I just read the flappy diagnosis on Gregs Tip page, and noticed that it mentioned that if your flappy is not working "you should see a lack of low end torque" with a surge at 4000 or so rpm. (my 87 does this and the flappy is sticky---I'm working on that ;-0). Anyway, From reading the rest of the tip, it seems counter intuitive to me. As far as I understand, when the car is started, (flappy is closed initially) with a brief open and close (as a test??). Then as you drive off (flappy closed) until you gun it and as you approach 4000 rpm the flappy opens.
If the flappy for the most part (at least for passive drivers) is closed (I'm assuming that closed is from 0 to 4000 rpm) it then opens at 4000 rpm thus tuning for higher air flow.
If this is the case, I would suspect that "failure mode" is no vacuum or problems with actuator and the flappy stays in its "closed" position (tuned for 0 to 4000 rpm performance). Now I would suspect that acceleration and torque should be normal up to 4000 and if the flappy doesn't open then no surge of power (or torque) at 4000 (or even a loss of power)??!!??. The opposite of what the tip says?????
What's the story, Is poor off the line performance with a surge at 4000 rpm a flappy problem ? Or possibly something else?
Thanks in advance,
From: "Tom Middleton" <firstname.lastname@example.org>
Date: Fri, 14 Jan 2000 14:58:12
>If this is the case, I would suspect that "failure mode" is no vacuum or problems with actuator and the flappy stays in its "closed" position (tuned for 0 to 4000 rpm performance). Now I would suspect that acceleration and torque should be normal up to 4000 and if the flappy doesn't open then no surge of power (or torque) at 4000 (or even a loss of power)??!!??. The opposite of what the tip says?????
I'm not sure the terms terms "closed" or "open" have a lot of meaning in this context - but what do I know? I guess we could say that the flappy is "closed" if the spring than causes the flappy to return to the low-rpm (long runner) configuration is not compressed and "open" when the vacuum actuator rotates the flappy, compresses the spring, and routes intake air through the short intake runners.
From my personal experience your analysis is correct. If the flappy is not rotating to the "open" position at ~4000k rpm you will notice a significant lack of acceleration. If the flappy is stuck in the rotated position you'll have poor low-end performance with a surge after 4k rpm.
Diagnosis of the flappy is easy if you have a hand vacuum pump. I haven't looked at Greg's pages recently so I don't know if flappy diagnosis is covered. We could go over it for those new to the list that haven't felt the power (or lack of power) of the flappy?
-- David Chamberland
Thanks for the info Dave (and Jonathan),
I just tested the unit with a vacuum tester.
The flappy was a little sticky initially but wd-40 took care of that. Now, on start up I still don't get the quick rotation and I don't get the rotation when rpm >4000. So, I pulled off the vacuum line from the solenoid to the flappy actuator (output of solenoid), and applied vacuum. The flappy rotated 90 degrees and held until I removed vacuum. (good ;-) .) Next I proceeded to reconnect the vacuum lines and then I pulled off the vacuum line coming from supply (input into the solenoid). I applied a vacuum and it held. The car was running and I revved past 4000 rpm (as best as I could tell from the sound) and the flappy did not move and vacuum did not drop off.
All this leads me to believe that the solenoid is toast. Before I get a new one, can someone tell me where the electrical input to the solenoid comes from? I have the manuals and couldn't find it and the electrical diagrams are just a little difficult to follow. Also what does this solenoid cost? Major bucks????
Thanks in advance,
>on start up I still don't get the quick rotation and I don't get the rotation when rpm >4000.
>So, I pulled off the vacuum line from the solenoid to the flappy actuator (output of solenoid), and applied vacuum. The flappy rotated 90 degrees and held until I removed vacuum. (good ;-) .)
Very good. This means you don't have to remove your air intake to fix the problem.
>(input into the solenoid) ... I applied a vacuum and it held... and the flappy did not move and vacuum did not drop off. All this leads me to believe that the solenoid is toast.
>Before I get a new one, can someone tell me where the electrical input to the solenoid comes from?
The solenoid's electrical connector is wired into the main engine wiring harness. I just glanced at the MY 88 wiring diagram and it seems to indicate (as I suspected) direct connection to the LH-control unit. (I don't remember your MY but it should be wired the same for all MYs with the flappy.)
>Also what does this solenoid cost? major bucks????
Can't be that much. Contact one of the big three.
-- David Chamberland
Have you tested the solenoid yet? the connector is right on it and you
use the remote +ve post. I bet the solenoid is ok (click click).
my guess is the vacuum feed line from the brake booster is melted like mine was. In this case of course the line holds vacuum and I got faked out too until I disco'd both ends and retested!
check it out,
The flappy will ONLY move if the engine is *under load* above 4000 rpm.
This means you must floor the throttle from idle through 4000 rpm if you
really want to see the flappy move, to get the brain onto its high load map.
Solenoids don't often fail. To test the solenoid operation, simply pull off the rear connector and apply 12V and GND to the two terminals. There should be an audible thunk, and if there is vacuum available the flappy will rotate 90 degrees.
To check the signal to the solenoid solder a 12V bulb to a long pair of wires and very carefully fit the wires into the solenoid socket and the fit the plug so that your bulb is in parallel with the solenoid. Make absolutely sure nothing is shorting out. Carry out the hard revs test above and you should see the light come on at 4000 rpm or so when the signal is sent to activate the solenoid.
Jonathan M Rackowe
1991 Porsche 928 GT, Manual, Baltic Blue/Linen Leather
1973 MGB Roadster, 4spd+Overdrive, British Racing Green/Yellow Ochre
At 21:11 6/03/00 -0500, David Chamberland wrote:
>The flappy currently in question is the "dual resonance intake actuator flap" which is housed in the inner-most bowels of the air intake manifold. Below ~4000 rpm the flap is in a position to direct intake air to the heads via long intake runners. Above ~4000k rpm the flap rotates 90 degrees and routes air through shorter intake runners. The net effect is to tune the compression wave of the vibrating air in the intake to force a little more air into the heads.
Someone please correct me if I am wrong.
Incoming air is directed to the from the throttle body via a 'Y' shaped pipe to the 2 plenum chambers. The inlet runners are actually fixed in length, and 4 run from each plenum chamber. With the flap in the open position, the 2 plenum chambers are joined by a large (about 100mm outside diameter) pipe which houses the flap. This effectively creates 1 large plenum chamber.
With the flap closed, the intake system is reminiscent of a dual-plane manifold, as found on any number of traditional V8 motors. A dual-plane manifold promotes low-end torque, at the expense of high end power.
With the flap open, the intake system is reminiscent of a single-plane manifold, as found on any number of traditional V8 motors. A single-plane manifold promotes high-end power, at the expense of low-end torque.
With our flap, we get the best of both worlds. It like being able to remove the baffle between the 2 sides of a dual-plane manifold. Has this ever been tried ?
Porsche did introduce variable length intake runners, called Varioram on the 993, where (from memory) sleeves on the intake runners withdraw, allowing the remaining portion of the runners to breathe from a secondary plenum.
>Don't worry. Some owners have removed the radiator flappies since they can cause problems one way or the other when they don't work right.
I collected a large rabbit, or small hare whilst traveling at about 100 (in real money). The poor animal's carcass remained wedged in the grille, and had penetrated far enough to smash off 3 flaps. One further, and perhaps unanticipated function of the flaps is to protect the a/c condenser, the drier, and some associated pluming from miscellaneous debris that may find its way through the grille.
1988 SE (sic) Black/Schwarz/A1
To check the basic operation of the flappy -
1. Remove the rubber cup and try to turn the valve stem - should turn easily (1/4 turn)
2. On the Drivers Side - just in front of the distributor - find a solenoid that is about the size of a 35mm roll of film. Carefully disconnect the vacuum line that runs under the intake - using a vacuum pump (hand-held Mighty Vac - $25) attempt to pull down the system - the flappy should move easily - and hold a steady vacuum for at least 1 minute.
Under the members area on here - Tony H has a page 'V1 UhOh' that has some more info.
'87 S4 Auto
If you drive an S4 - up 928, check the vacuum connections to your flappy
solenoid, located on the front of the left (USA driver's side) cam cover.
The vacuum source should be a white line that runs from a four-way connector on the rear of the engine to the port on the bottom or end of the solenoid. This line should have vacuum any time that the engine is running.
The line to the flap actuator should be attached to the side port of the solenoid. This line should hold vacuum when you suck on it or apply a vacuum pump.
Where the lines are attached DOES make a difference. The source line is connected to the bottom or end connection port, and the actuation line is connected to the side port.
The solenoid must apply vacuum when commanded by the LH ECU, and must also release the vacuum instantly when commanded.
The end connector port for the source line is either blocked (no power) or connected to the side port (power applied).
The side port is either open to outside air (no power) to release the flap, or connected to the vacuum source (power applied) to apply the flap.
If you hook them up backwards you will have a vacuum leak any time that the flap is not actuated, and the flap will remain actuated for much longer than desired.
While there are quite a few detail changes in the 928 Intake, the most obvious major change is the intake manifold system, with the Heimholtz Resonator (flappy valve).