11 April 2017

How to make your classic car’s fuel delivery system dependable

A few weeks ago, I introduced the idea that, when a vintage car dies while being driven, most of the time the cause isn’t some random lightning bolt from the blue, but is instead one of The Big Six (ignition, fuel delivery, cooling, charging, belts, ball joints). This week we’ll drill down into the fuel delivery system.

On a vintage carbureted car, the fuel delivery system is simple, consisting of just a fuel tank, rubber and metal fuel send lines, a low-pressure fuel pump, a fuel filter, and one or more carburetors. Mechanically fuel-injected cars from the ‘50s, ‘60s, and ‘70s add an injection pump or a fuel distributor, injectors, a high-pressure fuel pump, a pressure regulator, and a fuel return line. Electronically fuel-injected cars kick the level of complexity up significantly, incorporating an electronic control unit (ECU) and a variety of sensors.

But no matter which configuration you have, it all starts with clean gas being pumped at the right pressure through leak-free lines.

Check for Leaks!

You can have a little coolant or oil dripping, but not fuel. Because gas is so flammable, there needs to be a zero-tolerance policy. If the rubber fuel lines and clamps in your vintage car are original or haven’t been changed in, well, you don’t know how long, they should probably be replaced. In addition to the rubber lines themselves ballooning or cracking, the bite of the rubber against whatever metal tube it’s attached to, and the bite of the hose clamp into the rubber, weaken with age, allowing leaks to form.

Further, on a fuel-injected car, the fuel pump pressure is high enough that it won’t just leak a little—it’ll spray fuel. Conversely, on carbureted cars, old braided cloth fuel lines at the gas tank can sometimes be porous enough that, during a springtime start when the float bowls are dry, the low-pressure mechanical fuel pump will try to pull gas out of the tank and instead will suck air through the lines, preventing the float bowls from filling up. So, replace those old fuel lines!

On fuel-injected cars, there are also rubber seals to check. I don’t mean the rubber o-rings at the injectors; these typically don’t cause fuel to leak out. On mechanically-injected cars such as my 1972 BMW 2002tii, old rubber seals at the injection pump can be a major source of fuel leaks, spraying fuel everywhere when they deteriorate. Changing these when you change the rubber fuel lines is good insurance.

leaking 2002tii injection pump seals
Leaking o-rings in the injection pump of a BMW 2002tii

Clean Gas: Performing a Full Back-To-Front Sort-Out

If a car has been sitting for years, the fuel system will almost always require attention. A primary reason is that gasoline itself is problematic. Gas that sits can do one of two things. It can slowly evaporate, leaving a gummy varnish. Or, if it’s oxygenated fuel with ethanol in it, it can absorb water. Gas tanks in vintage cars are usually steel, so water will cause the tank to rust. If a car is run with a rusty tank, the fuel pump will send the rust toward the engine. At a minimum, it can clog the fuel filter and any small mesh screens. If rust gets past these, it can clog up the jets and passageways in a carburetor, or the fuel injectors in an injected car.

rusty injector
Rust-contaminated injector in a BMW 2002tii

A back-to-front fuel system sort-out is flat-out necessary in a long-dormant car, but is also great prophylactic maintenance in a driver before a long trip. First, open up the gas tank, and smell, then look. If it smells like varnish, you need to drain the tank and clean the varnish out with solvent. Be sure to check the pick-up tube that sends the gas to the engine, as this may also be clogged with varnish.

If, on the other hand, the gas smells like, well, gas, look through it with a flashlight for rust and sediment in the tank. If fuel with ethanol in it has absorbed water, though, you can’t really see that. For this reason, you should drain whatever old gas is in the tank of a car that’s been sitting, even if you don’t see or smell anything amiss. And you’ll often be surprised at the amount of rust and sediment that comes out.

Next, remove every rubber fuel line, then use a compressor and an air nozzle to blow through the metal line that runs to the engine. Wrap a clean rag around the end of the line so you can see what’s coming out. If it’s rusty, continue to blow until it’s not. Replace with new rubber fuel lines.

Remove the fuel filter, tap the inlet onto a paper towel to look for rust contamination, and replace it with a new filter. If the car has any fuel screens, be certain to check and clean them.

If the fuel pump is old, or if there’s any evidence of rust in the fuel tank or filter, just replace it. I’ve worked on cars where the tank was cleaned but the fuel pump wasn’t replaced, and the pump was full of rust and continued to spit it forward.

fuel pump rust mound #2
Rust in a BMW 2002 electric fuel pump.

If the car is carbureted and you found rust in the gas tank, pull the top off the carb and check for rust in the float bowl.

Lastly, connect a pressure gauge with a tee to the fuel line where it enters the engine, start the car, check for leaks, and verify the correct fuel pressure for your model.

Sudden Death

If your car is driving down the road one moment and dead in the breakdown lane the next, and it has spark, make no mistake about it, the prime suspect is the fuel pump. Mechanical fuel pumps in carbureted cars use a pushrod, usually run off a lobe from the camshaft, to push a lever that moves a diaphragm. The diaphragm can tear or lose its elasticity, or the little lever can wear down. In an electric fuel pump, the fuel itself actually cools the windings of the electric motor. This makes electric fuel pumps susceptible to contamination in the fuel tank. If an electric fuel pump dies, sometimes it’s bound up with rust or sediment, and rapping it with a ratchet wrench handle (or, if it’s an in-tank fuel pump, smacking the bottom of the fuel tank) will dislodge the rust and get it going again for a while. Replace it as soon as you can.

An electric fuel pump is usually controlled by a relay, and relays do sometimes die. Look up where your relay is, and make a little jumper wire so that, if the fuel pump dies, you can pull out the relay, jumper pin 30 (power) to 87 (fuel pump) to bypass the relay, and see if that gets you going.

Slow Death

There’s an old saying: If a car feels like it is running out of gas, it probably is. If you’re certain it has gas in the tank and an even spark, the problem could be that the fuel filter or fuel screens are clogged. A textbook symptom of this is when a car sputters and dies, then starts and runs five minutes later and repeats the process. The fuel pump is probably pushing rust up against the filters and screens, and when shut off, some amount of it is falling off. At a minimum, change the filters, clean the screens, and, as soon as possible, check for contamination in the tank.

Clean gas and screens. New lines and filters. New fuel pump. Get on down the road!

(Next week: The cooling system.)

Rob Siegel has been writing the column The Hack Mechanic™ for BMW CCA Roundel Magazine for 30 years. He is the author of Memoirs of a Hack Mechanic and The Hack MechanicGuide to European Automotive Electrical Systems. Both are available from Bentley Publishers and Amazon. Or you can order personally inscribed copies through Rob’s website: www.robsiegel.com.

10 Reader Comments

  • 1
    Jeff Gillespie Hollywood, Fl April 12, 2017 at 16:09
    Hi everybody, my name is Jeff and I work in the diesel fuel injection business, which uses the same design fuel injection pumps as the old gas injection used, such as the Bosch system. I can tell you from expereince, use rubber fuel lines that are rated at twice the pressure you intend to use. If it is a car more than 10 years old, replace those lines with new ones. The bad thing about gas fuel injection is that ANY leak, no matter how small can cause a fire and destroy your vintage investment. Also, some of the Bosch inline fuel injection pumps used on Porsche and Mercedes were not lubricated by engine oil. This was done to prevent gasoline leakage from getting into the engine oil and diluting the oil, therefore the injection pumps had their own lube oil supply which must be checked, changed and inspected on a regular basis. Failure to do this will ultimately end in pump failure, and there is a very limited supply of USED parts available now. For gas lines, filters, supply pumps, if in doubt.......replace it. A clean fuel system from tank to injector is a must for any fuel injection system.
  • 2
    Bill McKivor Seattle April 12, 2017 at 16:10
    Rob has covered most of what might happen---here are a couple more- The fuel tank many have been coated with a sealer many years ago, and the protective sealer has reacted to the new fuels, causing it to peel off. Driving down the road, it winds up plugging the fuel line in the tank, and the car quits. Shutting the car down, and sitting for a while, it starts back up---but the problem is still there. Another rather weird possiblilty---it happened to me. Bought a 53 Willys car some years back, engine had all been rebuilt. I could drive it around 2 miles, and it acted like it was running out of gas---if I let it sit for a while, it would start right back up and run for another 2 miles. Obviously it was a fuel problem, also seemed to have something to do with warming the car up---and it proved to be a faulty gasket between the intake manifold and the body of the block. When it warmed up the gasket allowed too much air into the carb, so it actually was running out of gas, in it's terms. A new gasket fixed it right up. So, if the usual suspects do not find the problem, look for the unusual. Bill.
  • 3
    Jim Traverse City, Mich April 12, 2017 at 20:33
    Last year, driving down a country road in my '64 Chevelle SS convertible, enjoying every minute until the gas peddle whiffed. I pulled over, feathered, pumped, throttled and sputtered home, barely. A few days later started the car, very short rides, haven't had a problem since. I suspect "something" clogged the gas flow. I think I'll change the fuel filter tomorrow before I head down that country rode again. Thanks for your Article. Jim
  • 4
    jon crane rochester mi April 12, 2017 at 21:20
    My gas tank had a couple of inches of fine white sand in the bottom that clogged everything. Where did that come from?
  • 5
    J. K. Salser Garland, TX April 12, 2017 at 21:26
    With the advent of ethanol, maintenance of fuel systems have become even more high maintenance. Even with a fresh fuel system in place, constant monitoring is essential. I recommend regular maintenance at more frequent intervals. I have touched what appeared to be a sound fuel line and had it become wet and begin dripping gasoline. Ethanol causes deterioration from the inside-out. jk
  • 6
    john lyons brooksville,fl April 12, 2017 at 21:49
    i have a 1988 ford ranger/2.9-v6- auto. trans/ just over 100000. orig.mi.- replaced in tank fuel pump,fuel reservor-between hi &lo press.pumps, above 190,degrees, not hot-but will vaporlock.?????- cool down runs excell. has 160 deg.thermostat, has never been run hot,two temp gauges,elec & mech. what could be prob,clean radi,circulates good,trans coolers run seperate from rad. new plugs,wires, no fault codes showing up on test,run straight antifreeze, not diluted. only happens in traffic, with ac on.not on open road, i am bewildered with prob. thk u ..john
  • 7
    Mike McCarthy Huber Heights OH April 12, 2017 at 23:41
    Great insights, photos just like my 72 2002tii, have enjoyed Rob's Roundel column for years.
  • 8
    HUGH B. WEST Akron, Ohio April 13, 2017 at 14:26
    Has anyone got suggestions for a 1927 Chevrolet that spends most of the time in storage & only out for a couple of local car shows. It was last run using the choke in & out & only getting up to min. speeds without cutting out & sometimes stalling engine.
  • 9
    richard petrocik ishpeming,mi April 13, 2017 at 10:13
    i have a 1970 dodge dart swinger 340 4 speed. when the car is parked for even a short period of time the fuel is gone in my clear glass fuel filter. put on a new carb and fuel pump still having same problem . no leaks found. any ideas on what is causing this ?
  • 10
    Warren Hendricks West Jordan, UT April 13, 2017 at 12:28
    I used to have a 1969 GTO that would suddenly stop running. It would start again after 15 min or so, run for a day or two, and then stop again. The problem was found to be a screen on the fuel line inside the gas tank that was partially clogged. Some of the crud would fall off the screen after a few minutes but then quickly accumulate again. The problem and its cause now seem obvious but at the time even mechanics at the dealership were not aware of the existence of a fuel screen inside the fuel tank.

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