bad miss under load - 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 03-18-2008, 01:44 PM   #1
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Default bad miss under load

Yesterday, leaving saint john, going up a hill, the tranny is in top gear, and the engine is missing randomly. Its pretty frequent. Just a random shudder, like a misfire. Idles smooth, WOT was smooth. Driving on relatively flat areas with OD, seemed to work good.
Sympton seemed to go away after 1/2 hour to 45 mins driving.


This morning, (-10 c out) drove back to SJ. The miss was worse. By the time I got to SJ, it was missing if you put much of a load on. WOT and it misses more. Still has power, not much hesitation.

Scantool shows 0 KR at idle. Got codes 23, 43, and 65. IAT is pegged right at -40, and does not change even though its in the shop. Not sure what it will be with an increase of engine speed, and i still need to do some test driving with the scantool to see what the KR is. More than liekly, i'll change the sensor when i get home.

I'm going to do some testing on the knock sensor when i get home tonight. Whats the liklihood of those going bad? At least I have some spares if i need em. Should also see about fixing the IAT, but don't see that being a contributing factor to the miss.
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Old 03-18-2008, 01:46 PM   #2
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plugs and wires to start
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Old 03-18-2008, 02:23 PM   #3
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The IAT can be a factor, as your engine coolant (ECT) sensor is also. Both affect timing and fueling.

Make sure your IAT is connected. If it is, test it using this:
http://www.bonnevilleclub.com/forum/...e=article&k=24

As you can see in that fine article, if the sensor is disconnected (open circuit) it will read a high resistance (infinite), and produce a LOW temperature reading.
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Old 03-18-2008, 03:17 PM   #4
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Plugs done last year, gapped to .060. Wires were in good shape. Looks like AC delco ones, they don't look original, but you never know.
My instructor told me to check my wires (mine'* still functioning ) and check the coilpack resistance. Guess I have enough info to start somewheres when I get home tonight. Hopefully i'll make it, (hr and 10 mins)...
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Old 03-18-2008, 03:49 PM   #5
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Coil pack troubleshooting is in Techinfo. Link at the top of the page.
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Old 03-19-2008, 08:42 AM   #6
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Well, ran like crap getting home, but i made it.

Took my hand, pulled the #5 plug boot first thing I did when I got home. Came off rather easily. When I looked at the boot, soot fell out of it. Looked at the plug. The metal attachment was still on the plug. carbon covered....

Needless to say, it got a set of napa belden wires right away...

Jeez, sometimes the simplest things...
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