Chim guys are good guys (and Ginetta owners are OK too)

[griffter]

In response to a call for bits so I could implement closed loop fuelling using the standard 14CUX on my precat Griffith, Pupp and 900T-R both offered me clean, straight, used components at very fair prices.

I'd like to thank them both - they're both active and well known here - for their assistance, and particularly their trust (neither wanted cleared payment before despatch). 900T-R was very patient while I fannied around trying to send money abroad.

These guys are great PHers and have my utmost thanks.

I should also thank blitzracing who assured me it was possible and worthwhile. The car starts and runs, with lambda feedback at the ECU. I have yet to drive it...

Now all I need is a Chimaera body shell

[blitzracing]

Mines switchable on the dash, and the only real difference is a slightly snatchy low speed response (very slight) and fractionly poorer "instant" pick up on the cat map. But it now does 26mpg, compared to the 18 it did on the a non cat map (This was remapped for maximum power when I first got the power by JE, but too much fuel was going in). On the 3.9 TVR catalyst chip I have installed, the non cat map appears to have been altered as well over the Range Rover map as it runs fairly rich throught out the rev range, and gives you instant "bang", but Ive not checked the MPG on this one.

Mark.

[cloggy]

You can always trust a Dutchman in a Chimaera.

[griffter]

Mark, thanks. It's because - following your warnings - that I don't know whether the non-cat map on the cat 4.3 chip I got is really for a 4.3 or just the unaltered 3.9 one that I haven't done this. I have a perfectly good 4.3 non-cat TVR ecu, so it'd be interesting to compare that map with the non-cat map on the cat map chip.
I intend to have a play on the rollers at the Griff Growl where I may learn more.

As a thought, would the lambda reading be of any use when using a non-cat map? To see if it was horrendously rich/weak? (ie if it's weak it might be the 3.9 map...).

[blitzracing]

Yes monitoring the lambda reading is fine. You are looking for over .7-.8 volts all the time the throttle is open,(top end of the lamda probes response) but it can go even higher under hard acceleration. The voltage drops to zero on the overun. Dont assume that it will run lean on a 3.9 map, its more a matter that the airflow scaling is wrong as the engine draws more air at any given RPM / throttle opening, but I dont know the effect on the fueling. Basically if it does run a bit lean, you could add a couple of psi to the fuel pressure to richen it, but this will also affect the amount of correction the ECU has to apply in catalyst mode. Suck it and see as they say, as if it drives OK in closed loop (no bad snatching), and you can maintain .7-.8 volts above 3400 rpm, then its working just fine. A rolling road session might liberate a few extra horspower, but at least you wont damage the engine by running lean if the lambda voltages are high enough.

Mark