random downshifting/snubbing out? - 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 05-19-2008, 10:36 PM   #1
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Default random downshifting/snubbing out?

i've searched for a while looking for any symptoms similar to mine, and haven't found any that were exactly the same.

I have a 94 bonnie SE, and ALL at once the cruise control would either not work, or it would randomly downshift and the CC would kick off. also, at slow speeds, the idle dips, and kills the engine if approaching a stop sign. I must shift to Neutral and restart. the car runs fine at highway speeds, but usually stays out of top gear.

It did throw a code, and the code says misfire in cylinder 4. I replaced all the spark plugs, the wires, and swapped the coil, but nothing changed. I also checked for intake leaks. nothing. I figured because of high mileage and short trips, the inside (hotter) cylinder 4 could have a clogged injector. I ran a whole tank of Industrial strength detergent mix from GM and still same thing. I think my next move is to switch the injector.

Also, if i start up cold, i can drive about 7 miles until the cruise will flip off and it starts going in and out of top gear. it runs cherry up until that, and usually doesn't have a problem at stops either.

If not the injector, what else?????


??????
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Old 05-20-2008, 05:15 PM   #2
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so i switched out the injector, and nothing. is less likely to snub out, but same behavior still. Also, i forgot to mention that if from a stop I put the pedal to the floor, it will shift at about 3-4k rpms, and not actually rev out. eventually it will upshift to top gear, at about 50. If i let my foot up about 1/4 the pedal it will downshift. The transmission is good, and no signs of slipping. what can this be?
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Old 05-20-2008, 08:54 PM   #3
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I Have no experience with this situation, but have you checked your fuel pressure? And all of your vaccum lines? Both of these can cause erratic behavior with fuel delivery.
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