FICM Cooling and Minimum Fuel Flow Needed

[Modified]

I was talking to a Diesel Mechanic I just learned of, about installing a lift pump with a secondary filter, to reduce gas buildup with the Duramax. This Mechanic wasn't familiar with this setup, or the Duramax, but bought up a good question.
He talked about these new fuel systems, and how they flow a ton more fuel than is needed for the engine for combustion, and thought this may be needed to adequately cool the Fuel Injection Control Module. He also cautioned if a Lift Pump with inadequate flow was used, the truck may run great, but inadequate FICM cooling may result, and we may not be aware of this, and FICM overheating may result, and cause electrical failures.

1). Is this logical?
2). What is the GM Minimum Fuel Flow Recommendation?
3). Should this be considered when choosing a lift pump?

[jbplock]

Modified,

You bring up some good points. The fuel DOES cool the FICM. I'm not certain but I seem to remember reading somewhere that a code would be set if the FICM got too hot (can anyone confirm this?). Also, all (Chris, JK, Tommy, others) who have installed a clear hose before and after the FICM have seen (air) bubbles in the fuel coming out of the FICM – caused by heating of the fuel (?) Outgassing (?). On my setup with an AC Delco lift pump, I have no air in my post-oem Mega. (Without the lift pump I did have air in the filter). I also think your mechanic friend is correct that about not adding too much restriction to the fuel flow. The AC Delco pump’s design allows a flow of fuel when it’s not running. We have checked this by pulling the fuse and measuring a normal (with LP) vacuum at the Schrader valve. When the pump is running I believe it is adding to the flow and not restricting. smile.gif

[DmaxMaverick]

Excellent observation.

There would be NO issue of insufficent volume for the FICM. I would be more concerned with changing from suction to pressure. Leaks may result, leading to a fuel soaked FICM.

The original system is suction supplied by the fuel pump. This pump is still in OEM operation, unless it is replaced by an aftermarket unit, or fails. Adding a lift pump will ADD to the available volume. The pressure has to overcome the vacuum. If you install a lift pump that decreases the volume, then you are also increasing the vacuum. As long as the system stays pressurized, there will be no fuel volume issue.

[jbplock]

Originally posted by DmaxMaverick:
... I would be more concerned with changing from suction to pressure. Leaks may result ...

... Adding a lift pump will ADD to the available volume. The pressure has to overcome the vacuum ... Exactly!
If adding the lift pump shows a leak, that's a good thing since it was most likely leaking undetected under a vacuum. Pressurizing the system can also enhance the seal of OE QD (quick disconnect) fittings in our system. These are the same type of fittings found in pressurized gasoline systems. QD’s have been known to leak in a vacuum system and these types of leaks are not easy to find. For example (IIRC), a-bear found a leak at the QD tank connection which he fixed by replacing the OE line with a length of 7/16 id gates hose and clamps. Also, the pressure regulated lift pump (http://community.webshots.com/album/77018086bLHHHC) configuration some of us are using allows the pressure to be adjusted to near zero psi at the input to the OE pump (mine is set for 0.4 psi at the schrader valve). This is just enough pressure to overcome the vacuum restriction of the filters and prevent/reduce heat/vacuum induced gas formation.
smile.gif