Distinct issues with PCM/ALT charging & speedo
 

So, first time caller long time listener. My old dad & myself’s pride and joy: a 93 D250 2wd Automatic. I recently replaced the wiring through the “duck foot” and most all fusible links via a blueSea150 hub and a separate hub for a mega fuse that accommodates the alternator power supply/ circuit. All this because I started seeing a lot of corrosion.

for the last couple of months, I haven’t had a Speedo. I believe the tach works as well as a/c (it’s winter now, hard to find a chance to check). I have a potentiometer installed by previous owner so my overdrive “works” whenever I chose. However, when I started the truck the other morning (first time in a month after this wiring project) I noticed my alternator cycling— I’ve always noticed a slight tick on the batt. gauge when I have my turn signals on but the other day after starting after the long sitting the interior lights were pulsing in correspondent time with the alt cycling. Put my meter on battery. It’d go up to 13.2v(+/-) and then nothing. Then cycle again along with throwing some strangely high voltages a time or two.

my question is, after alot of reading from you good folks: is the CPS still a viable candidate for checking? If so, what do I start to check i.e. the gap between balancer/sensor, wiring to plug, but which pins/wires do I need to probe? I should also just mention I’m a curse and also possess frighteningly little amounts of understanding with electrical applications BUT I have FSM—just would rather try to learn Arabic. Thank you all in advance, anything helps.

First off welcome to the forums, does it quit cycling after the truck warms up? after you first start these trucks below about 38 degrees the grid heaters cycle for a few minutes, is this what you are talking about?

My bet [same as nonrev]....You are experiencing the grid heaters kicking on and off. They are a major electric draw when they click on.

Gonna take some more readings today. Let it warm up a while and see
 

I’m gonna let the girl heat up for a while today and see what it reads. I don’t wanna sound insane but I didn’t realize the draw of the grid heaters

Oh ya they draw a lot of amperage.

They draw enough I here the motor load up, watch the headlights dim and the voltage gauge drop.
Then 10 seconds or so later the light brighten back up....then dim back down. My truck does that 1/2 the year living this far north.

I get that here too if I get an early start before the sun can do its thing...[coffee]...Ben

Drive it for a bit, let er heat up, and see if the issue goes away. It was 31* F here this morning, and the grids cycled for at least 3 or 4 minutes or so.

A good rule of thumb is to not have any electrical items on when the truck is warming up, this way the alternator does it's job and isn't over stressed having the A/C blower, radio, lights or anything else going on at the same time.

Update 11/18/22
 

Hey guys, so I went and took the truck for a test drive—first time since having done the fusible link project. It ran well and I noticed that the Alternator was charging fine after it warmed up. The AC works. But I get maybe ~10mph tops on the speedo and unless my potentiometer is out of wack the overdrive was acting wonky.

it’s an automatic tranny and I’ve cleaned, inspected, replaced the sensor that goes into the transmission body—no luck.

before I put the truck up today I did the key-ignition fault code trick and got a hamper load that I’ll sit down later and write out/decipher and throw that on a post here.

I would think disconnecting the cable going to the grid heater would be fine for checking the cycling issue. If it is cold out and I need to give it a shot of starting fluid I do that to keep from grenading the intercooler.