LN3 miss...pulse - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-13-2006, 09:17 PM   #1
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Default LN3 miss...pulse

well I can't figure this issue out...

I have to be driving at 45 or above

a miss will develop...but only once, thats right one miss. It feels like a pulse a monentary pulse within 5-8 seconds of each other only when the car is coasting. Under accel. the car runs great. wires are new no change, coils are new no change.

also when this occurs vacuum gauge twitches with the pulse and rpm(drop 100) twitches with the pulse also.

I also tryed downshifting when coasting and it only amplifies the pulse in firmness, not in time inervals

I am stumped
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Old 04-13-2006, 10:54 PM   #2
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That doesn't sound too unusual. When coasting down, depending on speed, the deceleration fuel cutoff can activate. It causes a somewhat regular drop in rpm for a moment and then back again. I believe it is emissions related to keep the engine from loading up on fuel. You might watch the injector pulse width to see if there is a change that accompanies the rpm drop. If the TPS signal is below a few percent of full throttle it will also unlock the torque converter.
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Old 04-14-2006, 11:55 AM   #3
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Default pulse

In addition to the above there is also an issue with Buick 3800'* for bad springs on the IAC valve which cause a decel pulse and even stalls the motor in some instances.
Sound like yours is related to the converter lockup if its happening around 45 mph.
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Old 04-14-2006, 02:34 PM   #4
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Clean your battery cables really well and retighten them. Your voltmeter should never drop while the engine is running.
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Old 04-16-2006, 02:26 AM   #5
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my volt meter isn't dropping. The IAC sounds like a good place to start looking thankyou.

a decel pulse is the perfect way to decribe it. Its to small of a pulse to be the TC and I can downshift into 2nd gear and it will continue to occur.
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Old 04-19-2006, 08:39 PM   #6
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well I replaced the IAC and still no change.

I did start monitoring the injector pulse while this is happening and I can feel the pulse and sometimes the injector pulse just twitches and other times it goes to .0 and right back up. The only this I have noticed that the injector pulse zeros out after the decel pulse.

still stumped
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Old 04-20-2006, 07:35 PM   #7
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I really need help to figure this out
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Old 04-20-2006, 08:42 PM   #8
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Did you put dielectric grease on the plugs. It sounds a lot like an ignition problem. Do you have access to a timing light. One can be used to see if there is constant spark.

I'd still recomend cleaning the batter cables, it'* an often overlooked problem.

-T
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Old 04-20-2006, 11:37 PM   #9
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What is the O2 voltage doing during this "pulse"? Does this "pulse" feel like a misfire? Need a better description of what exactly is happening...
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Old 04-21-2006, 10:56 PM   #10
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I remember monitoring it and not noticing anything weird, but will report back with findings
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