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No Pulse on fuel line No. 2

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Recently , I just sent the whole lot-MU, injectors and injector lines to an expert for refurbishment and recalibration. Cost a bit but having this work done totally transformed the car.


Before it was hard to start, unreliable , used far too much fuel and left my clothing unwearable due to smelling of petrol. After the PI components were rebuilt/recalibrated my TR again became the car I wanted in 1969.

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If one puts abig filter verticly mounted befoer it enters the MU

wid fuel int top, an outlet at bottom

then all this ..air.. that gets into folks injectors will stop happening,


yer PI is on a v similar method of working as an olde type deisel,system,

{ mechanical pressure }

and they wont run wid the slightest amount of air in system


injectors cant open cos of the air being compressed

thats why deisel injectors needed bled whenst a new filter was fitted.

its basicly the same for yer PI set up.


what hardship is there in fitting another filter to solve all PI TRs quirky problemos,!!!



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Hi Marcus,

Good to see you posting on here!

Your idea makes me wonder:

is your thought that any air will stay in the filter during running and return to tank when the engine is stopped?

Because I cannot see air going up against the flow of petrol as long as the pump is running, given the flow rate (velocity).

The old CAV filter had a venting connection for this, as we know.

But if you drive with almost empty tank, and the pump starts screaming during fast cornering I guess some air is sucked in too. Where does this air go?

The engine is not much affected by that.



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I don't have the original fuel tank and pumping system for my Pi, at all. This dates from when I ran the Vitesse estate, that had a wide, flat fuel tank, under the rear load area. The tank was baffled, a bit, but Triumph had recognised the surge problem by building-in a small fuel pot in the bottom of the tank. But it wasn't sufficient for Pi, and even with a fullish tank, air would be entrained and the engine would stutter and misfire on corner exit.


So, I installed a proper 1L swirlpot, and a Facet Red Top to keep it filled. This does the job well. See pic of the system installled in the esate's successor, SofS.




But I notice a symptom of the system indicates that fuel drains out it when standing. It's wired with separate switches to the Facet and Bosch fuel pumps, and the 'correct' starting sequence is to turn on the Facet, to fill the swirl pot, usually in about five seconds when the pump note changes, and then the Bosch pump. Thus just whines away, no note chnage, but if I wait twenty seconds, the engine will fire instantly whereas it needs at least twenty of starter churning before it will fire if I try right away.


Thus, I suspect that on standing, the swirl pot empties back into the main tank. It is above it, to give the Bosch a small head of pressure on that intake, so this is a desirable design fault! The fuel probably goes backwards through the Facet, which is known to be possible if it's not running. Air will return to the swirl backwards through the normal return line. Not much to done about that, if I want to keep the pot above the Bosch.


But the Bosch needs time to fill up the PI system before fuel reaches the injectors reliably. This can only be air entering the injectors as fuel drain back towards the Bosch and tank, probably by the return line from the Metering Unit. But clearly in this situation there is no need for tapping or needle pulling. The fuel pressure and the M/u expel the air automatically.


This doesn't answer the OP, who has a single malfunctioning injector, or anyone installing a Pi system, when that will be full of air, and elaborate bleeding procedures may be required. But it does illustrate the problem that Pi has with air in the system, that a carburettor with a float chamber will not, and offers a solution to anyone with a slow starting but otherwise healthy Pi. Run the pump for a few seconds, twenty or so, before using the starter!



Edited by john.r.davies
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  • 2 weeks later...

Dear All

The car is great once more - thank you for all of your posts. I'm far from expert but I did think that the metering unit would push fuel to the injector, regardless! It turns out that the injector does somehow help in the delivery of fuel! I bought a new injector and she runs good again. I have one faulty injector (refurbed in 2016 apparently) which I will get to Mr K _Raven_Smith in due course for a proper job!

thanks once again, the forum proves a valuable resource!



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This is a good topic, and one I've been researching as my new to me TR6,has started being a bit rough at lower revs.


I checked each injector line and one isn't pulsing, so my next job is to try and bleed that injector,thanks to all for the comment's

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With the car idling, I took out the injector and sure enough nothing coming out. As there was no visible nipple I gently tapped it while holding it up and eventually fuel started to spit out, I put it back and the engine ran better, took out the adjacent one to see what the flow should look like and it had a nice conical spray,I pulled the non working one back out and it was also making the correct pattern of flow and the nipple was back out too

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I've had the spray catch fire. No visible source of ignition other than the idling hot exhaust manifold or a possible quiet backfire through an inlet valve. I quickly put it out and the only damage was to the no 5 nylon injector line.


I now test my spray patterns with all of the plugs removed and safely earthed on the far side of the engine- the starter spins the engine surprisingly quickly when it's in in this condition.

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Good point on doing it safely. I think the o ring can't be any good as the nozzle part inside can slide out with no effort, also no clip is fitted near the pin.

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