K Jetronic issue

[beagle2022]

Hi folks,
1979 280sel. Running rich all the time.  Fowling spark plugs and insane fuel consumption.  A quick check shows a/the culprit to be a dead temp sensor on the cylinder head on the exhaust side (the one closest to the front).

When I short the circuit to earth on a warm engine it idles more smoothly and stinks less.

Am I on the right track here?

Also I am having trouble sourcing the part.  My usual supplier sent me to MB themselves.

Will a second hand one do or should I spend the kids inheritance on the genuine article?

I am new to this system so would appreciate any wisdom and experience, including part sources.

Thanks.

Peter

[Big_Richard]

the temp sensor for the instrumentation gauge will have no effect on the K-jet system

the 100c switch for the aux radiator fan also advances ignition timing to keep engine idle revs the same at higher temps - are you hearing a relay type click when you short this thing to ground ?

theres also a thermo time switch that allows/disallows the cold start injector to operate, though from memory that has 2 pins.

If its the 100c switch that magically makes your engine run better i would start with checking your ignition timing as per the book.

[koan]

the 100c switch for the aux radiator fan also advances ignition timing to keep engine idle revs the same at higher temps - are you hearing a relay type click when you short this thing to ground ?

Does it?

Aren't you thinking of the A/C advance/retard adjustment when the compressor pulls in?

koan

[Big_Richard]

the 100c switch for the aux radiator fan also advances ignition timing to keep engine idle revs the same at higher temps - are you hearing a relay type click when you short this thing to ground ?

Does it?

Aren't you thinking of the A/C advance/retard adjustment when the compressor pulls in?

koan

Yep, it does.

Its not only there to turn the fan on and off, look at the wiring diagram 

[TJ 450]

MT... I remember having a fundamental disagreement with this a while back.

I must admit, I never bothered to follow up on it though. I'll have a look, as I struggle to think of a reason why this would be necessary.

Tim

[koan]

the 100c switch for the aux radiator fan also advances ignition timing to keep engine idle revs the same at higher temps - are you hearing a relay type click when you short this thing to ground ?

Does it?

Aren't you thinking of the A/C advance/retard adjustment when the compressor pulls in?

Yep, it does.

Its not only there to turn the fan on and off, look at the wiring diagram 

Yes I did and it doesn't.

koan

[Big_Richard]

wrong.

[Type17]

K-Jet does not alter the timing - the only timing changes that happen on a K-Jet car are from the vacuum advance and the bob-weights in the distributor (which are common to most late 20th century carb and pre-EFI setups)

When a fuelling system alters the timing, it's not K-Jet - probably a KE variant.

I have seen things that do a similar job - on MB R113s (Pagoda), there is a linkage that opens the throttle butterfly a tiny bit when the gear selector is put into D or R, to lift the revs a bit - this does advance the timing, but only through the vacuum or bob-weights in the distributor, not by directly altering the timing like a modern setup.

[s class]

Use a voltmeter to check the signal at the cold start valve.  You want to ensure that it is not running all the time.  


If that checks out, then you have a basic mixture problem  THis could be poor adjustment of the CO mixutre screw (need a CO meter to check this), or warm-up regulator problems.  

You can verify the WUR operation with control/system pressure tests.  If the results are not in spec, it may be the WUR, or the pipework to the WUR.  Also check the vacuum connections to the WUR.  If there is a vacuum leak there, the WUR will be permanently sitting in full-acceleration enrichment mode.  

If you lack specialised equipment, then start with the basics - use a voltmeter to check electrical connections to the WUR and CSV.  Also, use the meter on ohms mode to check the resistance of the coil in the WUR.  Next, check all the vacuum lines.  

A CO meter is actually worth buying.  You can get a cheapo Gunson  CO meter on ebay - I got mine for about US$200 including shipping to South Africa.  It has paid for itself a few times over given the cost of fuel these days.  

[TJ 450]

the 100c switch for the aux radiator fan also advances ignition timing to keep engine idle revs the same at higher temps - are you hearing a relay type click when you short this thing to ground ?

Does it?

Aren't you thinking of the A/C advance/retard adjustment when the compressor pulls in?

Yep, it does.

Its not only there to turn the fan on and off, look at the wiring diagram  

Yes I did and it doesn't.

koan

I just checked it out... MT is correct.

See "note 9" if you don't want to analyse the diagram.

Tim

[koan]

the 100c switch for the aux radiator fan also advances ignition timing to keep engine idle revs the same at higher temps - are you hearing a relay type click when you short this thing to ground ?

Does it?

Aren't you thinking of the A/C advance/retard adjustment when the compressor pulls in?

Yep, it does.

Its not only there to turn the fan on and off, look at the wiring diagram  

Yes I did and it doesn't.

I just checked it out... MT is correct.

See "note 9" if you don't want to analyse the diagram.

What diagram are we talking about?

Can't find it any of my diagrams.

koan

[TJ 450]

This is the one MT sent me; It's down the bottom of the document.

link

Tim

[Big_Richard]

I shall also add, that while thats a USA wiring diagram, i have confirmed this functionality on my own AU delivered 6.9.

Its possible i guess that the euro engine cars do not have this feature.

[koan]

OK guys I admit you are correct regarding the 280 wiring.

MT what test did you perform determine the similar functionality on your 6.9?

koan

[Big_Richard]

This is what happens on my AU delivered 6.9

Its my understanding that the following are true.

aux fan either turns on with 100c coolant switch or the 80 something degree refrigerant temp switch.
ignition change over valve activates when the compressor is active and also when the 100c switch is closed.

when the vacuum plumbing is correct, the change over valve only achieves anything with the throttle plate in its home position. so it doesnt in any way change ignition timing off idle speeds.

I confirmed this many times by shorting my temp switch wire to ground - the fan goes and i hear the change over valve go clunk at the same time. My wiring is all original too.