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Walbro FRC-10 - Low Fuel pressure

BigBlueChevy

Compression Ignition Addict
Messages
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Location
Pennsylvania
Well, the good news is that my air conditioning finally works again as of today. Blows an ice cold 50*F out through the vents. The bad news is while under the hood checking everything I noticed on the gauge that my fuel pump outlet pressure was dangerously low. Normally it will float around 13-15psi. Today after I got home it was doing 0-3psi. Possibly even going into a vacuum since the gauge has a stop at 0.

I know I got a real NASTY batch of fuel 2 weeks ago that was pissing off the optic sensor enough that it would set a code, and I'm going to stop by Empire CAT tomorrow to pick up a new Secondary Filter just incase the filter is plugged. I'm hoping this is just a crappy fuel / plugged filter related problem and not a failing FRC-10 problem. Anybody else having an issue like this (or similar) with there Walbro pumps? I made a video to give a better demo:

http://www.youtube.com/watch?v=4HcSuKTKROE&feature=youtu.be
 
Only person who has killed one was Warwagon as far as i know. He had to run it hard to do that too. Hope its just a filter, kinked line, or faulty gauge (well the gauge might cost more than the pump lol)
 
I have seen this before. The prefilter is plugged. (prefilter means any pre lift pump filter or screen.) The pump goes for the intake stroke and the IP suction pulls a vacuum on the guage. The pump then pumps fuel causing a pressure spike. Do you have the screen still in the Walbro? This can plug as well.

My gauge would show a vacuum and you are likely puling one to hammer the needle that hard.

Possible bad tank cap pulling a severe tank vacuum.

Where did you get the bad fuel, in AZ?
 
It does sound like pre pump restriction. Try blowing the line from pump back to tank sock. If this works it might only be a temp cure as the sock will crud up again. As WW said check the screen in the bowl of the LP to.
 
Something interesting I noticed this morning. After sitting all night I fired it up this morning and popped the hood. Fuel pressure was hoping around at 6-9psig. Drove to class as normal (2.5 miles) with roughly 10 minutes of idle time and popped the hood again. Sure enough, fuel pressure was doing the same as the video shows again. I will need to get a vacuum gauge hooked up between the tank and the primary filter.

Is there a way to test the tank cap? I would imagine it has some kind of relief function at a certain vacuum or pressure? I'm going to run outside and see if taking the tank cap off raises the supply pressure. Sure would be nice if all it was was a bad cap!
 
Something interesting I noticed this morning. After sitting all night I fired it up this morning and popped the hood. Fuel pressure was hoping around at 6-9psig. Drove to class as normal (2.5 miles) with roughly 10 minutes of idle time and popped the hood again. Sure enough, fuel pressure was doing the same as the video shows again. I will need to get a vacuum gauge hooked up between the tank and the primary filter.

Is there a way to test the tank cap? I would imagine it has some kind of relief function at a certain vacuum or pressure? I'm going to run outside and see if taking the tank cap off raises the supply pressure. Sure would be nice if all it was was a bad cap!

You've already answered your question about the problem. I would be willing to bet you have debris in the tank or screen in teh pump that settles out over night, but once you drive it covers the filter over again. this is a very common issue with fuel tanks that have debris in them. All is well once it settles out, but after a 10 or 15 minutes of driving and running the debris gets clogged up on teh pick-up screen and chokes the pump off.
 
WarWagon. I got the fuel from the Chevron station at Rancho Santa Fe blvd and Dysart Road.

Pulling the cap off with the engine running doesn't make things any better or worse, and if you mash the pedal from idle the gauge drops down to 0psi and holds (so essentially a vacuum).

FERM. I was pretty much figuring that the tank sock was clogged. I suppose its just one of those things that you hope won't happen. I did notice that the bottom of my fuel / water separator bowl has alot of crap in it. It actually looks almost like sand. Alright well I'll plan to drop the tank at the next school open shop. There is no sense (or room) for me to do it at the apartment complex really. I don't suppose there is a sockless tank draw straw kit anybody sells for our trucks is there? Also, has anybody tried using the Metrum fuel sending unit that Leroy sells? MY fuel level gauge has been on the fritz anyway.
 
I don't suppose there is a sockless tank draw straw kit anybody sells for our trucks is there? Also, has anybody tried using the Metrum fuel sending unit that Leroy sells? MY fuel level gauge has been on the fritz anyway.
Just remove the sock, the inlet will still be about as far down as it will go.
I've used the MRFSU they are Awesome!:hihi: I won't be able to send one til Oct 1 though. Take a measurment of the depth you need while doing the fuel sock then I can make the MRFSU custom for your tank as they all seem to be slightly different.
 
No worries, I saw on your website that everything will be down for all of September. I hope all is well. Actually if anything that will prevent me from buying the METRUM unit now and save some coin till I get back to the east coast. I figure I can drop the tank in about 2 weeks from this Saturday and just clean things up / remove the sock. I can replace the old rubber lines that are up there as well come to think of it. Both the supply and return are 3/8" yes?

As always thanks for the help Gents.
 
If you can make it to Fountain Hills me and another fellow are experts at dropping the Fing tanks. I think we got 10+ times on my rigs alone.

Does the fuel have any unusual odor?

The warm up may be a kinked hose. Check the FFM to chassis line in back. Sand in the bowl means the lift pump screen will be plugged. You may have to pull the pump apart and clean it out as well.

A cat filter head and filter/water separator bolted to the floor to get it high enough is a great pre-filter. Loose the tank sock. Replacements do not have the by-pass valve unless by the dealer. The by-pass valve will starve you for fuel.

I have the MRFSU in my 1993 and 1995 and they work even in corrosive slime bug filled fuel. Same stuff that eats factory sensors for breakfast. Burning oil needs a friend to ship stuff for 30 days...

If you have the pump number call the AZ weights and measures and report the station now! If they find something your labor etc is covered.
 
If you can make it to Fountain Hills me and another fellow are experts at dropping the Fing tanks. I think we got 10+ times on my rigs alone.

Does the fuel have any unusual odor?

The warm up may be a kinked hose. Check the FFM to chassis line in back. Sand in the bowl means the lift pump screen will be plugged. You may have to pull the pump apart and clean it out as well.

A cat filter head and filter/water separator bolted to the floor to get it high enough is a great pre-filter. Loose the tank sock. Replacements do not have the by-pass valve unless by the dealer. The by-pass valve will starve you for fuel.

I have the MRFSU in my 1993 and 1995 and they work even in corrosive slime bug filled fuel. Same stuff that eats factory sensors for breakfast. Burning oil needs a friend to ship stuff for 30 days...

If you have the pump number call the AZ weights and measures and report the station now! If they find something your labor etc is covered.

War Wagon,
The weird part is. I'm not having any drivabillity issues. The truck runs down the road with almost no trouble at all, even in the higher RPMS and still pulls "hard" on the highway. So getting to you would probably be almost no trouble at all. I'm going to do some diagnostics on it this weekend and I'll report back with what I find before condemning anything just yet. I will however be pulling the sock off before I head back East for sure.

The fuel didn't "seem" to have anything wrong with it, and the water separator has not a drop of water in it, just those fine particles of... "grit" building up on the bottom. I may consider investing in some comp-u-chek fittings from Cummins and T-ing them into the inlet / outlet of the fuel / Water Seperator so at later times I can read the pressure drop across the filter rather than just blindly saying "yeah that looks bad". No kinked hoses, and other than #7 leaking at the body(another issue I need to fix), no leaks either.

Next time I pass by that station I'll pull the pump number and call them up. I had no idea one could just call them up to report a possibly problematic fuel station. Wish I had known that a few years ago. I really appreciate all the info, like I said I'll report back once I have some more hard evidence as to whats going on here.
 
Like a few of the guys said, it's the tank sock. Your truck is doing exactly what mine did. If I went on a 30 mile work trip, it would stall within 300 yards of the same spot it stalled in the day before. It was that consistent. Blow backwards through the fuel line (after removing the cap and making sure the tank isn't full), I promise your problem will go away for a litlle while.
 
Problem isn't the tank sock. I did some diagnostics on the system this morning and found that the pump is the issue.

The problem got worse yesterday afternoon. Drove to a friends house and when I got there popped the hood to find my fuel pressure was 0psig. The needle wasn't moving at all. Rode with a friend and picked up my air compressor / hose from my apartment and worked on things this morning. Blowing back on the lines doesn't change a thing. No air leaks in the fuel lines. And if you jump the lift pump with the engine off, the needle just barely lifts off the resting pin. Made about 1 psi intermittently. Fire up the truck and it makes about 2 psi intermittently. I would say 75% of the time the needle was just laying on the resting pin indicating a vacuum. The truck runs and drives just the same. Doesn't stumble, doesn't buck or misfire, and has no issues in the higher RPM's.

The only other possibility could be that the gauge has gone bad and I'm flipping over nothing. I'm going to try plumbing another mechanical gauge I have into the system just to double check my readings.
 
Well I feel stupid. Here I was ready to blame the pump. Thankfully, its not the pump, rather its the gauge. I picked up an adapter to thread in place of the current mechanical gauge and it was pretty obvious as I was loosening up the gauge that was the issue. Its a glycerin filled gauge and the little air bubble that's supposed to be at the top was non existent, but instead had diesel fuel mixed in it. Now, I'm no EARL gauge engineer, but I'd say the fuel is not supposed to be floating around inside the gauge... Anyway, hooked up a diag. gauge of mine and low and behold it builds 14 psig of fuel pressure with no issue at all. Oh well, Guess I'm going to the hydraulic shop tomorrow to get the gauge warrantied.

Thanks for all the suggestions folks! I will however be going to open shop in 2 weekends and dropping the tank to get the sock off before I head back east. Its alot easier to change a spin on filter on the side of the road than drop the tank :eek:
 
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