Loss of power

[stagnasty]

I have a 1978 Triumph V8 powered manual Stag, I have been experiencing a loss of power occassionally over the past few months. This has now reached a level where I am unable to drive the car any distance furrther than a few miles before it suffers a severe power loss with the car eventually cutting out. Application of more throttle makes no difference to the situation, the car does not respond.

The Oil Pressure is good at idle and the Coolant Temp is at Normal- no sign of overheating at all.

The spark plugs are iridium and have less than 3k on them, it has Lumenition Optronic Ignition fitted, new Hot Wire Leads/New Coil (12v).

I have checked the Stromberg Carb Diaphragms, OK no tears/Holes. The fuel pump is an SU type (OEM Spec) it ticks away very well.


There is a fuel filter fitted in line with the carb feed pipe in the engine bay, it is new and of the yellow element type.

The ignition timing is correct as is the CO reading.

Any Ideas?

[73stagman]

When it loses power does it backfire and spit or does the power just fade away.

[stagnasty]

Loss of power

When it loses power does it backfire and spit or does the power just fade away.

No it just fades away ...no spluttering or missing...just gradually dies!

[V Mad]

It is best to do some tests to see what is happening. When the engine dies and will not restart, see if there is a spark at the king lead.

You should be aware that Lumenition is a good system until it starts to break down as some do. Before you decide to suspect the Lumenition though, check that your coil is properly connected via the ballast resitor (search for previous info on ballast) as coils can break down especially if overloaded.

[stagnasty]

I have tried two new coils from different suppliers, also i understand that the Ballast resistor in integrated in the wiring loom on this car, also the lumenition power module is brand new.

[73stagman]

It sounds like a fuel / air / mixture thing.
You need to do as Chris says and run some tests whilst its running but also check all the choke cable linkages and throttle linkages to make sure they are all fixed at their settings. I guess the engine restarts after a while?

[stagnasty]

The engine restarts almost starightaway, and will rev very freely at a standstill, just does not perform at all under load.

[stagnasty]

Oh and all the linkages are fine , all works as it should.

[73stagman]

you need to check for air leaks around the inlet manifold. Also check that the air intakes are clear and that the vacuum advance mechanism on the dissy is working. Try to get a timing light on it whilst increasing the revs and you will see if the timing advances as the vaccum builds.

Also I believe you can get this or a similar problem if there are issues with floats in the carbs and the engine ends up flooded but I know nothing about Strombergs so will bow out of the issue if this is proven to be the problem

[stag157.7]

Welcome to the forum


float levels too low.incorrect needle valves fitted
temp compensators opening too much and weakening the mixture(more so with hot engine),blockage in fuel filter,fuel tank breather inoperative,carb pistons sticking

if its a coil problem does the rev counter will die?

Give you something to work on


alan

[V Mad]

I have tried two new coils from different suppliers, also i understand that the Ballast resistor in integrated in the wiring loom on this car, also the lumenition power module is brand new.

If its a Mk2 car then ballast was in the loom, BUT, is it still there? Test to see if it is still there. Old cars have often been messed around with by people who change things either deliberately or inadvertantly.

[pcoleman]

had something very similar and car just died at speed with no warning,changed the fuel pump and 90% cured,put the old coil back on (new aldon igniter was too much for my crappy leads)and changed the king lead and 100% cured.
good luck with it. peter

[flying farmer]

Almost certainly a fuel problem. If the ignition is failing any cylinder that does recieve a spark will still fire normally giving a very juddery drive, whereas fuel starvation will lead to a gradual fade away.
Check you have fuel flow at the carbs.
Do not discount a bit of dirt swilling around in the fuel tank. I once had a V8 Dolomite which suffered the same symptoms, in desperation I swilled out the tank to find the back half of a wasp and a few rust flakes. The dead wasp was getting sucked into the fuel pipe, then would fall out when the ignition got switched off only to do the same again a while later
Neil

[AlanD]

agree with Neil, sounds like fuel, i had this for a while, i broke down completly, wards fitted a new pump and hey presto, a gradual loss of power, roll to a stop, restart her fine, then a while later it would happen again, fuel pump ticked great at a standstill, but under load the delivery was very poor and it gave up in the end, on the bloody motorway when i was overtaking a HGV !! typical

alan