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Lurch When Shifting Gears


bilbo

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I have been having a problem with my Ranger since I got it two years ago that I haven't been able to pin down. The truck will sometimes lurch like it cuts out for a second when shifting gears, or letting off the throttle and accelerating again. It runs fine after warmup and on the highway, etc. But I can reliably make it do this by letting it idle for a while then driving it. Stop-and-go traffic will do it, too. This didn't occur really at all when it was cold during the winter.

I was thinking maybe while idling something gets heat soaked, maybe a temp switch related to the emissions control system that then makes an adjustment. I haven't seen any overheating or anything like that.

Could it be something with the catalytic converter? Or bad fuel pump/vapor locking? I have a fuel pump that I got on sale on my shelf, maybe I'll just put that in and see what happens.

The truck is a 1983 with feedback carb and 4 speed. Has anyone else experienced something similar? I haven't been able to find a diagram of how the emissions control components really work and what they do. I suppose nothing like that exists as it probably would have been a trade secret or something back in 1983.
 


RonD

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Carbs have an accelerator pump, just a rubber diaphragm that pumps in more gasoline when you press down on gas pedal.
It is on the float bowl of the carb

Labelled Pictures of carb here: https://www.ranger-forums.com/4-0l-ohv-sohc-v6-tech-33/2004-transfer-case-control-module-140263/
I think you have the 2150A

Carbs use Jets that add fuel to the air stream by Suction/vacuum
When you press down on the gas pedal, even a little, throttle plate opens and vacuum drops and so does fuel flow from the Jets momentarily.
The accelerator pump is needed to compensate for that change in vacuum levels, it adds a little or alot more fuel until vacuum level stabilizes again.

A hesitation when pressing down on gas pedal can be failing accelerator pump.

It can also be distributors vacuum advance, check vacuum hoses for leaks, when you accelerate the spark has to be retarded for the Richer fuel mix or engine will stumble/hesitate
 

bilbo

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2WD
Total Lift
0
Total Drop
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Thanks for the reply. I thought about the accelerator pump, as it ties so close to the symptoms, but wouldn't that be all the time if that were the cause? I'm going to try running the vacuum advance directly off of the manifold instead of the switch thing it's connected to now. Could it be that heat or something is affecting the diaphragm itself and causing these problems?
 

RonD

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Yes, heat is a factor with air:fuel mix, and a carb can not adapt like computer fuel injection can to warmer air, or colder air.

Warmer air is lighter, i.e. "hot air rises" because if floats on the cooler air
This means less fuel should be added to get correct mix for summer temps

So carb may be running engine too Rich for the air temp
Idling causes even higher engine temps so even warmer air

14.7:1 is the air:gasoline mix ratio and it is a WEIGHT ratio, not volume
14.7 POUNDS of air to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline

So it doesn't take much air temp change, or Altitude change, for a carb to get "out of tune" for the environment it's in.
 

bilbo

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Is there even a way to adjust that? I think the jets and stuff are permanent from the factory. There is a needle valve for idle mixture that can be adjusted, but it's supposed to be set and then the hole plugged. It does smell pretty rich at idle, but runs well. I still think it's a temp-related switch or something since it either happens or it doesn't, no in-between. It's weird because when I push the pedal down the engine takes off like it's supposed to for a half second or so, then cuts out for a half second or so, then takes off again. The problem isn't really at idle. I'll try messing with that screw and look into the accelerator pump anyway.
 

tomw

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It may be off the wall, but bad plug wires that are intermittent in their symptoms can act as described. When you go to up shift, for example, and let off the gas pedal to try to prevent over-revving when you push the clutch pedal, the engine may go 'balky' and seem to want to STOP. It makes smooth shifting difficult at times. I chased that problem for years, and had replaced the plug wires previously, so did not consider them a suspect. I even removed all the injectors and inspected the inlet for screen being blocked. New fuel filter, which was 'interesting', as I was fearful of damaging the housing which is like hens teeth to find. I swapped the TFI, and still had the problem.
Finally measured the plug wire resistance. Several had too much (open...), so I dug around in my pile of old parts and got 4 decent wires. That fixed the problem.
tom
 

bilbo

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Location
South Florida
Vehicle Year
1983
Make / Model
Ford
Engine Type
2.3 (4 Cylinder)
Engine Size
2.3L
Transmission
Manual
2WD / 4WD
2WD
Total Lift
0
Total Drop
0
Thanks, I'll check into the plugs and wires, too.
 

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