|
XK140 running problems
XK140 Running Problems
Can any of you experts offer some advice on how to cure the running problem
I have with my 1956 XK140 FHC. I have only owned the car for 1 year (It had
been standing in a garage since 1984), and have just got it through its MOT
. So I would like to take it to Donnington in June for the 50th celebration
- even if it does need lots more love and care. On the basis that she
starts and idles with no problem, I have focused on sorting the
steering/brakes etc. to get it roadworthy. The car will now start and drive
for about 10 minutes but then faulters/backfires, and appers to be running
on only 4 cylinders. If I leave it to cool - I can start all over again for
another 10 minutes or so. I've checked points/plugs etc and the fact that
it runs fine for a while suggests the problem is not ignition (doesn't
it?). Do I have a fuel overheating problem, and if so how can I find out
and cure it. Someone has suggested the Carbs should be sprayed with
cleaner, or a heat 'sink' should be attached to the fuel line under the
bonnet. The only thing I have done which may have affected under bonnet
cooling, is that I have removed and not refitted the radiator cowling.
Could this be causing the problem ? Any advice is welcomed - but keep it
simple please. - Mike Jan-Janin
Mike, Sounds like it could be vapor lock caused by the high temps. around
the fuel lines, however; I had a similar situation some time ago and it
turned out to be the ignition coil heating up and causing an ignition
problem. Good luck with your problem. - Gene Burda
Mike: I have found that the rad cowling is an internal part of the cooling
system and will cause increase in running temps if removed as the air that
should be pulled through the rad at low speeds is pulled from the sides.
The running problem sounds like fuel starvation. The tank screen in the
drain plug can become fouled and restrict fuel traveling to the carbs.
Remove the fuel line to the carbs and allow the fuel to pump into a can to
check for adequate flow. Prior threads discussed the proper fuel rate for
SU pumps. - Good luck. Bruce Baysinger
Mike, I too, would agree that it sounds like a fuel problem. One simple
check: After you shut the engine off following it's backfiring etc., when
you wait the required time and turn the key on again, does the fuel pump do
a whole lot of clicking as though it's refilling a float chamber/bowl? If
it does, that would be an indication that the fuel flow was being
interrupted or was inadequate (bad pump). If the pump only gives a couple
of clicks after the waiting period, that should be an indication that the
float chambers/bowls are nearly full and the engine was not fuel starved
when you shut it off. In the meantime, you could start planning some short
trips. :-) - Dick Cavicke
Mike, I've just returned from a 1000 mile vintage rally with my 150; there
was another 150 on the rally with the same symptoms as you're describing.
The mechanics cured the problem by replacing the coil. Don't know if it
will work in your situation, but you might want to check yours out. Good
luck - Ron, '59 150 dhc
Dear Mike, Sometimes it can be a coil or condenser that will break down
when it gets hot. I would start with the condenser it is the easiest and
cheapest to fix. - E.W. Blake
Mike, I go with a fuel problem too. I went through a similar thing with
mine. The rubber hose from the fuel inlet to the tank was deteriorating on
the inside and small pieces of rubber were blocking the fuel lines. -
Regards, Jim Voorhies
Mike, I do not claim great expertise here, but I suggest you look for an
eletrical problem - these are always most prominent when the car gets hot
and resistance increases, I believe. So check the coil and all
connections. - Regards, John Elmgreen
Update 8/22/98........
I was going to say that you could sell it to me that would cure your
problems for sure. Then I see that you are in England, so there goes that
thought. The next thought is replace the fuel pump that should cure the
problem. - Chad Bolles Jaguar Performance, Inc 306 Valcour Rd Columbia SC
29212 803 798 3044, FAX 803 798 4512
I had a similar problem with my XK150, and to my surprise the oil inside
the coil was gone, causing it to overheat. Once that happened, the car
broke up terribly. After cooling for a few minutes, it would run fine.
This also happened on my XKE, and after realizing I bought two coils from
the same
supplier, changed both, and they both run fine. Try shaking the coil, and
if you hear nothing inside, that might be the problem. - RJBasso
Coil data is as follows: Primary resistance 4.0-4.4 ohms; approximate stall
current 2.9 amps, approximate running current 1.0 amps - Bruce Cunningham
Good afternoon all, Important point here...Do you have a ballast resistor
in the circuit? Now of course a more significant question is do you need a
ballast resistor?! :-| On this age up to some of the later year 'merican
cars there was a balast resistor placed in series with the primary side of
the coil. As I understand it the Lucas "Sportcoil" is 12 volt to start out
with so it doesn't need a balast resistor. Muddy waters here I'm afraid.
:-( Anyway...In my other Brit cars there is a ballast resistor that is in
series with the primary side of the coil. History lesson anyone? :-) When
voltages were switched over from 6V to 12V the coil was not changed to
allow continued usage of existing parts. The resistor is bypassed in start
mode to give the highest possible voltage to the coil. All in all a pretty
good strategy. Most of us know this so excuse my pontification. Let's look
at the numbers above with Ohms law in mind. (V=IR) With a primary
resistance (R) of 4 ohms and a stall current (I) of ~3 amps we get V=12.
This is expected. So maybe a ballast resistor is not needed. OK, SOMEONE
GET OUT THEIR WIRING DIAGRAM. WE NEED HELP HERE. With the points closed
about 1/3 of the time we get an average current of 1A. So the above numbers
fit in with my version of reality. One would expect high resistance on the
secondary, the turns ratio in many cases is about 4000:1, and the secondary
uses a very thin wire. Bottom line...Most cars require a ballast resistor.
If none is present the coil will run hot and eventually boil all the oil
out of it at which point it runs REALLY hot and burns the insulation off
the wire, end of day for the coil. Klaus mentioned it became "very hot"
before the engine even started. Not a good sign. New coil is indicated. But
what caused the coil to fail? Age, no balast resistor, vibration causing
the oil to leak out, some combination of these?? Tough questions especially
by long distance diagnosis. Is this an answer?? I think not but hopefully
it adds some understanding to the situation. I'll pull the covers over my
head now and quiet down. - Cheers, Ken Boetzer
To all, How hot should a coil get. During a reluctant start-up after 1/2 or
more idleness, I could not put my hand on the coil (Lucas) Is this normal?
- Klaus Nielsen
I think the only reason a coil should heat up is because it is sitting on
top of a hot engine. It should not generate a significant amount of
internal heat in normal operation. - Bruce Cunningham
Bruce, Sounds like I have a problem. It became very hot before the engine
had warmed up. - Klaus Nielsen
The coil (non ballasted) will get hot if left sitting with the ignition on
and the engine not running. It is not unusual for the engine to be
reluctant to start in this conditikon, but should be OK after the coil has
cooled off. - regards, Mike Morrin
Klaus, I just found a coil @ XK Unlimited that is aluminum with a screw on
wire cap that looks fairly nice. They did not have these earlier so I am
going to try one. First, my water pump is being rebuilt at Terry's, new
Lucas wires are on the way a distributor cap with screw on caps for the
wire has just arrived with all the extra little tid bits etc. I should be
ready to try her again next weekend. - E.W. Blake
Ken, As I mentioned a minute ago when I was talking to Klaus, I just
purchased a coil that is to look more original. The old coil is shorting
out and the smoke is leaking out... ( Quiet Klaus ! ) You know that all
Lucas components run on smoke, and if the smoke leaks out , things stop
working... Anyway, The old coil is blue in colour and I believe it is a
Mallory or Mallroy something and it had a resistor on the side mount. The
resistor gave up as well when I tried to investigate the problem by
handling it. Someone had repaired it before from the looks of it. Do I need
to find a resistor to assist my new coil? It does not call for one in the
parts book unless I am using the mallory. If so, What should I get? there
are quite a few to choose from @ NAPA. Would a resister for a 1956 Buick
work? - E.W. Blake
>Do I need to find a resistor to assist my new coil?< That depends on the
>specification of the coil. If it is 8V, or says ballast, then it needs a
>resistor, otherwise probably not, although it is sometimes difficult to
>tell. If the primary resistance is much less than the original Lucas
>coil, it probably needs a ballast. Yes any 12V ballast will do. -
>regards, Mike Morrin
To all, A ballast resister knocks the 12v supply to the points down to
about 6v. Points will last a long time at 6v. The ballast resister is by
passed for starting (12v to points). After the engine starts the resister
is switched back in and the points see only 6v. The points will burn up
quickly at 12v constant supply. Early Lucas distributors had the resistance
built in, hence no external resister. - Johnny, Houston, Texas XK140 OTS
Points don't burn up as much as they are eroded by the transfer of metal
from one point to the other. You will notice that when one point has a pit
in it the other one will have a peak corresponding to that pit. The tiny
spark between points has a high enough current density that it kind of
sweeps a few atoms of the metal conductor along with the flow of electrons.
The capacitor in parallel with the points is supposed to be just the right
value to approximately zero out the current surge when the points open and
close at a nominal RPM. If the capacitor is lower than that value, metal
will transfer in one direction and if it is higher than optimum, metal will
transfer in the other direction. The rule with negative grounds is "points
pitted positive, capacitor too high". I think the rule holds for positive
ground as well. If you have a capacitance meter, you can compare values of
old and new capacitors to select one higher or lower to correct observed
metal transfer - we used to do that when I was a mechanic about 40 years
ago. If you don't have a meter, you can try replacing the capacitor and, if
you are lucky, your new one will be closer to the optimum value than the
old one and your points will last longer. If you stumble upon one of
optimum value, your points should last a very long time. This is probably
more than you ever wanted to know about points but I think it's
interesting. - Bruce Cunningham
I truly believe thast this is an "old wives tale" and has no basis in
engineering. The purpose of the capacitor is to reduce arcing at the
points, but the value of the capacitor HAS NO BEARING on the direction of
the current and hence matal transfer. - regards, Mike Morrin
It is the Lucas coil with the internal resistance, not the distributor. -
regards, Mike Morrin
If this is truly an old wives tale, there must be some other scientific
explanation for the observable fact that the pitting and the corresponding
peaks actually happen on a pair of points and it's not always in the same
direction. I'm certainly open to consideration of alternative theories. I
do know for sure from my professional experience as an electrical engineer
that metal migration happens with high current
densities - it's a significant problem in microcircuits. It is also true
that sparks have very high current densities. Any other theories out there?
- Bruce Cunningham
Here is a published source of the reported "Old wive's tale" regarding
ignition point pitting. The Automotive Technician's Handbook by William H.
Crouse and Donald L. Anglin (1979). Page 63 (of 664) states: "To correct
point pitting, note the following: If a negative point loses material, with
the buildup on the positive point, then one or more of the following steps
should be taken. 1. Install a new condenser with a higher capacity. 2.
Separate the low- and high-voltage leads or move these leads closer
to ground. This reduces the capacity effect between these leads. 3. Shorten
the condenser leads if possible. If the positive point loses material and
the buildup is on the negative point, instal a new condenser with a lower
capacity, move the leads closer together or away from the ground, or
lengthen the condenser lead." I'm not certain whether William or Donald was
the "older" wife. :-) - Dick Cavicke
I still do not believe it. I must admit to having forgotten the details of
the mechanism of material transfer on the points, but I am still certain
that the direction of transfer has nothing to do with the size of the
capacitor.
>2. Separate the low- and high-voltage leads or move these leads closer
>to ground. This reduces the capacity effect between these leads.
This is demonstrably rubbish! Running the leads twisted together for 1
metre would give a coupling
capacitance less than 50 picoFarads, if the points capacitor is about 100
nanfafads, a 1 meter change in wire length would give a change of 0.05%
capacitance, absolutely negligable. (note that the manufacturing tolerance
of the capacitor is typically +/-20%, so you would need about half a
kilometer of wire to compensate for the range of manufacturing tolerences.
>3. Shorten the condenser leads if possible.
If we are shortening the leads to reduce the indiuctance, The free-space
inductance of copper wire is about 50 nanoHenries per meter. The iductance
of the coil primary is probably in the order of 500 microHenries, so the
effect of an extra meter, would be about 0.01%, again negligable. If on the
other hand we are shortening the leads to reduce the stray capacitance, see
my comment above.
>If the positive point loses material and the buildup is on the negative
>point, instal a new condenser with a lower capacity, move the leads
>closer together or away from the ground, or lengthen the condenser
>lead."
The previous arguments still hold.
>I'm not certain whether William or Donald was the "older" wife. :-)
I am sure neither was an electrical engineer. (what were their electrical
qualifications?) - regards, Mike Morrin (B.E.E.)
Ken, Thanks for the review. I will look into the resistor issue. For the
record, the coil ia brand new as is the wiring; and as I noted to Dick, the
problem was in all likelihood caused by yours truly, leaving power to the
circuit while fiddling about. When I fired it up yesterday, the coil did
not get unduly warm even though the engine is reluctant to stay running at
first. It takes several attempts to get it going. It fires weakly without
backfiring, but has difficulties keeping running continously. BAttery is
new, fuel pressure is good, floats are set correctly and once it decides to
run, it idles smoothly at 1000-1100 and starts instantly when hot. Might I
have a troublesome solenoid in the auxiliary electric unit. How loud should
the "click" be as I cannot hear it activate. Thanks - Klaus Nielsen
E.W., As you can see in my answer to Ken,my bits are new and should not
cause Me problems. Therefore it is most likely me who is short on the
learning curve and I'm just crawling one step at a time.
Specifically to the coil, mine is marked "Lucas" the cylindrical part is
bright aluminium and the cap is brick red. Let's keep swapping notes. -
Regards - Klaus Nielsen
Oops!! My error.... I meant to say the early Lucas COIL has the resistance
built in. Not the distributor.
Thanks for the correction, Mike - Johnny, Houston, Texas XK140 OTS
Klaus, If you sit in the car with then engine off and turn the key on, you
should be able to hear the solenoid click followed by the click, click,
clicking of the fuel pump. And after the car starts you should hear a
noticeable hissing from the aux starting device. If both of these are
negative then
you may have a faulty solenoid or thermo switch. To test the thermo switch
(which is more likely to fail than the solenoid) simply clip a ground wire
to the screw on the terminal where it comes out of the water manifold near
the thermostat. With this grounded the aux device should be engaged at all
times. If this fails check the continuity of the solenoid. - Regards,
Dick White
Dick, Hi Coach! Have not heard anything resembling a hiss (and don't tell
Cathy). She says I can't hear anything these days. I'll check the items
tonight and report back tomorrow. Thanks - Klaus Nielsen
>Would a resister for a 1956 Buick work?
Is a '56 Buick 6 or 12 volts? All kidding aside, I really don't know! :-(
There, I said it. What I would do in your situation would be to go to the
local parts store and ask to measure as many coils for primary resistance
as they would allow. My belief is that the coils designed for a balast
resistor will measure about 1/2 the resistance of the coils designed for
straight 12 volts. See how your "unknown" coils compares and set up the
system based on what I believed to be requirements of the coil. Let us know
how you do. - Ken Boetzer
power = current X voltage. For the static coil current of 2.9 amps this
results in 35 watts of power
being dissipated by the primary winding in the form of heat - about as much
heat as a 50 watt incandessant light bulb probably as some of the power in
a light bulb goes into light. This is enough to make the coil warm or maybe
even hot to the touch if left on for a long time but it should not burn up
the coil. My small soldering iron creates 30 watts worth of heat so if I
use that to try to heat up the coil, it would have about the same effect as
leaving the power on the primary winding. If you have done any soldering,
you can imagine how long it would take to get the large mass of the coil
hot. - Bruce Cunningham
Thanks Mike, you win. There must be a reason and possible remedy for the
point metal transfer phenomenon and, while the referenced book was not the
first I have read with that theory, your explanation certainly casts doubt
on it and the recommended solutions. Over the years I never had a
condenser/capacitor tester. I just resorted to filing the points and/or
replacing them and the condenser with stock items, without particular
regard for the direction of metal transfer. (Tongue-in-cheek)
Mike's associating some of the terms of his EE background with our old XKs
opens up all sorts of possibilities for new columns in John Elmgreen's data
base. If anyone still has their original microHenries or picofarads, what
color are they? - Regards, Dick Cavicke
>...original microHenries or picofarads...< Boy, these JCNA judges are
>preparing to get tough. :-) - Dick White
Dick, Bruce and all, Thank you for your replies, As I understand it, the
value of the capacitor is rather like the weight of the flywheel. The
smaller it is, the better the performance, until you get
to a critical point where things don't run so well. In the case of the
capacitor, there is a wide range of values which work acceptably, Lucas
presumably selected a value in the centre of the range to minimise
problems. I will try to find some more information on the points pitting
phenomenom. My father was actually an expert on this subject 30 years ago,
but this is one topic where he did not teach me the details (or I forgot).
I think the whole thing is a bit academic anyway, as there would be few XKs
which do enough miles to need their pitted points replaced more than twice
in their owners lifetime. I presume you need to replace the points at
least twice to be sure you have got the correct value of capacitor. -
regards, Mike Morrin
Why not replace the points with one of the electronic systems. I believe
there are one or more which fit entirely in the distributor and require no
external mods for the concours types. I think one of them is Ignitor?? -
Dave and Linda Freeman
It's all my fault Klaus, I wanted to be like you when I grew up now look at
the mess you got me
in.... - E.W. Blake
Klaus, It sound like your starting carb or the sending unit for your carb
is not working properly. Just thinking out loud! - E.W. Blake
Mine (coil) is aluminum with black on the end but and it has a screw in
type wire cap as does the distributor ports. - E.W. Blake
I called Allen @ XK and he say's he doesn't think it needs a ballast. I do
not have the water pump on the car yet, but I wanted to see what happened
if I turned the car over. It started right up, sounded good, and I
immediately shut it down. Now at least, I know it is firing on all six. If
I put coolant in and it fouls out the plugs again, I will bush it off the
nearest cliff.. - E.W. Blake
That's the spirit E.W! .....Oh, can I have your water pump before you
dump your car over the cliff?
(If not, can you tell me how much a rebuilt pump costs from Terry's?-I need
one too one day) - Regards, John Morgan
They are rebuilding my old one for $75. American. - E.W. Blake
I installed the Ignitor brand on my red 150 OTS just recently. Since I have
not been on a good "start-and-use schedule", I was constantly having hard
starting problems on this car. Fortunately, the task only involved removal
of the distributor cap and a few passes with the point file to get a good
spark. However, that was getting to be a bit tiresome. But now that process
is history. The nice thing is that the electronic ignition system fits
completely within the distributor and is completely hidden from view as all
appears perfectly normal and original. (And so far it works well!) I am not
aware that an electronic ignition system is available for the 120. Perhaps
one is on the market. If so and it fits within the distributor as the 150,
then I'll retrofit a modern unit and smile as I read pitting point
discussions. Incidentally, my kit cost approximately $115 USD and it came
from British Auto in New Hampshire. - Bob Oates (West Virginia)
John, You might want to check Joe Curto's price for waterpump rebuilding.
He will also install E-type impellers if you wish. - Regards, Klaus Nielsen
Bob, Have you converted your car to negative ground? It was my
understandind that the Ignitor won't work with positive ground. - Ron '59
150 dhc
|
Main
Page
View the latest posts from our Forums via an RSS Feed!
