[W126 Coupe] CIS-E Blues

[Robert Karl Stonjek]

Dick,
I tested the Throttle Valve Switch (as it is referred to in my manual) and it is within spec.  I also tested it at the three pin socket you mention.  I just wasn't familiar with the effect it actually has on the CIS-E.

Fuel flow was the first thing I instructed my mechanic to check, including pumps and filters, and though the pressure was slightly down at first this seems not to have been the problem.  My mechanic changed the fuel filter and the pressure returned to spec. with no change in performance.

Note that the problem goes away when the EHA is disconnected, eliminating everything outside the EHA-CIS loop.  This eliminates fuel flow problems such as caused by pump, Fuel distributor etc.

The problem is most noticeable with the throttle open full, but that probably has more to do with the power needed to get up to high revs in the first place.

The CIS-E instructs the EHA to make the fuel ever leaner with higher revs, which eventually causes power loss and missing.  It is suppose to instruct the EHA to enrich the mixture.  This it does when the engine is cold (open loop operation) but not when hot (closed loop operation).  Naturally one suspects one of the devices the CIS-E senses, but I've tested them all (I think) and none show any obvious faults.

I suspect that the CIS-E has a fault.  I could fool it into open loop operation by changing the sensed temperature, but the CIS-E relays the temperature to other devices and so they would not operate normally unless I change the sensed temperature in the CIS-E itself (at just the right point).

What I need is a circuit diagram of the CIS-E itself, or any similar CIS-E device (one of the Porches used the same unit?).  I can then test my theories quickly and simply, as electronics is my area of expertise.

Thanks,
Robert

> Robert:
> 
> Anuj is referring to the 'wide open throttle' position on the throttle 
> position sensor (TPS) which has two states idle position and WOT.  It's 
> a 3 pin connector that is cabled to the base of the air flow meter just 
> above the intake manifold and is attached by two screws to the throttle 
> valve.  The sensor simply sits atop the throttle plate horizontal shaft 
> and based on the shafts position knows the state of the throttle. 
> 
> I thought you said you had tested all of the sensors effecting the 
> CIS-E.  So, assuming your electrics (plugs, wires, rotor) are in good 
> shape it sounds more like you are dealing with a fuel pressure drop at 
> 4k rpm or greater.  That's why I suggested checking the pressures to see 
> if fuel pumps, filters, accumulator etc are all in working order before 
> stumbling down the path of a new or rebuilt fuel distributor.   So, if 
> electrics check out you have to go the route of fuel pressures check next.
> 
> Regards,
> 
> Dick
> 
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