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Discussion Starter · #1 ·
Hi JRV et al,

How does one


Hi JRV et al,

How does one measure the duty cycle (DC) of the frequency valve on 328 (K-Jetronic with lambda) system? The Probst Bosch book mentions using the "frequency valve DC testing terminal" - where is this (is one present) on the 328 to connect dwell meter? How do you set DC with your dwell meter?

Thanks,

Carl
 
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Discussion Starter · #2 ·
Hi Carl,

the FV DC is check


Hi Carl,

the FV DC is checked at the FV by hooking the 2 wires from the old timey Analog Dwell Meter set on 4 Cylindersetting, one DM wire to one each of the FV wires by slipping the protective rubber boot back on the FV wiring connector and inserting small adapters into the plug that can be reached by the DM wire clips. Once connected start engine and once closed loop condition is reached a properly tuned engine would read a Duty Cycle of 45%-55% needle gently swinging back and forth...if the Duty Cycle is out of spec...it will be neccesary to access the Mixture Control Screw at the Fuel Disttributor...for rich condition the MCS would need a CCW turn for correction, if the Duty Cycle indicates Lean Condition the MCS would need a slight CW adjustment...each time replacing the FD access port screw to plug the air leak which will cause erroneous readings. Each time an adjustment is made the 02 sensor should be unplugged, make corrections at MCS as necc. , replug 02 sensor..check DC.

To perform this test properly the engine should be warmed to open loop, O2 sensor connected.

All adjustments should be in small increments, access port replugged after each adjust and 02 sensor unplugged while adjusting and replugged after adj. and before rechecking DC.

Is any of this clear???

Regards, JRV
 
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Discussion Starter · #3 ·
Hi Carl,

I brought the Bosc


Hi Carl,

I brought the Bosch book home in case you need any clarifications, so I'll have the reference material handy.

But perhaps I should clarify how a FV works...as we know the Bosch CIS FI system works by metering air flow and with fuel held at a constant but specific pressure controlled by the Aux. Pressure Reg. K-Lambda works the same with the addition of a release valve (FV) inline with the pressure side...by opening and closing this injector called a FV,,the mixture can be minutely & rapidly controlled by raising & lowering the System Pressure - High Pressure = valve closed=lean mixture, to Lower Pressure = valve open-richer mixture. This Valve (injector) is called the Frequrncy Valve. Thru electronics controlled via computer the readings of a heated 02 sensor are converted to signals sent to the FV opening it more rapidly allowing pressure to escape, or more slowly holding more pressure. In this manner the actual fuel muxture can be richened or leaned depending on the Frequency the injector operates.

This system cannot or does not compensate for faulty system pressure or many other possible malidies.



Regards, JRV
 
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Discussion Starter · #4 ·
Thanks for your insightful exp

Thanks for your insightful explanation JRV. This is actually how I have been checking the FV. I see the 50%DC(according to my analog dwell meter) non-fluctuating at cold, them once warms moves to 75%DC once warm, also non-fluctuating. Very strange (I was expecting the 50% figure)but Mr. Foley sees same numbers (factory settings) that I do.

Have exchanged protection relay, jetronic ECU, both relays, tested diode, O-2 sensor. Any thoughts on why we *both* would see these numbers? Are the cars set extremely lean from factory?

Thanks once again for your time & help JRV. the board & members are a superb resource.

Carl
 
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Discussion Starter · #5 ·
>>Have exchanged prote

>>Have exchanged protection relay, jetronic ECU, both relays, tested diode, O-2 sensor. Any thoughts on why we *both* would see these numbers? Are the cars set extremely lean from factory? <<

I know there is a statement saying pre-set at the factory and needs no adjustment throughout it's life. But that was wishful thinking or having a fantasy!!! All Fuel Distribs fall out of adjustment, get dirty, wear, and need corrective attention from time to time. It wouldn't surprise me at all to find both cars have been adjusted a time or two already after leaving the factory.

If I'm reading that list correctly I do not see where the Fuel Mixture has been readjusted to spec? Have you opened the Idle Mixture Access Port and readjusted the mixture?

Regards, JRV
 
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Discussion Starter · #6 ·
Hi again JRV,

Wish I could


Hi again JRV,

Wish I could tell you I did this the "right" way. Using my Gastester CO machine, adjusted to 1.2% CO very close to current setting. Then (shade tree time!) turned mixture "rich" CCW until popping in exhaust almost resolved (about 1/4 turn)...this corresponded to CO about 2.8% but idle sped up. Ran fine except now cold-starts (until warm) very rugged wants to almost die.

Turned further until idle speed dropped (about 1/4 turn CCW more) then returned to baseline. Turning "lean" (CW) from baseline get about 1/8 turn before engine begins to falter. Reading DC while doing this, it decreases to about 70% then cannot turn further without stalling motor. So physically cannot achieve the 50% DC.

So no, did not set properly (smile). And I know you can't really help much without knowing proper data and I respect your professionalism in refraining.

But interestingly, turning CCW (rich) increased DC to 82%. Why would this be?

Carl

PS All of the above with O-2 sensor connected
 
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Discussion Starter · #7 ·
I think what may be going on i

I think what may be going on is the 02 sensor is trying to do it's job against the tide. In theory all the 02 is supposed to do is keep the static mixture setting between two small varibles...variables = + or - stoiometric..

So by leaving the 02 connected while turning the mixture screw you are forcing a fight between static & optimum...an 02 is not really designed to "set mixture" it is designed to moderately control it once it is set properly.

First I would try setting CO to 1% 02 disconected and also any air intake corrections necc. to set idle speed to the proper spec...idle speed is controlled by air intake volume..sometimes it's a back & forth game between air & fuel when all the settings are out of whack...but what you want to see is 1000rpms & 1% 02 Disconnected...the computer runs the FV at the default setting while this is carried out...then, once the baselines are corrected and set the 02 can be replugged to do it's job.

Regards, JRV
 
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Discussion Starter · #8 ·
Thanks JRV - shall do all of t

Thanks JRV - shall do all of this (was going to reply yesterday for some odd reason my ISP server was down).

Removed cam covers to check camshaft alignment (correct) ordering gaskets will post results once reassembled.

Thanks again JRV,

Carl
 
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Discussion Starter · #9 ·
Hi guys. I am not sure if thi

Hi guys. I am not sure if this will help or not but from what I have read 75% is a very high duty cycle and means that the FV is returning a large portion of fuel to the tank. This reduces the upper and lower chamber pressures causing a richer mixture. So I would think this could be a problem if it is truly at 75%.

JRV can you clarify what happens when the 02 sensor is disconnected on a K-Lambda 308. Does the Lambda Control ECU do anything at this point? I know the FV still functions but what is its duty cycle at this time? Will the car run rich at all times? I have seen a few 308s that had their 02 sensors removed when a Tubi or Ansa was installed and I was wondering how the car functions and what components are/are not functioning with the removal of the 02 sensor. Thanks.
 
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Discussion Starter · #10 ·
Hi Rich,

the FV still funct


Hi Rich,

the FV still functions at the computers default setting and the car runs off the mechanical settings built into the system.
 
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