so we shut off the truck and started it again and now it has very low power and is running very rough. it is very slow to excellerate rpm even when not moving.

i have 3 rangers so i switched out a bunch of parts and nothing has made a diffrence so far.

changed exhust side coil pack,
added gas,
checked air filter
changed MAF
pulled plugs though it ran the same on 3, then switched that wire and still did not make a diffrence and i cant really get that one to have a spark.
checked fuel pressure.

one noticeable thing is the tachometer also stopped working, does this run off the crank sensor?

i am thinking we should change the crank sensor or the ecm next , any advice?

 

Yes and no on the CKP(crank position) sensor, CKP sensor wires run to the ICM(ignition control module),located on the front of the lower intake manifold, the ICM sends a PIP(timing pulse) to computer, this pulse is also used for the tach, main purpose is to time fuel injectors and also allows computer to send the ICM spark advance suggestions.
The ICM also runs the coil packs directly.

Missing CKP sensor data causes a no start, no spark, no fuel.

The ICM's were a common problem between '89 and '95 on the 4cyl engines


Your description changes half way down, you start off with low power and slow RPM response then suggest a misfiring cylinder, #3?????

If you have 1 out of 4 cylinders not working that would cause 35%-40% power drop and slow RPM response, not 25% because the other 3 have to drag non-functioning parts around so less power and more drag.

A cylinder fires because it has 3 things
Spark, at the right time
Fuel, in the correct air:fuel ratio
Compression, above 120psi

Compression should be the first thing you check, it is a mechanical process so can't be intermittent like spark or fuel, so once tested it can either be ID as the problem or taken off the table as the problem, no tail chasing as with spark and fuel.
1991 2.3l should have above 150psi compression in each cylinder
You need to test all 4 with one spark plug remove on each cylinder during test

Before doing compression test, unplug both coil packs and crank the starter motor a few times.
As you remove 1 spark plug from each cylinder check it for fuel, each should have fuel on the tip.
Leave both coil packs disconnected for compression test.

Spark plug tips can tell you alot about what is happening inside a cylinder.
Google: Spark Plug Condition

Lots of pictures to see on what the tips can tell you.