Engine/Transmission (1994 - 1998) No tach and not chraging

[ndurbin]

No tach and not charging

Tonight while out running some errands the tach started to jump around a bit at first. Well I thought okay I bet the connector just infront of the #1 valve cover has wiggled loose or something. Pulled over and checked it, everything was ok. Hopped back in the truck and took off again, no tach signal at all now. Weird. Checked the other gauges, everythings fine but the alt. gauge low (great here we go again I thought). Well I keep an eye on things as I finish up the errands and head home. In the 30 mile drive home the tach did flicker back on once. Alt. gauge came back up briefly then everything went dead again. In the drive home the battery (in the process of relocating them) was completely drained down to nothing. I pulled into the driveway with no headlights and everything that was electircal that I could shut off was off and it was dead.



The alt. is new so I don't think it's the problem. I would guess it's probably my engine RPM signal pickup is not working or the PCM took a dive ($$$$). Are their any test proceedures for the RPM signal pickup? What is the proper clearance for the sensor b/w the balancer? Are their any other things I need to test out?



TIA

Nathan

 

[JKouzez]

i just got done dealing with this, try doing this, your engine speed sensor could be bad or maybe you just hit a hard bump and disturbed it. the sensor is on the harmonic balacer slightly loosen the two bolts holding it on then place a piece of cardboard between the sensor and balancer and firmly push the sensor down on it. this should give you the proper spacing then tigthen the nuts back up. if the tach does not read then the computer does not think the engine is running thus will not turn the alternator field on. let me know how it goes.

 

[Vaughn MacKenzie]

I wouldn't automatically trust a new alternator Nathan, your symptoms tell me it's DOA. Try checking it with a voltmeter or take it to an auto parts place and see if they'll check it for you. It could be as the voltage dropped your sensor(s) started fritzing out. I had the same thing when the alternator died on my Bronco II. At about 8 volts electrical items and sensor starting doing bizarre things.



Vaughn

 

[McCRam]

Vaughn-Would the tach quit working if it was just the alternator?



ndurbin-Do the grid heaters cycle? If not unplug the crank sensor, and see if they cycle. If so, the crank sensor could be bad.

 

[crabman]

Engine Speed Sensor

nd,

The correct air gap is . 049" min. to . 051" max. Do Not adjust over the 2 gaps on the pulley or you will damage the sensor upon startup. Use a non-magnetic feeler gauge. (brass)

Sensor bolts are torqued to 18 ft. lbs. & use dielectric grease on connections before connecting.

To save yourself some grief and time, Charge up both batteries and have them load checked. 2. ) Take off alt. and have it bench checked. Be sure to have batteries disconnected before taking out alt. or you could blow the large fuse (120amp) in PDB.

Post here with results.

crabman

 

[K5IP]

Nathan,

You are correct in assuming that the engine speed sensor is responsible for your alternator not charging. It provides a necessary input to the pcm before it will turn on the alternator.

The fact that the unit was intermittant until you took the connector off, and now is completely gone indicates connector problems to me. I'd go back over that connection again. They can look ok but still be bad. Use a contact cleaner, conductive grease on it. Mine needs a nylon tye wrap around it to keep it working.

The speed sensor has three leads, one is ground, one is a 8vdc reference from the pcm and the third is the signal line. The signall output will switch between 8 and o vdc each time the notch on the damper crosses the sensor (it's a hall effect switch). The best way to monitor the output is with a scope, but you can probably detect the operation of the switch by watching it with a volt meter while cranking the engine.

Sorry I can't give you the wire colors I don't have my service manual with me.

Roger

 

[ndurbin]

First off thanks for all the info. I haven't had a chance to get out and test anything yet (was alil cool and breezy today and no indoor shop). I'm leaning towards the RPM sensor being outta whack or bad. I didn't mess with any connections other than to insure they were tight. I did clean the connection infront of the #1 VC back when I changed the alt. about a month ago (wasn't any need to do it then as it was clean but wanted to rule it out). As tomorrow is suppose to be alil warmer I well get out and do some poking around. Well post results tomorrow (hopefully their good and not that expensive).



Thanks again

Nathan

 

[Howard Durand]

Make sure all associated ground connections are good.

 

[ndurbin]

Well I got out and checked the connections and grounds. And they all looked good, sprayed alil contact cleaner on them just to make sure. Switched batteries and tried to start. Got alil juice but no start. Weird, tried again. Not a damn thang this time. So my next step is to pull the starter off, test it and go from there. Which if this starter is toast it'd be #2 in less than 3 months. Thank god for warranties.



Nathan

 

[BBrooks]

Did you recently replace one battery and not the other?? My brothers did that and it would drain the new battery.



Boyd

 

[ndurbin]

Nope just have one battery on the truck right now. I'm in the process of relocating them back along the frame rail under my flatbed, so I took the second one out.



I'm letting one battery trickle charge over night and see what happens tomorrow hopefully if I am feeling better (really sucks working outside with a cold).



Nathan

 

[ndurbin]

Well the problem is fixed. Guess it was a bad/dirty connection somewhere (none really looked dirty or loose). Put the battery back in this morning and it fired right up and everything was working.



Thanks again

Nathan