New plugs, bad MPG - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-04-2012, 03:59 PM   #1
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Default New plugs, bad MPG

Hi all,

I replaced my plugs a couple of weeks ago, I was getting around 25 MPG, and the new ones are giving me 18.

I don't race so what'* up? They're Delco copper plugs... gapped to .060

Thanks

1992, bonny SE
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Old 04-04-2012, 04:07 PM   #2
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Did you properly seat all the wires? Is there a chance a wire was damaged when you pulled it off? Is your car hesitating on acceleration? Is the CEL lit? Is it flashing?

Inspect the area to see if you disconnected or broke anything when you changed the plugs. Look for any disconnected or damage vacuum lines.
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Old 04-04-2012, 04:26 PM   #3
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Yes, everything was seated correctly. I'll pull the wires and run a resistance test through them. No CEL light or flashing.

I'll check the vac lines as well.

Thanks!
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Old 04-04-2012, 06:19 PM   #4
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Pull the plugs again and inspect them. If any look different or odd, take a picture and post it up here. You may have a bad plug.
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