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Rich to lean, back to rich


1 throttle plate per cyl!
Dec 7, 2006
Knoxville TN
Questions on diagnosing CIS fuel problem.
Veh in question is an 1983 245t.
Engine is stock,
Turbo is stock (fresh rebuild),
Replumbed with new silicone hoses,
New Bosch o2 sensor (before turbo),
Open 2.25" exhaust with stock muffler (no cats),
new in tank fuel pump that is operational,
new fuel filter,
and absolutely no vacuum leaks.
Recently installed a wide band bosch o2 sensor with A/F gauge setup from AEM.
VDO boost gauge says 9 psi until 3700 rpm then peaks to 12 psi.
A/F is 10.0! at idle, as soon as the throttle is pressed it spikes to 16 ish and stays there until 2.9psi of boost is reached, Then immediately down to 11.5 all the way to max boost.
Seems I have a part load lean condition. This is my first turbo vehicle so I'm a little green.
I'm familiar with turbo lag, but that is definately not what I'm experiencing.
I'm a Technician by trade, however I'm not just not familiar with the system. Need some direction where to start and how to test the components (haynes manual is kinda vague).
I would suspect fuel pressure issue, but it does not make since to be so rich at idle and full boost and so lean at part load.
I have played with the adjustment on the fuel dist but If I lean it out more at idle then as soon as I open the throttle I go way lean and get some sputtering/lean misfiring? until I hit the 2.9 psi mark and the boost enrichment kicks in.
If anyone can lead me in the right direction I would appreciate it.
By the way the timing is set dead on.
Voltage is steady at 8.58v, thats with the sensor still plugged in. Shouldn't I have fluctuation?
rich mixture

If you know the Kjet system electrical parts are working correctly. It's time to get a fuel pressure gauge on there and check the control pressure. The warmup regulator, also called the control pressure regulator controls the main operating mixture of the engine. It's the gray metal unit bolted to the block behind the distributor and under the intake manifold. You'll see an electrical connector on it and two fuel lines with some vacuum lines. You'll want to verify the electrical connector is getting power to it. As it warms up it raises the fuel pressure. The idle mixture is adjusted with a screw in the fuel distributor but the warmup mixture and running mixture is controlled by the control pressure regulator. The Bentley manual is the best easily available reference for the specs of the fuel pressure. Basically, the center connection on the fuel distributor is a feedback of fuel pressure which controls how high the fuel plunger is inside the fuel distributor. If the plunger has high control pressure it keeps the plunger lower and makes a leaner mixture. You connect a fuel pressure tester inplace of that line that runs from the center of the fuel distributor to the control pressure regulator. The gauge setup uses a valve so it can pass fuel through and measure the pressure. The valve also lets you shut off fuel flow so you can measure the system pressure and the rest pressure.

Sometimes the control pressure gets too high because of a clog in the control pressure regulator. This makes the mixture too lean and maybe someone who worked on the car before you tried to compensate for that with richening up the idle mixture.
Yes, Peehound, The frequency valve does buzz.
I'll check with some of the older techs at the BMW dealer I work at and see if one of them has something I check the pressures with. I know some of the older bmw's used similar set ups.
I've suspected the WUR/CPR to be a possible cause, I just don't know enough about the system. Looks like I need to do some reading. I'll check all the electronics, sensors, and signals to rule that out, then I'll check my pressures.
I'll keep you guys posted. Thanks for the insight.
Here is what I have so far.
The CPR is a Bosch 123
Checked voltage to CPR- Batt voltage present.
Checked resistance of CPR- 18 ohms.
Ambient temp at time of testing was around 70 degrees F. Spec should be 11.7-12.9 ohms with ambient temp above 63 F. That tells me that its out of spec, but would 5 ohms above spec cause my problem? I have the CPR off the vehicle right now. Is there anything else to check while I have it off? If not I'm going to put it back in and check my pressures.