tach malfunction at high rpm- Bad CPS???

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getblown5.9

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On my second hook at Numidia when I was bringing her up in the R's my tach dropped out at about 4500rpms and went erratic even tho the motor still ran fine. I came down the track and it was bouncing all over, but then once the rpms come back down it works fine.

If the CPS goes bad what are the symptoms? Or do you think maybe the screws are loose and at high rpm the sensor is moving away from the cam gear and not reading properly?
 
I'd say the cam sensor would definitely cause your problem t.j. You can probably take it out and double check of isn't loose, broken, or has a bunch of chit stuck to it. I don't think they are that expensive.
 
I had mine go bad and it would randomly loose signal/not charge and then come back up fine after a few miles. Thought it would throw a code but I didn't find one with the smarty. And trucks didn't mis a beat since its a P7100 pump now. Put a new one in and all is good.
 
Brett you still got the 12v in your truck or did you go back to a 24v head?

Yea ill see if i can get that sucker out this week and inspect it but I wanna have a spare here just in case it is bad. Should be real fun to get to with the pump and everything in the way!
 
getblown5.9 said:
Brett you still got the 12v in your truck or did you go back to a 24v head?

Yea ill see if i can get that sucker out this week and inspect it but I wanna have a spare here just in case it is bad. Should be real fun to get to with the pump and everything in the way!
Click to expand...

Yeah it's still a 12v, should be easier to get to than with the vp44 since the p7100 is narrow, mine was easy to change, just had to remove my throttle bracket.
 
My truck done the same as TJ's. And I have a brand new cps. I thought the ECM just didn't like those r's and was in denial.

Turns out I had a bolt fall out of the tone ring. The ithe two were loose and it was eating the case and cps. I still ain't found the missing bolt.......
 
Thats about what mine did then the tach quit working altogether and the alternator wasn't charging. Put a new Crank sensor on and it works now. Sorry thats on my 95 not the one in the signature.
 
what kind of tach? i have experience with auto meter tachs not working at high rpms, above 3k. fixed their tach and told them about it but they were not interested.
 
It is still the factory pickup that gets it's signal from the tone ring on the cam gear. It probably wouldn't be a bad idea to check the connections on your cluster.
 
Everything else in the cluster still works, its the tach only that dropped out on me.

Ill fiddle with the CPS tonight and see if its loose.
 
If seen one pin not work before. It's possible. Don't rule out the simple chit.
 
I could see that if it didnt work at all...its only drops out at high rpms, thats why i think either the sensor is bad, or its loose and high rpms vibrates it and it loses the connection.

ill check it all out tonight
 
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