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Old 10-17-2017, 10:36 AM   #1
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Join Date: Dec 2016
Location: Boston MA
Default engine stumble/bog on a cold B21ft

Hi all, i have an 84 245 Ti that i am just getting back on the road after it sat for a couple years with the PO.

Since the history of the car is a little vague, I have replaced the battery, rotor & cap, plugs, ign wires, fuel filter, air filter and needed to swap the fuel distributor to address a missing cylinder.

im noticing an issue that is a little weird, but not really causing significant issues yet.

when the car is cold. giving it a small amount of gas, for instance stopping at a stop sign and then slowly inching out to make a turn into traffic, the rpms drop pretty low in what feels like a stall. giving it more gas seems to consistently bring it back out of the "bog zone" and i have not actually ever stalled the car when this happens. after 5-10 minutes of driving this issue seems to go away.

This is a kjet car, so everything about the fuel delivery is a little bit weird to me, but i am eager to learn. any advice is welcome.
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Old 10-17-2017, 12:42 PM   #2
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Join Date: Aug 2015
Location: Central NH

Similar thing happened on my ‘79 kjet 244 - was a flaky thermo time switch. Would activate cold start injector and flood engine. If it happened under load or low RPMs car would die. Unplug the cold start injector and see what happens...
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Old 10-17-2017, 02:32 PM   #3
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Join Date: Nov 2011
Location: So Cal

K-Jet uses 2 different methods to enrich the fuel mixture under load when cold. Both systems are dependent upon the thermal vacuum switch. Systems with hoses going to the CPR use boost pressure to raise the fuel pressure directly. Those with a differential pressure switch activate a circuit in the ECU that adjusts the dwell of the frequency valve to enrich the mixture.

If the TVS isn't getting a good vacuum source or the hoses are split, the systems won't function properly. TVS's are known to fail as well. It should be open when cold and closed when warm.

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Old 10-17-2017, 03:58 PM   #4
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Join Date: Jun 2002
Location: S NJ, a suburb of Phila.

In general these are engines that have a warmup system but don't run all that well when cold. I always take it easy with the cold weather warmup driving on my turbo. It just isn't happy until fully warmed up. No real boost till the oil is hot.

Also during warmup with these I've noticed an in between zone where the o2 is still too cold to reference but the warmup is done. It will hunt at idle for a few minutes till the o2 is hot enough and the idle will smooth as the engine gets fully warm.
1982 242 turbo. 340k miles. Good stuff and lots of rust.
1993 245 Classic, 420k miles, enem V15. IPD bars and chassis braces. Simons sport exhaust from Scandix. sbabbs ezk chip. Been a good road warrior. Genuine Volvo rebuilt leaky M47.
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