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Discussion Starter #1
We have a 4x4 Ranger with rough idle, and the service manual recommends a leak-down test. However, there's no guidance on how to find top-dead-center. Bumping the starter and inserting something in the spark plug opening is inconclusive, as it seems like the rotation always lands at the same place. We are not sure where and how to manually rotate the shaft to get where we need to go.

Any advice, references to documents/images, etc. to help us find TDC would be appreciated.

The manual presumes that the test will lead us to an engine internal issue. But might it be fuel injection? Ignition?

While inexperienced in many of these details, we aren't afraid to take things apart -- just want to be moving in the right direction.

Doug
 

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You can pull the clutch cover and turn the engine by hand. You can't do it by bumping the starter. You'll also have to hold or use a bar to foul the clutch so the crank don't turn while doing a pressure test. I doubt that's your problem with rough idle though but it never hurts to check.
On those machines, unless its using oil or other symptoms are present, rough idle is often related to TPS, TBAP or CPS being dirty/bad or wire harnesses or connectors to them being rubbed or broken. They are also sometimes get cracks in the intake boot.
I'd probably start by confirming good fuel pressure at around 40 psi. New NGK iridium plugs. Closely inspect/test intake boot, plug wires and caps and all sensor harnesses and clean the TBAP with MAP sensor cleaner or electrical cleaner. If no improvement check TPS voltage for correct setting and smooth voltage increase with throttle with no jumps, drops or stumbles in voltage.
Here's a link to the Ranger forum about TPS settings. There's a bunch more discussions on there related to your idle issues on those machines as well if you search.
Good luck and keep us updated.
 

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Discussion Starter #3
You can pull the clutch cover and turn the engine by hand. You can't do it by bumping the starter. You'll also have to hold or use a bar to foul the clutch so the crank don't turn while doing a pressure test. I doubt that's your problem with rough idle though but it never hurts to check.
On those machines, unless its using oil or other symptoms are present, rough idle is often related to TPS, TBAP or CPS being dirty/bad or wire harnesses or connectors to them being rubbed or broken. They are also sometimes get cracks in the intake boot.
I'd probably start by confirming good fuel pressure at around 40 psi. New NGK iridium plugs. Closely inspect/test intake boot, plug wires and caps and all sensor harnesses and clean the TBAP with MAP sensor cleaner or electrical cleaner. If no improvement check TPS voltage for correct setting and smooth voltage increase with throttle with no jumps, drops or stumbles in voltage.
Here's a link to the Ranger forum about TPS settings. There's a bunch more discussions on there related to your idle issues on those machines as well if you search.
Good luck and keep us updated.
Thank you we will get to work!
 
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