What signals engine RPM in the engine bay?

[Mustang5L5]

What tells the car engine RPM? Where does the tach get it's signal from?

I have a problem with my tach needle "sticking" for the first few minutes on startup when it's cold out (under 32 degrees). It usually fixes itself after a couple mins of driving. WOn't happen in warmer weather.

I also noticed that a couple times when i rinsed down my engine, the needle would do the same for a few mins if it was warm out. The only times it has done it when warm has been when i wet down the engine bay while cleaning the engine (i don't do it too often anyway)

So what could be affected by temp or water to cause the needle to "stick"

 

[bdcardinal]

im gonna say its the CKPS (crankshaft position sensor).

 

[RedDaemon]

What tells the car engine RPM? Where does the tach get it's signal from?

I have a problem with my tach needle "sticking" for the first few minutes on startup when it's cold out (under 32 degrees). It usually fixes itself after a couple mins of driving. WOn't happen in warmer weather.

I also noticed that a couple times when i rinsed down my engine, the needle would do the same for a few mins if it was warm out. The only times it has done it when warm has been when i wet down the engine bay while cleaning the engine (i don't do it too often anyway)

So what could be affected by temp or water to cause the needle to "stick"

my car does the same exact thing, did u change out the gauge face plate?

 

[Mustang5L5]

Yes i did. I did it soon after buying the car and made sure the needles did not hit. It was fine for almost 2 years until this winter. Then it started to stick..but it's not hitting the face.

 

[RedDaemon]

Yes i did. I did it soon after buying the car and made sure the needles did not hit. It was fine for almost 2 years until this winter. Then it started to stick..but it's not hitting the face.

i was gunna suggest that, i have yet to check mine tho, itll happen in a week or so once i have time to take my dash apart

are u sure that the whole mechanism isnt somehow binding up not just the needle?

how the hell would u test the crankshaft position sensor?

 

[Mustang5L5]

Unsure really. I'm gonna take a look and see if i can see anything visually wrong with it. Perhaps there is a crack or something allowing water to get in and freeze on me?

 

[1BAD93]

subscribing

 

[myponyrocks]

take the guage pod off and use a fork to slightly pry the needle up a bit, it might be too tight against the backing.

*EDIT* Didn't read the part about the water, sounds like an electircal issue? Because IMO if the sensor was bad, it would gradually increase in frequency, not go away and come back some times.

 

[RedDaemon]

what is the needle made out of anyway? will it snap?

 

[Mustang5L5]

*EDIT* Didn't read the part about the water, sounds like an electircal issue? Because IMO if the sensor was bad, it would gradually increase in frequency, not go away and come back some times.

Well that's how it was. At first it was a once in a while sort of thing. It did it maybe once every couple months, then it started happening all the time this winter. I did some experimenting and found it would stick only when the temp was at or below freezing. After running the engine for literally 5 mins, it would slowly begin to sweep normally. Now that winter is gone, so was the problem.

UNTIL, i washed the engine this spring to get all the winter salt off. Next time i started the car, the needle was sticking again. Did it for 5 mins and then was fine. I washed everywhere in the bay so safe to say everything got a little wet.

That was 2 weeks ago. Hasn't done it since. I'm gonna try wetting the crank position sensor real well and see if that has any effect. Where is it located on the engine? Right up next to the crank pulley?

 

[Mustang5L5]

Ok one more question, where on the engine is the CPS located??? I couldn't find it

 

[bdcardinal]

front of the motor by the crank pulley.

 

[Mustang5L5]

That's where i was looking, but couldn't see anything.

I'll try again

 

[myponyrocks]

the needle is a plastic base with an integrated clear plastic needle, its not too weak that if you used the fork meathod you would screw anything up.

To the OP, let us know how you fix it, its an odd issue for sure, but with my luck I'll have the issue soon enough

 

[Mustang5L5]

Been raining so haven't had a chance. Early this morning it stuck on me for a couple revs. After a couple mins it was find. It was a cold rainy morning, low 40's...about the upper range of when i start to see it stick.