Engine/Transmission (1994 - 1998) Weird Charging/Electrical Problems

[Woodenhead]

Hi All



The other day when driving home I noticed my alternator (Gen) light came on and my volts were down around 12 as opposed to 14. If I wound it up to 2000RPM I'd get 14 Volts and the light would go out. I figured either my alternator was on it's last leg or since we had a foot of snow fall maybe all the snow blowing in the front was doing goofy things to the alternator.



Then the next day with the truck running I put an ammeter (DC Clamp on) on the wire from the alternator and read 1. 7 amps. The wire coming from pos side on the battery and read 10 amps. When I got back in the truck the volt meter suddenly dropped to 8. 5 volts (verified with meter on battery). While it idled my radio would come off and on by itself as I put the parking brake off and on (daytime running lights go off and on with brake). When I shut the truck off the volts on the battery went up to 10. 5.



Now the truck wouldn't start so I tried to boost it (with 3/4 ton Ferd) and it would try to turn over but didn't seem to have enough juice. So I went back to work baffled . I came out later in the day and it started under it'd own power (no boost required).



When I drove into the shop at work my ABS light would come off and on and my tach would drop to 0 then back up again.



I know a little about electrical but this ones got me stunned. I think maybe it's a bad ground somewhere but where? Maybe it's something else.



We've got lotsa snow in the past few days and there's plenty of ice and snow frozen to the undercarriage so it's been in the shop here at work since yesterday thawing out so I can work on it tomorrow.



HELP



Thanks,

Mike

 

[Desperado]

You may want to check out the engine seed sensor. I had a similar problem it turned out to be the engine seed sensor.

 

[Woodenhead]

Desparado



Thanks for the tip. My tach was doing goofy things awhile back and I unplugged and cleaned the speed sensorwhich seemed to fix it. I'll check it out but the tach problems came after the other symptoms. Also, do you think this would make my voltage and charging system act the way it is? I'm not sure what all the engine speed sensor is connected to.



Thanks again

Mike

 

[Desperado]

The engine seed sensor tells the pcm that the engine is running, witch then activates all of the electrical stuff.

 

[Andy Redmond]

With the moisture you have described, you may have a popcicle inside the speed sensor elec. connector. The fan has frosted it good?



Use some contact clr. , wd40 (water dispersant) etc. and some dielctric grease.



Then see if the gremilins are gone.



Have you tested both batteries?



Often one will go bad and suck the other one down shortly thereafter.



Good luck

 

[C. Harlan]

your PCM may be going out... my best friends brother's went out, and it had similar symptoms as well. . keep that in mind.



-Chris-

 

[Howard Durand]

I agree with Andy, check the batteries.

 

[illflem]

Some folks with aftermarket batteries such as Optima will often use a spacer under them so the hold down bolts don't bottom out with shorter batteries. What happens with a spacer is the battery temp sensor under the driver's side battery doesn't make contact.

No problem when it's warm out but when it gets cold the sensor tells the PCM the battery is frozen, alternator then puts out low or no voltage. Low voltage can then cause the other problems you speak of.

Make sure the actual battery case is touching the sensor if it isn't already.

 

[Woodenhead]

I think it's fixed



I let the truck sit inside for a couple days to thaw out. The when I started it (boosted) I had the same problems. Then I cleaned all the battery terminals and grounds but none were in too bad of shape. Then I installed a new alternator and charged the batteries with a charger. Truck fired up and all the weird problems were gone. I think once the altenator died and my voltage started getting low the PCM started acting up because of the low voltage.



Another interesting note. My alternator has always caused a bit of whining in my CB and it was getting worse lately. The new alternator has eliminated all of the whining .



I'm still going to load test the batteries since they got drained pretty bad.



Thanks for all the tips.



Mike

 

[Dennis Garrett]

Don't underestimate how screwed up things can get with a bad body ground. I've had body ground failure on three vehicles, and they all acted about like your's did in your first post.

 

[Deezul1]

Mine did some weird stuff off and on and it was a bad battery.

 

[Dfuruness]

I had the same problems. I replaced my alternator and installed two new batteries. No problems now...

 

[Monroefiredog1]

Despardo, Said:



You may want to check out the engine seed sensor. I had a similar problem it turned out to be the engine seed sensor.



Despardo, How long did it take to figure out that the Eng Speed Sensor was bad. I am having the same problem, but I don't know if thats what is wrong. Is there a way to check it, before I buy one? Could it also be the Battery Temp Sensor? Any help will be greatly appreciated... .



Thanks,

D. L. Brookshire

 

[Desperado]

Originally posted by Monroefiredog1

Despardo, Said:



You may want to check out the engine seed sensor. I had a similar problem it turned out to be the engine seed sensor.



Despardo, How long did it take to figure out that the Eng Speed Sensor was bad. I am having the same problem, but I don't know if thats what is wrong. Is there a way to check it, before I buy one? Could it also be the Battery Temp Sensor? Any help will be greatly appreciated... .



Thanks,

D. L. Brookshire

That should have said SPEED sensor, just washed my hands that day and couldn't do a thing with them. As to the question, I ended up taking the pick-up to the dealer the monday after I found I had a problem and they tried the pcm, then the speed sensor. I don't know of a way to check the sensor, the cost of one is about $73. 00 and don't know anything about the battery temp sensor, sorry I can't help out more.

 

[JoshPeters]

you should be able to check the speed sensor with an Ociliscope. It should have a steady pattern.





Josh

 

[Howard Durand]

D. L.



Before doing anything else, unplug the engine speed sensor where it connects into the wiring harness and thoroughly clean the contacts, plug it back together and try it.



If that doesn't go any good then You can check the speed sensor reference voltage (ignition key on, engine not running).

The reference voltage should be either 8 volts or 5 volts depending on the year of your truck.

(94 & 95 trucks will read 8 volts and the 96 will read 5) Beyond that, I don't know but would guess they would continue with the 5 volts.



With the connector apart, hold the end of the cable coming from the PCM so that you are looking into the connector. The middle wire will be the supply and should read either 8 or 5 volts between it and engine ground.

Or looking at the wires, the supply wire will be either orange or purple with a white tracer, depending on the year.

The sensor ground will be black with a light blue tracer. The third wire should be grey.



There is not much you can do to test the sensor itself without the proper test gear but make sure the sensor ground is good. It is combined with several other grounds and connected to the engine block on the driver's side next to #1 valve cover.

 

[Monroefiredog1]

Engine Speed Sensor

Originally posted by Howard Durand

D. L.



Before doing anything else, unplug the engine speed sensor where it connects into the wiring harness and thoroughly clean the contacts, plug it back together and try it.



If that doesn't go any good then You can check the speed sensor reference voltage (ignition key on, engine not running).

The reference voltage should be either 8 volts or 5 volts depending on the year of your truck.

(94 & 95 trucks will read 8 volts and the 96 will read 5) Beyond that, I don't know but would guess they would continue with the 5 volts.



With the connector apart, hold the end of the cable coming from the PCM so that you are looking into the connector. The middle wire will be the supply and should read either 8 or 5 volts between it and engine ground.

Or looking at the wires, the supply wire will be either orange or purple with a white tracer, depending on the year.

The sensor ground will be black with a light blue tracer. The third wire should be grey.



There is not much you can do to test the sensor itself without the proper test gear but make sure the sensor ground is good. It is combined with several other grounds and connected to the engine block on the driver's side next to #1 valve cover.

I have already checked the ground, and it is good, I even grounded it again, did'nt make any difference. There are two wires that have power on them at the plug, while unpluged. Is this normal? I don't want to replace the ESP if its not bad. Whats the chance of the Battery Temp Sensor being bad? Have you seen one go bad? Thanks for the help,



D. L. Brookshire

 

[Monroefiredog1]

Eng Srpeed Sensor

Originally posted by JoshPeters

you should be able to check the speed sensor with an Ociliscope. It should have a steady pattern.





Josh

Thanks Josh, I will have it checked...



D. L. Brookshire

 

[Monroefiredog1]

ESS

Originally posted by Desperado

That should have said SPEED sensor, just washed my hands that day and couldn't do a thing with them. As to the question, I ended up taking the pick-up to the dealer the monday after I found I had a problem and they tried the pcm, then the speed sensor. I don't know of a way to check the sensor, the cost of one is about $73. 00 and don't know anything about the battery temp sensor, sorry I can't help out more.

OkThanks Desperado, I will check it... .

 

[Howard Durand]

D. L.



My Haynes manual states that there should be a "pull up" voltage on the third wire that changes between about 0. 3 volts and 5 volts when the slot in the vibration dampner passes under it. (it reads the highest when the slot passes under the sensor)

With it unplugged you will probably have about 5 volts on the open end of the grey wire coming from the PCM