MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - fuel starvation

I have a 1958 mga 1500. She starts fine, idles and I can drive her about 5 minutes and then she won't hold an idle and then dies. I've put in a new gas tank, fuel pump and my lines are clean. Now my gas gauge is not working. I can wait a while and she will start again run fine and then die, any suggestions?
m mckeon

Make sure that the gas tank filler cap is not sealing so tight that it is causing a vacuum in the tank. If you open the gas cap and hear as swooch of air this is the problem.
Gordon Harrison

Your filter may be plugged so it is hard to get the necessary pressure to feed the carbs. I'd look there if Glenn's suggestion is not the culprit
David Holmes

You also lost your ground or earth connection to the fuel tank causing your gauge problem. Your sending unit and/or tank are no longer grounded.
Mark Carr

IF your problem is the fuel cap not venting, I "think" that you should hear the fuel pump clicking away very fast as it tries to build pressure but can't. A cloged fuel filter, before the pump would act the same but you wouldn't get the whoosh at the as cap. A clogged filter after the pump, would cause the pump to stop as it thinks the fuel is pressurized all the way to the carbs.

If no luck on the above two items, I subscribe to the "90% of all carb (fuel) problems are ignition related". How long after it dies, do you have to wait before it will restart? If it is 5-10 minutes, your problem could be a heat sensitive ignition coil.

Chuck
Chuck Schaefer

Could also be running too lean (weak mixture), causing a vapour lock when the carbs get hot. Also, have you checked whether the float needles are sticking, or that the float levels are correct?
Peter.
P. Tilbury

After it dies take the covers off the float bowls and check if there is any fuel in the bowls. If not, then yes it is a fuel supply problem somewhere.
John DeWolf

It really sounds as if your fuel tank vent is plugged. The vent is in the cap. When it dies, immediately remove the float bowl covers. If they're dry, remove the fuel tank cap. Turn on the ignition and if the float bowls fill up, your cap vent is the problem.
Mike Parker

If the tank vent is clogged, the pump will not run very fast, it will stall and not run at all, just the same as if there is a clog on the outlet side of the pump (the only time the pump will run very fast is when there is a large air leak on the inlet side of the pump or if there is no fuel in the tank - the ultimate air leak). It is very important to check the tank vent first, by removing the filler cap. If you have a clogged vent that is causing the problem, it is stalling the pump in a current on condition, which will damage the pump if power is left on when this condition exists. For further Troubleshooting tips, see the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

Sounds to me like it could be a faulty coil, failing once it warms up.

Oh, I just saw that Chuck said that already, I'll go back in my box!
Neil McGurk

I find that there is no need to remove the float cover, an empty bowl will give a tinny rattle when tapped with a finger, a full one will give almost no sound.
I am more inclined to think this is an electrical issue but check the bowls first.
Either the coil or an earthing problem somewhere. Check that the fuel pump is working as a bad earth on that will stop it working (it is mounted on an insulated plate). Just bridge an earth wire onto a clean bit of the pump body if that is the suspect.

Neil
Neil Purves

A number of years ago the coil bracket on my 1958 MGA wore thru the coil and the oil leaked out. The car would run fine for 5 minutes or so and then quit. After 5-10 minutes the coil would cool off and it would start and run fine. I figured it was fuel and looked there first. Oil on top of the generator was the first clue that it was not fuel.
Bill Haglan

It is VERY unusual for the vent in a standard MGA fuel filer cap to be clogged. They more often have a habit of slopping fuel on the paint work. Even if you soldered a plate over the vent hole the cork gasket would likely not seal well enough to draw a vacuum in the tank. Also generally impossible to use enough fuel to draw a tank vacuum in five minutes. Clogged fuel filter prevents fast flow and/or fast running, but will seldom keep it from running at idle speed, especially if it was running fine for the first five minutes. Vapor lock is very unlikely after only five minutes of running, as it requires very hot engine compartment.

Sounds like a lot of money spent on guessing. Always do the diagnostic work first to determine the problem before spending time and money on parts. When engine dies after five minutes of normal running it is either faulty spark (none) or incorrect fuel mixture (to much or too little fuel). This is simple stuff, and you don't have to guess, just take the diagnostics one step at a time, and start with the quickest and simplest test.

First step is to determine if you have lack of fuel or lack of spark. Next time it dies, pull a spark plug wire, stick a screwdriver (with insulated handle) in the connector, hold it close to a head stud, switch on, crank engine, and see if it has spark. If no spark you may assume the entire fuel system is fine (until proven otherwise), and you just avoided a lot of messing around.

If good spark (1/4-inch blue spark in open air), then check for fuel. Disconnect feed hose at rear carb, switch on, observe flow, should be a gusher, at least one pint per minute. If no flow or very slow flow, the problem is before the hose. If good flow at the hose, the problem is with ONE of the carbs.

If you get that far and still haven't figured it out, come back with the results of diagnostics up to that point, and then on to the next step (direction depending on results of first tests).
Barney Gaylord

Barney - "...but will seldom keep it from running at idle speed, especially if it was running fine for the first five minutes."

I agree that this is an unusual failure mode, but it will happen if the filler cap vent is clogged and the tank has been recently filled. It was that very situation that led me to discover that the filler cap vent on our MGB. On a long road trip, we started having an intermittent starvation problem, that happened so seldom that I had no way to troubleshoot it (it would clear as soon as I got to the shoulder of the road and might not reappear for the rest of the day). My first indication that it might be a venting problem was right after filling the tank and the problem hit several times in quick succession within the first five minutes of getting back on the road - the penny finally dropped and I removed the filler cap and the problem went away. I always raise the possibility of this problem occurring for the very reason that it is an unlikely situation and not something that a person is apt to think about. It is also a very easy possibility to eliminate very quickly and easily by just removing the filler cap - if the problem doesn't, go away after doing this, one possibility has been eliminated quickly and one can go on to other troubleshooting (basically I am lazy in troubleshooting - eliminate the easy stuff first). Cheers - Dave
David DuBois

Maybe I should extend the comment slightly (with more emphasis). When I say "very unusual", what I mean is virtually impossible with the standard MGA filler cap, unless someone has tampered with it. See here: http://mgaguru.com/mgtech/fuel/fs102.htm

MGB certainly has a different style twist on fuel cap with a decent gasket and a small vent hole (more easily clogged). Later model MGB even have intentionally sealed fuel cap used in conjunction with the vapor recovery system. If you have the late model fuel cap on the early model MGB it draws a vacuum. If you have a kink in the late model MGB vent hose or pipe it draws a vacuum.

MGA has none of this. The only way to have a clogged filler cap on the MGA is to install a non-standard filler cap (like MGB twist-on type for instance), or maybe to intentionally solder up the splash guard plate in the original MGA fuel cap (and also replace the cork gasket with rubber). The MGA fuel cap will vent and leak like a sieve (bless it's soul), but it won't get plugged up.

Yes, you can leave the MGA fuel cap open for a while to see if it makes any difference (but I would bet the farm that this is not the expedient route to solving the current problem).
Barney Gaylord

Dave, of course you are right. What the heck was I thinking?

I believe that the non-working fuel gauge is a red herring and not related to the engine problem. On my car, I've run a dedicated ground wire from one of the sender unit's screws to chassis ground.

Based on my personal roadside experiences, I would start at the ignition side. Maybe a heat sensitive coil or perhaps the infamous disty rotor. I've had both.

The coil began to fail at highway speed with a stumble. Slow down a bit and it was fine. Speed up and it stumbled again. Slowed down and it was fine. It seemed like a fuel delivery problem at first. Then the rain came and I didn't have any problems with it. The next day, I checked out the ignition and everything seemed just fine. Of course it was cool. About a week or so later, on a nice hot summer day, it finally failed totally. I poured water over the coil to cool it off but it was too late. It was a gonner.

The bad rotor failed more like: Stumble....stumble... stumble... DIE. Never to start again. That one took me about an hour to diagnose after swapping out plugs and a coil. I usally tested the ignition by removing a plug and placing it on some metal looking for a spark at the gap. No spark. So I swapped out the coil. NADA. Then the plugs. Then I tested it using the center HT lead directly from the coil. Couldn't rationalize why it wouldn't start. It finally dawned on me about the rotor.

Maybe some of these symptoms are familiar?
Chuck Schaefer

One way to find out if it is a "overheated" coil is to throw a wet rag over the coil ater the car has stopped. If it starts once the rag is on it, then obviously it is a faulty coil.
My original coil lasted 48 years. Then had two modern replacements in 18 months!
Peter.
P. Tilbury

This thread was discussed between 03/09/2009 and 04/09/2009

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.