MU calibration

[piersmcg]

Knowledge about Metering Units seems to be kept very secret - hopefully we can bring some out here.

 

I was reading my workshop manual (hence the posts!!) on the operation of the MU. It states quite clearly not to:

a. Adjust the calibration screws

b. Adjust the "full load" screw

d. Adjust the "fuel cam" screws (why d. and not c. I have no idea - it's an American manual!)

 

Now that's a little bit like red rag to a bull, but I've read enough horror stories of the PI system, and as mine (touch wood) seems to be perfect I don't want to mess.

 

BUT, I'm interested in finding out ...

1. What do the calibration screws actually do?

2. What does the full load screw do?

 

I can only assume that they adjust the amount of fuel delivered to the injectors under different conditions, but I've seen "Metering Unit set up for fast road" - what does that mean?

 

More postcards ...  

[jean]

Piers, I have exellent diagrams and documentation of the MU (TR6PI Bentley Manual - Lucas training cards) I can scan them in and send them to you as attachment in JPEG, I will resize them to acceptable file. Further have a look at the following website, it will throw some light on the calibration

system of the MU.

http://www.kvaleberg.no/t_pi.html

Did you ever visit the VTR of America website ??

http://www.vtr.org

Lots of information about all subjects in the maintenance manual and many links.

If you have a Fast Internet Box also have a look at

http:www.buckeyetriumphs.org

Complete manuals can be downloaded  about TR gearbox/overdrives etc..

Regards  - Jean-

[Andy Moltu]

Full load screw - it sets the maximum amout of fuel per injection at full load (throttle fully open so that the inlet manifold pressure is at its least vaccum...) This is what the "choke" does in effect it allows more fuel in per injection.

Unless you have a substantally modified engine you shouldn't need to open this up. (For a 3/4 race cam & modded head this can be opened up to a gap of around 63 thou - the measurement being done with a feeler guage between the cam & roller found under the rectangular cover of the MU)

 

The other adjustment rings under the top cap of the MU adjust the fuel settings at different levels of inlet manifold depression - the partial vaccum sucking against the force of the springs under the rings.

Egil Kvaleberg gives a good illustration of how the MU works

 

Lucas Pi information

 

Why shouldn't you touch them? More to the point do you need to?

(1)Is your engine modded - then possibly you may need to increase the maximum fuel delivery and adjust the delivery curve. best done on a rolling road by someone who knows how to adjust the MU such as Jon Wood at Classic Racecraft.

(2) Has someone else mucked up the settings already?

(3) Have all the other tuning parameters been checked such as timing, throttle ajustment, vaccum pipe, seals, injectors and fuel pressure?

If you have checked these and these and the MU is out of warranty then by all means have a go but it's pretty hard to get it right without a rolling road or a calibration device - Egil goes into this on his web page.