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MG MGB Technical - Help! I can't get the kids to school! My fuel pump is wierd!

Gentlemen, Start My Engine!

I have a fuel starvation problem in my early '74 B-GT which struck half way to the kids' school this morning (my wife has had to change her commute in recent weeks so the usual family Jeep wagon kid-hauler is not available, temporarily).

Symptoms are as follows: Car slowed in manner obviously due to fuel starvation. I pulled over and ran the standard checks of the fuel filter/lines. Eventually I discerned that ignition systems were all go and I had little to no fuel delivery from fuel pipe under hood. While checking the flow of fuel, I noticed that every time I shut off the ignition a nice little burst of fuel came from the fuel line. If I feather the ignition between the run and accessory positions, I get flow to open air that appears just fine. If I simply leave the ignition in the run position with the fuel line open to air, there is intermittent flow but mostly no flow. I was actually able to drive home by feathering the ignition switch between the run and accessory positions! Wierd, no?
Right now, the pump clicks as normal and the car starts and runs fine with no apparent fuel delivery problems. I'd like to fix this intermittent problem before heading out on the road again. Any ideas? Is this a ground (earth) problem? Are the points the culprit? I very much appreciate your advice.
Thanks,
Dean
Dean Lake

Dean,
Your pump should be wired not wierd. ;-)
Sounds like you may have a bad contact in your switch. When in the run position its on some corrosion so you don't get full current to the pump but when you move the switch gets a better contact.
Leland Bradley

Next time this happens, undo the gas filler cap. If you hear
a "whoosh" sucking sound, there's something clogging the
gas tank breather lines or charcoal canister.

Also, if the pump is ticking, and there's no fuel or weak flow
...the fuel intake tube in the gas tank may be clogged, or
the valves in the fuel pump itself are kaput. These valves
use a paper-thin plastic reed and they often crack and split
with wear. Victoria British carries these valves and they
aren't too difficult to swap out.
Daniel Wong

Of course, there's the old, on-the-road fuel pump fix: bang the hell out of it with a screwdriver handle. This is the emergency repair for stuck fuel pump points.
Dan

Sounds like the contact in the pump is stuck closed, which is why it only pumps as the ignition is switched off. As a temporary measure give the pump a bump (but switching the ignition on and off several times may just also work for a while), in the longer term refurbish the contacts. The pump should have either a capacitor or diode that helps reduce contact arcing and hence sticking, temporarily disconnect and check you have an *increase* in arcing compared to when it is connected. If the arcing is just the same the capacitor/diode is also faulty and should be replaced.

PaulH.
Paul Hunt

Paul,
I based my comment on Dean's statement that the pump ran fine with the switch moved off of the on position but would not pump in the on position. I fully agree that the problem is normally the pump contacts.
Leland Bradley

Before I converted to a Rover V8 and added a new fuel pump I too had problems with the stock MGB pump. For the first few years I owed the car all was well, then I notice that after filling up with fuel the pump would stop pumping and I had to bang it to get it going again or just drop a line and let it pump through, like a vapor lock. After several more years of being unable to exactly pin point the problem, I found the banging wouldn't even work. The only thing I could do was to pull the wires off and on several times, I guess in hindsight I was making a better contact for the point, and then it would run again. What I eventually did was to take the pump apart and used compressed air to blow it out, put it back together and it ran fine until I replaced it because on new fuel requirements. Start with the simple stuff and go from there.

Bruce
Bruce

This thread was discussed between 02/10/2001 and 04/10/2001

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