The tach must be lying..

[Derek The Great]

Hey fellas,
I finally did the tach cluster switch for my tach-less ranger.. I did what i usually never do, I settled on one of the 5000 redlines, which are a dime a dozen.. I used to visit the boneyard in search of the 5500 redline (which is correct for the 4 bangers) but could never find one so this time around i found a donor exploader with a good cluster. Being a 3.0 the redline is 5000.. I did the swap and all was well. The tach works but i dont think its right. i have 3.73's out back and P205R14 tires.
-At 85 mph in 4th the tach reads 3k
-At 70 mph in 5th it reads slightly under 2k (i even attached a pic!)

At 85 in 4th, the engine sounds like it can't take too much more abuse.. In fact, if im in neutral and rev it past 4k, the gas pedal starts to vibrate- that seems all kinda wrong to me...

So, does this seem right to you guys? what are you running at those speeds, in those gears??
Thanks,
Derek

 

[Ozwynn]

I am not sure how the ranger tach hooks up but the one that went into my Suburban was triggered from the coil and it had switches on the back for 4,6, or 8 cyl..... maybe the tach thinks its hooked to a v6.

 

[Derek The Great]

Thats what I'm thinking.. There's a chip you can switch out (on the left side of each cluster) and i'm wondering if i should have switched that out or if i actually need a tach from a 4 banger

 

[Hawk1339]

There are online calculators to determine what speed you should have with respect to tire diameter, gearing, and transmission ratio at a given RPM.

Here is one such calculator.

As for using a 6 cylinder tach in a 4 cylinder, it might be necessary to disconnect one of the wires going to the tach. This is C250, pin 9, black/yellow wire. C250 is the vertical connector on the left side of the cluster, facing the back of the cluster. Some schematics call this the cylinder select. On a 6 cylinder it is grounded. For a 4 or an 8 cylinder pin 9 needs to be either disconnected or connected to the tach signal on C250 pin 8, tan/yellow.

Also, the "chip" on the left side of the cluster is probably the fuel slosh circuit and has no bearing on tach operation.

Update: The 93/94 schematic shows the BK/YL wire as open (no connection) but the 92 schematic shows the connection to the TN/YL wire. Maybe try it unconnected first, then try connecting pin 9 ON THE CLUSTER to pin 8, the TN/YL wire. DO NOT CONNECT THE BLACK/YELLOW WIRE TO THE TAN/YELLOW WIRE.

This is a link to the 92 tach circuit schematic.
This is a link to a document with 93 instrument cluster schematics.

 

[Derek The Great]

I'm not sure what diameter my tires are, but i estimated 36 inches..
I put in 3k rpm, 36", 3.73, and 1 (1:1) for 4th gear at 85mph, and got 86.17, pretty close... hmm...

 

[Ozwynn]

you got 36s with 3.73s on a 4cyl??????????????????????????? takes like what ...... 2 weeks to get to 55?

 

[Hawk1339]

I'm not sure what diameter my tires are, but i estimated 36 inches..
I put in 3k rpm, 36", 3.73, and 1 (1:1) for 4th gear at 85mph, and got 86.17, pretty close... hmm...

Here's another calculator to determine your tire diameter. For example, a 205/70/14 is 25.3" in diameter.

 

[Derek The Great]

Using 25.3" as the diameter the result is 60 mph... 25" doesnt make much sense though, the rim itself should be 28 inches in diameter...

 

[Hawk1339]

Using 25.3" as the diameter the result is 60 mph... 25" doesnt make much sense though, the rim itself should be 28 inches in diameter...

Huh? The diameter of a fourteen inch rim is... fourteen inches.

Here's the math without the calculator:

A 205/70/14 tire has a tread width of 205 mm or 8.07 inches. Section height is 70% of that, or 5.649 inches. Multiply by two (two sections of tire, one on either side of the rim), 11.298 inches. Add rim diameter, 11.298+14= 25.298 inches total tire diameter. Round it off to 25.3 inches.

 

[locovaca]

I got both of my clusters from a V6 engine and did not have to change anything wiring wise (one was a red line at 5000 from an explorer, this one is a 5500 from a Ranger). If I had to guess the module is either bad or someone took the needle off and didn't know how to put it back on correctly.

I have the same gears, and if memory serves correct I was running about 3000 at 65 mph in 4th, and 2500 or so at 70 in 5th. I'm not running a ranger cluster (and my new one has an inaccurate tach, go figure), so I can't verify those for you.

This might help you as well: http://www.therangerstation.com/tech_library/gearandtirechart.html

 

[fastpakr]

As locovaca said, the tachs are identical regardless of engine as long as they're from a compatible year RBV. I'm running a cluster from a 4.0 Explorer in my 2.3 Ranger. Dead on accurate, simple plug and play swap.

 

[Derek The Great]

Huh? The diameter of a fourteen inch rim is... fourteen inches.

Here's the math without the calculator:

A 205/70/14 tire has a tread width of 205 mm or 8.07 inches. Section height is 70% of that, or 5.649 inches. Multiply by two (two sections of tire, one on either side of the rim), 11.298 inches. Add rim diameter, 11.298+14= 25.298 inches total tire diameter. Round it off to 25.3 inches.

Thanks Hawk,
I feel like an idiot I figured "R" meant Radius.... Thanks for the explanation, now I actually understand what the numbers mean

 

[Derek The Great]

As locovaca said, the tachs are identical regardless of engine as long as they're from a compatible year RBV. I'm running a cluster from a 4.0 Explorer in my 2.3 Ranger. Dead on accurate, simple plug and play swap.

It was, but why does it seem like my engine is going to expload when I hit about 4k? (the engine sounds good, but the gas pedal vibrates and it just doesnt seem right to me) I'm actually scared to try and push it to its advertised 5500 redline..
for shits and giggles, The tach says I'm at 2k at 70 mph in 5th. The calculator says i should be going about 51 mph in 5th at 2k rpm...

 

[Derek The Great]

...this one is a 5500 from a Ranger)....QUOTE]
You wouldn't still happen to have that 5500 would you??

 

[Hawk1339]

Thanks Hawk,
I feel like an idiot I figured "R" meant Radius.... Thanks for the explanation, now I actually understand what the numbers mean

The "R" stands for "Radial". The only stupid questions are those that go unasked.

As for your tach reading error, I still think you might want to try the connection experiment as detailed in post #4 above.