Stock Tach stuck at 4k

[fordplay2]

I have taken it apart, and everything looks ok. I put it back together and it just goes right back to 4k rpm's. Im really kind of stuck on this one. Could the problem be with the voltage reg behind the dash, or the module on the distributor? It was an automatic a few months ago. I know they sell module's for standard and auto, but would that really be an issue?

[FoxBodyNick]

Maybe have to re solder the connections....

or

You can do some testing with a VOM but for some tests you will need a break-out box and access to the Powertrain/Emissions Diagnosis Manual.

Here is the pinpoint test:

G1. Check supply to gauge.
Check voltage at pin C251-10, circuit 640 (R/Y). If battery voltage present (with key in ON position) then check gauge ground (see G2). If B+ not present then service circuit 640 and/or fuse 15 (10A) for open; retest system.

G2. Check gauge ground.
Use ohmmeter connected to known good grd, connect 2nd lead to circuit 397 (BK/W) and 651 (BK/Y) at connector pins C251-7 and C251-9. Measure resistances.
If less than 5 ohms go to G3. If more than 5 ohms service circuit 397 (BK/W) and 651 (BK/Y) for open; retest system.

G3. Check tach input circuit
Disconnect cluster connector C251. Install EEC-V breakout box to PCM connector C294. Use ohmmeter and measure resistance of C659 (O/W) at EEC 104-pin B/O/B pin 48 to cluster connector C251-8, circuit 11 (T/Y). Is resistance 1.8 ohm or less? Yes: Got to G4. No: service C659 (O/W) / Circuit 11 (T/Y) for open; retest system.

G4. Check cluster clip to cluster circuit connection.
Reconnect cluster connector C251. Use ohmmeter to check resistance from the tach connector clips to the instrument cluster printed circuit. Is there less than 0.2 ohm resistance? Yes: Go to
G5. No: Replace connector clips; retest system.

G5. Check printed circuit.
Use ohmmeter to check the following:

C251-7 ----- 397 (BK/W) ----- Ground
C251-9 ----- 651 (BK/Y) ----- Ground
C251-10 ----- 640 (R/Y) ----- Run/Start power
C251-8 ----- 11 (T/Y) ----- Tach input

[YALE]

Does it still have the stock auto computer?

[fordplay2]

Does it still have the stock auto computer?

Yeah im pretty sure it does. The problem is im not sure if it was doing it before the trans swap.

[fordplay2]

Wow Nick, you just made my head hurt.....

Thanks man, i will print it out and see what i can do.

[91CoupeMike]

Does it still have the stock auto computer?

What does that matter?

My car was an auto car, has the auto computer and the tach works fine. It's 5 speed.

Check the wires coming off of the coil and TFI module.

[YALE]

What does that matter?

My car was an auto car, has the auto computer and the tach works fine. It's 5 speed.

Check the wires coming off of the coil and TFI module.

I'm asking the questions here. Just the facts, ma'am.

[91CoupeMike]

I wish I had a haircut that cool..

[fordplay2]

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