Vehicle starts to stutter at forty eight mph

1997 CHEVROLET SUBURBAN
168,000 MILES • 5.7L • V8 • 4WD • AUTOMATIC
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DDB7133
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Vehicle starts to stutter at forty eight mph and goes on up . Religiously starts at forty eight. ODM code shows a misfire on number five cylinder.

Here are the maintenance activities from earliest to latest:

Removed catalytic converters and replaced with test pipes.
Replaced gas tank, fuel pump, fuel filter and spider modification fuel rail.
Replaced rotor cap, fist cap, wires and plugs.
Replaced TPS sensor.
Tany shop validates torque converter on newly rebuilt transmission.
Valves adjusted. Timing checked with diagnostics.
Fuel pressure is 58 psi.
No other codes except misfire on number five cylinder.
Spark plugs removed, threads cleaned and replaced.
PS.
When torque converter is taken out with diagnostic tool, problem goes away. All work performed by dealership and OEM parts.
Dean
803, 493, 2508
Mar 26, 2018 at 2:09 PM
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ASEMASTER6371
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Good evening.

Torque converter taken out? please explain.

I would also suggest replacing the plugs. they may look good but can still cause a misfire.

Roy
Mar 26, 2018 at 3:03 PM
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DDB7133
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Torque converter shift was disabled somehow by use of the diagnostic machine as we drove down the road.
Spark plugs were brand new two weeks ago along with tune up. All plugs as well as wires, rotor and distributor cap have been removed, inspected and tested twice during the final run.
The stutter we feel is just like running over a power line in the road. It happens in overdrive as well in third gear. It starts exactly at forty eight mph and continues up in speed on a cold and hot engine. Rebuilt engine and transmission with less than 1,000 miles.
Mar 26, 2018 at 5:09 PM
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ASEMASTER6371
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Okay.

I suggest going to a parts store and getting an additive for transmission shutter. you just add it to the transmission and drive it. if it is the issue, it will disappear in about twenty miles of driving. that will tell us if it is the transmission or not.

Roy
Mar 27, 2018 at 3:30 AM
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DDB7133
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Will try, thanks Roy.
Mar 27, 2018 at 4:52 AM
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ASEMASTER6371
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Keep us updated.

Roy
Mar 27, 2018 at 4:55 AM
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DDB7133
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Roy,
Well 500 miles with sea foam in the tray and no change. This has got to be electricle or sensor related to start at 48 mph every time. Any more ideas ?
Apr 2, 2018 at 12:50 PM
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ASEMASTER6371
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Sea foam??? I never told you sea foam. I told you to get the additive for torque converter shutter. Sea Foam has no effect on the shutter.

Roy
Apr 2, 2018 at 12:54 PM
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DDB7133
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I'll drain and try that. Do you know the name of it.
Apr 2, 2018 at 5:22 PM
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ASEMASTER6371
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This is what I use all the time

Roy

https://shop.advanceautoparts.com/p/lube-gard-lubegard-instant-shudder-fixx-19689/10436769-p?c3ch=PLA&c3nid=10436769-P&adtype=pla&gclid=Cj0KCQjwqYfWBRDPARIsABjQRYwtkYxRRNDrDkh3qcd0FEYUzBZEIyvbOC9KcWyadRyVftwYqU6j090aApofEALw_wcB&gclsrc=aw.ds
Apr 2, 2018 at 5:40 PM
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DDB7133
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Hey Roy,

You're a freaking genius. 2 applications of that shutter lubricant did the trick and was evidence enough to get the tranny shop to install a brand new transmision instead of rebuilding the old one again even though it only had 1500 miles on the rebuild.
Apr 3, 2018 at 11:38 AM
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ASEMASTER6371
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Nice, glad to hear we got it right.

thank you

Roy
Apr 3, 2018 at 11:45 AM