Re: [doc] Cold Start Switch?

[Nick Tomlinson <nickandkathryntomlinson@xxxxxxxxxxx>]

Yes, as Martin says, it 'sets' the mixture rich by running the frequency valves' duty cycle to 60% by lambda switch or WOT switch (or 50% if just oxygen sensor fails). This assumes that the mixture set by the allen key adjustment on the metering flap is set correctly. This is why the books states to set the fuel adjustment so the frequency valve's duty cycle is 45% (38 to 50% oscillating).
 
If the fuel mixture is too lean or too rich to begin with, the cold running of the engine when the duty cycle is 'fixed' until the oxygen sensor is warmed up, this will give feedback to the fuel computer and the system will then try and self correct.
 
This assumes that the fuel computer is working ! Make sure the frequency valve DOES buzz (quick check). If it doesn't then use wiring diagram to make sure battery voltage is present. If not then usual suspect is wrong type of relay in module #12
 
http://www.specialtauto.com/delorean-parts/relay-compartment-references.html
 
You can check the WOT and lambda switch back at the fuel computer conenctor at between pins 5 and 7.
 
Don't forget you can get muck stuck behind the fine mesh in the CPR. Remove both bango's and blow out using an air line.
 
Interesting to hear about these failures. Amasing realy as it's only a bimetallic strip  (with a heater coil round it), connected to a diaphragm.
 
Exhaust gas shouldn't be mega thick diesel bus black, a fine trace is normal.
 
Moral of the story?
 
Don't mess with the allen screw (or tweak and fiddle) unless everything else is tested and is OK !
 
NickT.
 


Martin Gutkowski <martin@xxxxxxxxxxxxxx> wrote:
What I'm about to write assumes the engine -did- run fine and has gone 
wrong, not having been fettled with by anyone.

When the lambda system fails (duff sensor, stuck full throttle switch, 
duff thermal switch) it results in the lambda system setting the mixture 
rich. As the mixture needs to be rich when cold, this usually results in 
just fairly heavy hunting at idle at all times, and when revved, black 
smoke comes from the exhaust.

When a CPR dies, it -usually- gets stuck at 3.5bar control pressure 
which is correct for a hot engine. This results in a lean running 
condition when cold and causes hard starting, poor idle and the 
inability to rev (accompanied with pops and bangs from the air intake). 
Things really get messy when the CO screw is messed with to account for 
this. This is the most likely cause of John's problem

I've also seen CPR's die showing cold control pressure (1-1.5 bar), 
Primary pressure (5 bar or thereabouts) and the wierdest one of all 
which showed complete open bleed-off - ie control pressure of nearly zero!

The hot start relay is redundant on cars with fuel accumulators and 
won't do anything unless the missing ground wire is added.

Martin

Nick Tomlinson wrote:

> I have seen the K-Lambda Jetronic engines run a bit naff if they are 
> not set correct, yet run OK once warm because the Oxygen sensor over 
> compensates.
>
> The Duty cycle of the frequence valve via fuel computer (or diagnostic 
> plug) should be checked for best tolerance, or use an oscilloscope on 
> the oxygen sensor.
>
> The best course of action would be to check fuel pressures etc and do 
> a full diagnostics.
>
> There is another white relay holder (3 wires) for hot climate 
> countries to pulse the cold start valve during engine cranking. This 
> is normally shoved out the back near the fuel pump relay.
>
> NickT.




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