Rpm


#1

My RPM dial on my Ford Explorer doesnt move sometimes when I’m driving. Does this indicate it’s not shifting correctly?


#2

No, if the transmission was not shifting, the RPMs would increase to a great extent as you gained speed, and you would hear a great deal of engine noise.


#3

It can only mean 2 things.

Either the Tack isn’t working or the Explorer isn’t running. The Tack measures engine speed (RPM’s - Rounds Per Minute). If the tack is at 0 RPM’s and it’s working properly then the engine isn’t running…Visa Versa…If the Engine is running and the Tack is at 0…then there’s a problem with the tack.

Personally I wouldn’t worry about it. A Tack is probably the most useless instrument on a car today. I see no value in a tack what so ever. Maybe when you’re trying to diagnose a problem…but then you can hook up an external tack.


#4

Thanx!!:slight_smile:


#5

By the way, the RPM dial is called a tachometer (pronounced tak-ometer).


#6

Interesting viewpoint, Mike. I do see a lot of value in tachometers, and I bet other people here do, too. On the other hand maybe you have perfect pitch and thus can tell just how fast your motor is running. I cannot.

An example is just how fast the motor is running at a given road speed, this can tell you something about transmission efficiency. The only real reason I use my speedometer more is speeding laws. Idle speed actuator problems can be narrowed with the tach. Lots more.


#7

Could just be the lubrication in the tachometer. If all SOUNDS good ( engine and transmission ) then it probaly is. My '91 Explorer tachometer was tempermental in cold weather, you could drive for hours before the tach would “wake up” but nothing was wrong otherwise and we just learned to live with it.


#8

I think I agree with Mike. (We sometimes argue even when we agree!) Most of the cars sold in the US have automatic transmissions. How would an automatic fuel-injected car benefit from having a tachometer on the dashboard? With a manual transmission, a tachometer can help you keep from redlining the engine, but a rev limiter could do the same thing. My motorcycle doesn’t have one and the only time I miss it is when I am adjusting the idle speed.


#9

Gauges, including tachometers, do NOT get lubricated.


#10

ken–From your description of the alternator problem, I would say that you merely had a bad electrical connection-- most likely a bad ground. As Jay indicated, tachometers do not get lubricated.


#11

To accurately adjust the idle speed, you really need an external diagnostic tachometer. The in dash tachs are usually laughably inaccurate at idle speeds.
I owned a Honda 550 four and I never could get it to idle at the specified rpm so I just adjusted a good idle speed by ear. Later on, I put a diagnostic tach on the bike and found that the idle rpm was almost exactly on spec, my instrument panel tach was just way off at speeds under 1000 rpm.


#12

Even with a manual tranny I never saw the use for a Tach. I can tell when to shift by listening and feeling the engine. I think people who rely on the tack aren’t paying attention to their engine. I’ve yet to really see a use for a tack in a every day commuter car. If someone has a real use for one I’d like to hear it.


#13

true and possible. we never diagnosed further because it was such a minor issue. The tach and speedo are lubed only at assembly ( as a 34 year parts man, I’ve seen many new and old here on my counter ),they are driven by magnetic attraction and my assumtion was that after 12 years the needle portion must be a bit dry. Then we gave it to my sister in-law and she also sees no need to pursue it further, just one of those quirks in an older truck that you learn to live with.


#14

They begin life lubricated, but as you say, do not ever, during their life span, GET lubricated further.