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Old 06-18-2020, 07:38 PM   #1
Mini-Skoolie
 
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Sending unit replacement

Hey all, gonna replace three sending units on my skoolie. Not getting accurate readings at all and getting tired of the guesswork. The coolant temp sensor, the oil pressure sensor, and the fuel tank sensor. In doing research, I’m finding that prices range between $30-$300 per unit. And most seem to be a “universal fit.” Not too confident in that since there seem to be many different types of sending unit all of which are universal fit.

Begs the question. Where is the best website to buy a cheap but decent sending unit that I can be sure will fit?

Who has done this before and what do you suggest?

Bus is an ‘88 GMC Bluebird. Engine is the 8 cyl 8.2L Detroit Diesel fuel pincher engine.

Thanks for your input!

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Old 06-18-2020, 09:41 PM   #2
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if all the gauges are bonkers i would first check anything they have in common such as voltage/current supply or bad ground. odds that all the gauges lost senders at the same time are high
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Old 06-19-2020, 12:59 AM   #3
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Well when I bought it, they were like that so I can’t be sure if they all went out at exactly the same time. Ammeter is fine, gives a decent reading. But I definitely can’t say the same for the other three. Already sanded down each gauge terminal and added some dielectric grease. Didn’t seem to help. Will check the current supply and such. Any idea of a good place to buy sensors if nothing changes?
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Old 06-19-2020, 08:42 AM   #4
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the wiring for those go thru a few modular connectors on the way out to the engine. check them as i had some trucks that had bad corrosion on them. had to cut and bypass these connectors to make his dash work. the wiring is added in stages so follow the harness and disconnect every one to look at spray them before reassembling then with a contact preserver or electrical grease.
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Old 06-19-2020, 08:45 AM   #5
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sensors have to be matched to the gauges. some do not interchange with other brands. use oem equivalent parts for correct readings or buy a aftermarket set of gauges
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Old 06-19-2020, 08:49 AM   #6
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if your gauges do not read in numerical increments consider a new gauge set also if your turbo equipped i would add a boost gauge to know if you get any leaks on your aftercooler system and turbo condition.
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Old 06-19-2020, 08:52 AM   #7
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please check dash ground goes to a good ground hook a wire to dash and hook it to a known good ground or negative terminal of a battery. i have a 25 foot 14 gauge jumper that is getting worn out but helped me often over the last 30 years
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Old 06-19-2020, 08:57 AM   #8
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one extra note the ammeter is completely separate from the other gauges as it does not ground on the dash actually does not ground at all for it to operate. the only ground it needs is for the dash lite
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Old 06-19-2020, 10:51 AM   #9
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one extra note the ammeter is completely separate from the other gauges as it does not ground on the dash actually does not ground at all for it to operate. the only ground it needs is for the dash lite
I was gonna add this -- glad you did!

Even quality after market gauges are often only accurate +/- 10% --
That means a temp reading of 200°F is anywhere in the range of 180° to 220°F... PICK YOUR RELATIVITY METER WISELY...

Gas gauge especially will work off a specific ohm range -- no such thing as a universal replacement electrically speaking the universal part is adjusting the float arm swing to your fuel tank...

And does an '88 GMC really have an ammeter gauge?! To be accurate that means all the buses alternator output passes through that gauge. This design is why so many IHC Scouts have electrical fires...

The other gauges will go through a CVR and if that's bad will be the source of all the gauges being bad.

A good wiring diagram of the truck will tell you how that's handled.
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Old 06-19-2020, 10:55 AM   #10
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im sure that in 88 the ammeter used a shunt to measure it so as not to run a large cable thru the dash. still not a grounded system also good point banman about tolerance issues on cheap gauges. this is why i prefer mechanical gauges
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Old 06-19-2020, 11:04 AM   #11
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im sure that in 88 the ammeter used a shunt to measure it so as not to run a large cable thru the dash. still not a grounded system also good point banman about tolerance issues on cheap gauges. this is why i prefer mechanical gauges
You're probably right about the shunt... But I'd want to confirm that...

The International Scout did not -- I've added a shunt wire to mine -- other's bypass the ammeter altogether and add a volt meter instead.

You'd be surprised, even autometer and vdo are often very proud of their "accurate to 10%" crap...

Now would be the place for Cadillackid or others to chime in about replacing it all with a digital - blue tooth setup...
(The fuel tank would still need a working float/sending unit)
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Old 06-19-2020, 03:08 PM   #12
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for my 86 8.2 fuel pincher
my local NAPA has or can get most of the parts i need.
i also have places somewhat near me called
Canady s truck parts
Hunning s truck parts
and Clark power services
my oil presssure sending unit was just the plain jane 30$ type i think mine was like 23$ from napa.
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Old 07-13-2020, 08:28 AM   #13
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Quote:
Originally Posted by mmoore6856 View Post
if all the gauges are bonkers i would first check anything they have in common such as voltage/current supply or bad ground. odds that all the gauges lost senders at the same time are high
Found a pretty nasty ground going to my starter solenoid. Seems to run a bunch of grounds together from different places, including from the coolant sensor. (Photos attached) Is it normal for them all to be bunched together like that? What should I do about it if not?
Attached Thumbnails
BEBDCD9D-D485-49FF-87B7-B9390FDBC558.jpg   B39FE0B6-A7D1-4E3A-99BD-FB396F34B269.jpg  
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Old 07-13-2020, 09:34 AM   #14
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even if that is not the cause of your problem, those connections look like trash. You should clean them up and replace them all.
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Old 07-13-2020, 09:35 AM   #15
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Quote:
Originally Posted by silvermachine View Post
Found a pretty nasty ground going to my starter solenoid. Seems to run a bunch of grounds together from different places, including from the coolant sensor. (Photos attached) Is it normal for them all to be bunched together like that? What should I do about it if not?
That is normal. If the connector ends are corroded, clean them.


Do you like Hawkwind? I like that song "Silver Machine". I really like Hawkwind, but, alas, don't have much by them....hard to find
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Old 07-13-2020, 12:37 PM   #16
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That is normal. If the connector ends are corroded, clean them.


Do you like Hawkwind? I like that song "Silver Machine". I really like Hawkwind, but, alas, don't have much by them....hard to find
Ha! Yes I am a huge Hawkwind fan. I had the opportunity once to open for Nik Turner— what a dream, man! The dude really couldn’t be nicer. Still absolutely ripping the sax after all these years. He’s gotta be at least 150 years old by now.
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