What signals the injectors to fire?

[Andy Moltu]

To centre the butterflies, loosen the screws that hold them into the spindles slightly. Then open the butterflies and let them snap shut a couple of times and then nip them up.

Unless you have a very early car with no air bleed screw, the butterflies should be closed at tickover. (The fag paper trick is for the early cars where you had to set the tickover by having the butterflies slightly open). The butterflies should open synchronously, which is near impossible with a worn CR linkage.

Bleeding the injectors is best achieved with a fully charged battery. (If you need to as generally they will self bleed). Crank over and pull the injectors out one by one, carefully to avoid spraying fuel carelessly. If spraying put back and move to next one. If not spaying, tap it then gently tweak the nipple open if that doesn't work (awaiting the cries) and release. Ideally have the injector pointing up so air rises to the end.

If after that one or more still does do the trick, remove and blow out injector with an airline to shift debris and free off if simply stuck, replace and try again.

Don't underestimate how badly a mal adjusted set of butterflies can make a car run. Easy to think you have a misfire.

[john.r.davies]

As I'm on my hols, with only a mobile to post on, I cant show a pic of the bleeding trough I made.   A foot and a half long, a narrow trough with a flange above that has holes for the injectors to sit in.  I can clip it conveniently above the engine, and easily see which are firing, not as easy  in a tin can.

Andy, thank you for the point about later systems with the air bleed screw.    With injectors that have the 'needle' out of the nozzle, won't pulling on that clear debris better than an air line?

John

[Andy Moltu]

Surprisingly the debris doesn’t often “float “ of the injector which is where an airline (or foot pump with a cut down air bed adaptor to make a good seal) comes into its own. 

Once you get the car started, that’s half the battle done, the increased supply voltage and frequency of pulsation rapidly self bleeds the remaining injectors most of the time. 

[PodOne]

Andy/John

Just to add.

I found the nut on the end of my compressor air line (BSP?) was the right thread to screw the injector into which gave an air tight seal.

Out of interest my push in injectors have no pin (pintle) tip just a round ball. How do you bleed them on the car given you cant pull the pin?

Which are the better design and preferable or are the two designs comparable?

Andy

[JohnC]

On 6/25/2023 at 9:57 PM, SlickV8 said:

Hi John. I thought the aim of bleeding the injectors was to string them up & run fuel pump until they are all dripping??

To clarify: If the engine is not running (but the fuel pump is) there should be zero fuel coming out of the injectors. Fuel should only flow when the shuttle moves back & forth which can only happen with the engine running. Well, I suppose it could theoretically move once if the engine stopped at exactly the point it was about to, but not again. If there is flow under these conditions, even a tiny dribble, the MU needs to be looked at. There must be something in it allowing fuel past where it shouldn't. One of the big O rings, or even the shuttle.

If the engine is running then all injectors should spray. A dribble means something is wrong (covered by others in this thread).

Glad to see you've got it running better. As Andy says, the goal should be to control the idle with the air valve screw. You should be able to stop the car by screwing it all the way in. That doesn't mean the butterflies must slam shut, just that they let through precious little air. Again as Andy says, the butterflies must open synchronously for the pickup to be hesitation free. I balance mine at something between 1500 and 2000rpm with the air valve closed (using the throttle stop screw to hold the revs). That seems to work well, but it certainly isn't the only way. My logic is that 2000rpm with no load is a nearly closed throttle, which is where we most need everything to be balanced.

Have fun with it

John

[Roadrunner Paul]

I must echo Andy’s post about getting the throttle butterflies correctly adjusted. I have a TR5 with the single air bleed screw.

My TR5 had a well known specialist’s underslung throttle linkage fitted together with Bosch conversion, modern PRV, overhauled injectors and metering unit. It was jerky below 1800 rpm in fourth gear and never seemed happy at low revs. Local TR Register Devon guru Dennis Hobbs checked out the fuel injection system for me - fuel pressure, injector spray pattern, etc. We went for a test drive - still a bit jerky - Dennis was not satisfied so removed the plenum again. The culprit - no 6 cylinder butterfly was partially open at tickover. The throttle linkage has fine adjustment screws fitted and it needed less than 1/4 turn to correct the fault. 
 

To say that the car was transformed is an understatement! It will now happily pull from 1200rpm in fourth gear with two occupants and for those of you who know East Devon it will traverse Newton Poppleford in overdrive third on the A 3052 - no mean feat indeed!

If you have an air bleed screw setup, check that there is no air being drawn through the butterflies at idle. In my case it was visually obvious that the butterfly was open but you could always use a bit of tube (eg 1/2 inch water tubing) to listen for any air movement through each butterfly.

Happy motoring!

Paul

[SlickV8]

Typically the day job got in the way this week but yesterday, after a week untouched, I pulled out choke, span the ignition 4 times in approx 5 second bursts and on the 5th turn it fired up and settled straight on a fast idle on all 6.  Hooray!

I’ve sent the original injectors off for exchange but the admittedly manky old ones I had spare seem to be working well for now. 

Re setting the idle, I confess I had been trying to get it set with the Fast idle screw fully in, it’s possibly half a turn out now and the car will stall if I screw it all the way in as I now understand is correct….another lesson learned

thanks again all, invaluable. I’m now fitting the seats while waiting for a brake bleeder to arrive and hopefully out for a proper first drive later today. 

 

[Mk2 Chopper]

Good result!

Gareth