Replace FFM

[aschooley]

I bought a 84 basket case a few months ago. I was hoping all it has wrong was a dead lift pump and some other maintenance issues, like bad batteries and fluids/filters. I replaced the lift pump with another mechanical one and replaced the filter. It took a lot of cranking and wd-40 but I got it started. Now that I proved it would run I started putting some money in to get it road worthy.

I have replaced all of the fuel line from the lift pump to injection pump with clear hose and I am getting flow back from the fuel filter back to the tank, the hose to the injection pump stays solid with no air. I have pressurized the system from the return line and can't find any obvious leaks, the thing is so dirty and full of every fluid everywhere, unless it was a gushing leak I don't know that I could find it either. It drains back really quick though. Within 5 minutes the hose from the lift pump to the filter is completely empty (I bypassed the hardline)

I read somewhere that newer lift pumps have a check valve, I replaced mine with whatever carquest had in their system, most likely without one. I have read that the Stanadyne housings can crack enough to let air in but no fuel out, especially around some of the sensor housings in the back.

Rather than messing with it any more, (I already spend $50 on two new plastic air bleed screws), should I just rip the whole thing out and put in a Racor 10micron filter/water separator? If i do should I put it between the two pumps like the factory unit or should I put it before the lift pump? What flow rate should I look for?

Thanks in advance.

 

[iamdave0887]

Start with the restriction switch in the filter housing. Mine leaked and let air in to the system. The restriction switch is roughly a quarter in size and seals with an o-ring. The original o-rings were not rated for ULSD, as it didn't exist at that time. Once the ULSD hits it, the o-ring starts to deteriorate until you get a leak.

Mine never leaked while running. Once the engine was shut off i'd start to see a little bit of fuel on the ground right under the engine. I went nuts trying to figure out what the problem was. It would start really hard after sitting for ~8 or so hours. It's start right up, then stall and i'd have to crank the life out of the starter to get the engine to fire again. Once running, it was fine until i shut it off again and let it sit. That's the main symptom of air in the fuel system. All this time i had an electric lift pump, so it wasn't nearly as much of a pain as it was with a mechanical lift pump, but it was still a pain.

Turns out GM knew what a basket case that restriction switch was, as they deleted it in the later model fuel filter housings.

No sense in replacing the filter housing when a 25 cent o-ring is all you'll need if it is the restriction switch that's leaking. You can't buy that filter housing form the dealer anymore.. It and all the parts to it, have been discontinued by GM.

Never seen one of the housings crack, but i suppose it's possible.

 

[Acesneights1]

Bad shaft seals on teh IP will cause drainback as well. My CUCV is a MF to start if I let it sit for a few days. I may put an inline check valve in it. Dave, does my CUCV have the FFM with the thing you were talking about ? It's an 86.

 

[iamdave0887]

Does your FFM have 3 plugs or 2 from the wiring harness.

If you have the restriction switch you'll have a 3 wire connector and 2 2 wire connectors. The 3 wire is the WIF. The 2 wire connector(black-ish looking non-weather pack connector)going to the top is the fuel heater. The 2 wire going "into" the right side behind the filter and in front of the filter manager itself is the restriction switch.

If you have just a single 3 wire and a single 2 wire(square black looking non-weather pack connector) then no you don't have it. Mine no longer has it. I installed a filter housing that i purchased from Bk95td that came factory without the restriction switch.

Not sure which year GM dropped it. Only way you can tell is to look. I can tell you your 90 burb most likely doesn't have it. If anything swap the 2 housing over and see if your starting problem is gone.