The V8 Owners Forum -

Guys im looking for some help, ive recently had a rolling road set up on the megasquirt, the tuner had issues removing a ramp in the map around the 1600-1800 rev range, this coincides with the idle issues ive been having lately in this area. The car intermittently holds the idle in this rev range which most of the time can be cure by a blip of the throttle.

Im using a vitesse twin plenum which im guessing is the the cause, ive removed the plenum and under close inspection both the throttle mechanism and butterflies appear to be working as they should?

i cant find any air leaks or play from the pedal to the linkage so im out of ideas.

My options as i see it are either persevering with the twin plenum but cutting of the throttle bodies and finding a suitable donor, possably a pair of v6 omega throttles or going back to my old 72mm set up which will mean changing everything from the inlet manifold upwards

any thoughts to the cause

mooose wrote: this coincides with the idle issues ive been having lately in this area. The car intermittently holds the idle in this rev range which most of the time can be cure by a blip of the throttle.

Sound like idle speed hang-up, common affliction of the twin plenum.

see the whole nine yards and setup solutions here

http://www.vintagemodelairplane.com/pag ... ing01.html

as a matter of concern, your non original jury rigged throttle return spring looks to be at a very inefficient angle.

The quadrant has to be pulled directly downwards with considerable force to overcome any friction problems elsewhere in the mechanism.

This is how it should be



Also, have you removed stuff from the plenum heater block below the tunnels and left an air leak thereabouts where the bolt holes are tapped into the tunnels.

Regarding air leaks into the inlet tract, try testing for them with some plusgas.

The spring on the top of the quadrant is just an additional to stiffen the pedal feel a little, im running one at the bottom also.
I wasn't expecting this set up to be so temperamental.

You mention an additional spring connected to the link between the butterflies do you have any footage of this in your library?

To my way of thinking that extra spring is adding unnatural friction to the throttle assy and would be undesirable regarding throttle action. To gain better pedal feel, it might pay you to deal with that issue at the pedal shaft or lever itself, so strain on the throttle assy is not affected.

My TP was similarly temperamental when I first acquired the car in 1993, but after I got copies of the literature and came to grips with the innards and their friction and lateral disc alignment issues in 1995, the Throttle assy has not been a problem since then, 16 years trouble free.

Scrupulous internal cleanliness and regular lube, are key.

The main problem is distortion of the rear spindle caused by internal friction and over-tensioned centre springs.

Lack of cleanliness also plays its part, as does the lateral misalignment of the discs in their tunnels - all mentioned in the pdf.

If you add tension to the centre as shown in these images that I collected over the years, then expect more problems than solutions. The rear spindle is simple not up to it.





others have plumped for centre pull as seen in the next image.



For the record I have no knowledge of whether it is good or bad, but at least the rear spindle is not compromised.

Sorry about image quality but they were cropped from images found on the web - but you get the idea.

Excellent, thanks for the help

Centre plumpeb throttle cable is used on J.E. Engineering cast version of TP :
http://community.webshots.com/photo/ful ... 9900tuSMlP

Wotland, i tried J E unfortunately he doesn't stock them anymore, he guessed around £900 to make a new one
Thanks for the picture that's the clearest picture ive seen of a centre pull.

Ramon i tried adding a spring to the centre spindle today and bingo no hang up, it sat at 800 rpm with no drama- ill play around with this idea and see what happens.

mooose wrote:Ramon i tried adding a spring to the centre spindle today and bingo no hang up, it sat at 800 rpm with no drama

And thereby - one is on the horns of a dilemna.

Now the input force to the rear spindle has to be increased to overcome the extra tension added to the centre junction.

As you will know, the rear spindle is a delicate brass item not built for strength.

Brass has a poor resistance to bending and rotational damage, and eventually, under the increased stress it will bend and break.

Now one is faced with either mending it or reproducing it.

Moolah - mucho!!!!

On the other hand one might review again and again the original Rover advises reproduced in the prior mentioned article and see if one can set the system up proper-like.

To whichever god thee pray, start practising!!!

Yesterday night I sent an MP to r2d2hp member to see if it is always possible to have copies of TP shafts in stainless :
http://www.v8forum.co.uk/forum/viewtopi ... c&start=15

Will be stronged than brass and avoid problem of poor resistance to bending and rotational damage.