The horrible P0307 code! Need help
Thread Starter
Teching In
Joined: Jun 2017
Posts: 38
Likes: 4
The horrible P0307 code! Need help Gentlemen,
I have a 2004 express 3500 that is beating me. Is it throwing a P0307 code and sometimes a P0300. When the check engine comes on, it flashes as well. The misfire goes away and then random comes back every 2-20 miles. While it was misfiring I unplugged the connector to injector 7 and tested it with a light for power (no power). Then it randomly comes back. Also, this Chevy express only has 17k miles and probably sat. I purshased a few months ago.
1. I started with the simple silly’s and changed the plugs & wires (P0307 still there).
2. Then I changed cylinder 7’s coil, (still there).
3. Cleaned all grounds and added a large one to the back of the head. (P0307 still there)
4. Changed #7 injector, plus injector cleaner in the tank. (P0307 still there)
5. Changed the computer. (P0307 still there)
6. Checked for vacuum leaks using a can of carb cleaner. Sprayed down the entire intake manifold and had no change in idle.
7. Checked fuel pressure. 58 psi with ignition on, 60 psi while running.
if anyone has any ideas on what this might be, please let me know! I’m out of ideas... thinking about changing out the engine harness next!
I have a 2004 express 3500 that is beating me. Is it throwing a P0307 code and sometimes a P0300. When the check engine comes on, it flashes as well. The misfire goes away and then random comes back every 2-20 miles. While it was misfiring I unplugged the connector to injector 7 and tested it with a light for power (no power). Then it randomly comes back. Also, this Chevy express only has 17k miles and probably sat. I purshased a few months ago.
1. I started with the simple silly’s and changed the plugs & wires (P0307 still there).
2. Then I changed cylinder 7’s coil, (still there).
3. Cleaned all grounds and added a large one to the back of the head. (P0307 still there)
4. Changed #7 injector, plus injector cleaner in the tank. (P0307 still there)
5. Changed the computer. (P0307 still there)
6. Checked for vacuum leaks using a can of carb cleaner. Sprayed down the entire intake manifold and had no change in idle.
7. Checked fuel pressure. 58 psi with ignition on, 60 psi while running.
if anyone has any ideas on what this might be, please let me know! I’m out of ideas... thinking about changing out the engine harness next!
Last edited by FJ60; Nov 17, 2018 at 11:28 PM. Reason: Error
Thread Starter
Teching In
Joined: Jun 2017
Posts: 38
Likes: 4
Correct me if I’m wrong...
Could I steal power for injector 7 from injector 5? Just run a jumper wire and see if that works. That would rule out power...
The pcm controls the ground of each injector I think.. Pin 43 is injector 7: So if I run a new wire from pin 43, straight to injector 7 and steal power from injector 5... There would be no reason for it not to work?
Could I steal power for injector 7 from injector 5? Just run a jumper wire and see if that works. That would rule out power...
The pcm controls the ground of each injector I think.. Pin 43 is injector 7: So if I run a new wire from pin 43, straight to injector 7 and steal power from injector 5... There would be no reason for it not to work?
TECH Fanatic
Joined: Jun 2003
Posts: 1,869
Likes: 99
Obviously you have checked all of the causes or not. There are a slew of them.
Did you check the wiring and connection to the crankshaft position sensor or the sensor itself?
I don't think it would be a good idea to drive the coil other than the way mapped from the PCM. Then you might damage the driver in the PCM.
I just went thru the same issue on my 98 Z28. No issue until the engine was replaced with a new engine. Then it started. Not sure what actually fixed it because I did three things at the same time. 1) I changed the coil harness on the driver side and 2) disconnected and reconnected the jumbled mess the installer made when connecting the three wires to the ground bolt on back side of driver side head and 3) disconnected and reconnected each injector plug. Also when doing so, I applied a good dose of dielectric grease to each connection.
GM tech (30 years) said it most always is a ground or a pin or female end that isn't making a good connection with the main one being the culprit. You got the main one to check, one for each coil, and one for each injector. With the wiring getting old and brittle, the coil harness for me was probably the cause since it had been removed and then reconnected during the install. So for me it was probably a new coil harness probably that fixed the my issue. I replaced both sides since each was 20 years old.
BTW - each coil wire in the coil harness is color coded so you should be able to test each coil wire in the coil harness with a probe from the main white connector. It's in the white connector that a tang might be bent just a little.
1: purple
2: red/white
3: blue
4: dark green/white
5: dark green
6: light blue/white
7: red
8: purple/white
During the diagnosis I also used a temp gun to measure temp at each exhaust manifold exit. When # 7 wasn't getting either fuel or spark it was cold. That's easier, however, since I have headers.
Did you check the wiring and connection to the crankshaft position sensor or the sensor itself?
I don't think it would be a good idea to drive the coil other than the way mapped from the PCM. Then you might damage the driver in the PCM.
I just went thru the same issue on my 98 Z28. No issue until the engine was replaced with a new engine. Then it started. Not sure what actually fixed it because I did three things at the same time. 1) I changed the coil harness on the driver side and 2) disconnected and reconnected the jumbled mess the installer made when connecting the three wires to the ground bolt on back side of driver side head and 3) disconnected and reconnected each injector plug. Also when doing so, I applied a good dose of dielectric grease to each connection.
GM tech (30 years) said it most always is a ground or a pin or female end that isn't making a good connection with the main one being the culprit. You got the main one to check, one for each coil, and one for each injector. With the wiring getting old and brittle, the coil harness for me was probably the cause since it had been removed and then reconnected during the install. So for me it was probably a new coil harness probably that fixed the my issue. I replaced both sides since each was 20 years old.
BTW - each coil wire in the coil harness is color coded so you should be able to test each coil wire in the coil harness with a probe from the main white connector. It's in the white connector that a tang might be bent just a little.
1: purple
2: red/white
3: blue
4: dark green/white
5: dark green
6: light blue/white
7: red
8: purple/white
During the diagnosis I also used a temp gun to measure temp at each exhaust manifold exit. When # 7 wasn't getting either fuel or spark it was cold. That's easier, however, since I have headers.
Last edited by dlandsvZ28; Nov 18, 2018 at 10:27 AM. Reason: Add additional info
Gentlemen,
I have a 2004 express 3500 that is beating me. Is it throwing a P0307 code and sometimes a P0300. When the check engine comes on, it flashes as well. The misfire goes away and then random comes back every 2-20 miles. While it was misfiring I unplugged the connector to injector 7 and tested it with a light for power (no power). Then it randomly comes back. Also, this Chevy express only has 17k miles and probably sat. I purshased a few months ago.
1. I started with the simple silly’s and changed the plugs & wires (P0307 still there).
2. Then I changed cylinder 7’s coil, (still there).
3. Cleaned all grounds and added a large one to the back of the head. (P0307 still there)
4. Changed #7 injector, plus injector cleaner in the tank. (P0307 still there)
5. Changed the computer. (P0307 still there)
6. Checked for vacuum leaks using a can of carb cleaner. Sprayed down the entire intake manifold and had no change in idle.
7. Checked fuel pressure. 58 psi with ignition on, 60 psi while running.
if anyone has any ideas on what this might be, please let me know! I’m out of ideas... thinking about changing out the engine harness next!
I have a 2004 express 3500 that is beating me. Is it throwing a P0307 code and sometimes a P0300. When the check engine comes on, it flashes as well. The misfire goes away and then random comes back every 2-20 miles. While it was misfiring I unplugged the connector to injector 7 and tested it with a light for power (no power). Then it randomly comes back. Also, this Chevy express only has 17k miles and probably sat. I purshased a few months ago.
1. I started with the simple silly’s and changed the plugs & wires (P0307 still there).
2. Then I changed cylinder 7’s coil, (still there).
3. Cleaned all grounds and added a large one to the back of the head. (P0307 still there)
4. Changed #7 injector, plus injector cleaner in the tank. (P0307 still there)
5. Changed the computer. (P0307 still there)
6. Checked for vacuum leaks using a can of carb cleaner. Sprayed down the entire intake manifold and had no change in idle.
7. Checked fuel pressure. 58 psi with ignition on, 60 psi while running.
if anyone has any ideas on what this might be, please let me know! I’m out of ideas... thinking about changing out the engine harness next!
Thread Starter
Teching In
Joined: Jun 2017
Posts: 38
Likes: 4
Update! With your guys help and great advance the horrible P0307 code is gone! It was definitely the injector losing singal. I found a sharp bend in the ground wire going to the pcm. When I would bend the wire it felt like the wire was broken on the inside. So I cut it out and reconnected. Everything is fine now!
Thank you you again for all your great advance! I really appreciate it!
Thank you you again for all your great advance! I really appreciate it!
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