Hesitation/shunting help.

[Robertjp]

natben said:

...the throttle body's are balanced even at about 6, but I do get some backfire through throttle body 3 when I increase revs with the air box off. If the body's are drawing in air would they stay balanced at say 6 across all of them or would one show up wildly out?

...But can I do it without making things worse! I have removed the fuel rail before when I had it powder coated but this feels like a far bigger job....

Edited by natben on Monday 22 April 22:23

You can balance them adequately but if they are pulling in air from elsewhere the flow will never be correct. The fact you are getting combustion in the TB suggests its running lean - i.e. too much air, i.e. you have more air than you should be getting in. If no. 3 is pulling 6 from the inlet...then its likely that air will be coming in underneath the TB flange. It COULD be the butterfly spindle holes leaking but nowhere near as likely and i think that would make them difficult to balance.

What i am trying to babble on about is yes you can balance them and still have them pulling air elsewhere and the AFR be wrong...

Neat idea powder coating the fuel rail. I may do that myself...did you need to bung the fuel line or just let it drain off and them once reconnected spin her up until the fuel pushes through?

[PetrolHeadPete]

Agree Robert...

On a related issue...I think I've finally nailed my "fussy" low speed running for good ! (I would find it near impossible to apply small amounts of gas...touching the accl lightly (very) would actually make the revs drop slightly when it was running at its worst...so you'd tend to over compensate and go from idle to over 2K in one step)

I've been busy doing this...

1. Did away with all the balance arms and adjuster screws
2. Did away with one throttle pot (parallelled feed to ECU on the GND and O/P wires of the remaining pot)
3. Linked all throttle shafts via flexible shaft couplers (with extra torsion stiffeners)
4. Move the single throttle pot to the middle of the engine so its actuated directly by the cable arm
5. All butterflies independently adjustable by undoing the shaft coupling lock screws to let them rotate ...each butterfly stops against its own air adjuster screw down through the body wall at the front edge

What a difference ! Instant throttle, smooth idling and most importantly none of that crazy tendency to slightly lean-out cyl 2,3,4,5 when you start to press the accl just before the original pots would see any rotational movement. Now the single pot turns exactly as the butterflies move. So the ECU sets the right params for the actual throttle opening, not some vague "guess" due to mechanical slop and twist. And it seems to stay set with no drift!

BTW: This is only to do with low speed drivability. With foot down it will make zero difference!

[SergSC]

pics plz!

[PetrolHeadPete]

Here we go

These are the couplers and extra stiffeners to reduce torsional twist, and you can see the adjuster screws



These are close-ups of the pot in the middle. Dont like the bracket that locates the pot but it works for now...allows pot to have angular offset






Look, no pot !

[crypto]

Great job ! I wouldn't have the courage to drill holes for the adjuster screws
Good to know that throttle pots are linear ...
Would it really have been necessary to move the pot to the inside if there is almost no torsional twist now ?

[PetrolHeadPete]

There was a tiny bit when I tried with the pot outboard. The return spring in the pot causes enough twist in the system to mean the butterfly at #3 is open by perhaps 0.3mm before the one on #1 has moved. Anyone who's tuned their throttles will appreciate that 0.3mm is a massive amount to open the butterfly...it'll pop and backfire at idle due to overleaning.

So I moved the pot to the middle. Problem solved. The nice thing is the outer throttles will now, if anything, tend to rich-up a bit due to lag. A much nicer way around. BTW: the shafts across all 6 bodies dont *quite* line up due to tolerances etc so the couplers take out that offset...but...the stiffeners add back just the right amount of "lock" to ensure they all move together and yet stay quite free to turn.

I bought a 2nd set of bodies from ebay btw...didnt want to drill the "real" ones
They also got the ball-race treatment on the shafts of course.

I can still report the "usual" lumpiness at light throttle / load at between 2000 and 2500. Almost like a misfire. That's been there since I bought the car btw and despite all these mods and various engine tweaks, its still there. Now the low speed side is fixed i'll have a think on this other issue.

[natben]

paulvx220T said:

I have had the throttle bodies off a few times, once to fit the gaskets and they a do make a hell of a difference. No more backfiring in the throttle bodies. A tip is to remove all the throttle bodies as one while still attached to the fuel rail. It takes a bit of rocking back and fore to loosen them where they are located on the dowels but it’s relatively easy and on the occasions I have done it this way I have not disturbed the throttle settings when I have checked with the syncrometer.

Paul

Paul, what type of Hex/Allan key did you use to remove the throttle body's, I have plenty of standard size keys but none of the 6mm ones will allow me enough leverage to get the bolts out and getting to the bolts on throttle body six looks like an impossibility. Is there more room in a Tuscan between number six and the bulkhead. I would like to fit the gaskets my self as it would help my knowlage and understanding of the car and save a few quid after spending on road tax, tyres, 12k service and MOT in the last month.

I would ideally like to do as you did and remove them in one go while attached to the fuel rail.

George.

[paulvx220T]

George, i had a T handle allen key from which i removed the handle and then used my socket set with a 6mm socket, this will give you plenty of leverage or cut down a standard allen a grinding wheel is best for this has the allen key is hardened steel.Access was restricted on number 6 but i had no problem removing the last two bolts. Remember to disconnect the Throttle pots.

Paul