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T77911S's Avatar
 
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if the AFR is too far off it cant correct it.
this can be due to an air leak
wrong control pressure
bad ignition
mixture set incorrectly
or just a bad O2 sensor.

in the end the mixture is controlled be a frequency valve (FV). it is on the back side of the AFM. you should feel it vibrate when the key is turned on.
i dont know how often these fail.

another place to look is under the drivers seat.
there is a computer that conrtols the FV. there is also a speed relay that controls the O2 sensor. this device is known to have solder joint problems. this can also cut off the fuel pumps.

the CD unit gets its power from a delayed action relay. this is the relay that keeps the ignition on after you turn the car off to burn off fuel. i would image it is prone to bad solder joints too.

did you connect the decel valve correctly? personally i would remove this device.

i would check the fuel pressures.
with the O2 not connected, set the mixture to spec.
connect O2 sensor and check AFR's

i would also check the throttle switch to make sure it is adjusted properly.

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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
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Old 11-03-2014, 08:27 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #41 (permalink)
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Just a guess here and maybe you checked already, the black relay in the back panel supplies power to the oxygen sensor make sure that is connected well. Don't know if using the stock oxygen sensor for your AFR gauge is correct either. How is your PLX gauge getting power?
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Old 11-03-2014, 08:30 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #42 (permalink)
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Quote:
Originally Posted by T77911S View Post
if the AFR is too far off it cant correct it.
this can be due to an air leak
wrong control pressure
bad ignition
mixture set incorrectly
or just a bad O2 sensor.

in the end the mixture is controlled be a frequency valve (FV). it is on the back side of the AFM. you should feel it vibrate when the key is turned on.
i dont know how often these fail.

another place to look is under the drivers seat.
there is a computer that conrtols the FV. there is also a speed relay that controls the O2 sensor. this device is known to have solder joint problems. this can also cut off the fuel pumps.

the CD unit gets its power from a delayed action relay. this is the relay that keeps the ignition on after you turn the car off to burn off fuel. i would image it is prone to bad solder joints too.

did you connect the decel valve correctly? personally i would remove this device.

i would check the fuel pressures.
with the O2 not connected, set the mixture to spec.
connect O2 sensor and check AFR's

i would also check the throttle switch to make sure it is adjusted properly.
Thanks. Very helpful. I will buy the fuel pressure gauges next, just to check this.

It makes sense to me that if the afr is too far off, the o2 sensor cant fix it. But connecting the o2 sensor makes it worse! That's the part I don't understand.

If the afr is 12, connecting the 02 sensor should drive it towards 14.7. But it does the opposite. Connecting it drives the afr to 10.

I will check to speed relay. I didn't know that effected the 02 sensor? I thought it just shut off the fuel pumps?

I will also check the fuel pump output this weekend, to make sure the flow is correct...

Thanks.
Old 11-03-2014, 10:50 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #43 (permalink)
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Quote:
Originally Posted by oilonly View Post
Just a guess here and maybe you checked already, the black relay in the back panel supplies power to the oxygen sensor make sure that is connected well. Don't know if using the stock oxygen sensor for your AFR gauge is correct either. How is your PLX gauge getting power?
With the PLX, there is only one 02 sensor. This feeds the module, which then displays your afr.

The module also has a wire to pass the 02 sensor info onto the cars computer, for folks that want to use the lambda function.

I will check the voltage output of this wire to make sure it is transmitting that the o2 sensor is reading rich. I suppose the unit could be bad. But I believe I had this issue before installing the afr meter.

So you guys are saying that the feed from the o2 sensor goes to a computer under the drivers seat, correct? I will remove the seat and check for corrosion, etc.

I do appreciate folks help. I hope this also helps others down the road.

Bo
Old 11-03-2014, 10:55 AM
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Just some educational crap to confuse things even more: The less O2 that the sensor sees, the lower it's millivolt output will be to the computer. When the computer sees the voltage dropping it will change the duty cycle on the frequency valve to lean things out (if I recall, said valve bridges the upper and lower chambers of the fuel distributor and - depending on it's duty cycle - has more or less of an effect on fuel pressures, thus changing the fuel/air mixture and AFR's). If you unplug the frequency valve, your car will go instantly very lean.

If you unplug the O2 sensor, the frequency valve will default to open loop at a fixed duty cycle of something like 50%. That's how I always ran mine because I didn't have to worry about smog testing and didn't have a CAT anyway. Makes it easier to tune in my opinion.

As Oilonly mentioned, that black relay is what sends power to the heating element internal to the O2 sensor. Without it the sensor takes too long to heat up or may not heat up enough to work correctly. Also, make sure you have the correct sensor for these cars. What came with your AFR gauge isn't necessarly what your Lambda system needs.

This is all from memory; I should pull out the ol' Bosch K Jetronic manual to refresh myself so I don't send conflicting info.
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Old 11-03-2014, 11:14 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #45 (permalink)
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The lambda pulse valve/inline injector returns fuel from the fuel heads lower differential pressure chambers to the fuel tank.

By returning variable amounts of fuel pressure from the lower differential chambers to the tank through the fuel return line the resulting small changes in fuel pressure in the lower chambers then has a subtle control pressure effect that raises or lowers the position of the fuel metering diaphram that is sandwiched in between the upper and lower chambers in the fuel head.

The diaphram is real close almost touching the bottom of the 6 seperate metering orifices that lead straight up to the injector banjo fittings. How close it is to those orifices is the final fuel metering valve in the fuel head. If someone like CIS Flowtech enlarges the inside diameter of those orifices by machining them a little bigger the fuel head will be able to flow more fuel when it is adjusted correctly.
The pulsing lambda valve gets removed when doing that and it's lower chamber female threaded fitting gets a plug and the return line short length banjo bolt that was in that fitting replaces the longer return line banjo bolt the control pressure regulator and lambda frequency valve banjo fittings were using together.

The lambda O2 sensor is a narrow band sensor. It reads and creates a micro voltage output in a very narrow range so it can keep AFR real close to 14.7:1 which was OK when gasoline had no ethanol mixed into it but that lambda AFR tune is a little too lean when accelerating using todays oxygenated ethanol blend gas and usually causes some mild surging you can feel during light throttle slow acceleration.

AFR gauges use a wideband O2 sensor that operates over a wide range. EFI designed and tuned for performance over fuel economy and emissions use them too.

There is oxygen in the ethanol molecule and it's 10% presence in E10 gas leans out the AFR a small amount.
Old 11-03-2014, 05:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #46 (permalink)
 
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Quote:
Originally Posted by JFairman View Post
The lambda pulse valve/inline injector returns fuel from the fuel heads lower differential pressure chambers to the fuel tank.

By returning variable amounts of fuel pressure from the lower differential chambers to the tank through the fuel return line the resulting small changes in fuel pressure in the lower chambers then has a subtle control pressure effect that raises or lowers the position of the fuel metering diaphram that is sandwiched in between the upper and lower chambers in the fuel head.

The diaphram is real close almost touching the bottom of the 6 seperate metering orifices that lead straight up to the injector banjo fittings. How close it is to those orifices is the final fuel metering valve in the fuel head. If someone like CIS Flowtech enlarges the inside diameter of those orifices by machining them a little bigger the fuel head will be able to flow more fuel when it is adjusted correctly.
The pulsing lambda valve gets removed when doing that and it's lower chamber female threaded fitting gets a plug and the return line short length banjo bolt that was in that fitting replaces the longer return line banjo bolt the control pressure regulator and lambda frequency valve banjo fittings were using together.

The lambda O2 sensor is a narrow band sensor. It reads and creates a micro voltage output in a very narrow range so it can keep AFR real close to 14.7:1 which was OK when gasoline had no ethanol mixed into it but that lambda AFR tune is a little too lean when accelerating using todays oxygenated ethanol blend gas and usually causes some mild surging you can feel during light throttle slow acceleration.

AFR gauges use a wideband O2 sensor that operates over a wide range. EFI designed and tuned for performance over fuel economy and emissions use them too.

There is oxygen in the ethanol molecule and it's 10% presence in E10 gas leans out the AFR a small amount.
Wow. Very helpful. Thank you.

So in this mechanism, why would connecting the o2 sensor make the afr richer? Shouldn't the o2 sensor read an already rich condition, tell the frequency valve on the metering plate to correct, and make the afr leaner?

If I check the voltage coming off the o2 sensor, and its correct, whats the next thing upstream to check as to why the system isn't correcting? Would it be the computer under the seat? If so, are their particular PIN volatges to check? Is there a voltage at the valve that can be checked?

As always, thanks!

Last edited by bpu699; 11-04-2014 at 06:18 AM..
Old 11-04-2014, 05:45 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #47 (permalink)
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Some more followup...

Posted this by acident in the 911 forum, rather than here. Oops.

1988 930. Some running issues as posted in another thread. Car initially ran great, but occasionally went extremely rich, and died. Randomly. Then, ran great again. Changed the ignition to MSD, seems to have helped. Car doesn't cut out and die any more.

Then, started to get really rich at idle all of a sudden. AFR slowly went to <10, and it stumbled. With the new MSD, it doesn't die anymore. Above 3000 rpm AFR's perfect, ran great. Disconnecting the 02 sensor "fixes" this, with afr's of 12.5 at idle, 14 at cruise, and drops down to 11 or so at full boost. Prior owner must have had the same issues, as the 02 was disconnected prior.

Also, fuel pumps seem louder than I remember.

I thought this was an 02 lambda issue, but folks recommended I check my fuel pressures. So, I did.

Not sure what to make of it:

FUEL PUMP DELIVERY (Reference is 1500cc/30 seconds)…… 1600cc/30 seconds if measured after 1st fuel pump. 2100cc/30 seconds at line from fuel filter to distributor (after 2 fuel pumps)

FUEL PUMP VOLTAGE, Running, 12.5V

CONTROL PRESSURE FLOW (Reference 160-240cc/Minute)… 200 cc as measured at the line from the fuel distributor to the WUR.

SYSTEM PRESSURE (reference 6-6.7 BAR, or 88-99PSI): I got 103PSI, but that might be within the error limit of the gauge.

CONTROL PRESSURE COLD (reference 23 psi at 50 degrees, up to 45 PSI t 90 degrees)….I did it when it was 50 degrees outside. got 40 psi for about 3 seconds (then WUR makes a squealing sound), then it slowly climbed to 55 PSI within 10 seconds. This is with the WUR power supply disconnected, and the car ice cold)

CONTROL PRESSURE WARM (reference 55PSI )…. I got 75 PSI after about 2 minutes, and then it plateaued…

I repeated it again, the next day...

40 psi cold, 55-60 psi warm...

Ok, so what does that mean and does it explain any of my issues? Clearly the warm and cold pressures seem off? But I thought a high control pressure makes a car run lean???

Is there an issue here, or not??? Remember, with the 02 sensor disconnected the car runs PERFECTLY. Its not lean, or rich, doesn't backfire, etc. It does stumble when first turned on for about 5 seconds until the idle evens out...

Is this a fuel issue, that the 02 lamba system can't overcome? Or is it just an 02 lamda issue, and the fuel pressures are just unrelated???

I calibrated the HF gauge against 2 other gauges, and it was spot on...


As always, any help appreciated. And hopefully this helps someone else too!

Plan to check the WUR filter next, and back flush the fuel lines... Odd. Car runs GREAT with 02 sensor diconnected...

JFAIRMAN...can a malfunctioning frequency valve cause any of this? The valve is LOUD. I thought I was hearing my fule pumps or CDI buzzing in the cabin... Now I suspect its the FV... Its muh louder than the fuel pump...

Bo

Last edited by bpu699; 11-11-2014 at 12:36 PM..
Old 11-11-2014, 12:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #48 (permalink)
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the fuel pump flow rate is measured out of the return side of the fuel head, IE the amount of fuel returning to the tank. dont worry about rechecking.

above 3k the O2 sensor is no longer used and it goes into open loop.

your control pressures are really high. 75 psi (5.1bar) . this will lean things out.
55 (3.75bar) is better. control should be 3.75bar.
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88 BMW 325is 200K+ SOLD
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Old 11-12-2014, 08:18 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #49 (permalink)
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Quote:
Originally Posted by T77911S View Post
the fuel pump flow rate is measured out of the return side of the fuel head, IE the amount of fuel returning to the tank. dont worry about rechecking.

above 3k the O2 sensor is no longer used and it goes into open loop.

your control pressures are really high. 75 psi (5.1bar) . this will lean things out.
55 (3.75bar) is better. control should be 3.75bar.
I know it should lean things out...but I am running rich/good...

I will check the mesh in the WUR today if I get time.

I am wondering if there is any way that I can be measuring this "wrong", but I don't see how...

I did have one thought last night, but haven't had a chance to check. I wonder if the HF tester screws in further into the WUR that another brand, therefore blocking part of the passage?

Based on how the car drives, and the AFR's, they seem reasonable (except idle with the 02 pugged in). With a control pressure of 55-75, I would think it should be crazy lean. It isn't...

Thanks for the comment, more to come...

Bo
Old 11-12-2014, 11:00 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #50 (permalink)
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Woo hoo... Thanks guys. Seems to be fixed...

I looked at the intake mesh in the wur. Honestly, it looked awefully clean. I used some air at 40 psi to blow onto it. Must have done something, as the cold control pressure went down to 35...

Then, blew out the tiny outlet-line from the wur to the fuel distributor. That knocked the cold psi down to 22-25 or so.

Warm pressure of 45 or so, at 45-50 degrees.

Started the car, ran absolutely like crap. Super rich idle of 10 or so. Adjusted the afr ratio at idle to 12.5 or so. Ran well again.

With the o2 sensor disconnected getting a cruise afr of 13.5 to 14 or so.

Stepping on it, with the turbo starting to kick in, drops to 12 or so. Couldn't go further as its snowing out side...


The 02 sensors circuit works again also. Yey!!! It does seem to vacillate more, though. Previously it kept the afr between 14 and 15... Pretty steady.

Thanks guys... Blow out that mesh in the wur, even if it looks clean... Seems to do something.

Thank you, Bo

Old 11-16-2014, 12:35 PM
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