Dead tachometer & under powered running

[dllang]

(and underpowered is saying something for this old slug). I have a 94 ranger XLT 169 K miles on it. The engine is the 4 cyl 2.3L slaved to a 5spd manual tranny. Last winter I replaced the timing belt, plugs (not Bosch), plug wires, and other general tune up items. A couple of months later, the tachometer started to show an odd reading. It would indicate about 1/2 of the RPM that I knew the engine was running (this could occure while driving, so I could see the change). Also, when the tack would act up, the check engine light would come on steady. Other wise, the truck was running fine. This past week, I noted that the tack is completely dead, and the Check engine light is on steady. I also noted that during acceleration, you can feel the acceleration strengthen and weeken as if it cannot decide which set of plugs to use.
Question 1) where does the tack get its signal?
Question 2) Are the tack and the poor running conditions likely linked?
Question 3) Does the Crank position sensor have any thing to do with all of the above? (its the 1st thing that came to mind, but I'm not that familiar with Ford designs)

 

[AllanD]

the Tach is driven by a tach signal from the ignition module.
the tan wire with the yellow stripe

The tach is wired in between Pin12 on the Ignition module
and Pin#4 on the powertrain control module.

Your intermittent tach function is a SYMPTOM of an intermittent contact
between the Ignition module and the Powertrain control module.

the Check engine light is on because the computer dislikes running without
a tach signal.

Why? that is for you to determine, loose connector fatigued wire
bad ignition module

what exactly? I'm a mechanic, not a clarvoyant.


AD

 

[dllang]

Thanks, thats already 100% more info than I was finding in my Haynes (its what I could afford) manual. P.S. I enjoy a mechanic with a good sense of humor. Now if you will further indulge me, can you please tell me where to locate those two control modules. I have located the tan and yellow wire in a couple of places, but most of it is covered by the harness protection wrap.

 

[AllanD]

The PCM (Powertrain Control Module) on your 1994 is mounted
in the driver's side firewall and is most accessable via removing
the drivers side inner fender.

the ignition module is the grey "box" mounted to the front surface of
the lower intake manifold.

AD

 

[marcy]

the Tach is driven by a tach signal from the ignition module.
the tan wire with the yellow stripe

The tach is wired in between Pin12 on the Ignition module
and Pin#4 on the powertrain control module.

Your intermittent tach function is a SYMPTOM of an intermittent contact
between the Ignition module and the Powertrain control module.

the Check engine light is on because the computer dislikes running without
a tach signal.

Why? that is for you to determine, loose connector fatigued wire
bad ignition module

what exactly? I'm a mechanic, not a clarvoyant.


AD

My Ranger has the same problem as explained by dllang. However, mine is a 1992 (2.3L) and not a 1994. I can find the tan wire with the yellow stripe on the PCM, but there's no such wire on the ignition control module.

Do you know which color wire I should check on the ignition control module?

Alternatively -- assuming the ignition control module is the same as on the 1994 -- could you help me identify pin 12 of the ignition control module? (My module has 2 6-pin connectors, one on top and one below.)

Thanks!
Marcy

 

[marcy]

Ok, so I figured out the pin numbers of the ignition control module. There are actually very tiny numbers printed on it, which are quite hard to see when the module is still on the truck. I'll post the numbering scheme here in case anybody else needs it.

Standing in front of the track, looking at the module, pin 1 is at the top-right corner. Pin 2 is to its immediate left, and so on, rotating counter-clockwise:

6 5 4 3 2 1 (top connector)

7 8 9 10 11 12 (bottom connector)

On the 92, pin 12 of the ignition control module has a black wire with yellow stripe.

And it turns out it was the ignition control module that was faulty.

Marcy