Just purchased my 1992 D2500 Custom Hauler and having issues . My alternator was not charging and my tach was not working along with my speedo as well . Of course being totally a novice , I assumed that the alternator was shot and replaced it , to no avail . There goes $167 . Drove it to the vehicle inspectio today , and out of the clear blue everything began to work for about 10 miles and then off again . Got home and got online and started doing a little research and was pointed to 2 possibilities . One being the crankshaft sensor and the other being the PCM . Really don't want to repeat my first shot in the dark technic , so was hoping for some insight and possible teat to determine for sure which it might be . Also would like to know for sure , where the crankshaft sensor is for sure located on my engine , before digging into anything . Any help would be greatly appreciated .

 

im 99.99% sure it will be ur tach sensor. its located on the front of the motor and reads off the harmonic balancer. good luck

 

Thanks for the info . That is going to be my first check point .

 

i would agree

 

A new wrinkle to the saga . I had replaced the alternator , and figured this to be a premature move as it did not solve the issue . I then took the truck to get tags and out of no where the alternator began charging and the tach started to work , for about 4 miles and then back out again . I took the old alternator in and was figuring that it would probably be a good one , as the new one made no difference , so rather than take the $40 core charge , I was going to keep it as a backup . Had them run a test on it , and it was indeed bad , so of course , now I was even more baffled . Now I am wondering if there is a test that I can perform to make sure the Crank sensor is bad , before I tear into it . I am a 34 yr electrician by trade so would be able to do some test , if I knew what readings from what wire , I am looking for . Is there a test that can be done , or is it just a hit and miss .

 

i'm gonna say that if it comes and go's then testing it will be hard to do...i would replace it...seems to be a fairly common problem

 

there isnt any test that i know of. but when the tach sensor goes out, they start working intermittently like your desrcibing occasionaly

 

I am starting to dislike this this whole deisel thing . I decided that I would try to wait on the crankshaft sensor problem for a little bit and just use the old school regulator to run the new alternator . A pretty straight forward deal , found in one of the post . Got done and sure enough the alternator starts to charge as it should ( still no tach ) and as you add load it climbs as it should , so all is good , can drive the beast to work tomorrow , WRONG . Try to start it next morning and everything seems OK except , no power being sent to the bendix of the starter , now what ? Oh well , diconnect the harness to the starter and use a jumper to send voltage to the bendix , and it engages and the key is in the on position , so she starts right up . Probably some sort of a safety in the start circuit has opened , will check it later . But hold on , why are all my dash lights and headlights pulsing , what the hell now ? Ok , I am an electrician by trade , this should be a simple thing to figure . It's pulsing with engine speed , so I am thinking I must not be producing a flat DC sign wave , and the alternator actually puts puts out AC , and then it gets chopped flat by the full bridge rectifier , Oh , OK then , maybe one or two diodes in the rectifier have gone bad , so let's find this little devil , got to be here somewhere , go online and guess what , it's stuck in that stuid little control module along with the non functioning regulator , or wait is it just the crank sensor , it's about to get pulled to the back forty to become yard art . What now , is my new alternator still good ? Do I have to buy that stupid module and the sensor to be safe , wheres my Camper special 383 , you sold it you dumm *** .

 

none of my trucks have a crank sensor so i may be wrong but i dont think it has anything to do with the alternator charging. and as for the lights having a pulse, ive seen many of these trucks that do this and have never actually found anything wrong with any of them. it only happens at low idle, correct? the only safety i know of in the start circuit is the clutch switch. reach up in there behind the pedal and unplug it and jump the wires. the next place to look is the starter relay on the left fender. its metalic looking and has a few small and a couple large wires going into itif u trace u will find one of the larger ones goes over to and down to the starter with the big battery cable. check to see if it gets power when u turn the ignition to start. see if the relay clicks. make sure it has battery power through the other big wire. if nothing else see if putting power to the one going to the starter makes it crank to make sure its not just a break in that wire. i have seen wires like that get moisture in them and corrode completely off inside the insulation and cause intermittent problems like u are having. let us know