Possible Dash or Computer Issue???

NickTF

NickTF

Single turbo turd.
Joined
Jun 4, 2007
Messages
5,887
I've noticed when I start my truck up in the mornings many times the tac will fall to zero and the voltmeter will start reading like it's only running on battery power. I have no grid heater so the grids pulling juice is not the issue. The generator light will come on along with this phenomenon some times but not always. Seems to depend on how long the voltage stays around 11-12 volts. Ideas on issues to check? I run one bigg 1100cca Dekka battery and a large 160+ amp (test sheet showed 195 amp peak) alternator.

I've also noticed that the voltage on the voltmeter reads higher during colder days and lower during warmer days. Truck has always done that with the stock two battery setup/stock alternator and the current one battery setup and big alternator. Is that normal?
 
This morning the voltage ran too high for a bit and then settled down. Not only did the gauge say this but my radar detector had a high voltage indicator come on rendering it useless until the voltage dropped back to normal.

Doesn't the PCM control the voltage of the alternator or is the alternator internally regulated?
 
Check the gap on your crank tach signal and the connector near the front of the head. Those usually tend to be the culprit.
 
CSnyder said:
Check the gap on your crank tach signal and the connector near the front of the head. Those usually tend to be the culprit.
Click to expand...

What is the spec on that gab again? Been a while since i've had it off (KDP fix). I think it's in my Haynes manual if someone doesn't know it off the top of their heads.
 
High voltage shouldn't have anything to do with the engine not picking the crank sensor up.

The PCM regulates the voltage on the system.
 
zstroken said:
High voltage shouldn't have anything to do with the engine not picking the crank sensor up.

The PCM regulates the voltage on the system.
Click to expand...

Usually low voltage is the problem. Today was the first time I saw the voltage go on the high side enough to cause an issue. Again, the tach would drop out when the voltage swung high just like it did when it swung low. Any ideas on what to check wiring wise if the PCM isn't regulating voltage properly? Is it normal for voltage to increase the colder it gets outside or is that a sign of an issue with the PCM's ability to regulate voltage properly?
 
had a no tack, and fuel gauge ,, found out it was the main power wire on the fuse block coming loose, don't know why but it solved my problem .. fuse block in the side panel drivers door
 
NickTF said:
Usually low voltage is the problem. Today was the first time I saw the voltage go on the high side enough to cause an issue. Again, the tach would drop out when the voltage swung high just like it did when it swung low. Any ideas on what to check wiring wise if the PCM isn't regulating voltage properly? Is it normal for voltage to increase the colder it gets outside or is that a sign of an issue with the PCM's ability to regulate voltage properly?
Click to expand...


I wonder if you should go through and plug and unplug your connectors on the PCM. Didn't you have something going on last year?
 
zstroken said:
I wonder if you should go through and plug and unplug your connectors on the PCM. Didn't you have something going on last year?
Click to expand...

I've solved pretty much any other issue I had that I can think of. This is something new. I've always wondered why voltage increases when it's cold. Truck's done that since i've had it IIRC.
 
Does your overdrive still work? My voltmeter was doing the same thing before my PCM went out. I never had issues with the tach like others have. While I waited for my pcm to arrive, I wired in an external mopar voltage regulator to charge the battery's. They dont cost too much to try.
 
NickTF said:
What is the spec on that gab again? Been a while since i've had it off (KDP fix). I think it's in my Haynes manual if someone doesn't know it off the top of their heads.
Click to expand...

I'm pretty sure it's 0.049"-0.051".
 
zstroken said:
High voltage shouldn't have anything to do with the engine not picking the crank sensor up.

The PCM regulates the voltage on the system.
Click to expand...

The PCM will not regulate voltage or tell the alternator to do anything for that matter, unless there is a tach signal...

Tach pickup can sometimes change gap (which should be around .050") and sometimes even get a loose connection at the plug.. Check it out. If not, I'd replace it.. It's not too expensive,,,
 
Sarge1 said:
Does your overdrive still work? My voltmeter was doing the same thing before my PCM went out. I never had issues with the tach like others have. While I waited for my pcm to arrive, I wired in an external mopar voltage regulator to charge the battery's. They dont cost too much to try.
Click to expand...

Wow back from the dead! How ya been Larry?

The trans will not go into OD when this happens but it happens so briefly it hasn't been an issue thus far. Come to think of it I have been in cruise control and had the trans kick out of OD about 3 months ago a few times but the problem just went away.
 
KILLER 'B' said:
The PCM will not regulate voltage or tell the alternator to do anything for that matter, unless there is a tach signal...

Tach pickup can sometimes change gap (which should be around .050") and sometimes even get a loose connection at the plug.. Check it out. If not, I'd replace it.. It's not too expensive,,,
Click to expand...


Yes I read the high voltage issue, and the post below referred to the crank sensor. Thought that is where they were going with that.

No crank sensor pulses, no charge!
 
KILLER 'B' said:
The PCM will not regulate voltage or tell the alternator to do anything for that matter, unless there is a tach signal...

Tach pickup can sometimes change gap (which should be around .050") and sometimes even get a loose connection at the plug.. Check it out. If not, I'd replace it.. It's not too expensive,,,
Click to expand...

Excellent. I would guess my issue lies here.

On a positive side note due to everyone not getting raises for about 3 years now in our company (some getting a pay cut) i have been given a company truck to drive daily so I will have time to address issues like this from now on.
 
Went and checked and the sensor was a bit tight in clearance on the drive side end of it. Reset the clearance to around .049" and only started it up once since but didn't see any voltage issues then. Truck is no longer DD so may take a while before it shows it's head again, hopefully it won't! The wires looked fine didn't see anything that was obvious.
 
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