Changed spark plugs now car runs like crap...?
06-16-2009, 11:52 AM
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Changed spark plugs now car runs like crap...? Hey guys, I just changed the plugs in my 9C1 Caprice yesterday. The originals had almost 77,000 on them, so I put in a set of Autolite APP106's (couldn't swing the $7/plug for AC Delcos 
). Now the car feels weaker, slower, less responsive, stumbles if I blip the gas quick in neutral, and if I give it a good rev it sounds like it's backfiring like crazy while going back down the revs. I opened the hood and checked, no plugs came out of the block, the wires were all still connected, the plugs were gapped at 0.050"... I hopped on it and the car was barely pulling past 90mph and wouldn't even squeal the tires.
I'm at a bit of a loss here except that the factory Opti might've decided now was a good time to **** the bed
). Now the car feels weaker, slower, less responsive, stumbles if I blip the gas quick in neutral, and if I give it a good rev it sounds like it's backfiring like crazy while going back down the revs. I opened the hood and checked, no plugs came out of the block, the wires were all still connected, the plugs were gapped at 0.050"... I hopped on it and the car was barely pulling past 90mph and wouldn't even squeal the tires.I'm at a bit of a loss here except that the factory Opti might've decided now was a good time to **** the bed
06-16-2009, 12:42 PM
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Are you sure all the plugs were gapped at .050? Are there any codes stored? What else did you did during the plug change? Were all the plug wires connected tightly?
06-16-2009, 12:42 PM
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If it was running well before the plug swap, and ran like butt after swap I'd check what was messed with last before jumping into opti or other ignition components.
So: are the plugs correct for your application....heat range ..
Did you reuse the original wires? (may have broke wire when removing it from plug) (wires in wrong order ..if new wires) (bad plug even though they all are new people have had bad new plugs .....cracked the insulator during install, jacked it up setting gap etc)
So: are the plugs correct for your application....heat range ..
Did you reuse the original wires? (may have broke wire when removing it from plug) (wires in wrong order ..if new wires) (bad plug even though they all are new people have had bad new plugs .....cracked the insulator during install, jacked it up setting gap etc)
06-16-2009, 12:59 PM
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No codes stored, didn't change anything but the plugs. I gapped them all at 0.050", although I'm not a computer so they may be in the range of .049"-.051" which really won't make a difference. I noticed when I took out the first plug that the new plugs were a bit longer, so I immediately went online to check part numbers before I put them in. Part number APP106 is listed as Autolite's plugs for the LT1, and is comparable to the AC Delco part number 41-906 which is listed as the Delco replacement plug for an LT1.
Yes, I reused the factory wires. I'm 100% they're not in the wrong order (changed one plug at a time
). I'm not sure if any cracked though, that I'll have to check but I don't think anything broke. Before I started the car I made sure I pulled on all of the plug wires a bit to make sure they were connected, and then pressed on them again to make sure they were on all the way.
My thoughts right now are that either the Opti is going for no reason, I'm not having much luck with these Autolite plugs (I've heard some not so flattering things about them), or it's something really stupid that I overlooked. I'm going back to my buddy's shop to check it out now, but any more thoughts would be greatly appreciated!
Yes, I reused the factory wires. I'm 100% they're not in the wrong order (changed one plug at a time
). I'm not sure if any cracked though, that I'll have to check but I don't think anything broke. Before I started the car I made sure I pulled on all of the plug wires a bit to make sure they were connected, and then pressed on them again to make sure they were on all the way.My thoughts right now are that either the Opti is going for no reason, I'm not having much luck with these Autolite plugs (I've heard some not so flattering things about them), or it's something really stupid that I overlooked. I'm going back to my buddy's shop to check it out now, but any more thoughts would be greatly appreciated!
06-16-2009, 05:45 PM
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I would be interested to know what some of the unflattering things you've heard about Autolite plugs. I've ran nothing but Autolites for the past twenty years and never had a problem. I won't use anything else. The last time I bought some I had a couple of ricer kids at the parts store telling me how bad they were and that I should buy some platinum multi tips...
06-16-2009, 06:28 PM
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I run Autolites on my supercharged setup believe it or not, they are the best plugs I used so I second your opinion Razor_Blade.
Unless it's a coincident and something else went wrong RIGHT at the same time you changed the plugs, it must be either plugs or wires no doubt (As long as you only started having this issue AFTER replacing the plugs).
In my opinion your issue is the gap on the plugs, take it down a bit it won't hurt anything and see what happens. Also, I know wires are kinda expensive but if yours have 70k miles or so on them, it's time for new ones brother.
Keep us posted please.
Unless it's a coincident and something else went wrong RIGHT at the same time you changed the plugs, it must be either plugs or wires no doubt (As long as you only started having this issue AFTER replacing the plugs).
In my opinion your issue is the gap on the plugs, take it down a bit it won't hurt anything and see what happens. Also, I know wires are kinda expensive but if yours have 70k miles or so on them, it's time for new ones brother.
Keep us posted please.
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06-16-2009, 09:16 PM
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I run Autolites on my supercharged setup believe it or not, they are the best plugs I used so I second your opinion Razor_Blade.
Unless it's a coincident and something else went wrong RIGHT at the same time you changed the plugs, it must be either plugs or wires no doubt (As long as you only started having this issue AFTER replacing the plugs).
In my opinion your issue is the gap on the plugs, take it down a bit it won't hurt anything and see what happens. Also, I know wires are kinda expensive but if yours have 70k miles or so on them, it's time for new ones brother.
Keep us posted please.
Unless it's a coincident and something else went wrong RIGHT at the same time you changed the plugs, it must be either plugs or wires no doubt (As long as you only started having this issue AFTER replacing the plugs).
In my opinion your issue is the gap on the plugs, take it down a bit it won't hurt anything and see what happens. Also, I know wires are kinda expensive but if yours have 70k miles or so on them, it's time for new ones brother.
Keep us posted please.
06-16-2009, 10:07 PM
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Don't close the gap on any of the plugs. You'll certainly notice less power from doing that, I had mine gapped at .035 not knowing they were supposed to be at .050 and it ran like crap until I re-gapped them.
06-16-2009, 11:17 PM
#12
sorry that's incorrect. .050 is a huge plug gap, nothing wrong with running them at .035. Maybe your idle will clean up a little at .050 but its alot more taxing on your ignition system up top. When you're making a lot of cylinder pressure like me, anything more than .035 COSTS hp because the spark can't jump the gap.
06-16-2009, 11:21 PM
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I'm just goin with OE specs. OP has no reason to run anything other than that. Like I said before, I've done .035 and it was sluggish in comparison to .050.
06-16-2009, 11:31 PM
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sorry that's incorrect. .050 is a huge plug gap, nothing wrong with running them at .035. Maybe your idle will clean up a little at .050 but its alot more taxing on your ignition system up top. When you're making a lot of cylinder pressure like me, anything more than .035 COSTS hp because the spark can't jump the gap.
06-17-2009, 02:08 PM
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Have you ohm'd the wires yet? I would get a multimeter and ohm check all the wires before just replacing them also. Anything over 1K I believe is problematic. Its something like 100 ohms per foot on average depending on the wires you have. I would check that out first...might find one bad plug wire and be able to replace it and verify that thats what the problem was before diving into optis and full plug wire sets and have it not fix the problem.
