instrument cluster IVR

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instrument cluster IVR

May 16, 2014, 11:16:45 AM

is it nessesary for the ivr to produce "pulsating" 5v instead of steady 5v out to the gauges?
meaning, is the bimetal ivr constantly heating / cooling thus opening and closing its internal wire wound contact?

speaking of gauges, is the eVTm accurate with the 5.0L diagram vs the 2.3L?

5.0 diagrams show the ivr powers the fuel and temp gauges
2.3 diagrams show the ivr powers the fuel, temp and oil gauges

instrument cluster IVR

Reply #1 – May 16, 2014, 12:49:50 PM

My ignition switch melted and i lost power only to the gas and temp on my 86.

instrument cluster IVR

Reply #2 – May 16, 2014, 04:57:04 PM

IVR powers water temp, oil pressure and fuel level gauge. And no, it isn't necessary to feed them with pulsating voltage. I have IVR mod (78T05) in both my birds and it works like charm.

PS: 5.0 refers probably to base cluster, which doesn't have oil pressure gauge.

instrument cluster IVR

Reply #3 – May 16, 2014, 05:20:43 PM

we worked on a temp high issue but conclude the temp is not high.
the resistance from the ign sw to cluster is 8.2ohms
we were able to dial counter clockwise the IVR calibration screw but my son decided he wanted to swap another IVR on.
if he had kept the one we tweeked, it would have yielded a lower temp reading.

we placed another ivr on and the same results
temp is up to the red when the radiator cap temp gauge reads 200

the gauge is reading 12.2ohms
the sender is new,
the wiring fromt he sender to the cluster has not been checked yet but if it were high resistance, then i would think the gauge would read low temps.

so,,
do you have a diagram on the ivr? you modified?

instrument cluster IVR

Reply #4 – May 16, 2014, 05:38:41 PM

i wonder if this symptom is normal, read carefully

-with the car running
-with the cluster pulled out enogh to get ot the rear
-wth my meter on the IVR ouput
i get dc volts pulsating between 8 and 12vdc

for some reason i thought the resistance wire made the 5v then the ivr fed the gauges... seems i have hit backwards.

with the cluster connector disconnected , i read battery voltage on the resistance wire, i was expecting a lower voltage.
the resistance on this wire was well within specs of 8.2ohms. the guage itself read 12.5ohms.

odly enoiugh, when we turn on the headlamps, the temp needle goes up about a little as well.

instrument cluster IVR

Reply #5 – May 16, 2014, 08:35:57 PM

Remember that the resistance wire doesn't limit Volts, it limits Amps. The IVR should be steady, not pulsating. If I ever end up with an IVR problem, I'm going to build a solid state IVR. So far, though...

instrument cluster IVR

Reply #6 – May 16, 2014, 08:54:02 PM

I wonder if you have a charging problem.

a high resistance to ground will artificially inflate voltage as well as.get worse as things heat up electronically.

another thing to consider maybe.

instrument cluster IVR

Reply #7 – May 16, 2014, 10:49:02 PM

i considered the resitance wire as to also include a voltage drop,, since it does act as a resistor., and in series there should be a proportional voltage drop.
the evtm / shop manuals state the ivr provides pulsating 5v

i also considered the ivr to be a somewhat additional resistive load and this coupled with the series resistance wire aided in getting the amps / volts conditioned for the gauges.

instrument cluster IVR

Reply #8 – May 17, 2014, 06:28:54 AM

I've never seen one pulse. For me they've always measured around 5v while fluctuating about .5v in either direction. So up and down a bit, but not something I would describe as pulsing.

instrument cluster IVR

Reply #9 – May 17, 2014, 12:45:23 PM

although this does not actually fix the "potential problem"
i am considering twisting 4 100ohm resistors in parallel then place this in series with the sender wire.
100ohm because thats what i have for some various clr items in my parts bin.
this should get me to a min resitivity of 25ohms signal to the gauge max.. not sure if that would reflect a pure "over heating" indication yet.

i would really like to figure out what the actual issue is.

instrument cluster IVR

Reply #10 – May 17, 2014, 11:08:55 PM

double post..oopps

instrument cluster IVR

Reply #11 – May 17, 2014, 11:09:23 PM

to solve this issue> "when i turn on the headlamps, the temp needle climbs up slightly"

i am considering using a product ive used in the past ~ http://www.rofu.com
There is a product #9148 which is a voltage converter.
it takes 12 to 60v AC or DC input and converts it to steady 12vdc out.

If i place this upstream of the resitance wire in series, the ROFU 9148 will then feed the ivr with stable 12v, thus what i suspect being the alternator increasing ouput when i turn on the headlamps will be nullified with this product... it will buffer out the influence of the alternator.

basically its going to end up being 12v dc input,, then 12vdc output.

now, if someone understands this circuit better than me,, here is what i am thinking if i want to iliminate the ivr........
since the guages are 12.5ohms.. in parallel being for the 5.0 only the temp and fuel are fed off the fuel guages........
then thats about 6 ohms resistance resulting in both gauges being in parallel,(excluding the downstream fuel fload variable resistor and the downstream temp sender.

should i put a 6ohm resistor on the oput put the ROFU so 50% source is dropped, and then each guage will then have the remaining battery voltage which is about 5 or 6 volts?

or,, would i place the rofu upstream of the resistance wire?,, this seems more logical to me, it would have to be wired driectly off the ignition switch where the gray/yel wire is and its output tied to the resistance wire,, thus everything upstream including the resistance wire would remain the same.

instrument cluster IVR

Reply #12 – May 18, 2014, 12:12:40 AM

I think if you eliminate the irv completely, your going to have to try a few different resistors to give you the exact correct value.

for example, the gas guage sender can be off by a good bit and still be within.spec. if you change the input voltage to make the dash input read correctly, you might alter the displayed voltage of the guage itself.

it makes sense to me to do away with the resistive wire all together, then use the output of your 12v regulator, and then ad the resistor as the new output for the irv.

running a voltage regulator off of a resistive wire just seems sort of silly to me.

instrument cluster IVR

Reply #13 – May 20, 2014, 09:59:35 AM

If you want to elliminate IVR completely, then you need constant voltage source, not just resistors. Why? Because Ohm's law. If your temperature, oil and fuel gauge reads high, there is some current flow and corresponding voltage drop on that resistor. When all the needels reads low, the current is way lower and voltage drop too.

I really don't know, why nobody listens to my advices with modifying IVR with 78T05 linear voltage regulator. You need just two more capacitors and everything fits perfectly inside the IVR case.

BTW, standard IVR will always produce pulsating voltage because of its internal design with bimetal switch.

instrument cluster IVR

Reply #14 – May 20, 2014, 02:00:05 PM

im listening,, i did mention the exact same delta you described on the resistors and thier application.. i get it.
my son may actually have a simi-bad battery so the alt might be loaded down more than normal, the arriving voltage at the IVR may be a tad too high.

are those two 10uF caps there?