RPM vs tach

[peganit2]

Umm, my 97 4.0 4WD auto will easily bury the tach and then some. It went WAY!!!past the redline and even into the speedo before I realised it. it has a 5500 redline, and if it's real, I must have hit 7000 plus.

Any thoughts???

aside; 4.0's aren't slow.

Second aside. It was WAY too easy to over rev it, so no lectures.

 

[peganit2]

in retrospect, the question is, is my tach messed up?

 

[Mightyfordranger]

Wow that must have been screaming hard and I can't say much about 4.0s but I'm surprised it held together past 6500 how long did you hold it for??

 

[fastpakr]

Is this a factory tach?

 

[peganit2]

As far as I know it's a factory tach, and NOT held long at all.

 

[Mike1919]

Does the tach rest at 0 with the engine off, and what does it read at idle? And by factory I believe he means, is it integrated within the dash cluster right next to the speedo or is it an aftermarket one somewhere else in the truck?

 

[PlumCrazy]

4.0s don't rev fast enough to hit 7K on accident. Most sound like they are coming apart at 5K.

Sounds like the tach is reading incorrect or someone put a newer cluster in. (I know the 03 tach read VERY wrong in m y 95)

 

[enjr44]

I would guess you have a different cluster in it. I think that if a cluster for a 4 was in there that needle would really zip around the clock.

And unless that auto is in "1" it would not let it go that high anyway. Maybe not then (rev limiter).

 

[fastpakr]

At least on the EDIS vehicles like my 94, tach signal is sent from the ignition as a standardized output so nothing changes on the cluster between engine types. I'm running an explorer (4.0 v6) cluster with tach with a 2.3 for cylinder and it reads correctly.

 

[peganit2]

Does the tach rest at 0 with the engine off, and what does it read at idle? And by factory I believe he means, is it integrated within the dash cluster right next to the speedo or is it an aftermarket one somewhere else in the truck?

Factory in dash tach, 0 rpm's off, 1100 in neutral, 900 in gear.

It didn't sound at all thrashed at that tach reading.

If it's off, would it be be linearly off?

 

[peganit2]

And unless that auto is in "1" it would not let it go that high anyway. Maybe not then (rev limiter).

Yes, a better question I should have asked. Should it have a rev limiter and what's the normal setting for it?

 

[Angie]

Probably the electric tach is screwy.

The truck I have been driving for the past year is a 92, and the guy i paid 500 bucks for told me it over heated. The tack reads 1100 at idle, 4.0 Auto. I know from the sound of the engine that it is sitting about 650 RPM not 1100. As I am driving the tach frequently jumps to 6000 or over and I know it is not past 2000 just by the way the engine is running.

all the gauges are screwed on the dash of this truck. I placed a water temp gauge in the truck and I can't get the temp past 200 all summer. the oil pressure fluctuates all over the place from the needle and i pay it no mind knowing nothing is wrong.

my guess place an after market tach and see what happens, or just listen to your truck's engine and get to know how it runs.... the tach is shorting out somewhere.