weird misfire issue
Thread Starter
Staging Lane
Joined: Jul 2008
Posts: 75
Likes: 0
weird misfire issue hey all, i have a problem that i cant get to the bottom of...
it is on a 2000 camaro v8.
number 7 cylinder has no spark at all.
no. 5 misses almost every time.
all others do miss intermittently, but the main ones being reported to the scanner are 7 & 5. ill also give a flshing ses.
i have changed the spark plugs, tryed a new set of plug wires, and swapped coil packs. however the main problem will not move from 5 and 7.
i have also sitched injectors around and it makes no difference. i can hear each injector turning on and off during operation. i dont think its a fuel delivery issue, since i can smell the raw gas on the plugs after i try diagnosing.
i have also tested the coil pack connectors on each side. it is getting 12+vdc key on, as well as ground and voltage reference. however, when i crank the engine over, there is no completed ground path pulsing on any of the terminals to each cylinder. but the engine will actually start and run. however it still has serious issues.
what is weird to me is, i dont get any signal for the coil to energize, yet it ill start and run. how is this possible?
is the ignition control module located in the pcm for this vehicle?
can anyone give me an idea of what to check next? your input would be greatly appreciated.
it is on a 2000 camaro v8.
number 7 cylinder has no spark at all.
no. 5 misses almost every time.
all others do miss intermittently, but the main ones being reported to the scanner are 7 & 5. ill also give a flshing ses.
i have changed the spark plugs, tryed a new set of plug wires, and swapped coil packs. however the main problem will not move from 5 and 7.
i have also sitched injectors around and it makes no difference. i can hear each injector turning on and off during operation. i dont think its a fuel delivery issue, since i can smell the raw gas on the plugs after i try diagnosing.
i have also tested the coil pack connectors on each side. it is getting 12+vdc key on, as well as ground and voltage reference. however, when i crank the engine over, there is no completed ground path pulsing on any of the terminals to each cylinder. but the engine will actually start and run. however it still has serious issues.
what is weird to me is, i dont get any signal for the coil to energize, yet it ill start and run. how is this possible?
is the ignition control module located in the pcm for this vehicle?
can anyone give me an idea of what to check next? your input would be greatly appreciated.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
The ignition is controlled by the PCM with is located at the rear of the RHS of the engine compartment.
Sounds to me like either a wiring problem to the coil packs you mentioned, or a problem with the crank sensor signal.
Does your scantool indicate RPM's while cranking...?
Sounds to me like either a wiring problem to the coil packs you mentioned, or a problem with the crank sensor signal.
Does your scantool indicate RPM's while cranking...?
Thread Starter
Staging Lane
Joined: Jul 2008
Posts: 75
Likes: 0
The ignition is controlled by the PCM with is located at the rear of the RHS of the engine compartment.
Sounds to me like either a wiring problem to the coil packs you mentioned, or a problem with the crank sensor signal.
Does your scantool indicate RPM's while cranking...?
Sounds to me like either a wiring problem to the coil packs you mentioned, or a problem with the crank sensor signal.
Does your scantool indicate RPM's while cranking...?
what is weird is when i was testing for ground signal for the coils, i was not getting continuity at the connector or at the wire right off the pcm connector. that is why i thought the pcm was bad and replaced it, but i am still having the same issue.
i did a little bit of diagnosing today and found that i was getting a shaky spark to number 7 . no flashing ses. as soon as i tap the throttle once, misfire, ses starts blinking, and no more spark to number 7.
just for kicks i also pulled out the crank pos. sensor and looked inside as a friend turned the motor over by hand. the reluctor wheel looks fine to me.
i was under the impression that the pcm acquired tach signal from the cam position sensor and not the crank position sensor, but i may be wrong.
also i cant use my scanner right now, since the battery on my laptop is no good.
is there a for sure way to test the coil pack primary circuits? something doesnt feel right about not getting a ground signal when trying to crank the engine with the coilpacks disconnected, but once connected the engine starts and runs, but drops cylinders.
also is it okm to disconnect the injector to cylinder 7 while diagnosing? i dont want to wash out the piston rings. i figure it cant hurt, since the plug is not firing anyway? yay or nay?
any help will be greatly appreciated....
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
The PCM determines RPM from the CKP (crank position) sensor.
I looked up some info (see attached).
Are you using a digital multimeter (i.e. has 10 MΩ input impedance)...?
If you swap coil #7 with another working cylinder's coil, does the problem stay on cylinder #7...?
Each coil has 2 wires from the PCM and 2 wires from power/ground (see diagrams)... did you check all of those for continuity with their respective "other end"...?
Yes, it's ok to disconnect injector #7 while diagnosing (regardless if the plug is firing or not).
You can use a LED test light (has two back-to-back LEDs instead of a light bulb, available cheaply from parts store) to probe between the two wires from the PCM (ignition control signal and low reference)... the LED test light should pulse while cranking or running.
I looked up some info (see attached).
Are you using a digital multimeter (i.e. has 10 MΩ input impedance)...?
If you swap coil #7 with another working cylinder's coil, does the problem stay on cylinder #7...?
Each coil has 2 wires from the PCM and 2 wires from power/ground (see diagrams)... did you check all of those for continuity with their respective "other end"...?
Yes, it's ok to disconnect injector #7 while diagnosing (regardless if the plug is firing or not).
You can use a LED test light (has two back-to-back LEDs instead of a light bulb, available cheaply from parts store) to probe between the two wires from the PCM (ignition control signal and low reference)... the LED test light should pulse while cranking or running.
Last edited by joecar; Aug 14, 2009 at 07:16 PM.
Thread Starter
Staging Lane
Joined: Jul 2008
Posts: 75
Likes: 0
The PCM determines RPM from the CKP (crank position) sensor.
I looked up some info (see attached).
Are you using a digital multimeter (i.e. has 10 MΩ input impedance)...?
If you swap coil #7 with another working cylinder's coil, does the problem stay on cylinder #7...?
Each coil has 2 wires from the PCM and 2 wires from power/ground (see diagrams)... did you check all of those for continuity with their respective "other end"...?
Yes, it's ok to disconnect injector #7 while diagnosing (regardless if the plug is firing or not).
You can use a LED test light (has two back-to-back LEDs instead of a light bulb, available cheaply from parts store) to probe between the two wires from the PCM (ignition control signal and low reference)... the LED test light should pulse while cranking or running.
I looked up some info (see attached).
Are you using a digital multimeter (i.e. has 10 MΩ input impedance)...?
If you swap coil #7 with another working cylinder's coil, does the problem stay on cylinder #7...?
Each coil has 2 wires from the PCM and 2 wires from power/ground (see diagrams)... did you check all of those for continuity with their respective "other end"...?
Yes, it's ok to disconnect injector #7 while diagnosing (regardless if the plug is firing or not).
You can use a LED test light (has two back-to-back LEDs instead of a light bulb, available cheaply from parts store) to probe between the two wires from the PCM (ignition control signal and low reference)... the LED test light should pulse while cranking or running.
if i swap an individual coil, or ever the entire coil assembly with subharness around the problem will persist on the same cylinder as before. thats why i believe the problem is in the main engine harness wiring, not in the electronics, or subharness connections.
the more i probe this problem i feel as if the pcm is only reporting a misfire on cylinder 5 and 7, but in fact all cylinders are misfiring.
as far as the coil wiring, i am aware that each coil will have a 12+ reference, ground , low voltage (ground) reference from pcm, as well as a trigger output signal (ground) from the pcm. the problem is that everything works as it should except for the trigger signal from the pcm. which is now why i believe the issue is in the crank sensor circuit.
last night i didnt have much time, but i dropped the starter and removed the part of the engine harness that goes to the ckp and traced it back. no obvious damage. took my test light and probed it for ground and it had solid ground. went to check for 12+ at the connector and the test light would take about 1-2 seconds to turn on, but the light was very very dim. all you could see was the filament turning orange, but no visible light was being emitted. i guess at this point i will be checking that pin on the pcm to see if it has a good signal there. if it does, then there is a problem in the wiring to that pin on the connector and it may solve my issue.
however if the voltage is down at the pcm pin, i ont even know here to look after that.
im not sure i understood what you meant by the back to back led test lights.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
Use a LED test light, this looks like a bulb testlight but has two LEDs (a green LED and a red LED), connected in opposite directions, polarity is indicated by which LED lights up... these draw a very small current and is safe for the PCM.
You might simply have a bad PCM.
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