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Hey Stu, for the RPM meter (tacho) its just come to my attention that i've been hitting fuel/ign cut even before i've reaches the Redline or RPM cut limit on the ECU.. but when i rechecked on my ecu reading, the rpm on the tach was lower than the actual ecu reading and even my defi VSD on rpm shows the ecu correct RPM while the oem tach does not. and the higher rev u go, the more worse RPM difference it is. i've tried adjusting the ECU duty output (HALTECH ECU) for the tach but does not response to any changes ive made. over the years the settiings on the ECU was spot on while tunning (Tach and ECU rpm reading was on PAR). can it be fixed?
 

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Stock Twins King
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Discussion Starter #22
Hey Stu, for the RPM meter (tacho) its just come to my attention that i've been hitting fuel/ign cut even before i've reaches the Redline or RPM cut limit on the ECU.. but when i rechecked on my ecu reading, the rpm on the tach was lower than the actual ecu reading and even my defi VSD on rpm shows the ecu correct RPM while the oem tach does not. and the higher rev u go, the more worse RPM difference it is. i've tried adjusting the ECU duty output (HALTECH ECU) for the tach but does not response to any changes ive made. over the years the settiings on the ECU was spot on while tunning (Tach and ECU rpm reading was on PAR). can it be fixed?
Hey Stu, for the RPM meter (tacho) its just come to my attention that i've been hitting fuel/ign cut even before i've reaches the Redline or RPM cut limit on the ECU.. but when i rechecked on my ecu reading, the rpm on the tach was lower than the actual ecu reading and even my defi VSD on rpm shows the ecu correct RPM while the oem tach does not. and the higher rev u go, the more worse RPM difference it is. i've tried adjusting the ECU duty output (HALTECH ECU) for the tach but does not response to any changes ive made. over the years the settiings on the ECU was spot on while tunning (Tach and ECU rpm reading was on PAR). can it be fixed?
Well it could be a couple things. Have you ever actually removed the needle at one point? It could also be the capacitors are getting bad. I recall there is really on 2. Could try installing/replacing with new ones?
248438
Tach Caps.JPG
 

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Thanks for the reply.. nope.. never open up the tach.. will try to replace the capacitors
 

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Hi Stu:
Thanks for sharing this...
My TRD Tach just stopped working..not sure why...I may have to send it your way..
Thx
 

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Stock Twins King
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Discussion Starter #25
Hi Stu:
Thanks for sharing this...
My TRD Tach just stopped working..not sure why...I may have to send it your way..
Thx
Hi Stu:
Thanks for sharing this...
My TRD Tach just stopped working..not sure why...I may have to send it your way..
Thx
Very rare for a tach just to stop working. I have seen it happen once when someone connected the battery terminals backwards and fried a resistor. 95% of the time it is something to do with a NA-TT swap. Or some wiring issues that feeds the tach. Also can be one of the 3 screws holding the tach in has backed out losing contact to the copper pads.
 

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You can also clean the green side of the board with some alcohol and resolder the connections with fresh solder. Ive seen some microcracks forming over the years that will eventually turn into cracks in the near future. just do it while you are replacing the caps
 

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Stock Twins King
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Discussion Starter #28
You can also clean the green side of the board with some alcohol and resolder the connections with fresh solder. Ive seen some microcracks forming over the years that will eventually turn into cracks in the near future. just do it while you are replacing the caps
Very true but not very common on a tach. I see this a LOT with HVAC boards. As well as ODO boards
 

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Thank you! This thread help me repair my speedo tach. All the information is useful! Not trying to steal the thread but would someone know the type of resistor that is located in the TRAC ecu next to the ecm? 2 of the resistor burn up in the trac ecu.
Thank you,
 

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Impressive information in this thread.

My mph part of the tacho will randomly either show 0mph....or 100mph....or even 180mph...all at random, regardless of whether I'm sitting at a steady 60mph or not. It usually works on short trips, but usually once warmed up a little, it'll start playing up.

Would this be something related to the VSS, or should I rip out the tacho and get medievil with a pair of pliers and a blowtorch?
 

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Just wanted to say thank you. It's been a longtime since I've been around. However since that time Stu has been contributing countless sources of information including developments from countless hours of experimenting with our beloved supras. He has always been very helpful and easy to communicate with. Thank you always
 

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So I have repaired a lot of speedo's over the years. It is quite a chronic issue as our loved Supra's are getting old and tired. So the capacitors start to go bad and cause it to barely move and stay under like 40mph. So just need to go buy 2ea 22uf 50V and 1ea 6.8uf 50v. Be cautious of polarity. Long leg of the capacitor is the positive. The Cap has a silver stripe donating that is the negative leg (shorter). Do yourself a favor and buy a small $8 spool of de-solder wick, like Gootwik to suck up the solder for easy removing of the old Caps.

Goot CP-3515, Desoldering Wick Braid, 3.5mm Wide, 1.5m long (approx. 5 feet) - - Amazon.com


EDIT: Some may have noticed that the Caps removed are 25v not 50v. It really doesn't matter which one you get. You may find that the lowest rating is 35v for the 6.8uf. Filtering the search to just "Automotive Purposes" really restricts the availability. "General Purpose" are way more abundant. Just get the cheapest ones close to these as these are like pennies.


Hi Stu,
My speedometer has trouble going past 45mph even when I’m clearly going over 65mph. If I could get a hold of a new speedometer head (83110-1B290) do you think it’ll fix the problem. Or more importantly does the part that I listed come with all the capacitors and good stuff like In your pic?
 

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Discussion Starter #34
Hi Stu,
My speedometer has trouble going past 45mph even when I’m clearly going over 65mph. If I could get a hold of a new speedometer head (83110-1B290) do you think it’ll fix the problem. Or more importantly does the part that I listed come with all the capacitors and good stuff like In your pic?
Just spend $5 and buy the 3 capacitors in this post and fix it yourself. Your issue is EXACTLY what bad caps will show
 

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^ Sounds like a good way to get out of a speeding ticket. Maybe hook up a circuit/switch that can select which caps to engage...one for normal and one for "calibration mode".
 

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^ Sounds like a good way to get out of a speeding ticket. Maybe hook up a circuit/switch that can select which caps to engage...one for normal and one for "calibration mode".
Haha it would be a good way! Im gonna try to attempt to replace the capacitors as Stu recommends. Forgive my ignorance but what is “calibration mode”?
 

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I was envisioning pressing a button that would engage the old caps, which would reduce the indicated road speed on the speedometer ("calibration mode"). Then you could have your speedometer "tested" and certified as reading low...an excuse for driving faster than the speed limit.
 

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