Author Topic: Transient cutouts in 3rd gear  (Read 1456 times)

beachbear

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Transient cutouts in 3rd gear
« on: February 08, 2022, 18:58:35 »
Recently, while driving along a nominally busy avenue with a regular interval of Stop Lights, my 280sl was held to 3rd gear (25 mph is where it consistently shifts into 4th). Along this stretch of road, if I needed to slow or coast, the engine seemed to lose power or even cutoff. But when I pushed the accelerator it would come back to life. If I came to a stop or a normal down shift occurred, it ran fine in 2nd or 1st. When I passed the congested part of town, and was able to run in 4th a just a little while, cruising in 3rd gear was back to normal smooth operation. The engine and injector pump were both rebuilt less than 10k miles ago. Maybe related: After receiving the rebuilt drivetrain, whenever I manually shifted into 3rd gear, I experienced a very similar issue. But with manually selecting 3rd, the engine behaved much worse. It seemed like it was being drowned in fuel. I would have to drive a mile or so to get the engine back to smooth running. Since then, I have consciously allowed the automatic transmission to do its own thing. The odd behavior I could just avoid is now something that makes town traffic something to consider.

Can anyone tell me what component needs attention? Is there a step in linkage adjustment that leads to behavior like this?
David White
'69 280sl automatic, 3rd owner since '82

beachbear

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Re: Transient cutouts in 3rd gear
« Reply #1 on: February 08, 2022, 19:03:42 »
Reading the entry by ScouseJames, another factor comes to mind. When the drivetrain was rebuilt I changed the ignition from an XR-700 to a 321 distributor.
David White
'69 280sl automatic, 3rd owner since '82

Pinder

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Re: Transient cutouts in 3rd gear
« Reply #2 on: February 19, 2022, 21:46:36 »
I have a 4 speed stick so maybe this does not apply to the automatic. There are switches on the manual gear box that cut out the fuel on the injection pump when down shifting from a higher gear to lower and also braking at the same time.  I ended up disconnecting that fuel cutoff solenoid on the injection pump so it did not do this.
1970 280 SL Light Ivory DB 670. 4 Speed manual shift no AC Limited Slip Diff.
1997 Corvette C5 Silver. automatic
2015 BMW 320i xdrive
2021 Mercedes GLS450 Silver