engine and drivetrain Fuel vapor-lock problem-need help.

[Napes]

This one has me, and several other knowledgable ' 02 people, stymied.

Every time we turn the car off for 10-15 min. (trip into a store, etc.) after it has run for 5-6 miles, or more, it gets a vapor lock.

Car details: Stock ' 76 engine with 118K miles, only mods are removal of all smog garbage, a Weber 32/36, and a tii exhaust manifold.

Never had this problem in the 11 yrs. we've had the car, but 1 month ago, in Phoenix with the official temp @ 114º, and the car parked in hot black asphalt parking lots, it started doing it. At that time we were able to start the car by pouring water over the original fuel pump to cool it - then the car would start. Car water temp was only about 1/8" higher than normal running temps.

Decided it was time to replace the original fuel pump with an OEM unit (from 2002 Haus), along with the push rod, insulation block and gaskets, and the car ran about 30% better than it even had since we owned it. BUT, now when we shut the car off, the fuel in the fuel filter (I tried two different, new ones) completely boils out of the filter in about 15 min. Then, as soon as the car uses up the fuel in the carb float bowl, the car stops. We have been able to re-start it by pouring considerable water over the fuel lines and fuel pump or by pouring small amounts of fuel into the carb to start the car and keep it running until the pump can refill the float bowl and filter. The fuel filter and fuel lines are elevated enough that they do not rest on the hot intake manifold or touch the head. Thus no direct heat transfer. When the car has been allowed to sit for about 1½ hrs. the fuel filter again fills up (to level of the inlet and outlet pipes) with fuel.

As stated above, we've never had a problem with this before now. My ' 75 has no problem either, running in the same atmospheric conditions. Any thoughts will be greatly appreciated. The filter, by the way, is located about 3" before the fuel pump.

Bob Napier

[pkbinplano]

I think my car has started doing the same thing. At first I thought it was my coil so I replaced it. It's better but still not fixed. I also have a new fuel pump to put on it. Will do that asap. My next step is to check all my fuel lines for deteoriation. It's possible that on the suction side of the pump back to the tank it's sucking air. You think the fuel in the filter is boiling out or just flowing back to the tank ?

[jgerock]

I would do a fuel flow test to see how much gas the pump is (trying to) deliver.

You might have a cracked line after the tank, sucking air instead of fuel.

[Swiftus]

I think that the problem lies in your choice to keep a mechanical pump. You are right that vapor lock has to do with fuel changing from a liquid to a gas, which is evident in your observation of the fuel in the filter boiling away.

The mechanical pump on the engine has to pull the fuel forward and up from the gas tank in order for it to reach the carburetor. The problem of the vapor lock comes from the preheating of the fuel BEFORE it reaches the pump. If you have a pump designed to pull a liquid (which is far less expansive than a gas) suddenly being asked to pull a gas, it simple will not do it.

The easiest and simplest solution would be to install an electric pump next to the fuel tank, where the gasoline has not had a chance to heat up because it is 10 feet from the engine bay, and have that pump PUSH the fuel forward. This 'pusher' solution solves vapor lock problems 9 out of every 10 times.

Another reason you may be experiencing vapor lock is because you removed the smog emission stuff from the car. This system was put in place to absorb and re-condense the expanded fuel gasses that were coming from the tank.

My suggestion to you would be to install and electric pump which should solve your problems.

(A simple demonstration of the electric pump can be achieved by first causing a vapor lock like you normally would, then filling a bottle with gas, disconnect the mechanical pump and instead connect the gravity-fed bottle of gas to the carb. . . The car should run like normal until there is either no gas left in the bottle, there is insufficient pressure, or your arm gets tired and causes one of the previous statements.)

[Mike87]

It could also be that you do not have a spacer between the intake manifold and the carb causing excessive heat to be transmitted to the carb. I had that same setup and ran a spacer without any fuel/vapor lock problems.

[Napes]

J Swift; The things you say make sense, except for the fact that all the smog stuff has been off of my car for 28 yrs. with nary a vapor lock problem. My current mechanical fuel pump has 180K miles on it. The smog stuff has been off of my wife's ' 76 for the past 11 yrs., again with no vapor lock problem until the past 4 weeks. Her car runs fantastically, except for this recent problem. I'm trying to figure out why it never happened before. I talked to a mechanic in Tucson, where it's over a hundred all summer long, who has worked on 2002s for over 30 yrs. and he said he's never seen a vapor lock problem with ' 02s.

Bob Napier

Mike#87; Yes, both of our cars have the ¼" thick spacer between the carb and the intake manifold.

[im3crazy]

i,ve had similar problem erratically but def based on outside temps. The above really nail the basic possibilities. however they don't ask the temperature of the gas in the tank. recently i noticed on longer drives my gas temp was really high , over 130 degrees. this is due in large part to the absence of a heat shield between tank and muffler. u may be experiencing a similar problem with gas tank absorbing high ambient and maybe reflected asphalt ground temps. u might measure temp at filter and at pump as well as gas tank. im installing a shield this week. good luck.

[Mike87]

I am wondering if there has been a change in the fuel composition that is causing it to be more easily changed into vapor? Just a thought if this problem is that recent. It has got to be something simple.

[TobyB]

Try this next time it does it:

Floor it as if to clear a flooding problem.

If that works, change the float valve in your carb...

t

[MMII73]

This is just a guess:

Could it be a clogged vapor line/charcoal canister?

As you draw fuel from the tank you create a vacuum, as the fuel heats up and gets agitated from driving it expands, when you park it cools and condenses creating more vacuum, after it sits for 1 1/2 hours the pressure equalizes.

Next time it happens open the gas cap and listen for that sucking sound.

Like I said, this is just a guess, I have no first hand experience with this problem.

[jimk]

You didn't say that the fuel filter is after the fuel pump. If it isn't, it can make the problem worse. Many want to put it between the pump and tank. Whatever particles pass thru the screen in the tank will pass thru the pump with no harm but need to be filtered better before the carb.

[BarryA]

with an old, high mileage pump several years ago (replacing the pump eliminated the problem) - best that we could figure, the old pump had a porous diaphram that wouldn't create enough suction to pull fuel through the pump after the car had "heat-soaked" for 10-15 minutes.

Couple of suggestions beyond those previously offfered - try running a length of NEW fuel hose from the main fuel line at the firewall to the pump without a filter in it (install the filter between the pump and carb) to eliminate any potential vacuum leaks at the filter. If you have a known good fuel pump on hand, try installing it and see if the problem persists (it's not impossible that the new replacement pump has a defect). Make sure that your fuel tank venting system is operating properly (restrictions in the venting system could cause a vacuum in the tank that the pump can't overcome.....)

[TobyB]

Many want to put it between the pump and tank. Whatever particles pass thru the screen in the tank will pass thru the pump with no harm but need to be filtered better before the carb.

Jim, I've had exactly the opposite experience- junk in the trunk

(tank, really)

rendered the valves in the pump ineffective and led to 'fuel starvation' problems.

Really.

Suggestion #2- put a temporary fuel pressure gauge on your car.

A bunch of fuel line, a tee, and some zip ties and you can have it zip-

tied to the hood air inlet bars.

I like the electric pump in the trunk

and a regulator solution,

but that's just my control- freakiness...

t

[Swiftus]

If you get a Carter Low-Pressure Pump (P/N P60504) it will only make ~3psi, which is exactly what a Weber carb likes. This means that you won't need a regulator! It is super simple to install and it can make a very large number of headaches disappear.

[Napes]

Problem appears to be solved. I greatly appreciate all who offered their thoughts and suggestions. As with new problems ask yourself what was the last thing you did. I half did this - I installed a new fuel pump, which was working great. I didn't pay enough attention to the other thing I did.

I though I'd install a new filter as long as I was going to replace the pump. Went to PepBoys, WalMart, AutoZone, and, finally, Checker looking for the small fuel filter I've always used (the one that's about 1¼" in dia. and is used on air-cooled VW Bugs). I was unable to locate one so I went with the smallest I could find which looks to have about ½ cup volume.

I decided to try Barry Allen's suggestion of running a new fuel hose from the firewall to the pump. Went to my friend of 25 yrs. at CarQuest (don't know why I forgot to check there for a filter) for hose and while we were comparing the 1/4" and 5/16" i.d. hose to the stock 8mm he brought out a filter to check to see which was going to work best. I was looking at the hoses when my wife, who was standing next to me, said, "Look, isn't that the small filter you've been looking for?" Yep, it sure was.

I again checked with Rob Torres @ 2002 Haus and he still recommended placing the filter before the pump. The OEM Pierburg also puts out 3 psi as per J Swift's suggestion, and this proved to be insufficient to deal with larger volume filter.

So far the new small filter seems to have solved the vapor lock problem.

I hope my experience will help others in the future.

Bob Napier