FFM fuel heater

[dbrannon79]

Hey fellas. Today I started going through the original FFM in an attempt to install it back on the 93 truck. Cleaned it up nicely but now I’m trying to make sure the fuel heater is good. I ohmed it out and get no reading on my meter. I have 4 other fuel heaters to play with so I tested each one only to find non of them show a reading on my meter.


took one apart and found a broken wire inside. Ohmed out direct at the element and I get readings but there is what looks like a temp limit pot switch that has no contentunitey. How do these heaters work, what controls them to regulate temperature in the winter?

 

[dbrannon79]

Well wouldn’t ya know it. While I was waiting for someone to chime in here. I decided to stick two of the fuel heaters in the freezer just on a hunch that the light pot temp switch was the actual control for the heater. Just took them out of the freezer and ohm tested them. Both are working!! Yay. Now time to wire it all up and test for leaks.

 

[dbrannon79]

So far no leaks.

 

[Will L.]

I know there is a fuel heater in there. I don’t think I ever had to test one, let alone replace one. Something about the coldest of winter day in the high 20’s making news for a week and old guys saying “I remember the day of the great freeze where we hit an incredible 27°…”

You get extra credit point for the filter location. Is your primer switch on the rear bracket mount or in the cab (not so subtle hint). Looks like enough room to put his friend “mr oil” next to him. Yes, I a jealous and missing fenders for mounting things.

 

[dbrannon79]

That little black square piece with the red dimple button and red wires is the primer switch. the PO had made those brackets for the FFM and wired in that switch. also not sure if he made the harness extension or bought it from somewhere that connects to the factory connectors for the FFM and runs them over to where the FFM is. the drain for the FFM is that large fitting thing under the master cylinder.

I had removed it all after one day of it all working fine, then the FFM started gushing fuel out. it was leaking so bad that I thought the housing had cracked. now that the winter season is getting near, I wanted to put it all back making sure it all worked including the heater in case we get another cold snap like we did when Texas hit 16 degrees! Plus I had replaced the FFM with a clear plastic inline gas filter!! needed to get that out of there before it clogged up on me LOL

 

[dbrannon79]

Well guys. I figured out why this FFM was leaking. Today I found it seeping fuel from the seal under the filter cap. Pulled the filter and since I don’t have and extra seal I decided to make one from some o-ring cord I have. I used one of the other FFM housings to size for the seal then went to install on the one I just put in the truck.

Low n behold it’s too big!! I’m going WTF!! Put it on the other housing and it fits nicely. Wore this is a trip!

I have three FFM’s here and two seem to have a smaller diameter than one. This is odd, this would explain why it will seal and then suddenly leak. The o-ring that goes inside the cap slips off the edge of the housing lip and them pukes diesel.

What do y’all make of this?

 

[dbrannon79]

I’m currently cleaning out the corrosion and grime from this other housing so I can swap them out on the truck. I’ve not seen this before

 

[dbrannon79]

Got it installed but I still had to crank on the cap with my filter wrench to get it to seal up. I don’t think I’ll keep it on here for long. Might end up going with the same filter setup I have on 95 truck

 

[MrMarty51]

Working on the back of the engine items.
The FTB FFM went back in.
Have a FP sending unit at the IP and another back at the AD lift pump and have a switch wired in to flip it from pre or post FFM.