|
 |
Fuel Delivery Troubleshooting Guide
By Dave DuBois
(Note: This guide was
written to MGs either older T series or the newer MGAs and MGBs. The
basic information applies equally to all marques using the SU electric
fuel pumps, with only the locations of components being unique to the
vehicle)
All of a sudden, as you are driving along without a care in the world,
the engine starts to stumble and finally quits altogether. You turn the
key off and on several times but the engine refuses to start. Absent
also is the reassuring "tick, tick, tick" of the fuel pump - damn! The
first response is to reach under the bonnet (in the case of the T series
cars) or under the car by the right rear tire on late TFs, MGAs or MGBs
and give the pump a few healthy whacks with whatever tool is handy
(please do the whacking gently with something like a screwdriver handle,
the idea is to get the pump to restart, not to beat it into a bloody
pulp). If the familiar ticking returns to the pump, you can continue on
your trip, knowing that you are going to have to do something about the
pump when you get home (and maybe have to whack it a few more times on
the way).
What happens if, after being whacked a few times, the pump doesn't
respond? First, while you are on the side of the road, remove the gas
cap. If you hear a whoosh of air entering the tank, you have probably
solved the problem. Just leave the cap off until you can get to an auto
parts store and get a new vented cap in the case of the early MGBs (if
the car is a T series, you will have to leave the cap open until getting
to your destination and then find a way to clear the vent in the cap).
If the car is a late MGB that is vented through the charcoal filter, you
will have to trace the vent line and find where it is clogged. If, after
removing the gas cap, you are still not getting fuel, remove the gas
line from the rear carburetor and with it positioned such that the gas
will go on the ground (I know, environmental concerns! But we are
desperate here, O.K.?), turn the key on. If you get fuel flow now, then
the trouble is in the carbs (stuck float, etc.). Still no fuel flow? Now
you will have to call AAA, a friend with a tow dolly or push the darn
thing home.
Next day, how to proceed? Buy a new pump (one of those square, run all
the time, make a lot of noise, Facet pumps), a new SU pump (maybe one of
those new, all electronic ones), get the old one fixed, or...? First,
let's make sure that the pump is at fault. Take a meter or test light
and with the key on, check for 12V between the terminal on the cap of
the pump and ground. If you don't have 12V here, find out where you are
losing it - you will have to go to your shop manual, look up the
schematic and follow the line back from the pump to the source of 12V.
If you have the 12V at the pump terminal, check that the ground is good,
either with an ohmmeter or by jumping a known good ground to the pump
with a piece of wire. If the ground is bad, again, trace the wire from
the pump to the ground point and repair the discontinuity (if you are
working on an MGB, the ground point is under one of the license mounting
bolts in the trunk). See my companion article on Ground Point
preparation at:
http://homepages.donobi.net/sufuelpumps/Other_Subjects/Electrical/General/Ground_Point_Preparation.pdf
If you are getting voltage to the pump and have a good ground, you need
a new pump, right? Not yet! There are a couple more checks to make
before condemning the pump, particularly if you noticed that the pump
was getting hot when you left the key on for an extended period of time.
Remove both fuel lines from the pump and turn the key on. If the pump
doesn’t run with both fuel lines disconnected, skip the rest of this
article and go down to the list of business or individuals who repair or
restore the pumps. If the pump runs ok with the fuel lines off, one of
them is probably clogged. Reinstall the fuel line from the fuel tank and
try again. If the pump runs and sends fuel out of the outlet fitting,
then you have a clog in the line to the carburetors. If the pump doesn't
run, or if it just clicks a couple of times and then stops and was hot
as stated above, you have a clog in the line from the tank to the pump
or internally in the tank (if you have a late TF, MGA or MGB, this would
have been indicated by the lack of gas running off your elbow while you
were disconnecting the line from the tank to the pump). If you have a
MGA or MGB, disconnect the fuel line from the fitting on the tank and
again turn on the key. If the fuel pump runs now, then the clog is in
the line inside the tank. If this was the problem, it is time to think
about getting the gas tank cleaned out or you will be facing the same
problem later on. Check whichever line has a suspect clog for kinks,
smashed line, etc. Try blowing it out with compressed air to insure any
clog is removed. If there is a filter in line, replace it with a new
one. Still not getting fuel? Now it is time to contact one of the people
listed below to take advantage of their SU fuel pump services.
There is one more situation that will cause fuel starvation that hasn’t
been addressed above. If your pump is running continuously, but no fuel
is being pumped in to the float chambers (and your pump is a SU pump
rather than an aftermarket pump like the Facet pumps that normally run
continuously), then you have an air leak on the inlet side of the pump,
or you are out of fuel. Check the fuel level in the tank, then check the
line from the fuel tank to the pump for any loose connections or holes
in the line. Be particularly suspicious of any flexible lines used to
transition the metal lines to the pump. If no leaks in the lines can be
found in the lines, try running a line from the inlet side of the pump
to a container of fuel. If the pump starts pulling fuel from the
container and stops pumping after the float bowls are full, then you
quite possibly have a hole in the pickup tube in the tank above the
level of the fuel. If instead, the pump still runs continuously and
doesn’t pull fuel from the container, the pump itself has a leak on the
inlet side and will need to be repaired. Again, contact one of the
people below for assistance.
Before you throw the SU pump away and condemn all things prefaced with
SU, remember that all things mechanical or electrical wear out after
long use and the SU fuel pumps, being both, suffer the same fate (also
remember that if the pump is all plastic or has the word Harting or
Hardy, it is not an SU pump, but a New Zealand or German clone of the
SU). The Mazda truck we used to have came with one of the square Facet,
run all the time, make a lot of noise pumps on it and after several
years it too, died. An earlier Courier pickup had a Japanese SU clone,
which also died. All of these pumps died somewhere around 75,000 to
100,000 miles, at about the same mileage that a new SU fuel pump will
fail. My point is that the SU fuel pump will last about as long as any
other electric pump that is on the market for use on the MGs, possibly
longer if it is an all electronic pump or one converted to solid state.
For SU fuel pump service in the US, contact one of the following people:
Tom Ball 330-666-2642 or 330-867-9800
Dave DuBois -
mailto:ddubois@sinclair.net or 360-479-0462 (after 9:00 a.m.
Pacific time please)
Jerry Felper -
mailto:felperg@earthlink.net or 714-630-1074
Greg Van Hook -
http://www.vanhookvintage.com or 215-262-8547
Lew Palmer -
mailto:lpalmer@roundaboutmanor.com
For SU fuel pump services in the UK and Europe, contact:
Burlen Fuel System (rebuild service for all SU fuel pumps) -
http://www.burlen.co.uk
For SU fuel pump service in Australia, contact:
SU Midel Pty Ltd. (rebuild services for double ended pumps and LCS
pumps) - http://www.sumidel.com
Note: If you also repair SU fuel pumps or know of somebody not listed
above who does, please send me an
e-mail with contact information for the person so I can add them to the
list of people to contact for fuel pump repair.
Updated 4/4/08 |
|
