No electronics…

Posted on November 5th, 2007 in Opinion,Peugeot by Julian Edgar

pug-engine.jpgPerhaps I am unusual in that as a guy in his mid-forties, I’ve owned relatively few carburetted cars. My first two cars were carby, but after that my main cars have always had electronic injection. And so I’ve got completely used to thinking in terms of cars with plenty of electronics controlling the fuel and ignition.

So it’s a real shock when I start thinking through modifications for my newly-acquired Peugeot 405 SRDT diesel. Clearly, being a diesel, you don’t expect to see spark plugs and an ignition coil and coil module and stuff like that. But the absence of a crank-angle sensor, MAP sensor or airflow meter, intake air temperature sensor and ECU comes as a bit of a shock. (The Pug injection is the old mechanical Bosch system, rather than today’s electronically controlled common rail system, that in many ways resembles a conventional petrol injection system.)

The shock isn’t so much in making changes to the fuel system; it’s in all the other avenues which are no longer viable. For example, the Independent Electronic Boost Control kit worked extremely well when I developed it. But I can’t use it on the Pug because there’s no electronically varying injector pulse width!  The Intelligent Turbo Timer  is another project that immediately springs to mind – but again I can’t use it because there’s no electronic indication of load.

And I’m finding that I really need to change completely how I think. A week or so after buying the car I was finding it harder and harder to get it started. The engine would crank many times before it sprang into action – to then, paradoxically, idle and run perfectly. What could be the problem? The cranking speed sounded a bit low so I put a multimeter across the battery – it showed just 7 volts on cranking! Hmm, I immediately thought, I bet the ECU can’t compensate in its injector pulse width when the voltage is so low – and the spark’ll be weak too! Except, there’s no spark and no ECU! Instead, the low cranking speed results in less compression pressure, and so temp build-up, and so ignited fuel. (I put in a new battery and the problem was immediately solved.)

None of these ideas is earth-shattering. But it’s interesting how I need to so dramatically change my mind-set – I guess, just the same as if I went back to modifying a carby car….

3 Responses to 'No electronics…'

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  1. Sami said,

    on November 6th, 2007 at 10:41 pm

    Well, the same thing happened to me in reverse when I started working on a Peugeot DW10B common rail diesel for my PhD. The only other engine that I worked on fairly often before was my father’s diesel Pajero with mechanical fuel injection. Needless to say, I was rather lost the first couple of weeks…

  2. Davidss said,

    on November 7th, 2007 at 4:35 am

    One ‘old’ idea that will work is your boost control system with pneumatic valves that first saw light on an Audi of yours.
    To put an additional development opportunity when using it, look for some way of capturing (recording) the rise of boost pressure against engine speed, to show how much pressure is being lost by the wastegate opening early.


  3. Julian Edgar said,

    on November 7th, 2007 at 7:19 am

    Yes I could use the ‘Audi type’ boost control. Re measuring wastegate creep, we have done so previously in this story –