FICM or Battery?
 

Hello everyone. This morning I cranked up my 2004 to head to work and I switched the scangauge readout to look at FMP voltage. When I turned the key it was 47.5 and as soon as I cranked it over the voltage kept dropping until it reached 43 and then it climbed back up to 47.5-48. I was wondering where to begin. I do not know exactly how old my batteries are (been on there at least 2 years since I got the truck). Can anyone point me to the right direction? I was thinking replacing the batteries could help it. When I'm driving it's fine, this just happens during a cold crank.

Find a parts store that does free battery testing, and have them check your batteries. If they are weak, I would definitely start there.

When I know I'm going out in the morning, I put a 1.5 Amp auto charger on my 6.0L service truck to keep the batteries topped up. Seems to start better when I do this.

I got them tested. At Napa. The guy testing them said they were right where they should be and he said the same about the alternator. However he did spot a little corrosion and he said even the slightest bit can cause problems. Another thing is be tested the batteries when it was hot and not cold. When I cold crank the voltage gets down to 10.9V and that's when the FICM voltage goes down. It also never stays with one constant voltage. It's always jumping between 46-48 unless it's cold where it gets down to 43.

Cold definitely make a big difference. I had some AGM batteries in my '01 Dodge, when it was cold it wouldn't start worth a ****. Tested good every time when they were warm though.

Another thing is that your batteries were likely fully charged, plus a surface charge. If the tester doesn't know to remove the surface charge, they will look like amazing batteries.

You could try the trickle charger over night and see what happens. That would insure your batteries are fully topped up. Checking all connections for corrosion and removing any corrosion is a great idea as well.

Well I sat the truck for 4 hours and afterwards I cleaned the corrosion off. The after start voltage didn't get as low as 10.9 but the FMP went down to 43.5. But back up again. Just baffling. Could be the FICM after all it's a 215k mile truck. Injectors are new though. Seems to run normal but the acceleration is a bit weaker now but I think that's low tire pressure. Kinda feels uneven the way it rides. Idk I guess time will tell.

Yep the FICM is bad. Started to sound a little rough this morning. Its in its early stages of failure so im going to fix it within the next week or so before it kills the injectors. Gonna try FICMrepair.com. Im gonna pay the extra $50 to swap out because i need my truck to get to work.