Holden Piazza temperature guage testing.

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sbs
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Holden Piazza temperature guage testing.

Post by sbs »

Hey their folks,
I have been having problems with the read-out on the temp. guage on the digital dash of my Holden Piazza. The guage consistently goes up into the red zone even on the coolest days and even though the engine is only warm to the touch.
I have put in a new thermostat - no difference, I changed the sender unit for the guage - no difference either, so my local auto electrician has asked me to see if any of you guys can give me the test procedure for him to test the wiring. I am sure their has to be such a test.
Thanks and best wishes, sbs.
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Post by IZU069 »

It's probably the dash....

I think the normal "short to engine" of the (single!) temp sensor wire is a quick test - the gauge should go full scale. BUT!!! Be warned - that test on MODERN cars is usually no longer appropriate and can damage ECUs etc. Same goes for fuel senders, oil pressure, etc etc.

But as I recall, the Piazza (with digi-dash) is the traditional "resistance to earth" sensing, AND where a short to earth will not blow the sampling circuit (most sensors have a minimum resistance; short shorts (to earth/body/engine) should not burn-out mechanical gauges, but some electronic "samplers" or gauges could be quick to respond, and smoking is a health hazard for them too).


Probably the only test is (variable) resistance straight to the dash. But without a appropriate harness (as detailed in the PiazzaManual.pdf), you have to relay on the integrity of whatever wiring is between your test resistance and the gauge.


But a broken signal wire should cause the gauge to drop to minimum (though I should check that), not high.
Hence I suspect the dash.
Alas after 25 years - dried capacitors, dry solder joints, thermal fatigue....
Usually the PSU (power supply) goes. In theory, a relatively simple replacement or fix. (Note: RELATIVELY - ie, compared to any other digi-dash "electronics" fix.)


But I'll see what I can find....
PM me if I delay or forget.


FYI - You may be too new to know - or maybe I never publicised? - but I was intending a digi-dash "repair". I intended to replace the guts with a new PSU and CPU. In fact Mark-1 was the duplication of the standard digi-dash features & behaviour, and Mk-2 was the enhanced version where anything could be added - ie, datalogging, temp & voltage etc alerts, flashing RPM or speedo (when too fast), trip readouts, fuel consumption, voltage priority (over fuel) etc etc - anything that could be displayed on the standard display. It was even going to have speech! I also considered including my self-learning sequential EMS... (Actually as redundancy - the same CPU would be used for both EMS and dash, but have 2 circuit, one dedicated to each. Then if the "EMS" breaks down, swap for the dash. Or invest in a 3rd spare that can be used as either.)
Intending to use some MPU-chip at the time, I'd now probably use the Arduino - a $40 CPU with USB that can easily be programmed and changed or interrogated by anyone. (Not that I''d use that for an EMS.)
Mind you, IMO the worst part is the total hacking of the very-layered and analog digi-dash. Strip out all but the displays and (probably) their drivers, the add the PSU & CPU. Lots of work AFAIK. And the one thing that is required for every conversion. (Though a PSU-only replacement option should have bee possible.)
The original "reverse engineering" would also involve a lot of effort, as would the programming etc, but once that was done, it's a PoP.
(Why all that? My original digi-dash was fine except for a faulty voltmeter (which I consider an ESSENTIAL requirement for vehicles). But to replace that circuit - OMG! It's under the display, and analog.... )

Alas blame RodeoBob. Thanks to him I got a Jackaroo for my round-Australia September 2005 trip so I didn't have to get my Piazza on the road.
Not that I was gonna do that dash for the "on the road" Piazza - I was going to design it on the road AFTER I had finished my self-learning EFI & Ignition system (in part because apparently self learning was impossible LOL! - especially sequential ignition or injection without a CAS (double-LOL!!)).
But blame Bob anyhow. He's used to it.

Oh - how is that Jackaroo going? Let's say I'm closed know to finishing it.
(Was my last update in 2006? Well the block made it to the front porch circa ~2009, and soon after to the wash. It has grown roots where I place it soon after and still has its even coast of 2010 surface rust.)


PS - Schedule update: In 2010 I revised modified my schedule by one - Sept 2005 is now Sept 2015. An IMO minor change of one mere unit.


Geez - I could have looked up that temp-dash info by now...

BTW - I assume you replaced the correct temp sender - not the one the ECU uses? (There are 2 aren't there? I recently forgot that the Piazza had an AFM - but hopefully Bob won't tell anyone about that... D'oh! Ater all, he is a mate. And one heck of a talented guy. (He's taught me heaps!))
IZU069 - ISUZU means a lot to me.
sbs
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Temp sender unit.

Post by sbs »

Hi there Izu,
Thanks for the indepth response to my enquiry and sorry for the delay in responding to you.
I have purchased a replacement new sender unit which I hope will arrive and turn out to be correct. If that does not work then, as a temporary measure at least, I think I will install an after-market temperature guage just to be able to drive the car. Let me ask you one more question, are you going into the digital dash repair area as you mentioned? It would be of real benefit to plenty of us around Oz and NZ.
Anyway I will hopefully get this problem sorted out, courteousy of your advice, and then look forward to the next thing that needs fixing, Why do we love these cars...
Thanks mate, best wishes, sbs.
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Re: Temp sender unit.

Post by IZU069 »

Is izu069 going into digital dash repair?
Maybe after I return from my 2005 roundOz trip, though I have yet to depart...


Let's say that recently I could have been fiscally forced to.
And if in receipt of the more than $4,500 someone once paid for a digi-dash repair, I may have fiscally forced myself to... LOL!


It is yet another project of interest, but that is twofold:
The first is the mere fix of replacement of the PSU or odd components (capacitors, diodes) that are the typical causes of failure.
The second is the other mentioned "full functional" replacement, and later enhancement of the guts behind the digi-dash.

The first should be relatively simple (though still maybe hours of initial investigation etc), and I have an obligation else intent to the supplier of my dead digi-dashes should the need arise.
The second was to happen during my round-Oz trip (whenever that occurs!). That is simply a thousand-hours labor of love or fun, but IMO nothing else.


As to certain specific repairs - like my digi-dash voltmeter, and quite likely the fuel gauge - they are complex and risky by their nature, and I don't even know yet if the chips (components) are still available. They maybe transferable from other dead digis though.

But still risky and certainly time intensive. Risky mainly to due the desoldering and resoldering of the displays.
And time, geez - a few hours at best?

And as to time, at what cost or pay rate?
I see the Piazza as owned by enthusiasts that do not or cannot spend big on things, though that is based on Belletts etc (well, at least the local Bellett club until some years back).
Plus I know the differences between promised to pay, and actual payments. (Hence my default deposit of 50% of expected cost up front for sparts etc.)

As to my renumeration, should I quote myself? I recently got paid $3,500 for 3.5 days work.
My last earning were over $10k for nearly 6 weeks work.
But both of those are likely to be unique, and I am back on welfare which only covers half of my needs.
So if in about 2months I have not gained suitable employment, I may be keen.
If I get lucky and employed as I desire (say $600 per week), then maybe as an extra earner....
Pity it isn't your voltmeter - that has a nice $10 solution.

Otherwise it is a labor of love - whether the desire to fix, or the desire to help (needy people with an excellent taste in cars).


Sorry, that's no answer, but simply my status quo.


I have more than enough projects. I am still ongoing with the disposal of my Wasp - a vehicle I was to keep for 12 months; it is now in its 12th year of registration! (The completion of the aforementioned Jackaroo and 4ZE1 block obtained in 2005 are required for that.)

And I am currently working on a certain device for vehicles with a view to sales. (It'll probably piss off established markets and cost a mere handful of dollars in comparison whilst providing superior application and performance.)
Plus another proposed business to which I have been invited.
And then...

As usual, I'll "look into" your problem. If only I can find my digi-dashes.
Oh shit - there they are - a mere 1.5 meters away. Fark - there goes that excuse! (But maybe if I don't tell anyone...?)

I could be swayed and re-prioritise, but it's sill the upfront investment in time which cannot normally (IMO) be covered by a single "cost of repair".
But your solution therefore lay in getting a replacement digi-dash - they have been available for $100. A digi-dash and an ANALOG dash were given away free a few years back (their 2 Piazzas also given away were advertised hereon).
Else I'd offer a change-over for any digis that I got working.


Yet another short reply...
IZU069 - ISUZU means a lot to me.
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