RennBod

Hi...

I have been searching the forums, and cant find the information I am looking for.

I have a 1990 964 turbo, and have just fitted a Tial wastegate, so am looking to increase my mixture CO to somewhere around 2.5 to 3.0 as advised on these forums.

I have disconnected the lambda/02 sensor (I have even removed the sensor all together and fitted a pipe into the hole for my 4 gas analyzer so I can read the exhaust gasses before the cats mess with them.

I have even located the mixture control screw (3mm hex head in the top of the fuel metering head)...

I am even sure its the mixture screw that I am adjusting, as when I press down onto the allen key I can feel the screw springing back up and down.

The odd thing is... no matter how many times I turn it clockwise or anti clockwise, i cant get the mixture any richer or leaner than 0.8% CO.

I have even pressed down on the mixture screw, which on my other CIS injection cars in the past (924, 924turbo and 911SC) has effected the mixtures and often stalls the car.

I even went to the extent of increasing and decreasing the idle speed, just in case the mixture was being over ruled by some gadget in the system keeping a fixed mixture at idle speed.

So anyway... I am going nuts, please help!! I am all ready to go and set up the boost and have some fun, but this mixture screw seems to do nothing.

HELP!!


So does anyone have any idea whats going on??????

nathanUK '81 930 G50

Can you feel it engage in the slot when you push it down and turn ?

RennBod

I can yes... If a carefully lift the allen key, turn a fraction I can feel that its not located, but as I turn it some more it will fall into place and lock into the hex... then if I turn it I can feel its certainly turning the screw.. but I can wind the screw into infinity in either direction without any change to mixture or engine running.

The really odd thing... if I push down on the screw, I can feel it springing, just as you should with a cis mixture screw.. But again, on most cars, doing this will cause such a massive change in fueling, that it will often stall.. with this one, i can push it down a quarter of an inch without any change in the mixture displayed or even in idle speed or running smoothness.

I would say I have a duff fuel metering head... but I took the car out earlier for a run with the boost wound down to 0.75 bar of boost and it drove perfectly.

This is really confusing me.

HELP!!!

Staffan

Yeah, you need to press the key down and turn it, that's the way to do it.
Don't turn it more than a quarter of a turn, that's plenty.
When I press down the key my car begins to stall but goes back to normal when I release, so I have to do it fast.

jeff91C2T

It certianly sounds like you're doing the adjustment correctly. Your discription is right on...

Just a couple of thoughts...perhaps the screw is backed out too far. Have you tried turning it too the right (continually). This should run the screw in all the way and make you run rich. One potential (and bad) cause could be the screw is stripped out.

On my 91, as mentioned earlier a small adjustment really makes a big change. I've recently installed a wide band and can easily see a 1/2 point jump in AFR with a small turn of the adjustment screw.

RennBod

So if you carefully locate the screw head, so you know the allen key is located, you can turn it without it adjusting? but if you press down and turn it, it adjusts?

I do hope that is it! I was begining to think that either Porsche are really cunning and have a tamper proof cap, with a hex head in it and just spins, just ot mess people up... or I had a stripped screw!

Anyone else found that they have to press down and turn?

nathanUK '81 930 G50

Yes, you have to push down to engage in the slot and then turn. Then release pressure.

Have you just been turning it without it being engaged in the slot ?

jeff91C2T

Correct...you need to push it down against the spring tension until it engages in the hex head. Then holding this tension you turn the allen screw. Remember, small adjustments (like a 1/4 turn) make for big moves on air fuel.

On a side note, I recently installed a wide band AF gauge. After finally getting this thing installed, I'm kicking myself for not doing it sooner. I can't imagine doing this work with out it. Disconecting your 02 plug WILL make your fuel mileage terrible. In my case...with it installed I'm geting 23 mpg on the highway. With it unplugged I was barely getting 15. The throttle response is also improved with the 02 sensor plugged in. What you really want is more fuel on boost. What I did was tweak the WUR. Although now I'm getting too much fuel so I need to get back in and reset it.

RennBod

What I have done so far... working with care like a bomb disposal engineer... carefully placed the allen key down onto the adjuster, then turned it very carefully until it drops into the hex head.. and then tried turning it each way without effect. But I am pretty sure its been located into the hex shaped hole from feel.

So just to check, as well as it being into the hex head.. I also have to apply downward pressure and turn, rather than just turn?

I will give it a go tomorow afternoon.. but before I get my hopes up too high.. just to confirm.. it needs downward pressure as well as being sunk into the hex headed hole of the adjuster itself?

lwilkins

Yes, the downward pressure is what engages the screw. When you apply downward pressure and feel the adjustment screw engage, then you are changing the mixture by turning CW (richer) or CCW (lean). Not before.

Good luck.

nathanUK '81 930 G50

Yep. You will feel the hex head screw drop/locate into the screw below.

RennBod

Thanks to you guys, I now have a 964 turbo with the mixtures set to 3.0% CO!!

I first took the car out with about 11psi of boost just to check everything was good.. and then slowley increased the boost until I was at 13psi (just to be safe) with BP ultimate fuel, tomorow I will maybe fill up with some optimax and perhaps wind her up to 14 psi.

So the last question is... should I leave it running open loop without the lambda, or once the CO is set, am I supposed to go closed loop with the lambda sensor connected??

So far I am running open loop without the lambda sensor connected and it all feels great.

But its now SERIOUSLY quicker, I would recommend a 9XX Tial wastegate and BOV to anyone!

I also need to thank you all again for helping make this all posibile without me having to call my local specialist for advice! (I am stuborn like a mule!)

nathanUK '81 930 G50

On a 930 you would leave the sensor disconnected, I guess the 965 is the same.

911addict

Did you leave the lamda disconnected in the end?

Will your set up pass the MOT?

nathanUK '81 930 G50

Not sure who you are asking Mark, if it is me the euro row zzz 930's do not have a lambda, but the USA cars do. My car is an original UK car, well it was original...