sensor as a cause. But there were no hard codes posted by the computer. I decided on replacing the sensor ($250) vs the fuel pump ($1200). After 6 weeks of driving no repeat. So far so good.
Thread Starter
Cruising
Joined: Jun 2016
Posts: 11
Likes: 0
HELP Code PO300
[QUOTE=rrwirsi;1592479528]
I never knew anything about a crank sensor until my wife's 2004 Murano just quick running while she was driving. Luckily she was in the Right lane was able to pull over. After the car was dropped off by the tow truck to the repair shop, it started. The repair shop tried to get the car to duplicate the problem for 2 days. No luck. The internet suggested fuel pump OR crank sensor as a cause. But there were no hard codes posted by the computer. I decided on replacing the sensor ($250) vs the fuel pump ($1200). After 6 weeks of driving no repeat. So far so good.
The car always starts and continues to rum but misses on cyl #8 so I don't think it would be a crank sensor or it wouldn't start. Thanks
I never knew anything about a crank sensor until my wife's 2004 Murano just quick running while she was driving. Luckily she was in the Right lane was able to pull over. After the car was dropped off by the tow truck to the repair shop, it started. The repair shop tried to get the car to duplicate the problem for 2 days. No luck. The internet suggested fuel pump OR crank sensor as a cause. But there were no hard codes posted by the computer. I decided on replacing the sensor ($250) vs the fuel pump ($1200). After 6 weeks of driving no repeat. So far so good.
Thread Starter
Cruising
Joined: Jun 2016
Posts: 11
Likes: 0
HELP Code PO300
Signal HI is the IGNITION CONTROLLED signal from the PCM that actually FIRES the coil! ... IF,,,,,,,,,,,,,,,, you have access to an old POINTS DWELL METER, you can actually read that signal! Or you can use an O Scope!
Just compare the readings from a known good working cylinder to #8 and the FAULT should jump right out!
NOTE! The ignition circuit wires are know to have damaged insulation!
Bill
Just compare the readings from a known good working cylinder to #8 and the FAULT should jump right out!
NOTE! The ignition circuit wires are know to have damaged insulation!
Bill
Thread Starter
Cruising
Joined: Jun 2016
Posts: 11
Likes: 0
HELP Code PO300
Signal HI is the IGNITION CONTROLLED signal from the PCM that actually FIRES the coil! ... IF,,,,,,,,,,,,,,,, you have access to an old POINTS DWELL METER, you can actually read that signal! Or you can use an O Scope!
Just compare the readings from a known good working cylinder to #8 and the FAULT should jump right out!
NOTE! The ignition circuit wires are know to have damaged insulation!
Bill
Just compare the readings from a known good working cylinder to #8 and the FAULT should jump right out!
NOTE! The ignition circuit wires are know to have damaged insulation!
Bill
Last edited by Dave4Vettes; Jun 22, 2016 at 08:13 PM.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Just curious if you swapped out the #8 plug as well as the wire? Know someone who had a misfire issue with relatively new plugs and it turned out to be the plug in the end even though when he looked at it he couldn't see an issue. If you haven't done it, might swap #8 and #6 and see if the miss follows the plug.
Thread Starter
Cruising
Joined: Jun 2016
Posts: 11
Likes: 0
Well thanks to all who helped. I had removed the plugs and wires but when I installed the I reversed the wire but not the plug so to not make too many changes all at once but at your insistence I did go back today and switch and behold the miss moved. So a new plug later all is well. I all my many years I've had weak plug, ignition, etc. foul a plug but never one that wouldn't fire the timing light. Thanks again.
