924Board.org

[Roger]

There were actually two problems.

Backfiring was most likely due to bad distributor cap, rotor, and plug wires. I visually checked the plug wires for spark or arcing. The wires were only 4 years old and they did not apprear to be worn or damaged. Shop found one wire as bad and replaced them with a Bosch set $$$. Dad told me these cars prefer Bosch parts. I also replaced the distributor cap and rotor but appearently I did not seat the cap properly, and the rotor wore a grove into one of the posts. Shop replaced the cap, and rotor. The backfire was gone, but the surging continued. I took the car back to the shop on Monday.

Surgining was caused by a bad conection to the frequency valve. I do not have a good understanding of the CIS injection system. So, if i do not explain this correctly please feel free to set me straight. I picked the car up as the shop was closing, so I didnt have that much time to talk to the mechanic as I would have liked. The frequency valve is conected to the computer. A fuel line comes off the pressure regulator to the frequency valve. Another fuel line comes out of the frequency valve and goes to the fuel distributor. The purpose of the frequency valve seems to be that it allows fuel to bypass the pressure regulator and enter the fuel distributor. This seems to be for increasing fuel under acceleration. Since there is no vacum line attached to the pressure regulator. This does not seem to be covered in the factory manual or they Haynes. The mechanic heard the valve opening and closing it mad a ticking sound at idle. This was due to the poor electrical connection. The frequency valve is located on the engine side of the fuel meetering unit under the rubber boot. He disconected the valve and the car was undrivable. When he reconected the frequency valve the problem was solved.

The first trip to the shop cost me $325.00. Parts were $155.00 and labor was $165.00. The shop set fuel mixture, replaced plugs, plug wires, rotor, and distributor cap. The car ran better but I still wasn't happy. The second time the car was in for 2 days. They did not replace any parts, AND THEY DID THE LABOR AT NO CHARGE. I really appreciate them and they are some good guys.

Tomorrow I am going to join the local PCA and try some Auto X. I am soo F-ing happy.
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

[Paul]

Check out pages 98 to 101 in the Haynes manual.

The frequency valve is controlled by the O2 sensor control unit which receives mixture info from the O2 sensor.

[gohim]

I am glad that you got the problems sorted out.

But it sounds like the shop shoveled you a big load, if what you wrote is what the shop told you.

[Roger]

Paul
I will check out the Haynes manual. I said computer I should have been more descriptive and said O2 sensor control unit. O2 Sensor is disconected, and the O2 sensor tries to lean the mixture. From the plumbing it appears that the frequency valve increases fuel flow to the fuel distributor. Though it is conected to the O2 sensor control unit it does not seem to be dependant on the O2 sensor.

gohim
Its about a 60/40 mix of what the shop told me and what I belive to be correct. I am not the best person to explain this system. I thought my experience might be usefull to others. So I am explaining as best as I can. Can you tell me which part or parts you dissagree with? Any info is appreciated.

I read your post on setting the fuel mixture. You are correct it is not that difficult. Since I was having fuel problems, I wanted to be absolutly shure it was correct. One question though by diconecting the ignition advance (black connector under the hood on the drivers wheel well) aren't you altering the mixture? Since the timing is retarted, (cant remember how much maybe 6 to 10 degrees) wont the fuel burn differently? Sorry another question. You refer to idle stabilization, I have only heard this in reference to Motronic systems. I thought the two black boxes inside the fender behind the drivers side headlight were the Hall sensor and the electronic ignition module. Any details would be appreciated.

All Board members:
THANKS FOR THE HELP AND ADVICE
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

[gohim]

The Hall Sensor is located inside of the Distributor.

The flat module under the black plastic box with two round connectors is Ignition Module (Porsche calls it the "Igniter"), and the black plastic box with the two round plugs is the "Electronic Idle Stabilizer".

The plug on the left inner fender IS NOT a timing advance/retard control. It is for enabling and disabling the "Electronic Idle Stabilizer". The Electronic Idle Stabilizer changes the Idle Speed by advancing and retarding the Ignition Timing Advance/Retard. The electronic idle stabilizer does not directly affect the amount of fuel injected by altering the timing (unless you are considering the fact that altering the idle speed changed the intake vacuum, which affects the air flow sensor plate), although the exhaust gas composition is altered by the timing change.

The stated factory timing spec. is with the Electronic Idle Stabilizer disconnected, and the engine warm (cooling fans should be cycling on and off). The Idle Stabilizer will fight any changes you are making to the Idle Speed and Mixture (which affect Idle Speed), if you leave it connected.
while you are trying to make adjustements.

This is the mistake that most people make when adjusting a late model 924. Most people don't disconnect the Idle Stabilizer when adjusting the timing, idle speed and mixture, so the engine will not idle, or run correctly at both cold start and not idle. Failing to correct vacuum leaks (usually cracked rubber vacuum hoses) leads to the the mechanic changing the idle speed and mixture to compensate. Over time, the adjustments get altered so out of wack that the primitive emissions computer and idle stabilizer can no-longer correct the mixture and idle speed, and the engine starts to surge.

You can tell how well a CIS car is tuned by listening to the frequency valve. If it is buzzing, the O2 sensor is saying that the exhaust gas readings are way off. It is normal for the frequency valve to click at times, but never constantly buzzzzz.

[Roger]

Thanks for the info
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

[epsylon]

after reading this post i got curious. i have a '81 and i am missing the idle speed stablizer. the only thing mounted to the driver's fender in that area is a rather large heat sink and the ignition control. there is a bracket that sticks out beyond the ignition control but nohting is mounted to it. my car idles fines, a little rough at cold start. i don't use the ac, maybe that is what the idle speed stablizer is good for.

did the '81 have these and if so is it real bad that i don't have one. maybe mine has been relocated or something. what does it plug into?
_________________
'82 931
'78 928
Howell Henderson
South Padre Island

[gohim]

You can live without the Idle Stabilizer, but your car will idle much rougher, with more rpm drops, than you would have if it was installed.

AC is not the only time that the Idle Stabilizer kicks in. Each time the cooling fans switch on, the headlights are turned on, and engine runs at cold idle, the Idle Stabilizer is utilized to keep the idle speed up.

All US 81 and later 924NA engines should have the Electronic Idle Stabilizer. The one in my car was defective when I bought it in 88, and bad connections in it kept the engine from starting.

First, are you sure your car is an 81? You would be surprised at the number of people who find out that the car they bought is not the model year on the title. If you car had an Idle Stabilizer and it was removed for some reason, the connectors for the Idle Stabilizer must be connected to each other, or the car will not start.

So, look around the left inner fender. You should find the large round plastic connectors plugged into each other up there. They probably fell down towards the front of the car, where the ground point is.

[epsylon]

yes, mine is definately a '81, weisach edition. i have all the paper work including the original window sticker. aparently my idle speed stablizer has been removed. i found two connectors plug into each other, it's funny what you notice when you look. so my next question is where do i get one of these? i read somewhere that it is a vw part. anyone know which models and years?
_________________
'82 931
'78 928
Howell Henderson
South Padre Island

[gohim]

Your best bet is to check the wrecking yards for 70-84 VW Rabbits, and Jettas.

I may have one spare left. At one time, I had three each of the ignition module and the idle stabilizer. I carry one of each in my traveling kit, along with a full set of spare relays.

[epsylon]

does anyone have a part number for this? i am assuming that by your response these cost a lot. great another reason carbs rock.
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'82 931
'78 928
Howell Henderson
South Padre Island

[gohim]

I have been told that the ignition module and idle stabilizer sold for between $100-$150 each when Porsche had them available. I cannot verify that, since have never purchased any new.

A couple of years ago, I was told by someone looking for replacements that these parts are no-longer available from Porsche.

If I have still have spares (I would have to check in the garage), I may be able to sell you them for $50 each.

[81turbo]

The parts bin sells new igniton control units for $50.09 and you get free shipping for an order over $50.

http://catalog.thepartsbin.com/?year=1981&make=PO&imageField.x=46&imageField.y=13
it's listed under engine electrical.

[epsylon]

i have a icu. my car wouldn't run without one of those. what i am looking for is an electronic idle speed stabilizer. this mounts on top of the icu.
_________________
'82 931
'78 928
Howell Henderson
South Padre Island

[Joes924Racer]

You need a part # for that part Epsylon??
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.