I ran the 'flag' test on my flappy. Nothing. It doesn't move. Not on start up. Not on revving.

Is there a trouble shooting procedure? The simple stuff to do before having to remove the intake.

How much horsepower am I leaving on the table without a happy flappy?

Thanks,

Cameron
'91 Euro GT

 

http://www.nichols.nu/tip442.htm

 

Thanks. I found it in parallel.

.....Cameron
'91 Euro GT

 

Here's my test. And I might say that it takes some serious throttle for the flap to open. There's a solenoid that opens the vacuum line to the flappy valve. When that gets a signal, it has voltage on it. So, I ran two wires from it to a lightbulb through the sunroof. When the solenoid gets activation power, the lightbulb lights up. I found that testing it on a steep hill was easiest. Mine also doesn't open upon starting of the car.


Hope it helps.

 

there is one thing that stands out, that seems to be missed on all this diagnosis. when you rev the engine to 4500rpm , you have to do it HARD, it cant be a leasurely accleration of the engine. the flappy works under load and its tough to do "under load" when you are not in gear!. so, a very hard wrap of the throttle will get it to move, and it sounds like you are killing the engine, but you are not. othewise, the only way to see it move is on the initial start up with the flag technique.

vacuum lines have to all be attached. this was the issue with mine. one line off, and the vacuum system doesnt do anything of what it is supposed to do. (except brake booster, which works as long as the line is connected)

mk

 

Before removing the intake I would suggest you undertake the following simple procedures:

1. With the engine stopped, disconnect the vacuum pipe from the control solenoid valve to the flappy valve and give it the old self "suck" test. You should hear the vacuum diaphram valve actuating and see the flag on the top of the flap valve shaft move through 90 degrees. If this happens the flappy valve, in itself is OK.

2. Replace vacuum pipe and remove inlet vacuum pipe to the electrical solenoid and whilst giving the old 'suck' test, actuate the solenoid valve by applying a voltage to the terminals. If all satisfactory the flappy should move as in 1 above.

3. If the flappy does not move then go through the procedure as described by Wally P in the Rennlist posts and check out the vacuum from the brake booster, via the non-return valve, the four way splitter and then up to the inlet to the fappy valve soleniod valve. You will need a fair bit of suck, but you should be able to detect any vacuum leaks. After each suck test of each line start the engine to determine that you have good suction from the brake booster.

If all is in order then all vacuum circuits and electrical circuits should be OK and it should work, so start up the engine, warm it up and then activate the throttle from with the engine compartment and when you get to the 4,000 to 4,500 RPM it should swing open. If it does not open then it would appear to be an electrical problem in activating the solenoid valve.

Hope this helps.

TAILS 1990 928 S4 Auto.

 

MArk is right, and this is confirmed on my LH test jig. Not only do the rpm have to be high for the flap to operate, but also the MAF volts (engine load) need to be high as well - like > 4v

It is very dificult to achieve this with the car stationary.

But it should twitch on start up, when there is an initial peak pulse through the MAF.