Hi everyone, I'm trying to sort an intermittent fault. its happened twice and its left me to limp home with a misfire and either down a bank or at across the engine. The throttle has to be finessed to keep the car going but won't cope with loading such as a gradient. Copious amounts of soot come from the rear, as my son will testify when he followed me. It suddenly comes on at say 75mph. I don't know what sensor is failing me; for example from other forum posts with similar symptoms it could be the coolant temperature sensor or intake air temperature sensor. My mechanic thinks it could be the manifold pressure sensor or the injection amplifier. It is linked to an overfueling of the engine? The car otherwise runs beautiful certainly at cold to warm. Can you help me make sense of my sensors? thanks Geoff, Norwich

Start with the basics. check all vacuum hoses, clean all injection related electrical connectors. check for leaky cold start injector.Check your ignition timing, insufficient timing leads to reduced manifold pressure and over fueling at light load. In the past I had a D-jet car with a crack in the MPS hose. Took awhile to find, worked fine and crack was sealed in the position I was testing it however it leaked when laid down in it's in service position.

Review this PDF for details and theory of operation. It's for a 4 cylinder Porsche but the ideas and principlas are the same. Jag used a amplifier that "multplies" the injector signal for use on 12 injectors.
http://w107.pbworks.com/f/DJetronic.pdf

have a look at this too.

https://www.youtube.com/watch?v=x3rQ...BcHATZQ8UNakPs

Thanks vm. I had my V12 specialist sort a lot off the issues such as the vacuum hose leaks and timing. This doesn't happen on every trip which is why its so annoying! I may go down the 'replace parts approach' for a reductive strategy. I'll definitely look at the MPS hose. thank you for replying !

Firstly, welcome to the Forums.

When the beast is sorted, please do an Intro in the New Members Area.

Based on what you are mentioning I reckon the Coolant Temp Sensor is at play. OK cold and warm, no good Hot. Unplug the sensor, shape a paper clip and bridge the 2 terminals in the plug, try again.

The Air Temp Sensor is only a trimmer, and if it fails will not cause soot.

The MAP, maybe, they are OLD now, and thats life. However, the symptoms are lousy running all the time.

Fuel Pressure Regulators, you have 2, and they are OLD also, and known to fail, BUT, again, not temp related.

The Throttle Switch, under the centre Capstan, sometimes goes hissy, but, once more not usually Temp related.

Has someone been fiddling with the engine lately?, that is always a go to place to start.

Around here we call it "throwing parts at it". Considered a crutch of a uninformed mechanic. However...In your case might not be a bad idea becasue the inevitable pile of removed and good parts will be considered "tested" and can be set aside as spares. known good spares for an old and rare car would certainly have value to whom ever owns the car. Also the change out process can sometimes reveal a loose wire or other anomaly that can only be exposed with a kinetic approach.

Might well be something very simple. A dirty air intake filter. When cold the car "enjoys" the rich mixture. Whenm warm not so, too rich. black smoke ensues...

Carl