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LT1-LT4 Modifications
1993-97 Gen II Small Block V8

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Old 07-01-2009, 08:26 PM   #1
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Default How to find bad spark plug?

As some of you may know I just installed new plugs (AcDelco) and wires (MSD) in my 94 z28. Now my car runs worst than before. Is there an easy way to check which plugs might be misfiring instead of me removing each wire and plug again for inspection?
That job was a PITA...will a spark plug tester work? and can you rent those?
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Old 07-01-2009, 08:40 PM   #2
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Unplug one injector at a time.
Do you have a flashing SES light?
Have you checked and re-checked the routing of the plug wires?
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Old 07-01-2009, 08:51 PM   #3
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Unplug one injector at a time.
Do you have a flashing SES light?
Have you checked and re-checked the routing of the plug wires?
Unplug one injector at a time when the car is running? what will this tell me? I only drove the car for about 3 or 4 minutes and turned around back home because it was shacking so bad but I didnt get a SES light. Wires are routed correctly.
As I said in another tread I think I may have broke a plug when I was tighening it because of the bad angle but Im dont remember which one. I didnt want to remove all plugs and wires again too find it.
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Old 07-01-2009, 09:39 PM   #4
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with it idling if you have a misfire that you are trying to nail down you unplug one injector at a time, if your rpm falls off a bit while it is unplugged plug it back in and move on to the next. When you get to one that doesn't affect your idle when it is unplugged you have found your bad plug.
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when i was rotating the motor it sounded like it was scratching so i put some oil in the spark plug holes and it seemed to get a little better...
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Old 07-01-2009, 09:50 PM   #5
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I have a used spark plug I can let go for half price if you need it.
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Old 07-01-2009, 09:58 PM   #6
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I have a used spark plug I can let go for half price if you need it.
Appreciate it but no thanks...i'll just walk down the street to the napa store and get another one.
I'll try that little trick tomorrow thank you.
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Old 07-01-2009, 10:22 PM   #7
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I have a used spark plug I can let go for half price if you need it.
Your generosity never ceases to amaze me.
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Old 07-01-2009, 11:03 PM   #8
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This ma be a dumb question but I have to ask it. LT1 get hot pretty fast so can I pull the wire down near the opti? Seems a little easier to me.
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Old 07-01-2009, 11:55 PM   #9
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Why would you pull a wire near the opti if the injectors are up in the intake manifold? Your not pulling spark plug wires, your unplugging the injector harness.
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Old 07-02-2009, 12:32 AM   #10
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If the guy only changed plugs and wire this problem should not be hard to diagnose. Check to make sure all your plug wires are going to the right cylinders if all checks out ok. make sure all your plugs are gapped to the right specs. and make sure none of the spark plugs are loose. some time the plug wire will go on but if you wobble it around your will see that it is not fully seated on the spark plug tip. If you didnt change anthing else other than plugs and wires this problem should be easy to track down
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Old 07-02-2009, 01:31 AM   #11
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This ma be a dumb question but I have to ask it. LT1 get hot pretty fast so can I pull the wire down near the opti? Seems a little easier to me.
Drivers side can be done with a pair of insulated pliers. With the engine running it is impossible to do the passenger side. Just pull the injectors one at a time.
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Old 07-02-2009, 01:31 AM
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