Got a couple of questions here as you may gather by the title of this post.... pretty sure they are all related.

99 Blazer w/110K miles

• I replaced the distributor with a new unit (including new CMP sensor) due to a P1345 code. Yep, the drive gear on the old distributor was beat to hell.

• New distributor, Blazer runs perfect, no miss, no hesitation, still have the P1345 code. CKP/CMP correlation FUBAR'd?

• Tachometer now has a case of palsy.... or to put it simply, the damn thing jumps around intermittently. There is no actual surge in the engine. The tachometer just jumps randomly as if it were an electrical gremlin. This is the only gauge malfunctioning.

1. First, I'm going to make a wild guess here that I need a CKP Variation Learn Procedure performed to get rid of that damned P1345 code since I have a new CMP sensor? I can start the Blazer, clear it with my code reader and all is fine. However, if I turn the Blazer off and restart it the code comes back. I am curious if anyone can tell me if the PCM checks this value only at startup or is it continuously monitored by the PCM while the engine is running? Why exactly is a CKP Variation Learn required? I understand what the procedure is but I am more curious why a new CMP sensor would require a CKP relearn? I mean is there that much of a variance from one new sensor to the next (as in no standard)? If a CKP Variation Learn Procedure is called for in my case then so be it.... I'm just trying to understand why these systems are engineered to require such procedures? In other words is there any REAL logic behind this or is it just a case of design engineers not being able to keep it simple? Just trying to understand the nature of the beast here I guess....
2. The issues I am experiencing with my tachometer seemed to magically manifest in conjunction with the new distributor/CMP sensor. Does anyone know if a new distributor and/or CMP sensor could make the tachometer schizo? OR.... since the tach relies on input from the CKP could the tach problem be some how related to needing a CKP Variation Learn Procedure?
3. What kind of scanner is required to do the CKP Variation Learn? Is this a feature that can be had in a "reasonably" priced consumer scanner or should I be prepared to cough up $5000 (not that I will!).

Any insight would be vastly appreciated.... thanks!

 

#1 - bingo, but I would check out the CMP & CKP sensor outputs to see if they have intermittent drop outs that could be causing your other symptoms.
#2 - I'm not sure that the CKP Variation Learn Procedure will have impact on the tach operation.
#3 - Not many over the counter scan tools are capable of properly performing the learn procedure. Just take it to the dealer and tell them you replaced the distributor. It should cost around $60...

 

I was having problems with tach jump in my '01. I pulled the CKP sensor, cleaned it off, reinstalled, and haven't had a problem since. There was crud all over it. You may want to try that. It's only one bolt and is easily accesible from under the truck.

 

Yeah, already tried that. Mine just had a bit of oil on it... wiped it off, re-installed and still got the jumping tach. I'm wondering if the CKP sensor itself can have an intermittent fault that doesn't set a code off? I'm hoping to thoroughly inspect the wiring this weekend to eliminate that as a suspect.

I really like my Blazer but damn... these things seem to be plagued with all kinds of electrical gremlins....

 

You can test the wiring between the CKP sensor and the PCM for poor connections or broken wiring.

 

I am planning on running through all of that this weekend. I am assuming that if the circuits have good continuity then I shouldn't see any resistance.

Assuming all wiring is good, can the CKP sensor have intermittent failure if it's going bad or do they just fail when they go? It doesn't appear there's a whole lot to the sensor itself... can the sensor fail between the female end of the plug and the brass slug at the end?

 

where is the ckp sensor located? and how do i just clean it of.?