Feels like one cylinder; missing is quite persistent, in both reverse, first and even third at low rpm (vehicle will choose third at low throttles if rpm exceeds about 1200). At higher speeds it runs fine.

There is a temperature operated vacuum switch behind the fan control switch on the front of the inlet manifold. Vacuum comes from a harness on the left, near ignition control, through the switch, then back under the fuel divider. Can't see where it goes.

If this is faulty, could it be the problem?
Where is it taking the vacuum to?
Why is it switched with temperature?

There is a crackling noise, sounds like EHT, that comes from the empty
space between the exhaust manifold and the water overflow, behind
the alternator. Plug leads are new and clean. It sounds electrical. Sometims, it seems associated with a miss.

Engine has done 260,000 km.

thanks for any help.

ps, on rhs of the sump, out come two pipes, covered with heat protection, going to a box in front of the pedals.
What are these? What's in the box?

 

The problem was a disintegrated resistor in the HT lead to no 3 spark plug.
Remnants of the resistor and cap must have provided a tracking path, which
was unreliable, and missing was occurring.

In the dark, it was possible to see glowing around the resistor shrouds, and,
a brighter spark when the breakdown arc occurred, causing cyl 3 to miss.

The person who decided to introduce electronic components into the HT
circuitry, inches from the spark plug, and above the exhaust manifold,
needs to serve a sentence burning his fingers and sharpening his profoundly
dim wits.

Imbecile! (from one who has also paid $25 x 8 for a set of new resistors on
a 3800 v8 "just in case" that's the problem.
And the becker mexico radio on that car does not work, waiting for a new software download. (the "justification" for these idiot-brained resistors was "to reduce electrical ringing which might cause radio interference."

fbs.

 

To explain/justify:
Consider a simple Kettering system; primary side 12V 2A, secy side need 12kV oc, so 1000:1 current division, secy is 12kv and 2ma.
Take plausible spark voltages, strike voltage = 2000v, sustain voltage
1000V. Then, put a 10kohm resistor in series. If current is 2ma, then
there is 20v across the 10kohm resistor. But there is 1000v across the
arc. The resistor dissipates power in relation to the spark in the ratio 20:1000. 98% of electrical power is dissipated in the arc, 2% in the resistor, which is therefore useless, ineffectual, and the product of at least 98% defective thinking.
In a different type of eletronic ignition system, quite similar comparisons would apply, as the spark, and primary input, are the same.
It is a totally erroneously placed, out of place, component, whose only purpose is to make additional trouble and cost for the end user.
QED