Fuel Enrichment and A/F ratio . . . Again (sorry!)

S

S2_ITBVW

New member
Hey, folks! We continue to make progress with the Jetta. The next time we go out we will have 13" wheels with the locked diff tranny. The last time out we were competitive, so we really feel like we are going to have "something" for folks one of these days. Things are certainly getting "fun."

As readers of this forum know, we have bypassed the knock box/O2 sensor so that we control the A/F ratio. We are also using the Autotech fuel module to enrich the fuel at WOT. This all seems to be working fine. We set the A/F mixture using the 3mm adjustment by the fuel distributor. We monitor the A/F mixture with a nice digital wideband sensor. But, it's not working perfectly. Here is how it goes . . .

During testing or qualifying we set the A/F ratio at idle in the paddock/pits. We usually set it at about 11.3/1. Then we watch the A/F ratio on the track. If we find the A/F ratio is where we want it at WOT (about 12.5/1) then we are happy and leave it alone. If not, we continue to adjust the A/F mixture with the 3mm adjustment in the pits until we have what we want on the track. The problem is, over the course of the weekend as temperature and humidity change, the A/F ratio changes. So, we can have things exactly where we want them during qualifying in the morning, then go out in the heat of the afternoon and everything is out of whack again. And, to complicate things, the starting point varies depending on the conditions. We can't always start at 11.3 because sometimes you end up where you want at WOT, sometimes you don't. I should mention that the variance is what one would likely expect as conditions change, so we do think that everything is working fine. We just want to have this stuff REALLY under control.

So, we know that some of you control your A/F mixture from inside the car with a potentiometer. This seems different to us than enrichening the fuel at WOT.

The schematics that we find seem to be for fuel enrichment, not for controlling the A/F ratio.

So, is enrichment different than controlling the A/F ratio?

If so, how do you control the A/F with a potentiometer from within the car?

Is there a schematic or some instructions for how to set this up?

As always, thanks!!
 
Fuel enrichment is controlling the AF ratio. Different words for the same thing. It is just a more direct route to get there, that does not wander as much as the AutoTech stuff - based on experiences like yours that I have heard.
 
S2_ITBVW said:
Is there a schematic or some instructions for how to set this up?

As always, thanks!!
Click to expand...

Start with this linky:
http://forums.vwvortex.com/showthread.php?3267302
wclark really knows his stuff so if you do further searching pay particular attention to his comments.

Personally, I've found adjusting the 3mm fuel enrichment screw to be a bad idea. Adjust it to near stock setting and leave it. It's an idle enrichment adjustment, not a WOT enrichment adjustment. It has a big influence on how the engine runs at idle and a very small influence on WOT. Anotherwards, requires a lot of adjustment to influence WOT fueling which will make it run shitty at idle. Which isn't really a concern for a "race" car but if said adjustments cause the engine to want to stall when revs drop to near idle then it's a big annoyance. There are other better ways to control WOT fueling, the wclark circuit being probably the best one unless you figure out how to do it internal to the ECU. ;)
 
I set my system to flow about 66gr of fuel per 30sec @ WOT ,per injector.
Then I make it idle. It idles like crap but makes good power, so i leave it.
I adjust the Mixture at the DPR setting or the 3mm screw and control pressure, CIS or CIS E.
The lower the control pressure, the more air passes.
My goal is to have enough fuel and the least restriction on the pancake. Read the plugs, make small adjustments.
If you see a temp spike on a long pull, you have too little fuel and/or too much timing.
Setting the mixture in the AM of a hot day is a safe way. As it gets hotter , it needs a little less fuel but the temps will also go up , so you will not loose very much power , just will darken the plugs a bit.
Never set the mixture on the Dyno with out adding a 1/8 turn rich,unless you like to buy pistons.
There is no money , so keep it fat and happy. IMHO. MM
 
We are going to ditch the Autotech unit and build the wclark unit. I'll keep you posted . . .

I had looked on Vortex, but I'm not sure I saw that exact thread.

Thanks, folks!

Dave
 
I agree that Walter has the most complete solution for fuel enrichment, however I went with simple and less likely to fail (and cheaper). The CTS lead from the ecu goes through a potentiometer to ground. I tell the engine how cold the coolant is, and it adds fuel based on it's map. I run a normally closed switch/relay in parallel with the potentiometer so that the ecu does not give it extra fuel unless I am near wide open throttle. When the WOT switch trips, it opens the relay.

The only issue I ever had was a relay that "chattered" at high rpm, resulting in not the expected enrichment.

This is easy to monitor on the dyno and on the track to ensure that it is working properly. An ammeter connected in series with the differential pressure regulator tells you whether the ecu is asking for the amount of extra fuel you expect it to. For example, if on the dyno the motor gives the best performance at a 12.6 AFR, and at that resistance setting the DPR sees 24mA, then I just check the ammeter that is zip tied to the dash for 24mA whenever I head down a straight at WOT. If I ever don't see that I have a manual switch in the relay leg of the circuit so that I can make the system only go through the potentiometer - as a back up.

You could simplify even more and just run a mechanical normally closed switch triggered by throttle pedal or linkage.
 
I go through a lot of trouble to keep the ignition and the fuel just right.
I set the timing fixed, no vac, no movement. Same the fuel. 63=65gr per 30sec@WOT. No computer.
 
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