I have a 1999 ford ranger xlt with a 3.0l flex fuel and it is a Automatic transmission with a tachometer. The tach works most of the time but ussually reads about 400rpm above the readout I get from the OBD port scanner. The reading from the scanner seems to be more accurate to me considering the engine sound and the fact that it is idleing when this is being observed. at Idle the tach reads about 1200-1400 rpm but the Obd scanner says it is 800-950 rpm. 800 is closer to the correct idle speed for the 3.0l correct? I know it is not 1200 rpm or higher. the tach will also jump around sometimes when the engine speed has not changed. Sometimes it even does it under load while driving, not necessarily at an idle. I have replaced the Crank Position sensor and it s has consistently read around 400rpm to high every since, and once stayed at 0 while idling. what else could cause that other than the crank position sensor. Do the rear abs sensors affect that or where do I go from here to get the tach on the dash working correctly?

 

The engine wouldn't run if Crank Sensor was the issue

In a 1999 Ranger the Tach signal comes from Computer(PCM) pin 48, not crank sensor(1995 thru 2003)
PCM uses the crank sensor timing for spark and injectors, but converts it to Tach pulse for sending out to cluster

PCM pin 48 runs to the cluster on a tan/yellow wire, connector C214 pin 15 of the only 16 pin connector on the back of the cluster

Most likely issue is a problem in the cluster, might be a bad connection on the back of the cluster, but most likely an internal cluster issue
1996 thru 2003 Ranger/Mazda B-series clusters are interchangeable, plug and play no changes in wiring needed

You can even use White Face if you want
Odometer can be an issue, hard to change those, doesn't effect anything but technically its illegal to swap in a lower mile odometer for purpose of deception in actual miles on the vehicle

Swapping out just the tachometer has its own issues, main one is getting the needle back on in the right place, lol, must do it with the clear cover off and engine running at a known RPM then push on the needle carefully

 

The dash was replaced by the previous owner with the white cluster from a 1999 Exploder when the also swaped in a 8.8 3:73:1 ratio rearend from the Same expolder. The Led bulbs he put in the Explorer cluster have never worked all the time and turn on and off while driveing the truck at unpredicable intervals. I did take it to a professional mechanic who said he straigtened out some of the connectors on the cluster to get the bulbs working correctly. that made all teh bulbs work correctly for about a month and then they have been back to what it was a the time we purchased the truck. The Tach however worked fine until about a year ago. We have owned the truck for about five years. Four of those the tach worked great. The oil presure gauge started intermintently going to zero after the mechanic looked at it and has done that untill I just now replace the oil presure sending unit. That seems to have fixed the oil presure gauge. Though I know it is not a guage but a stupid switch. I was thinking and hoping the tach was something simular and not a result of the previous owners jank cold solder joints and wiring practices. I have been chasing the bad wiring he caused since I bough the truck. There is a after market device or plug that is spliced into the blue yellow wire of the ignition switch that I do not like being there or the fact that is spliced into the ignition. I would remove it but I am afraid it is also tapping into wires that affect teh Pats system or it itself is a after market security system that works with the pats system and the previous owner just did not tell us about it. We asked and he said he did not know what it was. I have done my best to trace the wires by sight and with a electronic toner but I can not figure out where the connect to on the other end of the adapter without pulling the whole stinking dash apart. I am not doing that unless it keeps the truck from running. Though someday I may get brave and risk the function and drivability of the truck and rip the dash apart till I figure it out and redo all wiring to OEM spec. In the mean time I guess I will hope that is not what is messing with the dash cluster function and just go buy a new or newer Exploder cluster.
The mechanic was suppose to have fixed all noticable issues with the cluster. Maybe a resistor of something that has to do with the function of the tach went bad. Is it possible to repair the cluster I have but replacing or resoldering a new resitor or other part to the existing Cluster. If so what parts on the back of the instrament cluster circut pad should I be looking at for bad components or broken solder joints and the like?
The attached pic is of the aftermarket device I want to remove but fear will mess with the PATS system. Anyone want to take a stab at what that is and if it is safe just to cut the wires and reconnect the factory stuff the best i can?

 

No idea what that is for

I would suggest getting a Ranger/Mazda cluster with tach, 1996 thru 2003

He may have re-pinned some wires but would still have the same connectors so you can look at the below diagram to make sure wires are in the right place by color code, and re-pin as needed to correct Ranger configuration
It is easy to re-pin these wires
Use a tiny screwdriver or even a paper clip, push it in from the contact side while pulling on the wire, there is just a spring clip solder onto the wire, once its pushed down wire pulls out with the clip
Slide wire/clip back into the right place and it will lock into place