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| Tach reading high (Page 1/1) |
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TXGOOD
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MAR 25, 10:26 AM
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What do you guys think I need to check?
1988 3.4 pretty much stock TH325 transmission.
The tach shows the car idling at about 1200 which I thought a little high but I found out that`s pretty much what they idle at.
Upon acceleration, the tach moves steadily up and drops a little when the car shifts.
The problem is it`s reading about 4K and up at 60 MPH.
I don`t think the TCC is working but from what I have found out it only makes about a 200-300 RPM difference.
Even at 3800 RPM or so, if the TCC were working doesn`t that seem a little high for 60 MPH?
I personally don`t think the engine is reving that much but I guess I could be wrong.
Will a bad or failing tach filter most of the time make the needle jump or can it just steadily be off.
I have tried two different tachs with pretty much the same results.
Thanks[This message has been edited by TXGOOD (edited 03-25-2019).]
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Gall757
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MAR 25, 10:59 AM
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| quote | Originally posted by TXGOOD:
I personally don`t think the engine is reving that much but I guess I could be wrong.
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You could be right. The tach tends to read high as the components age.[This message has been edited by Gall757 (edited 03-25-2019).]
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theogre
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MAR 25, 12:41 PM
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ECM/PCM scan tool will accurately show Engine RPM. When they don't match then likely tach is bad.
Or can run power train math to show roughly RPM expected at given gear and MPH/KPH but is more complicated because need several gear sets and tire total size etc and many don't have some of data needed.
Example See my Cave, Gear Ratio------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)
The Ogre's Fiero Cave
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Mickey_Moose
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MAR 25, 02:52 PM
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My 88 auto (3.4l) runs ~3000 RPM at 60 mph IIRC. 
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TXGOOD
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MAR 25, 03:29 PM
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Thanks guys, I think I`m going to try the multi-tester method.
Apparently you can measure spark plug pulses with a multi meter and a wire near a plug wire and
convert that into RPMs.
I only have a scanner that reads OBD2 for when I had my 3800.
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Gall757
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MAR 25, 05:26 PM
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| quote | Originally posted by TXGOOD:
Thanks guys, I think I`m going to try the multi-tester method.
Apparently you can measure spark plug pulses with a multi meter and a wire near a plug wire and
convert that into RPMs.
I only have a scanner that reads OBD2 for when I had my 3800.
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Let us know if that works......I don't think I can count that fast.
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TXGOOD
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MAR 26, 09:30 AM
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Gall757
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MAR 26, 10:42 AM
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oh.... Digital Multimeter....heh. That measures HZ.....
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theogre
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MAR 26, 10:45 AM
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| quote | Originally posted by Gall757:
oh.... Digital Multimeter....heh. That measures HZ..... |
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And Most meters won't read.
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