The following Car Magazine article about fuel injection in the Peugeot 504 and Citroën DS21EFI was originally published in the May 1970 edition and is reproduced with the kind permission of Car.
Note: the pictures are not those originally included in the article because they were very poor quality Roneo (or Gestetner) photocopies.

At a time when the marque was generally pilloried by the majority of the UK automotive press, Car stood alone in its appreciation of the double chevrons.

Car Magazine MUCH MORE SQUIRT

Fuel injection transforms France's rival routiers, reports Ian Webb

Considering the palliative powers of fuel injection, it’s surprising that Citroen didn’t get around to using it on the DS years ago. Even when the first D model appeared, back in the mid-1950s, it was generally agreed that the only fly in an extraordinarily advanced pot of ointment was the relatively retarded engine. Agricultural was the phrase that fitted it best. And in the decade and a half that has passed since, rising standards have continued to outstrip what small improvements Citroen could make. The trouble, then as now, is that it is a big, old fashioned, somewhat slow-revving four. The long term answer was clearly to throw it away and start again with something else, preferably the flat-6 that Citroen in pre-Maserati days were constantly rumoured to be on the point of introducing.

But, of course, no such thing happened and finally, last September, Citroen succumbed to the attractions of fuel injection as a means of making a silk purse out of this sow’s ear. Would it be too cynical to suggest that the engineers were instinctively attracted by the prospect of having even more complication, further forests of pipes and tubes, in an engine compartment already jam-packed with paraphernalia? Whether or not that was their intention the result is that they have at last succeeded in making the engine entirely invisible beneath its canopy of ancillary items.

The method used is an adaptation of the Bosch electronically controlled injection already used by, inter alia, Mercedes-Benz and Volkswagen. If fuel injection is to justify itself as an alternative to carburettors then it can do so only on a basis of near-perfect metering of petrol into the inlet tract. Electronic control of the amount and duration of each squirt must be more accurate than even the most sophisticated mechanical arrangement.

The Bosch system has sensors monitoring engine speed, coolant temperature, throttle opening and atmospheric pressure. The information is fed to a transistorised, printed-circuit control device - one hesitates to use the ‘miniature computer’ phrase that publicity men bandy about so freely - and this in turn is linked to the solenoid-operated injectors to control the timing of each stroke.

The result is to push net bhp up by over 20percent from 106 to 125, which really is quite a reasonable figure for a crusty old 2.2 litre four like this one. Furthermore the peak of the power curve is moved down by 250 rpm to 5250. The improvement in torque, oddly enough, is considerably less marked, being less than 9 percent - it rises from 122lb ft to 135 - and is achieved at an unchanged 3500 rpm.

The Bosch system is offered as an extra on the more splendid Citroens in the top of the range, starting with the DS21. We tried it on a DS21 Pallas. It adds £240 to the price in Britain, bringing it up to £2490. Or in other words a l0 percent price increase in return for 20percent more power.

As a yardstick we also tried a Peugeot 504 with fuel injection. The system favoured at Sochaux is the Kugelfischer, as used on the 404 for years and by now thoroughly developed in its Peugeot application. A straightforward mechanical setup, its nozzles are aimed into the ports and are fed from a pump block mounted low down beside the canted engine.

Specifying this instead of the standard single carburettor puts another £156 on the price, making it £1656. Maximum bhp (gross, since Peugeot don’t go in for the net variety) is a little over 20percent higher at 103 bhp, developed at 5600 rpm against 5500 with the carburettor.

So with the mechanical injection setup on the Peugeot one is paying a relatively lower increase to get a proportionately higher power boost.

There is now, for the first time with a D-model Citroen, an (almost) unbroken, smooth supply of power from near idle speed onwards. The parenthesised ‘almost’ appears because there is a slight snag around the 2000 rpm mark.

This apart, the torque is spread with gratifying generosity and as far as the factory is concerned is the main area of improvement. Certainly one is encouraged to lug around in the higher gears more than before, safe in the knowledge that the engine will pull away cleanly and smartly.

(This feature, in the continued absence of a decent gearchange, is doubly welcome.) But there is also now considerable inducement to hammer the Citroen in a way that hardly seems to match its character, though it responds surprisingly ably. The fuel injection has greatly improved breathing at high revs and although the peak of the power curve has moved down, the rapid way it climbs up to the realms of 4000rpm and beyond encourages much brisker cross-country B-road travel than before.

Throttle response is perfect, even from cold. The abilities of the Bosch injection are such that for the morning commencement one simply turns the key and drives off. Rich mixture adjustment, additional squirts for clean throttle response, and all the rest of it, are remotely taken care of.

Petrol consumption is always supposed by its protagonists to be better with fuel injection-and frequently it is. The more accurate control of ingoing fuel, better mixing and generally more efficient use of the precious liquid are prime factors. Plus, in the case of the Citroen, the fact that lifting off cuts off the supply altogether until revs drop to 1l00rpm, when it starts again to prevent stalling.

The trouble is that one is encouraged to drive so much harder than before that the overall figure can easily drop well below the norm for a carburettor equipped DS. We got an average of 25mpg of 4-star and pushed it down to 20mpg when making generous use of the performance.

Top speed, thanks more to the superior aerodynamics of the DS body shape than to the new-found power increase, is an excellent ll4mph.

Acceleration, you will perhaps not be astonished to learn, is the best we have yet recorded with any Citroen. It comes in a long, not over-impressive rush, rather as though the car had automatic transmission instead of a four-speed manual. Violent starts produce momentary wheelspin to the accompaniment of a loud knocking.

The result of fuel injection on the Peugeot 504 is not to bring about such a tremendous improvement, but this to some extent is because the 504 has a better engine to begin with.

As on the Citroen, an automatic cold start device enrichens the mixture - and if you think that on a modern fuel injection system this is only as it should be then remember that the Joseph Lucas arrangement on the Triumph 2.5PI still has a manual ‘choke’ control. Again as on the Citroen, there is an instantaneous response to the first try of the starter and the engine immediately settles down to its normal relaxed tickover. Only once in our experience did the magic fail, when there was no answer to the first twist of the key and a loud bang from in front as it spat back in reply to the second. The third attempt was successful.

There is a certain roughness about the larger Peugeot engine that Kugelfischerisation does nothing to alleviate. It’s a matter of low frequency vibration rather than noise, so is felt rather than heard, and it seems to get no better even if one runs past the peak of the power curve up to a full 6000 rpm, as is possible in the lower gears.

Still, the injection does make the already respectable performance of the 504 into something altogether exceptional for a fairly large four/five seater saloon of 1.8litres. Here, at £473 more than, say, an Austin 1800S (and that extra cost includes import duty, purchase tax thereon, and the importer’s cut) we have something that will manage an honest 105mph, get near 110 with the mildest assistance from wind or gradient and out-accelerate most of its rivals in the 1600-2000 category. It would have shown up even better on the appended table had not a failing gearbox made the driver subconsciously wary of third-to-fourth shifts that all too easily ended up in an ear-assaulting attempt to engage reverse at 80mph.

This shortcoming notwithstanding, we enjoyed driving the 504 hard and fast, so came up with a correspondingly low fuel consumption figure of 24 mpg. This is still notably economical for the size of car, nature of performance potential and for the circumstances. It is, presumably, a function of the inherent fuel miserliness of injection, plus a better aerodynamic shape than the 504’s appearance suggests. At all events, gentler driving gives nearer to 28 mpg (of 4 star) and that is a very good figure indeed.