Hi, I would very much appreciate some pointers if anyonecan help please?
My car is a 1961 MK2 3.8 auto (DG), positive earth.
The problem I am experiencing is as follows
Under normal town driving, no problems, but when the car is under load (around3k revs on the flat or up a steep hill under wide throttle opening) car startsto falter and hesitate, revs start to drop away and it gets worse until the caris barely able to keep moving (I nurse it into a side road or similar) – notmisfiring as such, just complete lack of power/ willingness to rev. I havenoticed that when the power drops away and I indicate to pull in BOTH indicatorrepeaters illuminate in the pod.

On re-starting, all is well until under load again. Plus the indicator works asit should.
Car runs well at idle, oil pressure and temp look fine and ammeter looks OK too- no obvious 'drawing' problem - at 2k revs with lights and fan on, is showing'charging'
Not heat related - does the same on a just warmed engine.
So far have: I have been working on the basis of fuel or ignition problem. Dodgyearth ?
The battery is fairly new and always starts the car firstturn.
So, where does that lead I wonder? My thoughts include:
Failing dynamo? - is the dynamo failing to keep up with the demands under load?Does it rely on the battery to help and if that's not A1....
Voltage regulator fault?
Plug leads - look ok
LT lead - looks ok
Spark plugs recently fitted are NGK - but I think the problem pre-dates them.
Or could it be the Gearbox itself?
Some ideas of where to look (process of elimination) and how to test likelysuspects would be really helpful
Many thanks

Ian

 

to me it sounds like a distributor (ignition) matter. Although this is not my expertise.

start by checking the distributor Cap for any cracks.

also check that there is oil in the carburetter "piston bottles", remove each cap on top of each carb and look inside, there should be a little oil in there, use 20w oil. Do not overfill.

if the car starts and idles fine, then the fuel pump is working.

 

Reset or change points and condenser. Recheck timing. Check carbs for right oil level. Then check fuel pressure and volume.

 

Sounds like it's starved for fuel.
The float bowls are emptying under load and for what ever reason the pump can't keep up.
When was the last time the pump was serviced ?
Check that the float needles are set correctly and they are not sticking.
Check all fuel filters as well as the internal ones in the pump and the fuel tank.

Ignition coils can act like what your problem describes, check by substitution.
Bench testing a coil is not a good test, they can function normally on a bench, but under load the problem may arise.

 

Hi Chaps,


Thank you for your replies so far. I feel part of a very large family of Jaguar owners even if most of you are across the pond.


I will work through them and report back my findings.


Ian

 

I have only had the car for around 8 months so I will work through the fuel system starting with the pump fuel filter/s


Ian

 

The old saying is 90% of fuel problems are electrical. My vote goes to checking points, Condensor, and plug wires first.

Good luck!

 

Just seems odd that it does it only under load at such a specific time, and then everything appears fine again after restarting.
I find ignition problems effect the whole range of power, including poor starting, idling, and driving around town.

In the past I have had ignition problems in a number of cars and after replacing the usual _ points, plugs, condenser and even wires, the coil can give odd problems like Hartford is having.
The car can run and start fine, but there is a problem in the coil where it heats up beyond normal temps _ the resistance climes and the coil fails.
The system can't push enough amperage/voltage in the coil anymore due to the high resistance and the car just stops _ no more spark.
However in Hartford's case, the car starts right away again, so if it is a faulty coil, they don't simply just start working again.

It will be interesting to see what the actual problem is.
I have to ask, Hartford what do you mean exactly ?
"BOTH indicatorrepeaters illuminate in the pod"

Are you thinking that there is a short some where and the ignition is suddenly failing ?
Also, Hartford, do you have an Ohm meter, have you checked the resistance of your spark plug wires ?
Are you also using resistor plugs as well ?

 

As I was thinking. One of my minis had the same problem once. Turned out the fuel pipe under the car had been crushed (incorrect jack/hoist use?) and was restricting the rate of fuel flow. All was well until car was at speed. Stop for a while & the fuel pump had time to catch up & replenish the SU float chambers.

I don't think the fuel line is as vulnerable in the Mk 2, but may be worth checking for partial blockage etc.

 

There is a vacuum lead to the carbs. Clean out this connection to the carbs with a simple piece of wire. I had this problem on my Daimler V8 for months and months until I was told this by a friend who owned a 3.8litre Mk 2. Try it, it may work!

 

Reading this thread, and the symptoms it is very similar to what I had on an XJ6. This transpired to be fuel supply blockage at the tank filter. On the Mark 2 it's easy to see if fuel is lacking as the filter in the engine compartment has a clear glass bowl that should be full of fuel. If the car loses power, quickly stop somewhere, switch off the engine, and look at this filter.

 

Hi Chaps,


So far I have checked
Plugs
leads
Distributor cap
rotor arm
feeds to distributor- one lead has stretched so I will lengthen it.
Coil as far as all connections are OK
Fitted additional earth strap and cleaned up other earth points
Changed battery connections as one did fall apart
Cleaned out fuel filter
Just about to check fuel pump