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Intermittent gauge activity

Hey all, new here! Recently bought a 1997 CC Intrigue with 98k miles and everything (thus far) works great! And have been loving it on the road. Just one quick question: Are the gauges suppose to jump around a little?

The manuals say it is a DynoMax chassis, but the schematics say the gauges come from the Gillig wire harness. What happens is they will all be working fine, then either while just sitting there at idle, or while driving, they will "spaz" out a little bit. The temp will go from 180 to max (240), hold there for a moment, then fall back to 180 almost instantly. The voltmeter sits around 13 most of the time, then will suddenly drop to 8, the gauge beeps at me for a moment, then it jumps back up to 13. Oil pressure will do the same as well (hover around 60, suddenly go max high or 0, then jump back to 60). Sometimes just sitting at a light, or idling to air up, the speedometer will hop between 0 and 5 mph. As for the tach...no issues there.

But they don't do it all at once. I was thinking it was a ground, but they do this by themselves, independent of one another. Are these gauges being controlled by a box of some sort? I was thinking about just replacing those gauges and senders, but if there is a ECU in the middle of all that, then a simple gauge swap might be a problem?

It has the engine protection module installed, but the schematics just show that the switches connect to it vs the senders...so I don't think it is that.....that I know of. I temp gunned the thermostat housing and got 188F after a trip, and the gauge was reading roughly that, so at least the temp gauge is accurate enough, when it is not having a seizure.

Everything else is perfect so far. No rust, water damage, leaks, the 8.3 is the 325HP version P pump, and allison 3060, which also runs great. And she holds air for about 3 days before falling to around 60 psi.

So yeah! If anyone knows what might be causing this, let me know where to start probing first.

Thanks!
 :D

Re: Intermittent gauge activity

Reply #1 –
My '07 Allure does this as well, not exactly... But similar.
Speedometer is dead on some days, 9mph off others, and then 3mph off still others.

Re: Intermittent gauge activity

Reply #2 –
I have a '94 Magna with an erratic oil pressure gauge also... 'Been all over the engine, (Or at least as far as I can reach / see..) looking for the oil pressure sending unit and thus far have come up with a -0-...  Erratic gauges are most often caused by a poor connection, or a poor ground...  In my case, the only issue is the oil pressure gauge;  all the other gauges being rock solid, so that rules out a poor ground to the dash...  I haven't pulled the dash panel yet, but it's definitely on my to-do list... 

Re: Intermittent gauge activity

Reply #3 –
I recently purchased a 1993 CC Concept and a noticed a few of my gauges bouncing around a little bit as well.  I also noticed that when I changed my dash light control setting (brighter or dimmer) that made them move.  I have talked with old CC employee who suggested running a separate ground wire to one of the gauges. It seems they are all grounded with common daisy chain so if ground is bad, they will all be affected. I changed the light switch and it is better but not perfect. I have not yet ran a new ground wire.
mmillsaps
1993 40' concept
#5001