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Fifty50Plus · Posted: Fri Jun 07, 2013 3:44 am Post subject:

Ian,
After our talk yesterday, my buddy and I thought about it a little more. You were complaining about no revs and running hot per the plugs. That's a massive lean condition and we think a more probable cause than the missing sealing washer is that your frequency valve is not working.
We found that connecting and disconnecting the frequency valve behind the fuel distributor has almost three times the effect as adding or removing the sealing washer.
Since your car didn't have the sealing washer, it was causing the system to run a bit leaner but not too terrible (probably around 13.5-14.0 CO) If the frequency valve was inop, you might be around 15-17 CO

) and not able to pull revs.
Like I said, to test it at idle, unplug the electrical connection to the freq valve and you should have a noticeable change in RPM if it works. Otherwise, if no change in the idle speed, the valve is bad or your computer isn't sending it any voltage.
Either case is a simple test and fix. But get the wideband O2 probe and gauge for the WOT under load tuning.
Regards,
Chuck
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

Ian89C4 · Joined: 01 Apr 2011 Posts: 561 Location: North Carolina

Chuck -

After talking I was starting to think the same thing.

I also have a question...about air plenums. In the picture below the plenum attached to the car has an electrical connection on it for the air flow meter (I think), but this is not the one that came with the car when I first got it, however the fuel distributor that is on the plenum is the one that came with it. The plenum that the car with it was the one on the left. It does not have an electrical connection on it, and it also has a smaller plenum section as can clearly be seen. The fuel distributors have the same part number so no difference there.

I could not find a connector for the current plenum on the car, so I do not know if it is having an effect on the fuel issue that i am having.

Should I put the plenum on the left back on the car? I thought that they could be interchangeable, am I wrong?

Thank you for all of the help!
_________________
Ian Edgerly
North Carolina

Current:
1981 924 SCCA/ChampCar Weissach Race Car ("Serenity")
1987 924S ChampCar Endurance Car ("Der Weg")
1980 924 Euro ("Wahala")

Ian89C4 · Joined: 01 Apr 2011 Posts: 561 Location: North Carolina

The limited amount of research I have been able to do on the air flow meters led me to this one website from what look like Spain.

Here is the air flow meter that came with the car when I got it: Bosh Part number 0438120150. It appears that it is *only* for the 924 from 1980 - 1982.

http://www.partbob.com/engine/fuel-air-system/luftmengenmesser-bosch-0438120150.html?___store=spanish&___from_store=german

Here is the air flow meter that you see on almost every other 924 in the world and quite a few other vehicles. Bosch part number 0438120136.

http://www.partbob.com/engine/fuel-air-system/luftmengenmesser-bosch-0438120136.html

As I do not have a plug for the air flow meter sensor, I will put the smaller of the two air meters on and see how this affects things.
_________________
Ian Edgerly
North Carolina

Current:
1981 924 SCCA/ChampCar Weissach Race Car ("Serenity")
1987 924S ChampCar Endurance Car ("Der Weg")
1980 924 Euro ("Wahala")

Ian89C4 · Joined: 01 Apr 2011 Posts: 561 Location: North Carolina

I tried testing the frequency valve by hooking it up to 12V. There was a clicking. On start up the valve buzzes until I start the car and then I cannot hear it any more. I tried pulling the connector off of the valve while idling, but no dice, I did not hear a change.

How do I better test the valve?
_________________
Ian Edgerly
North Carolina

Current:
1981 924 SCCA/ChampCar Weissach Race Car ("Serenity")
1987 924S ChampCar Endurance Car ("Der Weg")
1980 924 Euro ("Wahala")

Fifty50Plus · Posted: Tue Jun 11, 2013 4:52 am Post subject:

Ian,
Regarding the air plenums; the one with the larger flapper opening is from an earlier car (77-79/80) while the smaller opening flapper is from the 81-82. Each plenum is normally connected to its associated fuel distributor. You have a mismatch between plenum and fuel distributor. The flapper arm pushes on the plunger on the bottom of the fuel distributor to vary fuel flow to the injectors and I'm willing to bet that the two plungers have different enrichment/demand profiles. We have not had the time to verify the sizing and stroke but the two flappers will rise to different heights based on the same cubic foot/min requirement when the throttle is opened. This mismatch may be the reason for a super lean condition if the late model plunger doesn't rise enough.
As for the frequency valve, putting on 12 volts should cause it to click once. Normally the computer will send duty cycle voltage to the freq valve to enrichen/lean out the fuel flowing to the injectors based on input from the oxygen sensor and other programming. The freq valve operates at 60 Hz so a 50% duty cycle would have it opening and closing 30 times per second (possibly the buzzing you heard). I believe that is the default mode with a failed O2 sensor and a working computer. We don't connect our wideband O2 sensor to the computer and rely on the default for some of the fuel. That's why I said the unplugging the electrical connection to the freq valve will give a change in idle RPM.
Chuck
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car

Ian89C4 · Joined: 01 Apr 2011 Posts: 561 Location: North Carolina

I still have yet to trade out the air meters. I am hoping it helps.

I have the AEM wide band in the middle of being put in...so hopefully I will be able to get good reading around 14.7 off of the correct meter.

As the fuel distributor that came on the smaller plenum had the two shims inside of it, I think I will toss them back in to get the tuning down.

Hope the track weekend went well for you guys.
_________________
Ian Edgerly
North Carolina

Current:
1981 924 SCCA/ChampCar Weissach Race Car ("Serenity")
1987 924S ChampCar Endurance Car ("Der Weg")
1980 924 Euro ("Wahala")

Fifty50Plus · Posted: Wed Jun 12, 2013 1:13 am Post subject:

Ian,
We are getting about 12.9-13.1 CO which gives us much more power than 14.7. Also, I wouldn't put those two shims inside your later model fuel distributor, rather put another larger sealing washer on the outside of the retaining bolt to enrichen the mixture.
Race at Summit didn't happen for us. The return spring on the throw out arm inside the bell housing broke, the shaft moved and popped out of the inner bushing. We had no clutch. PITA to fix but not costly. I'll get to it as soon as my lift is clear.
Chuck
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car