Repeating CAPS Failures - Need Help

[chipline]

Originally Posted by barmcd

The part number is 4928511 and I bought it from Capital Volvo in Montgomery, AL 334-262-8856. I bought two and with shipping it was ~$20.

Thanks for the information. I finally got some help and tighten the 3 screws that
Hold the pump on the housing. I’m looking at installing a FASS pump and bypassing the lift pump.

[BigLar368]

Originally Posted by chipline

Thanks for the information. I finally got some help and tighten the 3 screws that
Hold the pump on the housing. I’m looking at installing a FASS pump and bypassing the lift pump.

I ordered a complete FASS unit Tuesday. My plan is to remove the tank due to a large rust spot on the bottom and refinish the outside with new paint and clean the inside. After mounting the pump I am going to run a new supply line straight from the new pump to the secondary fuel filter bypassing the primary fuel filter and OEM lift pump. All the hoses after the OEM lift pump must have been changed by the previous owner as they are newer hydraulic hoses. After some looking under the RV I have found the original hose from the tank to the OEM pump has been rubbing on the frame for quite some time and it severely worn in that spot. It would have just been a matter of time...lol.

[Saf]

I don't understand all this about the lift pump, it is only used for starting period. Unless it leaks air or stops should be the only issue. Wouldn't a liquid vacuum gauge installed before the injection pump let you know that anywhere in the fuel system feed would show up as an increase vacuum restriction.

On a 83 Foretravel I installed a gulf coast filter with a vacuum and it would show when the filter was getting dirty because of restricted flow.

[TR4]

Originally Posted by Saf

Wouldn't a liquid vacuum gauge installed before the injection pump let you know that anywhere in the fuel system feed would show up as an increase vacuum restriction.

Yes, you could also use a fuel pressure and restriction gauge before the injection pump. This would show you fuel pressure of the lift pump for the brief time that it runs, then show you fuel restriction from the tank to the injection pump. Truckers use fuel restriction gauges to monitor their fuel filters.

Fuel Pressure & Restriction Gauges for Fuel Products | Racor News

Bill

[Smitty77]

Another observation shared with me from a tech. When the Lift Pump is done with it's start up duties 'lifting of fuel' - the CAPS takes over in drawing/vacuuming/sucking the fuel from the fuel tank to feed the engine. That length of draw from the tank to the CAPS - varies greatly amounts different applications. A truck driver, has side saddle tanks, relatively close, and with downward pressure from higher volume of fuel. A DP, can be from say ~30-45' in length. The fuel tanks are usually behind the front axle, so say it's anywhere from a ~20-35' direct run to the engine. Toss in bends, weaving the fuel line from the tank, thru the fuel filters, and up thru the now idle Lift Pump to the CAPS - and this range of actual fuel travel could be ~30 to long as 50'. (Though I doubt many 45' coaches, had ISC's or ISL's with the Lift Pump and CAPS combo!).

One of the most positive rationales for my decision to bypass the Lift Pump, and go with the FASS - was to have a 'Positive Fuel Feed' to the CAPS at all times. And, to avoid the air that can get into the fuel line prior to the CAPS, if a Lift Pump is failing and or leaking - from whatever the reason is.

I know many who decided to just install a newer Lift Pump - and move on. My Lift Pump was still in operating well, but I still decided I did not want to chance the much higher expense of a CAPS replacement, then a relatively (In the scheme of these expensive toys we're talking about.) Lift Pump replacement.

Several hundred of thousands of CAPS era engines are in trucks, RV's, fire engines, etc. - and doing well. So, this weaker link of the Lift Pump design (Again, especially considering the longer draws of fuel from a Diesel Pusher.) - are still serving many very well. It was my choice to go with this conversion, and eliminate the potential of a Lift Pump failure and or leak - taking out a CAPS/Injector Pump.

And yes, what happens if the FASS fails? Good question, but testing that I was told about verbally (And admit I did not 'fact check this' - if the pump fails after the engine is running. The CAPS still draws (I do like the term 'suck's'.) the fuel from the tank. It's not until the next attempted start, where the pump does not 'pump' that you will know you have a fuel feed failure.

I like the odd's of the FASS working well. The unsubstantiated thought that Positive Fuel pressure has helped in engine performance (If so, can not see it being detectible by mere mortals. But some say the see increase performance, and who knows. In come coaches with restricted fuel feeds, the 'sucking' may have not been adequate enough to maximize the CAPS feed of fuel downline to the injectors.).

Ramblings complete for now... and for sure OK for other's to look at things differently! No question one shoe does not fit all...

Travel safe, and have fun,
Smitty

[Jeff753]

Originally Posted by 79cvx20

Mine had a check valve in the primary filternt inlet. It was stoped up with plastic from the fuel line. Whatever you decide take the inlet line loose and check it. The plastic gets hung up there.

Interesting. Can you post a picture of this check valve. I replaced my leaking lift pump 4 years ago and my caps shortly there after.

[BigLar368]

Originally Posted by Smitty77

Another observation shared with me from a tech. When the Lift Pump is done with it's start up duties 'lifting of fuel' - the CAPS takes over in drawing/vacuuming/sucking the fuel from the fuel tank to feed the engine. That length of draw from the tank to the CAPS - varies greatly amounts different applications. A truck driver, has side saddle tanks, relatively close, and with downward pressure from higher volume of fuel. A DP, can be from say ~30-45' in length. The fuel tanks are usually behind the front axle, so say it's anywhere from a ~20-35' direct run to the engine. Toss in bends, weaving the fuel line from the tank, thru the fuel filters, and up thru the now idle Lift Pump to the CAPS - and this range of actual fuel travel could be ~30 to long as 50'. (Though I doubt many 45' coaches, had ISC's or ISL's with the Lift Pump and CAPS combo!).

One of the most positive rationales for my decision to bypass the Lift Pump, and go with the FASS - was to have a 'Positive Fuel Feed' to the CAPS at all times. And, to avoid the air that can get into the fuel line prior to the CAPS, if a Lift Pump is failing and or leaking - from whatever the reason is.

I know many who decided to just install a newer Lift Pump - and move on. My Lift Pump was still in operating well, but I still decided I did not want to chance the much higher expense of a CAPS replacement, then a relatively (In the scheme of these expensive toys we're talking about.) Lift Pump replacement.

Several hundred of thousands of CAPS era engines are in trucks, RV's, fire engines, etc. - and doing well. So, this weaker link of the Lift Pump design (Again, especially considering the longer draws of fuel from a Diesel Pusher.) - are still serving many very well. It was my choice to go with this conversion, and eliminate the potential of a Lift Pump failure and or leak - taking out a CAPS/Injector Pump.

And yes, what happens if the FASS fails? Good question, but testing that I was told about verbally (And admit I did not 'fact check this' - if the pump fails after the engine is running. The CAPS still draws (I do like the term 'suck's'.) the fuel from the tank. It's not until the next attempted start, where the pump does not 'pump' that you will know you have a fuel feed failure.

I like the odd's of the FASS working well. The unsubstantiated thought that Positive Fuel pressure has helped in engine performance (If so, can not see it being detectible by mere mortals. But some say the see increase performance, and who knows. In come coaches with restricted fuel feeds, the 'sucking' may have not been adequate enough to maximize the CAPS feed of fuel downline to the injectors.).

Ramblings complete for now... and for sure OK for other's to look at things differently! No question one shoe does not fit all...

Travel safe, and have fun,
Smitty

I was in the same position as you....our pump was working ok...I guess. We found paperwork that showed the PO had a leak fixed and it showed a new pump however when I was following the fuel filter change procedures the lift pump would never pull/push fuel into the filters. I always ended up filling them up the conventional way. I decided to install the FASS with the 2 filter housings on the pump. Along with that I installed a new SS braided PTFE pressure hose all the way from the new pump to the secondary fuel filter. I then replaced the old hose from the secondary filter to the injector pump with the same type PTFE hose. almost 2K miles on a trip right now and it has worked very well. I believe it has even helped out in MPG....power....not so much.

When I finished our installation I unplugged the fuse to the FASS pump and ran the engine for 15 mins on high idle. It continued to run with no problem. I suspect you might have similar results if you pump ever quits.

[TX Trouble]

When we got our knight late last year, finally got working on it and mounted a Fass pump on top of the first filter, old lift pump still there for the ride ONLY. Too much work to remove it. Made a trip to FL, ran GREAT. Thanks for the infro.

[Raybo]

A follow up on my Fass install on 5/17. Install 95 gph with 2 filters on 40 ft Dutch star 370hp pulling Honda Accord. Installed a pressure gauge on dash. With new filters pressure at idle was 20psi went to 16 on hard pull with full 150 gal fuel. When tank went below 1/2 pressure dropped 4psi do to the height of fuel in tank an about 5 psi @ 3/8 never went lower. With 6000 miles on filters 10 micron water an 2 micron fuel going South on I65 to golf shores @ 65 mph going up hills pressure dropped to 6 psi at 75 it dropped to 0 with 1/2 tank of fuel. Changed the water first filter in line pressure went up to 16 at idle an 12 on hard pull with fuel filled. The filter had debris along the intake opening of the filter. After a few more miles I changed the fuel filter an pressure went back to 20 at idle. So with out some kind of fuel pump you can loose 4-5 psi do to the amount of fuel you have in tank. Looking back all the problems I had was when I ran my tank bellow 1/2 it cost me two tows new lift pump and new caps pump about 7000.00. A Fass install will eliminate this with pressure gauge

[Ray,IN]

Deteriorated flexible fuel lines have killed a lot of injector pumps and lift pumps. The flex lines connect the lift pump to the steel lines, both feed and return, the fuel tank. The lines appear fine from a visual standpoint, but removing and inspecting the inside of the flex line will reveal the collapsed interior lining, especially if the lift pump or injector pump is repeatedly failing.
Some lift pumps had a screen in them to catch larger contaminants before they reached the fuel filter.

[dons2346]

Raybo, where in the system is the pressure gauge installed?

[BigLar368]

Originally Posted by Ray,IN

Deteriorated flexible fuel lines have killed a lot of injector pumps and lift pumps. The flex lines connect the lift pump to the steel lines, both feed and return, the fuel tank. The lines appear fine from a visual standpoint, but removing and inspecting the inside of the flex line will reveal the collapsed interior lining, especially if the lift pump or injector pump is repeatedly failing.
Some lift pumps had a screen in them to catch larger contaminants before they reached the fuel filter.

This is why I replaced the fuel lines all the way to the injector pump.

[Raybo]

I installed it between the fass pump an the caps. Measuring the pressure to the caps pump

[Raybo]

My fuel lines are a orange solid plastic rather hard piping.