924Board.org

[samivaan]

I have a problem with my 924 (-77)
I felt that everything is not right, and installed a lambda sensor.

Car is adjusted now a little bit rich, but most of the areas work fine. If I start to drive with full throttle, everything is fine, mixture is all the time a little bit rich, like it should be.

Small rpms works fine.

But, there is a area, 2500-3500rpm, where I have a problem. If I drive in that area, and open the throttle, mixture goes lean. Very lean. If I keep throttle full open, mixture comes back to rich after 4000rpm.

What can be a problem, that k-jetronic can't give enough fuel between 2500-3500rpm, if I start to get speed from that area? If I just cruise without increasing speed in area 2500-3500rpm, then mixture is right all the time.

[Mike924]

I recommend taking the fuel distributor and air meter out and giving them a good clean. In particular make sure that the level arm is free to move thoughout its travel.

Be careful removing the fuel distributor; the metering valve is not held in with anything and is free to slide out by itself. Clean this very carefully; drop it or mark it in anyway and it's scrap!

You will need a new o-ring between the distributor and the air meter and, preferably a new gasket between the air meter and the plastic air box. These items are cheap and easily available (from VW dealers for example).
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[OutOfTheBox]

cracked hose or brittle hose around clamps.

only sucks air when engine vacum is greatest ?

I find that when the hoses get old, they become hard & brittle, even if they are not cracked they leak around where they are clamped, but only under high vacum/boost.

You could spend weeks, checking this one and that, or you could rig up an air compressor, and perform a leakdown test, and know within minutes.

[Smoothie]

I see pretty much the same thing with a narrow band sensor and gauge - normal mix at idle, often reads lean during part throttle cruise, then extra rich at full throttle accelleration. My car runs fine, so I wouldn't obsess over the o2 sensor reading. My bet is you'll find the o2 sensor reading still about the same after the running problem is fixed - and that's most likely something like a vacuum leak.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Min]

what kind of oxygen sensor are you using to get this reading? .. if its a narrow band, ignore it, narrow band sensors don't show enough to allow for fine tuning.

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[samivaan]

Yesterday, I used CRC for air meter (not opened the meter, just outside clean for "moving parts") and opened all vacuum hoses, cleaned the contacts and tightened better.
Still that this is with narrow band sensor, mixture problem is 90 percently fixed. Now I can start getting speed from 3000rpm, and meter is not going to show lean. There is some 50rpm area in somewhere, where mixture sometimes goes lean for short while, but seems that over 900rpm area is fixed now.

So my guess is, that still that narrow band sensor is not accurate, it can understand difference between rich and lean mixture. So there is something "wrong" in system, if meter shows lean when opening throttle? At least in my case seems to be like that.

[Mike924]

The CIS is a mechanical system. It can only react in a finite time.

When you first open the throttle, the mixture will become lean until the lever arm in the air meter has had time to react. Then it will typically overswing and richen the mixture momentarily before settling down to a steady setting.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[samivaan]

Of course like that, but in my case that lean area was a long. 20 seconds, or as long, as I can get rpm over the 4000.
But if everything is good as new, that "lean time" should be less than a second.