engine and drivetrain Help With Hesitation/fuel Starvation

[Zorac]

im in vancouver (just drove from calgary) and now i'm stuck, car wont make it back home!

 

thouigh the trip it started hesitation (due to leaning out) and it got progressively worse through the trip.  replaced the fuel filter and fuel pump.  checked all my jets for a plug, nothing.  did the valves just before i left home (engine is a fresh rebuild with about 2500km on it before i left, 3500km now.)  it got so bad it stalled out on the highway on me.  waiting and then starting out again seem to improved the sitation.  highways speeds were almost impossible as it got alot worse when i went fast by the end of the trip (almost stalled out going up onto the fraiser bridge!).  the load at highway speed makes the hesitations come out for sure. 

 

would apprecaite if anyone has ideas (i do have limited tools with me), or knows a good shop for these cars in richmond area.

 

thanks.

[bmwfan]

There is a filter screen on the pick up tube in the gas tank, could be an issue. And depending on what carbs you have, may have in carb filters where fuel line/lines enter the carbs. Would also check the dist. Cap, rotor, trimming if possible. And check vac hoses and connections.

[Zorac]

If it was ignition wouldnt the a/f gauge read rich instead of lean like it is?  I'm running a Webber 38/38 and the car has been de-smoged, so no vaccume lines left.  I'll check the plugs again thouhg.  I did check the screen in the tank at the beginning of the summer and it was clean, I can check again though.  Not sure if the Webber has a screen, but I'll look for one.

[Simeon]

Fuel starvation is my guess too. Check pick up screen and any other screens and filters. Not sure if carb or injection but look for screens at the pumps (electrical, kfish or mechanical pump) 32/36's have a screen at the fuel inlet.

[Guest_anonymous]

3000ft elevation drop. You need to think about rejetting

[Zorac]

It did it regardless of different elevations, anywhere from sea level to the top of the coquahla, so I'm pretty sure its not a jetting issue.  When its not hesitating a/f is in the right range, but then the a/f will start spiking up and the car hesitates.  A small  wiggle of the gas pedal some time fixes it, but presumably the accel pump is just squirting a little fuel in to fix my lean condition when I do that.

 

I'll pull the inlet off the carb in the morning and check for a screen.

 

Any chance this would be a valve issue from them seating and going out of adjustment?

[eurotrash]

Its the tank screen / tired fuel pump syndrome.  Screen fills with silt, as you drive on extended trips.  Pump, even if new, can't pull enough gas and your bowl doesn't fill under high demand.  If  you have an older pump, it happens sooner.

 

Once it sits for a bit, or you stop for gas, the sediment falls away.  As you run the tank down,the sediment again becomes concentrated and the screen fills.

[Zorac]

Its the tank screen / tired fuel pump syndrome.  Screen fills with silt, as you drive on extended trips.  Pump, even if new, can't pull enough gas and your bowl doesn't fill under high demand.  If  you have an older pump, it happens sooner.

 

Once it sits for a bit, or you stop for gas, the sediment falls away.  As you run the tank down,the sediment again becomes concentrated and the screen fills.

With the sender in the tube above the screen, shouldn't see a drop in the tank level when it starts to starve then?  My fuel gauge has been stable, no fluctuations.  If there are fines in the tank, are they easily visible?

[Zorac]

On the same though, can I just pull the screen (in the tank off)?  That way it would get caught/trapped in the filter instead of settling back to the bottom of the tank?

[JerryC]

Sounds like fuel starvation to me too. However, do check your intake manifold and carb mounting hardware. Loosening in that area can happen and will cause a vacuum leak.

I think taking the screen off the fuel tank inlet is not a good idea. Good way to screw up the whole sensor assembly.

[darrinos]

I am having a bit of the same issue and have posted in the forum under "Not Getting Fuel". I removed my pickup tube from the fuel tank and there was no screen filter at all, only a small hole at the bottom. My car runs great for any amount of time, and then out of no where, runs out of gas. I have noticed air in the fuel line at times and have been trying to run down the source. Today it died from fuel starvation on a very steep hill at about 4000rpm. I'm stumped, but still suspect it's the pick up tube as I've not found any cracked fuel lines any where. Suggestions? I have a new fuel pump and a new filter, with new fuel line. I pulled the tube out of the tank and found a couple pieces of debris and removed them. The same issue remains.

[OriginalOwner]

 here's my story on topic.  My 1948 Chevy truck had this exact problem.  I discovered that the pickup tube inside the gas tank had 6 tons of crap wedged into it.  Overnight, sufficient amounts of gasoline would percolate through the crap, up to the gas level in the tank.  Upon starting, the engine ran fine.  But quickly enough the pump couldn't pull gasoline through the crap:  fuel starvation.

     I discovered the problem by forcing compressed air into the fuel line, in the direction of the gas tank.  Very little air actually went through the line, ergo, massive blockage in the fuel tank pickup tube.

     My soluion:  I punched a hole in the side of the gas tank and installed a fuel pickup tube of my own design and manufacture, with a screen on it.  Problem solved.

 

Another fuel starvation problem with the same truck:  a pinhole leak in the rubber diaphragm of the mechanical fuel pump.  Fortunately I could buy a rebuild kit for those old pumps.

 

Cheers,

 

Carl

Edited August 17, 2013 by OriginalOwner

[Zorac]

Thanks for ideas, keep them coming!

 

I cleaned a fair amount of crud out of the screen in the carb, removed the screen in the tank (and replaced with a large see though filter right where the fuel line comes out of the tank).  I have a second filter by the carb.  Both filter are clean and have fuel (both are roughly half full when the engine is running).  Fuel pressure is now 4psis at idle with the electric fuel pump, and was previously 2.5psi with the mechanical pump.  Car is now very rich, I had to put the idle screws a quarter turn in, and I wish i had smaller main jets with me (it running a a/f of about 10 when i stomp on it and stays there until I let up on the gas). No problems with hesitation yet (besides a small hesitation which appears to be from being to right when accelerating) while booting around the city yesterday.  Havent had it up to high pway speed for a sustained period yet to test though.  The combination of high rpm and a slight load for a period of time is what triggered it before.

[DUDONLY]

If you are running pertronix check the magnet under the distributor cap to make sure it hasn't slipped down the shaft.

hth