Instrument Cluster question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

82GMCShortBed · 07-31-2009, 04:42 PM

I have a 92 454SS and the tach always reads about 1000 rpms high and the speedo indicates about 15mph fast all the time.
It doesnt make sense to me that the two components are related except for the ground. All other gauges appear to be working OK.
It has the original coil, factory tranny and rearend and the correct size tires (275/60/15).
It doesnt appear to have any previous owner "modifications/enhancements". It does have a remanufactured ECM.
I am changing the coil this weekend (maybe weak signal causing tach issue??) but I dont think this would affect the speedo.
Any suggestions???

ChevLoRay · 08-01-2009, 11:39 AM

This isn't an answer to your problem, but it is similar to one I had on my school bus. You may wonder why I mention this, but let me tell you.

I smelled hot electrical odors one cool morning when I fired it up. Not finding anything out of the ordinary, I restarted it and the odor went away. Later that day, I noticed that my speedometer was not right. The speedometer needed was moving along with the tach (electronic) needle. I could accelerate from a stop, on a hill, and be doing an indicated 40MPH before the back of the bus got to the stop sign. I also noted that the voltometer was reading more than 12VDC, but less than the 13.8 -14.4VDC that it had done prior. After driving it like that for several months, because the "Powers that be" didn't think it was a big deal, the battery finally died and my electronically-controlled Allison transmission went haywire. The alternator had taken a dump and took the battery with it. I tried telling the "Powers that be" that I thought it was in the alternator but got no respect. A few weeks before school ended this year, it did it again. This time, they listened and replaced the alternator.

Now, I don't know if your alternator could be bad or not. I only chose to tell you this story so that you might think about it. Are you sure that the replacement ECU is the right one for that model? Is it possible that the P.O. may not have had it re-programmed for that model? These questions may be moot, but it's where my thought train is traveling. Good Luck.

JohnC · 08-01-2009, 02:45 PM

Quote:

Originally Posted by ChevLoRay

.... Are you sure that the replacement ECU is the right one for that model? Is it possible that the P.O. may not have had it re-programmed for that model? These questions may be moot, but it's where my thought train is traveling. Good Luck.

This was my first thought as well.

82GMCShortBed · 08-02-2009, 11:25 AM

Thanks for the responses.
I will check the alternator next week.

I checked the part number on the ECM against the replacement number on Autozone's website and it appears correct, but being a reman unit it could still be flaky.

ChevyTech · 08-02-2009, 11:39 AM

Do you know if the instrument panel has been changed?

On a instrument panel from a V6 truck the Tachometer will read to high of a RPM when put in a V8 truck.

If parts have been changed out there could also be DRAC issues. Do a search and you should be able to find information on this because we have discussed it in great detail in the past.

Here is one of them:
http://67-72chevytrucks.com/vboard/s...=1#post2952083

07-31-2009, 04:42 PM	#1
82GMCShortBed Registered User Join Date: Oct 2007 Location: Smyrna, TN Posts: 79	Instrument Cluster question I have a 92 454SS and the tach always reads about 1000 rpms high and the speedo indicates about 15mph fast all the time. It doesnt make sense to me that the two components are related except for the ground. All other gauges appear to be working OK. It has the original coil, factory tranny and rearend and the correct size tires (275/60/15). It doesnt appear to have any previous owner "modifications/enhancements". It does have a remanufactured ECM. I am changing the coil this weekend (maybe weak signal causing tach issue??) but I dont think this would affect the speedo. Any suggestions???

08-01-2009, 11:39 AM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Instrument Cluster question This isn't an answer to your problem, but it is similar to one I had on my school bus. You may wonder why I mention this, but let me tell you. I smelled hot electrical odors one cool morning when I fired it up. Not finding anything out of the ordinary, I restarted it and the odor went away. Later that day, I noticed that my speedometer was not right. The speedometer needed was moving along with the tach (electronic) needle. I could accelerate from a stop, on a hill, and be doing an indicated 40MPH before the back of the bus got to the stop sign. I also noted that the voltometer was reading more than 12VDC, but less than the 13.8 -14.4VDC that it had done prior. After driving it like that for several months, because the "Powers that be" didn't think it was a big deal, the battery finally died and my electronically-controlled Allison transmission went haywire. The alternator had taken a dump and took the battery with it. I tried telling the "Powers that be" that I thought it was in the alternator but got no respect. A few weeks before school ended this year, it did it again. This time, they listened and replaced the alternator. Now, I don't know if your alternator could be bad or not. I only chose to tell you this story so that you might think about it. Are you sure that the replacement ECU is the right one for that model? Is it possible that the P.O. may not have had it re-programmed for that model? These questions may be moot, but it's where my thought train is traveling. Good Luck. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

08-02-2009, 11:25 AM	#4
82GMCShortBed Registered User Join Date: Oct 2007 Location: Smyrna, TN Posts: 79	Re: Instrument Cluster question Thanks for the responses. I will check the alternator next week. I checked the part number on the ECM against the replacement number on Autozone's website and it appears correct, but being a reman unit it could still be flaky.

08-02-2009, 11:39 AM	#5
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,620	Re: Instrument Cluster question Do you know if the instrument panel has been changed? On a instrument panel from a V6 truck the Tachometer will read to high of a RPM when put in a V8 truck. If parts have been changed out there could also be DRAC issues. Do a search and you should be able to find information on this because we have discussed it in great detail in the past. Here is one of them: http://67-72chevytrucks.com/vboard/s...=1#post2952083



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