Tachometer not working why?

Tiny
DAVISMELODY6669
  • MEMBER
  • 1996 CHEVROLET SUBURBAN
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I may seem like a lost cause, I get rpm signal crazy and sometimes I don't get nothing. Noticed oil pressure gauge goes crazy too then back to normal. My test light lit up pointing to my feed for the ignition coil and ignition module and doesn't flicker while cranking. Also the control wire (white) is lit with test light (key off) when turning the key on the light goes off from coil n module. I checked the ground from module even while cranking the test light doesn't get dim. I have no spark. Test light is lit while pointing to the 20a fuse on the ECM1. With key on but when key off there's no light. I do not know what to do next.
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Tuesday, December 31st, 2019 AT 8:12 PM

10 Replies

Tiny
TOUGHDIVER
  • EXPERT
Hi,

If your RPM is erratic and your other gauges is giving weird readings you might have a faulty Instrument Panel Cluster (IPC). When I worked in the Chevrolet Dealership I replace them on a regular basis. I'm attaching wiring diagrams below for you to reference and use manual external gauge to check readings to diagnose.
Please let us know if this information is helpful for you and what fixed your problem.

Thank you
Joe T.
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Wednesday, January 1st, 2020 AT 3:36 PM
Tiny
DAVISMELODY6669
  • MEMBER
My signal wire from ignition coil and ignition module grounded out I have no spark
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Sunday, January 5th, 2020 AT 8:02 PM
Tiny
DAVISMELODY6669
  • MEMBER
I have power feed using a test light but no light point to the white wire. Idk how to make it ungrounded.I changed fuses and all sensors are new. No wires are touching metal to get grounded
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Sunday, January 5th, 2020 AT 8:04 PM
Tiny
TOUGHDIVER
  • EXPERT
Hi,

It's possible the distributor shaft broke or stripped drive gear, And not distributing spark or the crank sensor is shorted or have an open circuit and also not sending a signal, You will need to run diagnostics on the Ignition system, I'm attaching links and wiring schematic and ignition diagnostic charts for checking resistance and voltage drops on the ignition system below to help you test these components, also included information on Engine cranks but won't start enhanced diagnostics, Please let us if this is helpful and what fixed your vehicle or if you need more information.

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Thank you
Joe T.
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Sunday, January 5th, 2020 AT 10:01 PM
Tiny
DAVISMELODY6669
  • MEMBER
Can I do these test with the fuel pump relay off so I mess up the new injectors or get them flooded? I don't get spark from the coil I don't think it's the gear that's broken because it's new melonized gear for the cam.
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Monday, January 6th, 2020 AT 9:19 AM
Tiny
TOUGHDIVER
  • EXPERT
If your not getting spark at the coil wire with a spark tester, You need to start checking primary voltage for the ignition system. Check the under hood fuse box ( Cell 10 20A ECM 1 fuse replace fuse if blown ), If the fuse is good, You need to check for 12 volts at the ignition coil connector, (Key on engine off), with a voltmeter check the pink wire to the black wire with white stripe for 12 volts, If you have 12 volts unplug the ignition coil check the resistance (Ohms) from the coil towler to the body of the coil, If you have any resistance at all replace the ignition coil, Next unplug the crank sensor check for 12 volts at the pink wire and black with white stripe for 12 volts if you don't have volts repair open wire, If you have 12 volts replace the crankshaft sensor, Next unplug the ignition module connector and check for 12 volts at the pink wire to the black wire with white stripe, (If you have 12 volts replace the ignition module), If you don't have 12 volts repair open wire, Refer to the wiring diagram it will you locate wires. Please let us know if this was helpful and if you need any more information.

Thank you
Joe T.
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Monday, January 6th, 2020 AT 2:52 PM
Tiny
DAVISMELODY6669
  • MEMBER
The ECN didn't have good ground.
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Thursday, January 9th, 2020 AT 1:29 PM
Tiny
TOUGHDIVER
  • EXPERT
Happy to see you fixed it. Thank you for choosing 2CarPros, Let us know if you have any other vehicle repair concerns and we'll be happy to help you with information on fixing it.

Thanks again
Joe T.
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Thursday, January 9th, 2020 AT 2:53 PM
Tiny
DAVISMELODY6669
  • MEMBER
Okay, thank you for taking your time to respond to my questions.
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Friday, January 10th, 2020 AT 7:13 PM
Tiny
KEN
  • ADMIN
You are welcome, DUFFDIVER is one of our newest experts, he is quickly shaping up to be one of our best!
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Monday, January 13th, 2020 AT 1:41 PM

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