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TVR Tasmin, Injectors & Sensor Plate

Since I’m still waiting on the pressure testing kit to arrive, I got impatient and did some more testing.

I wanted to remove the injectors and see if any of them were leaking and what the spray pattern is.

The intake plenum needs to come off. before this can be removed though, the coolant block on the front needs to be unbolted. Unbolting this saves disconnecting the coolant hoses.

All the other hoses got removed, and the 7th injector was removed from the plenum. The plenum is held down with eight long bolts that go into the inlet manifold. Just a note, these bolts aren’t sealed off from the inside of the plenum, so will need sealant on them upon reassembly.

With everything disconnected and unbolted, the plenum just lifts off

Removing the injectors is fairly simple. The clamp on the pipes (which goes above, below and between the pipes), as visible in the lower Lh corner of the above photo, has to be removed to allow enough slack in the pipes, but otherwise its a case of removing the single bolt per injector, and then pulling it free from the manifold. They are meant to be sealed in, but mine came out suspiciously easily.

The rubber collar is weird. I presume/hope there is a normal O-Ring under it, as that is what all the parts manuals say it should have, and there seems to be no part for that rubber collar. I’ll have to carefully remove and reuse the collar.

Edit: Further to this, some more investigation has revealed why the parts guide only shows standard O-Rings and not a rubber bush… It’s not a rubber bush at all, but a plastic sleeve sitting on the normal injector O-Ring. Mine are just very compressed, so it looks like its part of the plastic sleeve.

New O-Rings were already en route, so that’s a win.

All the injectors look pretty rough, but I guess thats what 39 years of sitting in the intake looks like. The ends all look clean enough, with no obvious buildup. I did note that cylinder 6 was very wet upon removal, and a couple of others were damp. The engine has been off and cold for about a week, with no pressure in the lines.

Testing them isnt rocket surgery, just pop them all into jars, fire up the pump and see if they produce any fuel (which they all did to some degree), which indicates either the fuel plunger is letting excess fuel through, or the injectors are leaking. Further investigations show its probably a 50:50 on leaking or adjustment causing it.

With the pump running, lift the sensor plate in the AFM to its stop and observe the flow and pattern from the injectors. All mine seem to flow roughly the same, but the flow pattern out of all of them appeared to be rubbish, with minimal misting and heading off in all directions. That’s good, it confirms that buying a whole set of replacement injectors was the right decision!

One other thing that has been bugging me, was the sensor plate in the AFM. This is meant to be a finely calibrated instrument, but I think someone has mucked with mine before.

You can see in the above photo that it looks like the sensor plate (the disk in the middle of the cone) is sitting high with a gap under it. Well, it is.

From the below diagram, you can see the sensor plate sits at the bottom of a cone. As air comes in from the filter at the bottom, it comes in under the plate and a combination of that air coming in, and engine vacuum in the intake, lifts the plate to allow air into the intake. Lifting the plate also lifts the fuel plunger, increasing fuel flow.

The plate should be set to a specific height, which is more or less with the highest point of the plate flush with the lip at the bottom of the cone (before where it tapers outwards again, under the plate).

Mine was clearly sitting a lot higher than that. Not to mention the other issue…

The plate was off-centre. I even thought the plate was too big to fit through the opening, but it was just because it was off-centre.

I carefully backed off the center bolt, and centered the plate (this should be done with feeler gauges, but I did it by eye this time)

Now it fits through the opening

It was still sitting too high though

There is a spring under the plate that sets the height. The manual says to adjust it with pliers, but I’m damned if I can bend the thing.

I’ll keep at it and see if I can tweak it.

The other thing I noticed is that you can hear and feel the plunger moving when you manipulate the sensor plate. I’m not sure how normal it is, but my plunger seems very slow to return to the zero position. It doesn’t seem to bind and it moves smoothly, it’s just slow to return. I’ll be removing and cleaning this in the future anyway.

So that’s where I’m at. I’m waiting for a set of new injectors to arrive, and I need to remove the fuel distributor and WUR to clean them out. I’m planning on setting everything up from zero since I have no idea what’s been done to this by previous bodgers.

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Ron Wheeldon
Ron Wheeldon
3 years ago

This is really excellent writing and very informative. I am just tacking my 1981 TVR 280i Tasmin after neglecting it for years and was very keen to understand the FI system. This is wonderful reading for me, because I feel like I now actually know something about it.