Random RPM drop to 0 (tach only) then back up
05-04-2016, 12:33 AM
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Random RPM drop to 0 (tach only) then back up So an odd scenario I've had occur randomly that I'm a little lost on. LS1 motor swap, the tach signal works perfectly fine 99% of the time.
However, in some situations, (I've noticed it most often when it is raining, in 5th gear or so), if I really get on it the tach signal seems like it will just cut in and out, going to 0 then back up, then 0, then back up. Drivability seems fine, though usually when I see the tach drop I let off the accelerator immediately.
I'm not really sure 1) what would cause this, 2) why it only seems to happen in very rare situations, and 3) where I would even begin to look into diagnosing it. It should also be noted as well, if I start to speed up slowly and get to the same high RPM / load, it doesn't seem to happen. Only when I really get on it suddenly.
However, in some situations, (I've noticed it most often when it is raining, in 5th gear or so), if I really get on it the tach signal seems like it will just cut in and out, going to 0 then back up, then 0, then back up. Drivability seems fine, though usually when I see the tach drop I let off the accelerator immediately.
I'm not really sure 1) what would cause this, 2) why it only seems to happen in very rare situations, and 3) where I would even begin to look into diagnosing it. It should also be noted as well, if I start to speed up slowly and get to the same high RPM / load, it doesn't seem to happen. Only when I really get on it suddenly.
Last edited by Shigun; 05-04-2016 at 12:11 PM.
05-04-2016, 10:18 AM
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See, the thing is that it's not dependent on high RPM and I'm not getting a misfire that I can tell. Most of the time I can take it all the way to redline, no problem. It's just these odd scenarios where the tach just seems to die, come back, die, come back, die, come back. Speedo and all still works fine, etc.
11-10-2023, 02:19 PM
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Did you ever figure it out?
I'm having a similar issue (tachometer will just drop to 0), but only when I accelerate a little more briskly, minutes later, I will get two codes, one for the Cam position sensor and the other would be for the MAF.
I'm stumped as to what it could be. It's bugging me to know end.
Timing chain (I need a recommended mechanic in my area who will do it).
Bad / failing MAF sensor
Bad / failing Cam position sensor.
I'm having a similar issue (tachometer will just drop to 0), but only when I accelerate a little more briskly, minutes later, I will get two codes, one for the Cam position sensor and the other would be for the MAF.
I'm stumped as to what it could be. It's bugging me to know end.
Timing chain (I need a recommended mechanic in my area who will do it).
Bad / failing MAF sensor
Bad / failing Cam position sensor.
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Old Buzzard (11-15-2023)
01-31-2024, 09:17 AM
#6
Did you ever get this resolved? I am having the same issue. I swapped an LS3 stroker into my 2000 Trans Am and now the tach works until about 4K rpm then it drops out, only to start working again in about 15 - 30 seconds. I tried the pull-up mod and it didn't work for me.