RPM gauge not working

Beakster · Feb 5, 2010

Hi,

My RPM gauge always reads zero. I have plugged my laptop in with OBD2 and I can see the correct RPM read out, so I guess its a wiring problem.

Does the signal for the RPMs come from the coil packs, or the ECU? Any idea why the gauge would stop working? Common wiring fault or faulty gauge?

Thanks

wmburns · Feb 5, 2010

What MY car?

Low tech question. What model year car are we dealing with? The cluster is very different between a 1999-2004 vs a 1996-1998.

What mods have been done.

Have you checked all of the fuses?

Good work on the ODB2 scanner. The fact the PCM knows the correct speed means the problem has to be in the cluster itself (the Cluster gets the data from the PCM depending upon MY).

Beakster · Feb 5, 2010

Hi, thanks for the reply...

wmburns said:
Low tech question. What model year car are we dealing with? The cluster is very different between a 1999-2004 vs a 1996-1998.

It's a 1997 Thunderbird LX 4.6 V8. Its a pretty crappy looking cluster, and I think I read that the last year of thunderbirds used the same cluster as the Taurus to save money. (Sorry not a mustang, but can't find a good Tbird forum, and hopefully not too different given its same engine/ecu/manufacturer etc).

wmburns said:
What mods have been done.

None as yet, everything appears to be standard. RPM gauge broken since I bought last week.

wmburns said:
Have you checked all of the fuses?

Haven't yet, but will this weekend. Everything else seems to work correctly, and I couldn't see anything in the manual to indicate a fuse specifically for the RPM gauge so didn't think it could be a fuse.

wmburns · Feb 5, 2010

T-bird tach test

Ok, I am a Cougar/Thunderbird fan. I recently traded a 97 Cougar that I liked a lot (got a good deal). OK. the reference I have is for the 96 MY. There are differences but I hope they will not be too great.

OBTW, the tach signal comes from the PCM.

For what you are trying to do, you may need your own copy of the wiring diagrams. If trying to ohm out wiring harness, the connector diagrams are invaluable.

The hard copies or CD can be purchased from ebay.

>>>From 1996 Ford service CD Cougar/T-bird
PINPOINT TEST H: TACHOMETER NOT REFLECTING ENGINE SPEED

H1 CHECK SUPPLY CIRCUIT 640 (R/Y)TO GAUGE
l Turn ignition switch to OFF position. Partially remove instrument cluster as outlined, to gain access to the cluster connectors.
l Turn ignition switch to RUN position.
l Using a voltmeter, check B+ at Circuit 640 (R/Y) at Connector Pin C1-11.
l Is battery voltage present?

Yes
GO to «H2».

No
SERVICE Circuit 640 (R/Y) for open. RESTORE vehicle. RETEST system.

H2 CHECK GAUGE GROUND
l Using an ohmmeter connected to a known good ground, connect second lead to Circuit 651 (BK/Y) (875 (BK/LB) with 4.6L engine) at connector Pin C1.
l Measure resistance.
l Is resistance 5 ohms or less?

Yes
GO to «H3».

No
SERVICE Circuit 651 (BK/Y) or 875 (BK/LB) with 4.6L engine for open circuit. RESTORE vehicle. RETEST system.

H3 CHECK TACHOMETER INPUT CIRCUIT 648 (W/PK)
l Turn ignition switch to OFF position.
l Disconnect cluster connector C1.
l Disconnect ignition coil.
l Using an ohmmeter measure resistance of Circuit 648 (W/PK) from ignition coil connector, to instrument cluster connector Pin C1-18.
l Is resistance 1.8K ohms?

Yes
GO to «H4».

No
SERVICE Circuit 648 (W/PK) for open. RESTORE vehicle. RETEST system.

H4 CHECK TACHOMETER
l Reconnect cluster connector C1.
l Using an ohmmeter, check for continuity at all tachometer connector clips.
l Is there continuity?

Yes
GO to «H5».

No
REPLACE tachometer. RESTORE vehicle. RETEST system.

H5 CHECK INSTRUMENT CLUSTER PRINTED CIRCUIT
l Using ohmmeter check each circuit per chart for continuity from gauge connector clips to cluster connector C1.
C1 CONNECTOR
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³ Pin ³ Circuit ³ Function ³
ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´
³ 1 ³ 651 (BK/Y) ³ Ground ³
³ ³ 875 (BK/LB)(a) ³ ³
ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´
³ 11 ³ 640 (R/Y) ³ RUN/START Power ³
ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´
³ 18 ³ 648 (W/PK) ³ Tachometer Input ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
(a) - 4.6L engine only

l Is there continuity at all circuits?

Yes
REPLACE tachometer. RESTORE vehicle. RETEST system.

No
REPLACE instrument cluster printed circuit. RESTORE vehicle. RETEST system.

RPM gauge not working

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