Vaporlock-starving for fuel-THE FIX

[winime]

After many hours of sweat, aggravation, and frustrating  road trips, I finally fixed my, “VAPOR LOCKING, STARVING FOR GAS, CRAPPING OUT GOING UPHILL, PUT-PUTTING ALONG ON THE SHOULDER OF ROAD” Syndrome.
I began by:
Changing inline fuel filters (no help) paper cartridge filter in carb (no help) engine fuel pump (no help) drop and clean both fuel tanks, repair split hose on elec. fuel pump pickup line (no help) blow out all fuel lines with air hose (no help) rebuild carburetor (no help) another paper cartridge filter in carb (no help)  new distributor, plugs and wires (no help) aluminum foil and clothes pins on gas line (no help) fuel dryer treatment in tanks (no help) electric fuel pump relay (no help) another mechanical fuel pump (no help) replace steel line from pump to carb with rubber fuel line,  check paper cartridge filter in carb (no help)  fuel pressure regulator (no help) capped the E.G.R. valve (no help) freed up the sticking E.F.E. valve (no help) install cold air intake (no help)
The Fix:
I rigged up a fuel pressure gage from a T at the carb and mounted it on steering column, and set the regulator to 5 psi, and took her for a spin.
As usual she ran great for a while, and started the old crap again, this time I know that everything is good all the way to carb, because fuel psi is right on 5 lbs. Well I limped back home, and told the wife I needed $387.59 for a new Quadra Jet carburetor, (she gave me this really weird look) I said well, maybe I’ll try one more thing.
The next day I pulled the lid off the old dog house, and sat there, scratching my head, I took the little paper filter out, and tried to blow true it, couldn’t do it, so I left it out and put the fuel line back on, and took her for another spin, I was a little aggravated any way so put the pedal to metal, ran full out up hill, she never missed a lick.
So what’s Going On? I just checked that filter two weeks earlier and it was fine. I picked up the filter again and blew thru it, this time I could blow right thru, it occurred to me that earlier the filter was wet with gas, and now it was dry.
The only explanation I can come up with is that the gas and heat had swelled the paper, and choked the supply of fuel.
Thinking back, the time before I had checked it just before reinstalling (dry).
Well, anyway I went to AutoZone, and found this nifty little glass inline fuel filter, and installed it right at the carburetor. END OF PROBLEM (I hope)
Later, Ron
Ps. Told my wife I fixed the RV and saved the $ 387.59 (She’s happy again)

[DonD]

In my experience, that paper filter will swell when water gets in there, not allowing gas to pass  N:( ran into this issue while cruising the old AlCan Hwy in 1959. The old bronze filter won't pass water either but for a different reason. Hope your fix works!!

[Rickf1985]

A lot of people will eliminate that filter altogether. With two or even three filters in line before that one it is hardly needed. And that fitting on the carburetor can be troublesome after it is removed a couple times. Be careful of those glass filters, I had one that the media inside melted from the alcohol in the gas and it plugged up but looked fine. If you think about it you get roughly 7-8 MPG avg.. That is an average between deceleration where you are using no gas and wide open throttle where you are getting roughly 1/2 MPG. At wide open throttle you are using about 2 gallons per minute of gas! If you were to set up a small pump and hose so that you could see what that is you would be surprised at the amount of gas that has to go through those filters. They need to have very little restriction and a filter that small is a problem.

[GONMAD]

Hello All,   Be very careful with that glass filter! They are delicate & are prone to FAILURE! I have seen one burst apart under pressure & cause immeasurable damage to a classic car. Also I had one allow some kind of gooey crap onto one side of my Edelbrock 650 & I had to perform a Complete overhaul at a rest area. In short Don't keep in your system except for diagnostic purposes. Try using a metal inline filter BEFORE the fuel pump (possibly two if you're not sure of it). This will help the pumps last longer also. I hope you are planning to remove the pressure gauge now that you found the problem as in the event the gauge or line to it fails you will have a LOT of gas in your face before you can shut it down. We use a system that isolates the fuel from the part that goes into the passenger compartment with a diaphragm. Far safer than gas inside! Remember your after volume & not pressure. I'm glad you found your problem & shared it with us.     GONMAD

[legomybago]

i removed that filter too, but it still vapor locked. It's caused by the gas we use these days...(my opinion). The only way we were able to cure vapor lock on our 86' P30, was to install an electric pump.

[GONMAD]

I'm sorry, I was under the impression you had already installed an elec pump. Most pumps are gravity fed so be sure it's back by the tank as low as possible. I have supplied pictures in my photo section if you care to look. I used a Holley hi pressure unit & a regulator as a booster to the mechanical pump. Summit sells a unit that puts out 7 lbs & does not need a regulator as well. I had similar maladies & found out ALL my fuel lines were porous (even the generator lines) & had to be replaced including the bypass lines as my RV came from the upper mid west & had been in the flood of the 90's. Many days of consternation went into the ultimate fix.   Good to know these things beforehand when diagnosing these problems. I had absolutely NO knowledge of motor homes until I bought this rig in 2005. Had to tough it out over time. I had no idea this website existed then, It would have helped greatly.   GONMAD

[Old Toolmaker]

Congratulations on your success.  I too have been chasing that dog and my next step is checking the fuel pressure when the engine is hot and pulling just as you did.  I have *read* that the paper filter in the carb is also a check valve to keep the bowl from draining.  The rubber check valve portion can be removed -- so when I install the fuel pressure gauge I think I'll make sure that I've pulled the check valve off the filter. 

I have installed a Wix brand in-line fuel filter and water separator, a big unit intended for a diesel truck on the thought that I was experiencing phase separation of the water/alcohol and fuel.

I sit here slapping my forehead and saying D'oh! After all I've done is it really as as simple as removing the carburetor fuel filter?   

[ClydesdaleKevin]

I did all of that and more, and finally figured out it was the fuel pump relay, an unobtainable obsolete part.  I ended up rewiring the whole darn thing through a standard relay, and I'm right as rain now, with many miles and lots of hills (and weight) behind us.  The full writeup is somewhere on here...lol!

Kev

[winime]

Thanks for the heads up on that glass filter. I’ll definitely be pulling that off, (maybe I can use it on my lawn mower). As for the fuel pressure gage, I realy don’t  want to give that up, as it turns out it has been the best diagnostic tool “EVER” for fuel related problems, How ever I would like to go with a safer option, could you give a little more info on where to get that diaphram type gage?
Another concern I have is my fuel regulator, it’s an adjustable 0 â€" 5.5 lbs. round chrome plated about 2.5” dia. With a Knob on top, I got it at Auto Zone, Does any one know if these things are safe to run under the hood in high temps?
Thanks for the feed back, Ron 

[GONMAD]

I don't blame you for not wanting to give up the gauge. I get the autometer fuel pressure isolator kit from Summitracing. The kit #ATM 3313, ATM 3413, ATM 5813. Depending on the style you want. The regulator you have (Dial-a just) isn't  sufficient for a big block. If I'm correct it has 1/8" NPT fittings. Your fuel line size is 3/8". While it seems to be OK it does not flow the VOLUME needed. Use the Holley type adjustable regulator Same as the one used by the factory for the batchfire fuel injection unit. It has 3/8" NPT fittings & is adjustable from 0 to 15 lbs. DO NOT exceed 7 lbs. as the brass floats WILL collapse if any higher pressure is used. I use the dial type reg for the booster pump on my generator & it's set at 1.5 lbs. This assures fuel supply to the generator . Having built fuel systems for large displacement engines equipped with four stage Nitrous (450 to 600 additional HP) the demands are such that any starvation is catastrophic! Always have volume over pressure & you'll have no more problems. It really helps to get good relays to run everything on & use a keyed ACC tap on the fuse panel to activate everything. Happy RVing ALL   GONMAD

[Old Toolmaker]

Well, my electric pump fills the carb just fine -- but I do need to confirm that the mechanical pump is doing its job.  But pulling out the carb fuel filter and going for a test drive is more fun.

Regarding relays, I have good luck re-using automotive relays from more modern vehicles i.e when I scrapped my minivan I pulled all of the relays and put them in a box.  If you want generic new relays Automation Direct has always been my go to source.


<http://www.automationdirect.com/adc/Shopping/Catalog/Relays_-z-_Timers/Electro-Mechanical_Relays/Square_-z-_Cube_Relays,_Plug-In,_3A_-_15A_%2878x-z-_Qxx-z-H78x_Series%29/General_Purpose,_15A_%28781_-z-_782_-z-_783_-z-_784_Series%29/781-1C-12D>

[pvoth1111]

You replaced the one that's at/in the carb right....I wouldn't run it too long without that. my opinion..

[Old Toolmaker]

Holley has an electric fuel pressure gauge with a sending unit for less than $90 FWIW.

Regarding the carb fuel filter, GM relys on the sck in the tank and the carb filter.  I don't have a problem with my Wix filter replacing the functionality of the carb filter.  But then again I also carry a spare top gasket for the Quadrajet.   

[Lefty]

This may be a dumb question... but could you have possibly installed the filter at the carb backwards by accident? That would block the fuel flow 100%.


Multiple filtration:
In my opinion, the ideal setup would be a screen or sock located at the point of pickup inside the tank to catch any large debris... such as rust particles or dirt. This is critical if you have an intank electric pump... not using a sock will cause the intank pump to fail prematurely due to the added wear caused by the particles passing thru the impeller. It is not however as critical if you have no intank pump.
If not using a sock, due to not having an intank pump, and just having the pickup tube extending into the fuel, it is important to install an inline filter in the line PRIOR to the mechanical pump on the engine. This will prevent any trash or rust from entering the pump, causing it to fail or even clog. The inline types with hose nipples are fine, the better types are those that screw on like oil filters. Ideally, you can install a fuel filter and a water separator filter combo to ensure clean fuel free of water.

After that, there is no need for further filtration farther down the line to the carb. The fuel leaving the filter won't get any cleaner passing thru more filters.. but the resistance will increase. Case in point: Modern cars with fuel injections (which use much smaller orifices than those in a carb.) typically come equipped with only a sock at the intank pump, and a single inline fuel filter located on the frame rail or under the hood.... and last thousands of miles. They do not use any more filtration than that.

[ClydesdaleKevin]

P30s use a weird relay, now defunct, that has a safety feature built in.  One lead goes to a secondary oil pressure switch on the block.  Without oil pressure, it shuts off the electric fuel pump in case you crash.  But there is also some sort of little computer chip in there with a timer that allows the pump to come on with no oil pressure for a short time to allow you to start the engine easier, since the fuel tank is so far away.  Mine started to go bad intermittently, and it was driving me crazy!  EVERY other base was covered, and there shouldn't have been any vapor lock...but every once in a while the electric fuel pump would shut off for no reason, and I'd get vapor lock.  And it progressively got worse...and then died altogether.  3 fuel pumps later I finally figured out it was the relay.  And then also found out you can't get the part anymore.  So I ran new 10 gauge wires right to the fuel pump, and then used a universal relay and wired it in (with an inline fuse of course), bypassing the oil pressure switch altogether.  NO problems AT ALL since.  The bright side is that I now have 2 spare electric fuel pumps that are fairly new and still work fine...lol!

Kev

[winime]

Thanks again for all the good info.
Well, It looks like I’ll be trashing my brand new fuel pressure regulator, along with my brand new little glass fuel filter, Oh Well, live and learn (thanks to this awesome web site).
I like what Lefty had to say about  the number of filters in the line, my Winnie has an elec. Pump with a sock in the tank, I think I’ll put just one filter in front of the mechanical pump, and call it good, ( I'm leaving the filter out of the carburator ) I like the one the “Old Toolmaker” has with the water trap.
Like “Kev” I also had intermittent problems with the elec. Fuel pump relay, if I hadn’t installed a fuel pressure gage at the carburetor, I never would have figured it out.
I found wire diag. to hookup a head light relay and push button over ride switch, (lookup “where’s the fuel pump relay P-30”) Now all I have to do is turn on the key, push the little button, and watch the pressure come up on the gage, when she gets to 5 or 6 psi hit the starter, Verrrrrummmm.
I am definitely keeping my fuel pressure gage, right up there with other gages on my dash board, but I’ll be installing a little safer unit.
That all for now, a big “O” thanks to everyone.
Ron

[MotorPro]

If you have the regulater with the 1/4" fittings and it is up front near the carb it will feed plenty of fuel for a stock 454. While not as big or as reliable as the holley regs they work pretty well.

[DaveVA78Chieftain]

Reading through this I am not sure if you have replaced the stock fuel filter mounted halfway between the front and rear wheels.  Have you?  Also, are you aware the 85 1/2 to 89 P30 chassis has a fuel regulator for the in tank electric pump mounted on the frame aft of the rear wheels.  There a threads on here about that and how to repair it.

Dave

[Old Toolmaker]

That's where i put this one because I *thought* I was chasing water in my fuel.

http://www.wixfilters.com/Lookup/PartDetails.aspx?Part=33123

http://www.wixfilters.com/Lookup/PartDetails.aspx?Part=24309

I bought one spare filter.  I should be set for the rest of my life.

[Rickf1985]

I went to check mine there and all I found was a very short section of rubber line. Guess someone else found it first.

[Old Toolmaker]

Well, that being the case either buy a high quality inline filter or do the reading on phase separation in alcohol-gasoline blends and install a water separator filter where the OEM was.

[winime]

Thank's 'ToolMaker, that looks like a good setup, I suppose I can find that at AutoZone?

[Old Toolmaker]

They can order it but you'll find a better price on-line.

[winime]

Ok, Thank's a million

[Turbodime]

Ok, I've been having this same issue.  When I purchased the rig, the tank needed cleaning as it had sat for 7yrs and here in AZ 7yrs is not good for gas in a tank;)  Lots of sludge and a little rust.  I cleaned the tank, ran all new rubber gas lines. new mech. pump, new in tank pump with sock filter, new inline filter, and carb filter.  Plus I rebuilt the Holley PRV.
I get around 80 miles before it starts to act like I was getting vapor lock. What I came up with is the carb filter was plugged and I could barely blow thru it and it was swollen and hard to remove. I've done this four times.
The tank is spotless and the rubber lines are new. What I'm thinking is happening, is the hard lines have  dried up old gas residual and its breaking loose and plugging up the filter.  Just got back from a trip on Sat and 5miles before the house it started again.   

I don't want to replace the hard lines so I may just blow them out again, and look on the net to see what a good cleaner would be to soak them in.