Hi guys had a question regarding cmp retard. First off should it be checked at idle or at 2000 rpm? I had a Chance to get my 99 blazer on a computer and at idle cmp retard was 18. Is there any reason for it to become advanced seems from what I have read wear on gear gives you a retard. Thanks ahead of time guys.

 

ok figured it out tonight someone put distributor in one tooth off and I have about 10 degrees worth of wear on gear that put me at 18. Thanks any how

 

Distributor drive gear wear will cause CMP to change. If it's worn, replace it. CMP retard is checked at idle, immediately after snapping throttle above 2K rpm. 18 degrees is not enough to set P1345, but it is enough to cause some serious crossfire inside the cap. Crossfire in the cap will cause P0300 series DTC's to set. Spec is zero degrees, plus or minus 2 degrees. Adjustment is done by turning the distributor. The factory distributor hold down bracket will only allow a maximum of ~15 degrees total, (from one extreme to the other of the adjustment). If you need more than that, the bracket needs to be modified or replaced with an old style SBC, (small block chevy) hold down bracket, (Mr Gasket #1009). This will make the distributor fully adjustable.

 

Thanks for reply but still curious wont gear wear give you a negative degree? Mine is at +18. Im figuring it was toothed off at some time. does this sound right please let me know if im wrong.

 

Distributor drive gear wear will cause CMP to change in a negative direction. The gear on the distributor, (and on the camshaft), each have 13 teeth. Each tooth represents ~27.692 degrees of distributor shaft/camshaft rotation, and there's ~15 degrees of adjustment. Which means it may or may not be off a tooth when the gear wear is added into the equation. P1345 will set in memory and turn the SES light on when CMP retard is off by ~27 degrees, or more, in either direction. If you can see wear on the drive gear, replace it. Then check/adjust CMP retard.

 

so i can take my scanner and watch timing while my buddy turns the distributor to get it as close to 0 degrees as possible?

 

Camshaft retard has nothing to do with ignition timing. Turning the distributor does not affect ignition timing on this engine. Camshaft retard is viewed on a scan tool capable of viewing the streaming data. The el cheapo $500 scan tools can't do it. Adjusting camshaft retard is done by turning the distributor. It aligns the camshaft position sensor with the camshaft, hence the name. It also aligns the rotor segment so it is aligned with the terminals in the cap when the coil fires. This keeps crossfire inside the cap to a minimum. The PCM uses the data, along with crankshaft position sensor data, to detect and accurately identify cylinder misfire, that's it. Once it is adjusted correctly, you can unplug the camshaft position sensor and the engine will start and run with no difference in performance, BUT, cylinder misfire will not be detected, and a DTC will be set for the sensor circuit.

 

right now im at 17.5 degrees + on my 2000 blazer according to my scan tool sorry for thread jacking. figured we could all come together to help a problemed blazer owner!

 

You're not thread jacking at all, it's a perfectly good question relating to engine performance. Ignition timing and camshaft retard are 2 completely different things though. If you're showing 17.5 degrees, guaranteed you're looking at ignition timing. On your 2000, ignition timing at 17.5 degrees is exactly where it should be. What brand and model of scan tool do you have?

 

Ok last question I had by distributor out but I don't see any adjustment at all the bracket is flat on both side where it wraps the distributor and sides of distributor are also. where is adjustment or do I have to make hole oblonged for hold down bolt? Thanks for info much appreciated.