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Unread 08-16-2015, 11:24 AM   #1
87yj4play
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87 yj, no tach after 4.0 head swap

87 YJ, 4.2 block with 4.0 head using 91 YJ harness, the tach signal off the ecm will not work with non OBD1 tach, using C5 on the bulkhead to the tach I checked for continuity, then connected to the negitive side of the coil I am not getting my tach to work, tach worked before swap so I must not be getting positive power to the Tach, dose the tach positive feed off the bulkhead connector or the under dash fuse panel? also no power to the reverse lamps, are they related?

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Unread 08-16-2015, 11:58 AM   #2
Drednot
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Quote:
Originally Posted by 87yj4play View Post
87 YJ, 4.2 block with 4.0 head using 91 YJ harness, the tach signal off the ecm will not work with non OBD1 tach, using C5 on the bulkhead to the tach I checked for continuity, then connected to the negitive side of the coil I am not getting my tach to work, tach worked before swap so I must not be getting positive power to the Tach, dose the tach positive feed off the bulkhead connector or the under dash fuse panel? also no power to the reverse lamps, are they related?


You swapped in the head.... intake, fuel injection and all, correct?

Usually those bulkhead connectors need to be cleaned, greased, and worked back and forth to scratch all good connections
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Unread 08-16-2015, 04:54 PM   #3
87yj4play
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checked out bulkhead connector and have continuity at pin C5 to the tach connector and on the harness side of the bulkhead
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Unread 08-18-2015, 08:16 AM   #4
Que89YJ
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The cluster is positive the ground trigger is supplied from the coil. Make sure you are on the right side of the coil. You need the ecu side. The wire color that you don't wnt is the one that is the same as the injectors power.
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Unread 08-19-2015, 09:56 AM   #5
87yj4play
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checked continuity from coil to injector, that should be negative, ran jumper wire to c5 from coil, still no tach
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Unread 08-19-2015, 11:03 AM   #6
Que89YJ
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The Green/orange is the hot. You want the other one.
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Unread 08-19-2015, 04:29 PM   #7
87yj4play
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tomorrow I will get a chance to check that out and repost, Thanks
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Unread 08-21-2015, 04:22 PM   #8
87yj4play
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I have GRN/BLK - and Y/BLK +, used meter to find ground GRN/BLK ran jumper wire to C5 on bulkhead still no tach, are the Positive wires for the tach ran through the fuse panel? (All fuses are good) or the distribution relay box?
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Unread 08-31-2015, 10:26 AM   #9
Que89YJ
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Sorry Ive been out for a while dealing with BS. Did you check continuity from the gage harness to the lead you are hooking to the coil negative?
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Unread 08-31-2015, 10:49 AM   #10
mike134
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I don't know if this pertains to you, but maybe it is somehow common with an FI addtion?

when I bought my Jeep the tachometer didn't work. it is an 89 upgraded with Mopar MPFI.

The tach signal wire attached to the tachometer had 10 volts constant on it (not the 'tach' signal wire from the new computer, which was disconnected), but the other end of the tachometer's signal wire was not connected to anything (the previous guy tried multiple times to connect it to the coil judging by all the butt splices along the way in the engine bay). Somewhere between the tachometer itself and the wire end in the engine compartment it was picking up 10 volts. So when it was connected to the coil, it still wouldn't work. I just ran a completely new signal wire from the coil to the tachometer and it worked out perfectly.

Que was trying to help me through that one, but there was no way to predict that there would be that unexplained constant 10 volt connection on the signal wire.
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Unread 08-31-2015, 03:20 PM   #11
87yj4play
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Yes Que I did Check continuity from the Bulkhead Connector to the harness plug at the Tach. I have the dash back together now, where dose the tach get it's positive power? and it it 12 volts or less?
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Unread 08-31-2015, 03:32 PM   #12
Que89YJ
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It's 12 volts. I meant from the connector for the gauge on the tach itself. There are 2 nuts that hold it in and connect power and signal to it.
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