Team Green 16V

[mikinoz]

So you auto electricians, I have a plan that I want to run past you.

The fuelling in Digi2 is controlled by the coolant temperature sensor sending a varied resistance figure to the ECU. I am having problems when the car is cold with over fuelling and wondered if I could either set up a switched bypass of the CTS with a variable resistor so I can adjust the fuelling accordingly. Or another alternative is to have a 3 stage rocker switch that has 3 circuits - signal from the CTS, a resistance value that is early in the warm up phase and another a bit later.

Thoughts?

[Jarred]

I like what you're thinking.,

(not that I'm an auto elec)
I figure you'd want to alter the signal that the ECU reads from the CTS. I guess you'd want the switch going off to the ECU feed, and then some how have a piggy back of the CTS signal, as well as the original CTS signal feeding into the switch. (which I think's pretty much what you've said anyways).

Something that you may want to look at is a variable resistance potentiometer. (I'm pretty sure that's the name) Basically it's a resistor, that has a base resistance, and also a variable resistance. So you could have it set at Xohm and then get a round knob somewhere in the cabin to adjust the resistance as the car warms up. Sort of a "choke" if you know what I mean. And then once it warms up flick the switch and have the ECU read straight CTS.

I think it's worth a shot, (if you're game!) I've never fiddled with digi though. My solution to fixing digi was to get rid of it, and replace it with OBD1. (And the VR6 was to compensate for lack of power )

Hope that made some sense, and helps!

[mikinoz]

I am willing to give anything a go, I just need to learn enough so I don't fry my ECU!

Paging Julian Edgar!

[Jace]

Your constant 'tuning' makes me SO glad that I have a good old carby feeding my engine.

I would've rage quit by now!

[Preen59]

Heh, and people say to me "Won't those Webers be hard tune tune?"

One question i think is worth asking is why would you need to do all this? If it is essentially standard i would assume adjusting the already available variable inputs to the ECU should be enough to get the tune right? If not, something else is wrong.

Hope you get it sorted, Mik.

[mikinoz]

Yeah I don't know really. I am not sure what the reason is but when she is cold it is a bit rich to the point where it will start to soot up and sometimes stall, so if I can dial in the cold temp resistances then that could help.

I think there are many reasons for the car not running properly, heaps of different bits, age of some components, and the biggest factor is me probably tinkering too much! But I love it.

[Valver.]

Yeah I don't know really. I am not sure what the reason is but when she is cold it is a bit rich to the point where it will start to soot up and sometimes stall, so if I can dial in the cold temp resistances then that could help.

I think there are many reasons for the car not running properly, heaps of different bits, age of some components, and the biggest factor is me probably tinkering too much! But I love it.

Have you checked the plugs yet? What is the idle like when cold - what RPM and is it stable? And how long does it take to run 'properly'?

Also, how old are the injectors?

Given your setup, it's probably directly related to fuel pressure, though. The chip you have may be tuned for 3.5 Bar when running normally, but chances are the cold start map hasn't been adjusted for the higher line pressure (aftermarket chips very rarely look at this sort of thing as it's far more difficult to get a precise result with a bench tune)... So, when the ECU is richening up the mixture for cold start - based on a 3Bar FPR - it's now over-fuelling heavily.

If this is the case and it is running very rich, there isn't much you can do, except avoid starting the car cold and leaving it stationary to warm up (no one should do this anyway). You should also drive away and get it under a bit of load so the plugs don't foul up.

Modifying the signal from the CTS is definitely not a good idea, as this will significantly affect the map off idle. This is always going to be an issue with Digi-swapped 16vs: the cold start map and fuelling is much the same as an 8v, but the conditions under high RPM and peak load require a fair bit more fuel. Hence you cross one off by raising line pressure so the injectors do their job higher in the range, but you then forfeit cold start performance and the life of your plugs etc.

As mentioned on Vortex, pull the plugs and post a pic