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96 Trans Am LT1 Tach goes to zero Engine sputters and then

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runs fine. Tach still...
96 Trans Am LT1 Tach goes to zero Engine sputters and then runs fine. Tach still erratic! Any clue out there??
Submitted: 1 year ago.Category: Pontiac
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Answered in 7 hours by:
11/26/2016
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago
sprinkles08
sprinkles08, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 23,505
Experience: ASE Master and Advanced level certified. Factory trained with 17 years dealership experience
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Hello and welcome to JustAnswer!

If the engine runs poorly and the tach drops out then odds are you're losing crank sensor signal. The crank sensor signal is needed for spark and is where the engine speed signal comes from.

The first step in diagnosing the problem is to use a scan tool or code reader to see what fault codes are setting. Have you checked for codes?

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Customer reply replied 1 year ago
No codes are present. Drove it today. Tach was very erratic. Ran fine. Stopped for 2 hours and was very hard to start. When it did finally crank it sounded like
popping through the intake several times. The tach came on and off then ran fine again. Stopped again for 15 min. Didn't think I would get home. The same thing happened.
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

Do you have an actual scan tool or a labscope?

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Customer reply replied 1 year ago
I scanned for codes and came back PASS
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

If you have a scan tool then I would recommend monitoring the crank sensor signal when the problem is happening. It may take a labscope to see the signal dropping though because a scan tool may not update quickly enough.

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Customer reply replied 1 year ago
My cheap scan tool don't give live data. It just pulls codes. This started yesterday. I got home went to back into the garage and it died but started right back up. Spit and Sputtered but got inside. It seems to be getting worse.
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

That;s a code reader then rather than a scan tool. A scan tool is a multi thousand dollar tool that allows for reading live data, performing actuator tests and reading fault codes.

It's likely that you have a bad crank sensor but it would take some testing to know for sure.

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Customer reply replied 1 year ago
I've been calling around since you first said that. It's only about $75. It's worth a try. I will let you know.
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

Great!

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Customer reply replied 1 year ago
Of course the parts store was out of stock on the $75 Brand so I opted for new AC Delco crank sensor. $155.00. Didn't do it. Same problems!
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

I assumed you meant $75 was the diagnostic charge wherever you called. Anything at $75 is going to be a code reader, an actual scan tool will start at around $2,000.

You could have a crank sensor wiring or connection issue or the tach may be dropping because the engine controller is actually going down due to an internal failure or a loss of power or ground to it. You can do a visual inspection of wiring and connections and you can try to monitor sensor reference voltages when the problem happens to see if you can catch something dropping, but the ability to monitor data is most likely going to be necessary to accurately diagnose it.

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Customer reply replied 1 year ago
Come to find out the crank sensor has nothing to do with spark or tach signal. It only detects misfires. Thanks. Still having the issue.
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

The crank sensor is the main input needed for spark and is where the engine speed signal comes from, the tach shows engine speed. You either have a crank signal issue or the engine controller is going down.

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Customer reply replied 1 year ago
Well I have replaced the crank sensor and still have the problem. What is the engine controller?
Pontiac Mechanic: sprinkles08, ASE Certified Technician replied 1 year ago

The module that controls engine functions.

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Customer reply replied 1 year ago
Oh Good Grief! You're no help at All !!! Forget it!
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sprinkles08
sprinkles08
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Category: Pontiac
Satisfied Customers: 23,505
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Experience: ASE Master and Advanced level certified. Factory trained with 17 years dealership experience

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