Hello,
I have what may be a silly question but how can I tell if my gauges are reading the correct values?
Nikki
1989 Camaro

 

Well the factory gauges are notorious for being inaccurate. Theres really not precision instruments more of a basic general idea of how things are. For example my volt gauge reads just under 12V when in reality ive measure it to be a little over 14. If you wanted to know if yours were accurate it can just be assumed there not lol. If you were really concerned with how accurate they are you would have to compare there reading with actual testing equipment. For example oil pressure you would use a mechanical gauge that was actually calibrated not just an off the shelf gauge as who knows how accurate they are tough you can use them for a good comparison if they were a high quality gauge. Also even then say you did that and your oil presuure gauge yea 35 PSI but really it was 45 PSI the dosnt mean that all your gauge readings will always be off by 10 PSI it may be 1 psi off at a reading of 10 PSI and 15 PSI off at a reading of 60 PSI. It really comes down to how accurate do you need the gauges? For example like water temp will vary depending on where the temp sensor is installed so how important is it that the temp be perfectly accurate if its only representative of that 1 point on the motor? Then theres the fact even if you had a really accurate gauge its only as accurate as you can read it and most gauges dont have the resolution on the face to be read all that accurately. Even then there are gauges that will likely never be perfect like the speedometer. Not only is the gauge not perfect but the gears that drive the cable or sender arnt truly perfect either just a pretty good match for a given tire diameter/rear differential ratio. Really the only time you really need a accurate reading is when troubleshooting and that requires test instruments for everything else the ball park number is good enough. I wouldnt worrie about the gauge accuracy unless again you were concerned you had a problem in which case yea you'd need some kind of accurate measuring instruments.

 

That was an excellent reply and very insightful!!! thanks. i have a ?... My 84 Firebird says i never go above 3500 rpm. I have taken off from a dead start and just simply MASHED it to the floor, and it went up to 3500 almost exact and then shifted. almost every gear does the same. only way i get it above that is in neutral or park, which i only did once to see if there was a rev limiter, but it went up to 5500. tops out on my gauge at 6500. is it just inaccurate, or am i really not getting more than that? hmmm... THANKS

 

Well if you were confident that you were up to 5500 or so and the gauge was only reading 3500 or so thats inaccurate to the point we could concider it broken lol. For something like that you could compare your tach with another one or a dwell meter whatever was available as it may be the ignition control module that drives the tach and not the tach itself. Full throttle it really should shift later than 3500 but again you may have other issues like for example with your TV cable adjustment forcing it to shift early (incorrect TV cable adjustment will kill your transmission). The early 700r4s (im assumeing thats what you have) were prone to other problems as well. Its also possible its been swapped in the past (again early 700r4 were very prone to problems) and the shift points are incorrect for your application. Being that you can in neutral take the motor up to 5500 according to the gauge although it may not be perfectly accurate this kinda tells me that more likely your trans is shifting to early. Definitely check the TV cable adjustment.

 

Well, the reason I am asking is that both the ampmeter and the oil pressure gauges read very low and I do believe it is charging as the battery would be dead very quickly and it isn't. But I am a bit worried about the oil gauge, however, the engine is very quiet. If the oil pressure was low then the engine should be very noisy.

 

how exactly do i go about checking the tv cable? i just recently had a new tranny installed, but am incapable of saying which it is true to the fact that i have no clue. lol. but it shifts early, to me, i have driven other third gens with the 305 and 700r4 and it shifted later than mine, everytime. i was told the kickdown cable should be adjusted? when its cold, or just havent driven in over 3 hours or so, if i mash it to take off it dies. like it doesnt upshift and just dumps gas in and kills it. i have to repeatedly hit the gas over and over til it will upshift then after it does that, its fine.

 

Well the oil pressure sender are again pretty bad and will give flaky readings when bad. However oil pressure can get pretty low befor your really start to hear noise. Small block chevys technically can run approximately 7 PSI at idle and still be ok according to spec and will not make a peep. Granted thats not good but all im trying to say is oil pressure has to be very low to really start to hear like a clatter. The amp meter may read low as i cant remember how there wired in but they are measuring the charge or discharged rate. To be honest with you I didn't even think they came with amp meters only volt meters lol. If its aftermarket then its only correct if its wired in correctly. In theory for example if there was no electrical draw there would be no amp reading so they can real low depending on the load put on them. Being that i don't have an 89 i wouldn't able to tell you what a normal current draw was while running but your right if it wasnt charging you'd know about it. Course if you werent convinced the easy way to tell is measure the voltage of the battery. When the cars off it should read 12v about when the cars running it should read approximately 14V indicating the battery is being charged.

 

Sorry, it is a voltmeter, and it doesn't read to 12 at all, but will drop down to about 10 after the fast idle drops. The oil pressure gauge never gets above 10. Now I am wondering since they are both on the right side of the pod could it be that the wiring film is bad on that side??

 

Well in the tech article section of this web site someone i believe actually did a write up on adjusting the TV cable (or what your mechanic is referring to as a kick down cable). It sounds like yours is most likely not adjusted correctly.

 

Its not likely I mean anything possible if there one thing these cars have taught me its that lol. Though i still kinda doubt it as there pretty reliable and usually only break when theve been played with like when replacing the cluster then they can sometimes crack or tear and break. In that case though something would just not work at all or peg to a max or min reading something like that. The voltmeter could be inaccurate (ide concider it broken at that rate) i know mine is pretty bad as well. No harm in check the voltage with a volt meter though as low voltage or high voltages cause by a bad regulator or something can do damage. The oil pressure gauge is hopefully just a oil pressure sender but again if it is a legitimate reading then you could be doing a lot of damage and turning a salvageable motor into a boat anchor. I would fix that before really driving it again just to be safe.

 

My oil gauge used to do the same thing, in fact at an idle it read almost 0 PSI. I had the sending unit replaced and now it reads 25 PSI at idle and as much as 40 PSI when driving on the highway.

You should probable try replacing yours before I would replace the cluster, also the tach is known to burn a resistor or two and throw off it's readings.