85 corvette with flicker on dash and radio

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
85 with flicker on dash and radio . . .?
Hi everyone

I noticed a flicker with the dash lights and well timed high pitch pulse when the radio is on - as well as a moody tach readout - the interference seems to keep close time with what sounds like the pulses of the motor - I was wondering if anyone else has come across that? I saw somewhere that the '85 has a tachometer filter - does that have anything to do with it? - sorry this is on a 1985 standard

any thoughts or opinions would be greatly appreciated

Sean
grstrapS.jpg
http://garage.grumpysperformance.co...urrent-flow-grounds-and-more.3504/#post-54625

http://garage.grumpysperformance.co...hooting-tip-for-electronics.11317/#post-51557


https://batee.com/pages/repairing-the-1984-1989-c4-corvette-digital-instrument-panel-cluster-dash


http://garage.grumpysperformance.co...instrument-cluster-has-stopped-working.16375/


Id start by pulling trouble codes and checking fuses
but a loose electrical connections , bad electrical ground connection's on the battery and engine and frame would be very high on my list of potential causes,
Id also suggest testing the alternator, bad diodes or a defective alternator might be to blame, keep in mind the cars electronics are now 32 years old and the O.E.M. dash gauges are fairly well known for weak solder connections, and corrosion on push-on electrical connections, so the dash gauge cluster may need to be repaired or replaced.
as always ISOLATE AND TEST
I've seen guys rush out and spend hundreds of dollars on parts,too fix a problem, take a great amount of effort to tear apart the dash or other area and once the new parts installed it still won't work, so forced to do further research at that point they only then find a blown fuse or corroded electrical connection.(that was the true initial cause)
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G104-G107 are very suspect, it the dash and gauges are having problems

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reading through the links below and the sub-links will help you locate the source of the problem
and yes skipping the links and sub links that contain a huge amount of info is a mistake
this infos bound to be helpful at times
Sensor Locations

Sensor
Location

Engine Coolant Temperature Sensor. Front of engine, below Throttle Body.
Engine Oil Temperature Sensor. Left rear of engine, just above the oil filter.
Oil Pressure Sender/Switch. Top, left hand rear of engine.
Fuel Quantity Sender. Top of fuel tank, beneath filler pipe escutcheon panel.
MAT (Manifold Absolute Temperature Sensor). Underside of manifold air plenum at rear.
Outside Temperature Sensor. Right side of engine, top right corner of radiator.
In Car Temp Temperature Sensor. Coupe: above left seat near interior courtesy light, Convertible: center of cargo compartment lid.
MAF (Mass Air Flow) Sensor. Front of engine ahead of throttle body.
Oxygen (O2) Sensor. Left side of engine, in exhaust pipe.
TPS (Throttle Position Sensor). Right side of throttle body at the front.


Sensor Outputs:

Sensor
Measured Value

Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
Engine Oil Temperature Sensor. 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.
Oil Pressure Sender/Switch. 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F, 15,000 Ohms @ 40 F.
Outside Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
In Car Temp Temperature Sensor. 4400 Ohms @ 60 F, 2200 Ohms @ 85 F.
MAF (Mass Air Flow) Sensor. .4 Volts @ idle, 5 Volts @ Full Throttle.
Oxygen (O2) Sensor. .1 Volt Lean Mixture, .9 Volt Rich Mixture.
TPS (Throttle Position Sensor). .54 Volts Idle, ~ 5 Volts Full Throttle.
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having a wire roll caddy , thats easy to access or fabricating one for working around the cars helpful








http://garage.grumpysperformance.co...er-repair-or-replacement-link.1006/#post-8030


https://batee.com/collections/84-89-corvette-parts


http://garage.grumpysperformance.co...uys-don-t-look-at-the-clues.11176/#post-50124

http://garage.grumpysperformance.com/index.php?threads/chasing-a-crazy-electrical-glitch.986/

http://garage.grumpysperformance.co...wrong-after-alternator-swap.13580/#post-70168

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-6985

http://garage.grumpysperformance.co...wrong-after-alternator-swap.13580/#post-70168

http://garage.grumpysperformance.co...ir-of-circuit-board-solder-connections.16362/

http://garage.grumpysperformance.co...tting-out-low-voltage.12221/page-2#post-59599

http://garage.grumpysperformance.com/index.php?threads/electrical-problem.10714/

http://garage.grumpysperformance.co...ing-down-an-electrical-drain.8493/#post-37179

http://garage.grumpysperformance.com/index.php?threads/testing-an-alternator.3222/#post-46703


http://garage.grumpysperformance.co...lay-switch-locations-and-info.728/#post-54562

http://garage.grumpysperformance.com/index.php?threads/diagnoseing-tpi-lt1-problems.1241/#post-2648

http://garage.grumpysperformance.co...uel-injector-resistance-reading.606/#post-805

http://garage.grumpysperformance.co...rvette-after-battery-failed.10291/#post-41710

http://garage.grumpysperformance.co...questions-can-be-found-here.12892/#post-66934

http://garage.grumpysperformance.com/index.php?threads/engine-test-run-stand.930/#post-40783

http://garage.grumpysperformance.co...rical-glitches-in-newer-cars.5492/#post-18411

http://garage.grumpysperformance.com/index.php?threads/digital-dash-swap-questions.3399/#post-8970

http://garage.grumpysperformance.co...er-repair-or-replacement-link.1006/#post-8030

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-6985

http://garage.grumpysperformance.co...ntermitant-electrical-glitches.987/#post-1739
 
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1990 Tach Not working
The tach use to jump all over the place but now has dropped all the way to the bottom of the gauge past the bottom RPM mark. It does not move at all even when the switch is first turned on. I had thought that this required me pulling the cluster and sending it out for a rebuild but a member on a different forum said the function of the tach was unrelated to the circuit board that would be replaced and I would still have the problem.

If this is the case what else could it be and how can I fix it?

Thanks






if you have a gauge related problem, you always need too, drop back too the basics and verify the electrical connections too the tach,or any other component you suspect too be defective ,
pull trouble codes and check fuses,
and verify sensor or electrical feed and grounds of that signal are there,
and functioning correctly, before you start ripping out and replacing components




http://garage.grumpysperformance.co...lay-switch-locations-and-info.728/#post-54562

THINK LOGICALLY ISOLATE AND TEST,
CHECK YOUR FUSES AND FOR LOOSE ELECTRICAL GROUNDS
AND CONNECTIONS TO SENSORS!
USE A METER TO CHECK FUSES (REPLACE IF IN DOUBT!)
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GET out the multi meter, and a fuel pressure gage,
and do a few quick tests for loose electrical connections, look for vacuum leaks and consistent fuel pressure on the fuel rails
and verify the alternator voltage is at or above 13.5 volts,
when things don,t run correctly and the guys that don,t
pull the trouble codes, they are skipping a step that may waste hours
obviously the basics always apply ,


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http://www.testequipmentdepot.com/e...1100200223789&utm_content=All Extech Products
INFRARED TEMP GUN
you always need a base line to start from, on a corvette.
a logical step by step approach and keeping accurate notes helps.
youll NEED a multi meter, a shop manual
and a timing light and fuel pressure gauge at a minimum,
set and verify your ignition timing, pull trouble codes,set your tps and iac,, then check for vacuum leaks on the lines and intake,then get out your multi meter and verify all the sensors, chances are good a logical step by step approach will lead you to the problem, youll be amazed at what youll learn reading links.
use of a shop manual and multi meter
BOTH can be very helpful ,
IN
ISOLATING PROBLEM ISSUES
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MULTI METER

INFRARED TEMP GUN

TIMING LIGHT

COMPRESSION GAUGE

PRESSURE/VACUUM GAUGE
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read the links and sub links

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/

http://garage.grumpysperformance.co...oven-facts-if-your-in-doubt.13051/#post-69824

http://garage.grumpysperformance.co...u-need-to-know-setting-float-levels-etc.1115/

http://garage.grumpysperformance.com/index.php?threads/digital-cluster-repair.1007/#post-1822

http://garage.grumpysperformance.co...-system-trouble-shooting-flow-chart-info.596/

http://garage.grumpysperformance.com/index.php?threads/1984-fuel-pressure.11776/#post-55675

http://garage.grumpysperformance.co...ard-starting-tpi-crossfire-or-lt1-vette.1401/

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/

http://garage.grumpysperformance.com/index.php?threads/replacing-a-c-4-fuel-pump.33/

http://garage.grumpysperformance.com/index.php?threads/c3-c4-corvette-vacuum-diagrams.1773/

http://garage.grumpysperformance.co...ckpressure-hurting-your-combo.495/#post-26600

http://garage.grumpysperformance.com/index.php?threads/what-kills-o2-sensors.3049/#post-51701

http://garage.grumpysperformance.co...lay-switch-locations-and-info.728/#post-43477
http://garage.grumpysperformance.co...hink-logically-don-t-assume.12484/#post-62772
https://www.harborfreight.com/lcd-automotive-multimeter-with-tachometer-kit-95670.html
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related info

http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-69239


http://garage.grumpysperformance.com/index.php?threads/c4-c5-corvette-trouble-codes.2697/#post-7017
 
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