No more writer’s block Time to raise the bonnet
Nigel’s injectors play dirty
This should hopefully interest those of us with classics fuelled by Lucas petrol injection, mainly Triumph owners of course, though perhaps we have owners of Sixties Maseratis among our readers. I’ve found the Lucas PI system rather better than its troublesome reputation, but if there’s a weakness, in my experience it’s injector blockages. Uncle Joe’s fuel squirting device is sensitive to tiny specs of dirt, which lodge in the injectors and prevent their valves opening and closing. The result is a substantial reduction of power, or a misfire.
I’ve seen two such problems in the past couple of months. The first incident was on a Drive-it Day run with my local Nene Valley TR Register group, when heading to the Shuttleworth Collection. It’s an excellent day out at the Shuttleworth, near Bedford, with a remarkable collection of classic and vintage aircraft, plus a few cars and motorcycles.
Chris Johnston’s lovely TR6 dropped to five cylinders on the run. Arriving at Shuttleworth, Steve Denton – Triumph owner and Youtuber – jumped in to help, swapping the stricken injector for a spare he was carrying in his ’6. After bleeding the air from the replacement injector, Chris’s motor was immediately restored to perfect health.
The second incident involved my own TR6, while on my way to visit Alasdair Southall to collect a pair of his uprated Triumph rear hubs (more on these on p128 of this issue). Turning off the M6, the engine dropped to five or fiveand-a-half cylinders. With 70 miles to go, I tried a couple of quick fixes – but I must add that these don’t always work, and sometimes there’s no choice other than to clean the injector properly or even replace it. The first and easiest possible cure is to floor the accelerator and briefly pull out the choke. This makes the warm engine misfire even worse, but the increase in fuel flow can sometimes clear the injector. No such luck this time...
With the engine idling, it should be possible to feel a pulse in the injector feed lines. Five were thumping rhythmically, but No.4 injector had
no pulse, so I readied my fire extinguisher and removed the relevant injector keeper plate. Engine idling again, I pulled the injector from the throttle body, keeping it away from the hot exhaust. Sure enough, No.4 was dribbling, not producing the required cone of mist. I held it up high to see if there was any air that would bleed from the line, but again no improvement.
The final attempt was to pull the injector tip with my fingers – never pliers which can cause damage – to open its valve and dislodge any dirt, but the fuel continued to dribble erratically.
Not having a spare, I drove on with the stuttering misfire for 40 miles, and on reaching the M6, I fairly thrashed the TR down the slip road to join the motorway. Miraculously, it suddenly came back on all six as the injector cleared – and it remained fine all the way home!
I’ve since thoroughly cleaned No.4 injector and its metering unit non-return valve. Removing the injector from the feed pipe is simple enough; the pipe was disconnected at the metering unit end, then the valve could be unscrewed.
The valve, pipe and injector were blown through with compressed air before being refitted. The fuel line then needed bleeding, so the engine was started on five cylinders with No.4 injector held up high until fuel displaced all the air.
The reward was a fine cone of fuel mist, pulsing exactly as it should. Pushing the injector back into the throttle body, the engine immediately idled smoothly on all cylinders. A road test showed that my TR6 was back on song again.
If you have a Lucas Pi-equipped car, I hope someday, if your car is blighted by a blocked injector, one of these quick fixes may get your motor firing on all cylinders again.
■ practical.classics@bauermedia.co.uk