2.5 External Voltage Regulator

[JCaspary]

Hello all, I have a 98 2.5L I just picked up, working through tune-ups on it.

Long story short, it has a new alternator and an external voltage regulator. The VR ignition feed is plugged into the rear defogger relay port in the engine compartment fuse box. Problem is, when plugged into this feed, the voltage output jumps up to ~15.6 V (on a volt meter) while engine is running. If I pull this connection and plug into the common feed (straight battery power) it settles out at a very consistent 14.6 V.

Anyone else have trouble running an external voltage regulator on an ignition switched power supply?

Thanks

 

[Chris]

Can you just remove the external voltage regulator altogether? Not sure why this is needed. I thought the voltage regulator was build into the PCM.

 

[JCaspary]

Can you just remove the external voltage regulator altogether? Not sure why this is needed. I thought the voltage regulator was build into the PCM.

It’s been installed to replace the PCM regulator. I was told it went bad. I’d have to wire it back up to the PCM. If push comes to shove I will do that and get a new PCM if needed.

 

[Chris]

It’s been installed to replace the PCM regulator. I was told it went bad. I’d have to wire it back up to the PCM. If push comes to shove I will do that and get a new PCM if needed.

Interesting. I would think if the voltage regulator within the PCM failed that the PCM itself would be having other issues. I'm not the PCM guy though, that's @Wranglerfix.

This is a bit of an odd-ball scenario as I've never heard of someone running an external voltage regulator before. Maybe someone with more knowledge on this will chime in.

 

[Wranglerfix]

@JCaspary I can repair the 5 volt regulator and whatever else might be wrong with the pcm for 125.00 + shipping.

The external voltage regulator is used when the pcm regulator goes out.

 

[JCaspary]

@JCaspary I can repair the 5 volt regulator and whatever else might be wrong with the pcm for 125.00 + shipping.

The external voltage regulator is used when the pcm regulator goes out.

15.6-15.7 is what I’m showing when motor is running like in that video. If I move the red cable directly to the battery positive terminal or the common side of the relay port I get a clean 14.6v and engine runs/idles smoother.

 

[Wranglerfix]

Where does voltage drop when disconnected altogether? The 5 volt pcm repair is quick and common.

 

[Jerry Bransford]

I used to have to repair PCBs like that in a former life. I miss the smell of rosin-core solder but I definitely don't miss having to replace IC's (some up to 18 pins) without fawking up the circuit paths going to them lol.

 

[Wranglerfix]

@Jerry Bransford I love the smell of rosin in the morning!

The pcm below is out of a 7.3 Powerstroke with a bad microprocessor. A 45 minute repair for an expert and a core for a neophyte. I’m climbing the ladder but still the latter!

 

[Jerry Bransford]

Oh yeah, wicking braid I've used that stuff. I preferred a solder-sucker though, it's faster. Just keep your eye clear of it in action.

 

[JCaspary]

Quick update to this issue, I haven't had much chance to dig in with work this week, but I did try running straight to the battery for a few trips but ended up seeing the same issue with over-charging. Going to take all of this aftermarket stuff off and rewire into the PCM.