Update time. Vivadom daily driving has been pretty damn good. Especially when 2 months ago I finally got around to changing the voltage settings for the wideband O2 sensor on the ECU so that the ECU would get the same reading as what the Innovate gauge shows. It’s a common setting fault and took all of 5 mins to get them to read almost the same. What does this mean though? Well for ages the ECU and hence the tuning program, Tunerstudio, have been receiving a ‘leaner’ voltage than what the engine was really at. This meant that in tuning the final outcome was always a bit too rich. When the ECU was in closed loop ego control it would take my preferred AFR table settings and adjust to what it thought was correct.. which was not.
With the ECU now getting the proper signal we re-tuned the car on the way back from Blenheim to Motueka. It was too rich everywhere and after not long was leaned right back. Driveability remained the same, but tail pipe smells improved J I have not gone super lean, sticking to around 15~15.5 on cruise. We filled the tank back up in Motueka and the cars economy had improved returning 32 mpg (8.8l/100km). There is still room to improve but happy with that.
So this was all good and everything was fine and dandy for the last month or two. Then the other day while leaving town I started to hear a teeny whistle sound. I just put it down to the throttle body making the sound because sometimes it does just this. The other thing I thought it might be was the idle control valve. I didn’t look into it any further. However, over the next few drives I noticed it was hunting a little at really light throttle openings, like slowly accelerating away from standstill. Hmmmm?...
Then that whistle again, this time when I got home one evening. I popped the bonnet and listened around. I couldn’t pinpoint it but when I ran my fingers around the back underside of the plenum box where one of the runners joins I heard the note change. An air leak. Bugger. I looked with a torch and could just make out a little crack on one of the welds I had machined down…hmmmm. Bug-ger!
Oh well.. I was planning on doing a modification to the throttle body pulley so why not sort it out now. I drove the car into the Viva hospital and started surgery.
It didn’t take long to pop the bonnet off, unplug all the bits needed and start removing the inlet manifold. The trickiest bit was the return fuel line which was stuck to the pipe and hard to get too. One hour after having parked the car in the surgery and picking up the scalpels I had the manifold on the bench.
I worked out pretty quickly why the manifold had cracked where it had. To explain how we need to pop into the police box and go back in time….
Maybe not that far though. Lets try again…
Nup.. still too far. This time…
Errrgggg. Again…
Oh dear lordy..one more time…
Ahh… that’s better! Righto..now remember this original plenum chamber? Made from some bent up 2.5mm alloy sheet. It had buckled diagonally when welded and I had then set up the runner heights to suit when I tacked them in place. I had to try and straighten it so it sealed correctly (using our house as a press)..
It all worked out OK at the time because it flexed enough to seal when bolted down to the runner flanges.
However a few years later I had that backfire and blew the lid off. I then fabricated a new plenum from 5mm alloy sheet and its was nice and straight..
It did not flex. This is how I think the crack happened.
I decided I was not going to try to weld up this little crack because I knew the heat would warp the runner flange and nothing will seal. So I bought some posh looking South African epoxy putty, a bit like minute mend or quicksteel.
It requires a lot more mixing than the others but sticks really well and smoothed off nicely. Kevin kept guard while it set.
While the inlet was off I did some measuring and worked out the dimensions for a new offset/eccentric throttle body pulley. Then I machined down a lump of alloy bar and ended up with a new pulley.
I got to use our new mill with a 2mm slot drill ( I could have used a hacksaw and file but this was more fun..)
The new pulley effectively gears down the cable pull at the start of the throttle pedal travel and speeds up at the end making for a much easier off idle transition. You can see the difference between old and new here..
No more kangarooing down the road for people not used to this engine with its lightweight flywheel etc.
I refitted the inlet manifold, plugged everything in and tried it out. WAY BETTER!!! Went for a drive and its so much easier to ease the throttle on out of corners or from standstill. Much more user friendly and I now wish I’d done this mod ages ago!
Posted: Sun Dec 27, 2015 10:45 am
