Has anyone come across a FICM putting out way to much voltage? When the key is turned on, I get 58v, it stays at 58v when running. When the key is off, it cycles down to near zero volts before shooting back up into the 340 volt range, cycling back down to zero and repeating.

SO here's how the testing adventure has gone. I've been chasing electrical ghosts for a month. I had an almost random parasitic draw on my batteries. I could go to work and not have an issue for days, then the battery would be to drained to turn over, or other random days it would just barely have enough to crank and start.

I load tested the batteries and had the alternator tested, which both checked out. Finally I brought it to a shop and of course it stopped doing it all together.

Finally I went to start my truck two days ago it cranked, but wouldn't fire. The batteries had lots of juice initially, I basically tried until the batteries were getting drawn down and i threw it on the trickle charger overnight.

Yesterday, same thing, cranking no fire. Nothing out the tail pipe. I left for an hour came back, tried again and it fired up.

At this point at least I had something I could test, so I opened up the FICM to measure the voltage. When I first put the lead on the correct screw and the battery ground, I thought there was something wrong with the meter, it read 200 and something volts DC and dropping. I had someone turn the key and it immediately was reading around 58v. Had them turn it back to off and the voltage slowly dropped down to almost zero.

Thats when I saw it! Once it got down to near zero, it jumped back up into the 330v range! It slowly began dropping again from there. I messed around with it a little longer and discovered that no matter where the voltage was in the off position, as soon as I turned the key, it would go back to 58v. If the engine was running, it still maintained the 58v until the key was turned off and it repeated the drop in voltage to near zero before popping back up to 330-340v.

I haven't come across anyone having this issue, but I'm thinking its most likely the FICM itself. Has anyone seen anything like this before?

 

I'm a novice with FICM's but that sounds pretty whacky! I wouldn't think you should see that type of voltage at any point.

Is it an OEM unit or aftermarket 58v unit?

Hopefully Ed from FICMrepair.com will chime in. He's knows his stuff on these!

 

It might be a Swamps unit:
Swamps Heavy Duty Rebuilt 58V FICM

What's the actual current draw? I'm not saying 330V isn't what you're seeing but if the current is .001A then that's not a significant power draw.

 

I can't tell if its an aftermarket unit and I've only owned the truck since June. The truck was manufactured October 21, 2003, so right after they switched from 7 pin to 4 pin, so no way to see if it was swapped to the newer style.

I'll pull the unit off and see if I can tell, this afternoon.

 

Well... maybe this will save someone else a little pain and shame. I grabbed a better meter from my work tools and discovered that the cheapy meter I used before must have been switching to micro volts. sheesh. Well at least that's one less possibility as to why the truck is having these problems