Diesel Junkie

So after a lot of poking around with schematics, a test light and a voltmeter, all my connections seem good.

I have lost power to both sides of the alternator field when running.

The tach does not work, but does get power when the key is first moved to the on position cause it pops a little.

And the AC wont turn on.

THe Wait to start light does sitll come on though.

After some searches, i am gonna guess that this is most likely cause by a bad crank speed sensor. The gap seems good, <0.50, and the connectors look clean, but were not fully inserted, pushing it in further did not help.

Should i replace the crank speed sensor???????????????????????????????????????????? ????????????????????

It is funny too that the truck will start and run with the computer unpluged.... try that with a gas motor.

BearKiller

I would suspect a bad alternator.

What surprises me is that a 92 Cummins truck would have a computer.

Diesel Junkie

IT it snot the alternator itself at fault, like i said above the field control wires to the alternator are not high while the truck is running. The computer controls both of these.

wannadiesel

It has all the classic symptoms of the crank sensor. Follow the wiring as far as you reasonably can, and if you can't find any breaks or worn out insulation I think you ought to throw a crank sensor at it.

JD730

Its a simple thing by todays standards, controls the cruise control, OD if its automatic, alternator, intake heaters, get input from various sensors speed, tach, intake temp, etc. Starting put them in when they put the OD automatic in.

Diesel Junkie,
I don't have my book handy, but you can pull codes out by counting the flashes on one of the lights in the dash and then decode what it is. Might help, might not, but it can't hurt.

Does anybody know how to pull the codes with out a scanner? Is it On-off-on-off-on with the key? I can't remember right now.

wannadiesel

The crank sensor won't set a code - the computer isn't smart enough to realize that there might be something wrong if you're running down the road at 40 mph at 0 RPM.

All the crank sensor does is tell the computer that the engine is running. I wish they had used an oil pressure switch for that, it would have been simpler.

Diesel Junkie

Apparently these crank sensors are really hard to find. The only one dealership within about 50 miles supposedly has it and they are closed on Saturdays. Napa says the closest is in Oklahoma.

Anywhere to get one of these?

Diesel Junkie

Apparently there is a sensor at a dealer in Sacramento, and they are open to 3 today. I wanted to go to Tahoe this weekend anyways.... It is also funny that the dealership in Silycon Valley charges $130, and the dealership in Sacramento charges $105.

I have 5 volts supplied to the sensor, but the schematics say it should be 8 volts... ??????? what gives?... The funny thing is that most other automotive sensor networks i have worked on are 5 volt, and this thing is holding a nice 5.00V signal, not some random number.

Is there a way to test the pulse back from the sensor without an osciliscope before i pay big $$ for a new one???? All i have is my bluepoint multimeter. I dont want to drive to the lab at work and fumble around with scope that i dont really know how to use either.

charger 69

I wonder if that is what mine is leading up to.In real cold weather from time to time the speedo won't work and the overdrive doesn't work.Once the truck gets up to temperature it has come back.It did it the last time I started out with the trailer only it was a hot day but again as soon as it hit operating temperature it starts working again. Any ideas?

flashgordon

all thow i haven't dun it on a ctd crank sensor you should be able to run eng and get a voltage. turn volt meater to ac and you should get some kind of voltage thru it when the eng is running.

BearKiller

Thanks.

What year did they start this foolishness; and, is it also on the 5-speed trucks??

How big an undertaking is it to do away with and go mechanical??

I despise anything on a vehicle that is not mechanical.

The reason I am asking is we are looking for a couple more 1st Gen. trucks, one for my boy and one for a spare truck/engine.

Thanks.

wannadiesel

The foolishness started in '92 on both automatics and 5 speeds. You can put an old style Chrysler regulator on there with no trouble.

Diesel Junkie

Speed sensor replacement fixed the problem.

There is so much stuff on that truck that does run through the computer i would advise against by passing it unles you plan on rewiring most of the truck anyways, or are using the motor for a new application like a rock crawler.

Thanks for the input guys!