"Service Engine Soon" light came on the other day so got out the Hawkeye Total to have a look and it turned out to just be the SAI which has not been working correctly for a while. I have checked all the vacuum lines and replaced with a good set from a parts car but no change. Not worried about it as the car runs fine. While looking at live data out of curiousity I noticed the alternator was only putting out 12.9 volts which is not too good so I decided to take my spare to the local auto electric shop for a check out. The $10 test indicated it would put out 144 amps at 14.4 volts so that sounded like something I needed to swap in. I decided to also install the new belt tensioner and idler pulleys that I bought last year.
Removed the plastic guards over the belts and also disconnected the upper rad hose from engine and radiator to move it aside. Next step was to move the belt tensioner to allow slipping the belt off the alternator pulley. In my experience belt tensioners usually have a square hole into which you fit a belt tensioner wrench which is just a long flat bar with a square nub at the end. The one on the P38 does have this but it is obstructed by the alternator mounting bracket so you have to use a 16mm box end wrench on the bolt that holds the tensioner pulley in place to pry up the tensioner and release the belt. I had to put a short pipe on the wrench to get enough leverage. After slipping off the belt I tie it back with a bungy cord. There are two long bolts holding the alternator in place. Once removed you can pry up the alternator to release it. I did not disconnect the battery but very carefully removed the positive lead and put the end in a doubled up plastic bag. Just be carefull you don't touch the engine with your wrench or ratchet (I hate trying to reset my sunroof so don't like disconnecting the battery). Next step was to remove the small idler pulley below the tensioner using a 13mm wrench. A bit awkward with the fan in place but can be done. Once this pulley is off you can use a 13mm socket and rachet to remove bolt that holds the tensioner in place. Install the new tensioner and idler pulley. Last step is to replace the large idler pulley on the opposite side of the engine which is easy to do. Alternator is easy to refit if you tap the steel inserts to make sure they are all the way over in the aluminum bracket. Final result was 13.9 to 14.1 volts at idle. Now if I could get rid of that SAI related light....