My tach drops dead between 1900 and 2300 rpm. Runs fine everywhere I go except for on the interstate at about 65 to 70 mph. On interstate my tach goes dead and therefore I loose alot of turbo going up hills and accelerating. Anybody have any Ideas?

 

Your camshaft (or crankshaft) position sensor. It the sensor used by the ECM as a timing reference to time the injection events. It also feeds to your tach and tells the ECM if the engine is running or not.

The three main symptoms of this happening is :

1. Tach goes to zero, most noticeable and common symptom.
2. The volt meter drops to 12 V instead of 14 V. This is because the ECM uses the CPS to see if the engine is running. When it sees the loss of signal from the CPS it thinks the engine is off and thus turns off the alternator output (ECM controls that too).
3. The A/C compressor turns off. This is the least common symptom as you must have the A/C on to begin with to notice this one. The ECM also controls the A/C compressor clutch and will turn it off like it will the alternator upon loss of the CPS's signal.

 

I just replaced both the cam and the crank sensors and got my truck running again. When I started my truck I heard a clicking noise. Thought maybe it was just lifters from sitting for a while, but it was towards the bottom of the engine. Now the tach is doing what I said. The old crank sensor was chewed up pretty good. I think the same might have just happened to the new one. Is it possible to get the sensor in to tight to where it would do this or is there possibly something that is a deeper problem? Thanks for the input.

BP

 

Crank Position Sensor fixed mine.

Dave

 

if sensor is chewed it sounds like u need a new tone ring or u have a loose tone ring. get ready to shell out the dough if u cant fix it yourself, and if u do it yourself use loctite on those bolts.

 

i am soory i might have jumped the gun, it is possible to over tighten the bolt that holds the sensor in place, use torque wrench on bolt to 18 ft.lbs. but if your tone ring has fallen off or split dont be surprised u wont be the first this has happened too and it is a pos job to do.

 

I think I will try to put a new one in with less tork on the bolt first. Then if that doesn't solve it I guess to the tone ring we go huh. Thanks for all the input. BP

 

BP, while you have the sensor out see if you can see the tone ring through the hole. Might be worth checking out.

 

Jr, I will see what I can see. I think your telling me that I should be able to see anything obvious if there is something wrong with the tone ring? Thanks for the advice.
BP