Diagnostic gurus needed
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Diagnostic gurus needed
This is unrelated to a C5 or LS1 for that matter. But the idea here should be the same.
I have been working with a coworker trying to fix a misfire on her car. My scanner reads cylinder 5 misfire. So far I have changed the spark plugs, wires, and injector for that cylinder. I have verified that the coils are good with an ohm test, and that the injector has power (same readings as all the other injector wires). I have done a compression test and the cylinder is at 140psi and holds there fine.
The funny thing is that when I unplug the injector while the engine is running, I do not get a change in the way the engine runs like I do when any other cylinder is unplugged. (Hence why I changed the injector in the first place). This is the same even with the new injector.
Its a 1999 Grand Prix 6 cyl. Car is totally stock.
Basically Im wondering what I am missing here for tests.. any ideas? I watched the gauge on the compression tester climb three or four times which showed me the valve is opening and closing. I have verified fuel, spark, air, compression, and no vacuum leaks. So what else can I do before I take the valve cover off and start checking the valve train more in depth?
I have been working with a coworker trying to fix a misfire on her car. My scanner reads cylinder 5 misfire. So far I have changed the spark plugs, wires, and injector for that cylinder. I have verified that the coils are good with an ohm test, and that the injector has power (same readings as all the other injector wires). I have done a compression test and the cylinder is at 140psi and holds there fine.
The funny thing is that when I unplug the injector while the engine is running, I do not get a change in the way the engine runs like I do when any other cylinder is unplugged. (Hence why I changed the injector in the first place). This is the same even with the new injector.
Its a 1999 Grand Prix 6 cyl. Car is totally stock.
Basically Im wondering what I am missing here for tests.. any ideas? I watched the gauge on the compression tester climb three or four times which showed me the valve is opening and closing. I have verified fuel, spark, air, compression, and no vacuum leaks. So what else can I do before I take the valve cover off and start checking the valve train more in depth?
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
Melting Slicks
Joined: Jul 2012
Posts: 2,507
Likes: 9
GM injectors fire when GROUNDED by the ECU. That injector could have a bad ground. You can use a noid light to test if it's firing or use a pencil or screwdriver to listen for the ticking of the injector when the engine is running.
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
Carefully examine the connector for the coil and injector. Make sure that the female pins are not deformed and make good contact with the male pin on the component.
Check the wires for the correct power, ground and signals to make the components work.
Bill
Check the wires for the correct power, ground and signals to make the components work.
Bill
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
I will double check all connections. I will try a noid light and see if I get anything. Never tried that before. Makes sense.
Thread Starter
Melting Slicks
Joined: Jun 2012
Posts: 3,163
Likes: 6
From: Oceanside California
I do have a digital meter and tested with it, I am no expert, but I tested both prongs in the injector connector and verified that they are the same readings as all the other injector connectors. To me that says they are fine... but like I said, I feel like Im missing something here.
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Racer
Joined: Apr 2009
Posts: 488
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From: Myrtle Beach SC
Perhaps he is saying to swap the components from a known, properly-firing cylinder to the suspect cylinder, one component at a time. Slightly different from a wholesale changeout of parts. Also, if you change ALL of the parts at once, how would you know which component solved the problem? 
I think Bill is right. You're gonna need to troubleshoot this thing a little more. If you changed the injector, the plug, and the coil pack, it suggests to me that the problem is most likely in the wiring, as Bill so aptly suggested. If it hasn't already been suggested, I would also check the wiring and connectors of the PCM/ECU side of the harness, and the ground for that cylinder's injector. Just my $0.02
On a side note, it is somewhat annoying when people only chime in with their smart-a$$ remarks rather than making a positive contribution to the thread.
I think Bill is right. You're gonna need to troubleshoot this thing a little more. If you changed the injector, the plug, and the coil pack, it suggests to me that the problem is most likely in the wiring, as Bill so aptly suggested. If it hasn't already been suggested, I would also check the wiring and connectors of the PCM/ECU side of the harness, and the ground for that cylinder's injector. Just my $0.02
On a side note, it is somewhat annoying when people only chime in with their smart-a$$ remarks rather than making a positive contribution to the thread.
Melting Slicks
Joined: Jul 2012
Posts: 2,507
Likes: 9
Perhaps he is saying to swap the components from a known, properly-firing cylinder to the suspect cylinder, one component at a time. Slightly different from a wholesale changeout of parts. Also, if you change ALL of the parts at once, how would you know which component solved the problem?
I think Bill is right. You're gonna need to troubleshoot this thing a little more. If you changed the injector, the plug, and the coil pack, it suggests to me that the problem is most likely in the wiring, as Bill so aptly suggested. If it hasn't already been suggested, I would also check the wiring and connectors of the PCM/ECU side of the harness, and the ground for that cylinder's injector. Just my $0.02
On a side note, it is somewhat annoying when people only chime in with their smart-a$$ remarks rather than making a positive contribution to the thread.
I think Bill is right. You're gonna need to troubleshoot this thing a little more. If you changed the injector, the plug, and the coil pack, it suggests to me that the problem is most likely in the wiring, as Bill so aptly suggested. If it hasn't already been suggested, I would also check the wiring and connectors of the PCM/ECU side of the harness, and the ground for that cylinder's injector. Just my $0.02
On a side note, it is somewhat annoying when people only chime in with their smart-a$$ remarks rather than making a positive contribution to the thread.
Can you read??
Last edited by 3boystoys; Jan 1, 2013 at 06:12 AM.
Racer
Joined: Apr 2009
Posts: 488
Likes: 2
From: Myrtle Beach SC
Why yes...yes I CAN read...must have overlooked your noid light suggestion...
Le Mans Master
Joined: Sep 2003
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From: Farmington CT
Cruise-In VII Veteran
