Here is this morning reading at 31 F outside temp.

On start up there was no missing, fired up fine.

On start up: Battery 11.8 V until the glow plug stop, then up to 13.9
FICM 40, then up to 45.5 once glow plug stop.

Once warm, Batt 13.9 and FICM at 47 to 47.5.

Stop and start again after half hour: Batt 11.8, FICM at 45, then after glow plug off, 13.9 and FICM 47 to 47.5.

 

This is pretty much how mine behaves also.
I monitor the FLV (or FLP can't recall) and it'll show briefly 11.0 or 11.5 at
initial fire-up then pretty much stay 12-13 otherwise. Now, before
I replaced my batteries last month, I'd show 10 or 10.5 for a bit too.

 

I was reading in thec folder that before you do the test on FICM you must have at least 12.5 volt battery.

 

The FICM is basically a four channel switching power supply. If one of the four channels is dead, the other three will try to work but when the input voltage is very low, like when the glow plugs are on, they just can't keep up. What does 40 volts at start-up do? Well, the injectors have coils that actuate solenoids that fire the injector. When the voltage drops, the current draw goes up, The FICM tries and fails to supply that extra current, the whole thing starts to over heat, which rather quickly kills everything.

If your FICM is at 40 volts at KOEO, or at startup before the glow plugs cycle off, then it has failed (not "is close to failing"), and the only question is will you pay $250 for a repair, or $2250 for a repair and a set of injectors? Every single time you start it with that condition it's a crap shoot if you kill an injector, and even if they aren't dead yet, you are taking life out of them.

Brian

 

But if the batteries are too low, say 11.5 during glow plug cycle, would it be hard to get 48 volts from FICM? If this is the case, should I replace the batteries before I check the FICM?

 

Make sure your batteries are good. It looks like you probably have a FICM that needs some help though.

 

I will take a close look at the battery, but I will monitor the FICM too, thanks. I just do not want to touch the FICM if it ain't broke.

 

I want to chime in on this thread so I can get notifs. My truck has no problems that I know of, cold start/hot start all good. In the mornings I've started watching my FICM voltage on SC2, not running battery voltage, so dunno about that. KOEO FCM voltage is 49, as glow plugs warm it dips but still above 45. At initial idle FCM volts drop to 40-44 and hold there at normal idle, but as truck warms up, they come up. Installed high idle mod, because I noticed if I hold my foot on throttle at about 1k-1.2k FCM volts are at operating voltage. So now, I start truck, let it run a minute or 2 to "lube up" then kick on the high idle mod, and leave it be to warm up. You're saying this is "failed"? Need to know, thanks. AJ

 

ANYTHING under 45 volts at ANY time is considered a failed FICM.

Will it still run? Some do, some don't. Some quit at 44 and others pull down to 19 and still operate. Keep in mind the injectors depend on that voltage, the higher the better.

Josh

 

OK, I charged the batteries and cranked the engine. Before start up I was getting 48, during and just after the engine fired, FICM was reading 39 to 41. After glow plug cycle, it was reading 42 to 45, then after a few minutes it was between 44 to 46, sometimes 47.

So, like everyone says, I would say FICM is starting to give up. I will try a resolder and check it out, if it does not work I will send it for repair I guess.

 

You may want to talk to Ed @ FICM Repair because I think they charge more if you have attempted to resolder the FICM prior to sending it in.

 

Good point. Call Ed and do an exchange to lessen downtime

Josh

 

IIRC I remember reading that Ed was out of exchange units so don't count on that without a phone call.

 

I contacted him 2 weeks ago about the exchange program availability and it wasn't an issue.

And then my buddy goes and purchases a Rock Auto reman unit... d'oh!

Josh