I was driving home from work today when all of a sudden the Tach, AC & Over Drive went dead on me.

I checked all fuses and all were ok.

Any suggestions!!!!?????

Thanks in advance!!!

Luis

 

If it's not a fuse (which can LOOK ok but not be) then maybe it's a fusible link. Fusible links are usually near the battery and are wires with a "fat" section.

I suggest checking the fuses again, with an ohmmeter if you have to.

 

I'm thinking 'Crank Sensor'.

 

I was thinking that too Craig, but the a/c kinda throws that away. I wonder if the a/c clutch doesn't work, or the blower motor? If other electrical things quit working too, like the pwr windows if equipped, I would be checking the ignition switch.

 

I forgot to mention that the truck still starts and runs

I checked all the fuses with an ohm meter and also checked them for continuity and they all checked out good.

This morning I started it again and noticed the voltage was lower than usual. I disconected the battery terminals and the truck shut off. Could this be the alternator?

 

I think it may be the crank sensor too. The crank sensor tells the computer that the engine is running and at what speed. The computer then "excites" the alternator, which charges the battery and supplies approx.13.2-14.2 volts to the whole system and keeps that voltage. Now, if the crank sensor fails to pick up the engine speed, the computer does not "excite" the alternator, resulting in no charge and battery voltage only. If you have a good battery, it will start the vehicle ok, but after running for a while, the voltage will be pulled down from accessories and mainly the injection pump to a point where you get a "low Voltage" situation. This can cause all kinds of symptoms. The injection pump for one, cannot sustain fuel loading due to the low voltage and possibly will do exactly what you indicate. The compressor clutch on the A/C cannot maintain enough voltage to stay locked in so the A/C will not work. Everything pulls voltage, if it drops to say 11-11.5 volts, it will start causing problems.

I would suggest charging the battery with a good charger, running the truck to see how it runs, and then checking the voltage while off, and then running, with a volt meter, preferably a digital type. If the voltage is below 13, you have a charging problem, which could be the alternator, or most likely, the crank sensor.
BTW, I am no mechanic, but I did get a degree in Electronics Technology, and just "fixed" a 99 like this a couple of months ago. Three of the areas "top" mechanic shops had worked on this truck for a total of about 5 weeks. It went from one to the other, with the alternator being replaced three (!) times, of course to no avail. Then one shop pulled the entire wiring harness out looking for fusible links and broken wires. Couldn't find anything to cause the problem. I heard about the problem through a mutual friend and suggested the crank sensor. They replaced that, and then had to explain to the customer why it took so long. Ha Ha! I probably just got lucky, but it sure did make my head swell to the point I had to get a new hat!LOL The key was the Tach., if it is not working, the computer does not sense the engine is running, so it cannot send voltage to the alternator to charge the system.
Good luck, I hope I helped.
Chris

 

How hard is it to replace the crank sensor?

 

Try checking to make sure the connection is tight at the pickup. I haven't had any first hand experience with this, but a friend had a similar prob, no tach, no charge, his cranck sensor was the prob, he gave it a wiggle and voila. I believe it is just off the balancer?

 

Just tried the wiggle method. No luck but thanks for the info. I will try to replace the crank trigger.

 

The crank sensor rarely goes out, most times it's either the connection or the gap. The gap should be about the same thickness as a credit card.

 

Try setting the gap before you replace it. I think it is subject to get the gap knocked out of whack due to where it is at. Like Infidel said, a credit card should work, although it may mess up the credit card. It uses the Hall effect to pick up, meaning it has a magnet on the crank and each time the magnet passes, it induces a little voltage into the transducer, or pickup (sensor), this is how it works. Normally the connections go bad or the sensor opens for one reason or another.
Chris

 

May also be a broken CSS wire or even just a break in the insulation. CSS rarely fails. Double check the wire running to it. And yes the a/c won't work either. Without CSS, computer doesn't know the engine is running, so nothing gets energized. 5 months and lotsa new parts later, mine still wouldn't work. Then I found this site and within 2 days had recieved much help. Upon following theadvice received here, I found a broken wire to the CSS that when repaired, fixed it all. Mine broke right next to the connector at the front of the head. Good luck.

 

Hey guys, I replaced the crank sensor and that did the trick I couldnt have figured it out with out you.

Let me list the part number for it 4882763

I went through hell at the dealership. They pulled out 3 different sensors that were not the right ones and then said they didnt have it. Made me drive to another dealership 1/2 an hour away (that didnt have it) to find out that they did have it.

Now that I have the old one out, I will inspect it really good

Thanks for the help!!!

 

Excellent!

 

Glad we could help.
Chris