Monte951

I have an 88 951. Shes 3 weeks old to me. Ever since we got her home her battery would go dead and require a jump. We replaced battery and still the same thing. One night my wife noticed a hum from the engine. We looked and I grabed the first hose on the intake manifold closest to the nose of the car (the hose between the first two tunnels) and it was on, pumping away, pumping something at all times. (A Porsche guy said it was a hose to the Idle Air Pump?) Also when turning the car off we would always get a backfire after the car almost puttered out. The running pump would drain the battery in a day or two. My porsche guy and myself came to the conclusion that the solution was the DME relay. (the fuel pump was turning off but the Idle air pump and rest of the car wasn't) Well, I bought a new DME relay and now the starter comes on but the engine won't run I tried a used DME relay that i have in my other 86 NA and same problem.

Even if the DME relay is not the culprit (and i think it is) Why the hell would a new one make the car not fire up?

I'll be checking the terminals in the fuse box this afternoon because my only guess is corosion on the contacts where the relay seats.
Help...please.

quinnfiske

There is an idle stabilizer under the intake manifold. It is not a pump however, more of a valve. It should not be energized when the engine is off. It does not make a hum.

Maybe your fuel pump is running all the time. It is controlled by the DME relay and it DOES make a hum. The actual pump is located at the right rear of the car near the fuel tank. You can't see it because it is behind a plastic cover but you can hear it run. It should not run until the starter cranks the engine and continue when the engine fires.

Zero10

If its 3 weeks old to you, perhaps you have mixed up a coolant line with an intake line. There is a turbo water pump located near the front of the engine pay, driver's side. It pumps water through a hose and hums when it runs, so that would explain what you felt and what you heard. It also draws ~5-10A so it would explain why your battery is always dead.
Remove the turbo water pump relay and re-install it, see if that stops the humming noise. If it does the relay has gone bad. If it kicks back on as soon as you re-install the relay the temperature sensor is bad or the wiring is damaged. If the humming doesn't stop while the relay is out I'm totally wrong.


There is no such thing as an idle air PUMP, there is an idle stabilizer, which will vibrate lightly (inaudibly) while the ECU is on, but on its own it does nothing to move air, it requires engine vacuum to move any air at all. I think this is a good time to stop referring to him as your "porsche guy", we are your new "porsche guy"

Bri Bro

The idle stabilizer is a duty cycle valve so it does move toggle back and forth at a fast rate and makes a little noise. Bypass your fuel pump at the test connector and try it again. There is a circuit in the DME that turns on the fuel pump while cranking. As soon as the RPM are up, it is bypassed. In an accident, the fuel pump cuts off when the RPM drop below a set level with the ignition on. If the turbo water pump is running, try pulling the wire off of the temp sensor on the water pipe coming out of the turbo. If it stops, the sensor is bad.

theedge

A hum would most likely be the turbo cooling pump still running. Its mounting to the big heat shield that wraps around the brake parts. Go for a drive to get the car warmed up, park, wait a few minutes and feel the pump to see if its running. It should only run briefly after the car is turned off.

quinnfiske

The turbo water pump runs for 25 seconds after the ignition is shut off. I know this because I replaced the time-delay relay that controls it and timed it with a stop watch. It is possible for the relay to fail in such a way the pump stays running.

Zero10

Damnit, I said something wrong above. My coffee was still in the cup instead of in me so my brain was still off for the morning...

If removing and re-installing the turbo water pump relay causes the pump to stay off then the TEMPERATURE SENSOR is to blame, not the relay as I said earlier.
If on re-installation the pump kicks back on then the relay is shot.

As for the "unplug the temperature sensor" comment that should stop the pump in between 20-30 seconds, it shouldn't immediately stop.

Bri Bro

Yes, the relay or the turbo temp sensor can cause it to stay running. In operation, the turbo water pump will always run about 30 seconds after the ignition is turned off. If the tubo temp sensor is above the trigger temp, it will reset the pump to run until the temperature is below the trigger level. Pulling the wire off stops the turbo pump relay from being retriggered after the initial run period.

Monte951

Sweet jesus. This was my first post and you guys desended on this project like it was your own car. Many thanks. This fourum shall be my new home. As for the car, please keep in mind that:
the car runs fine, it starts with no problem, drives great, breaks the sound barrier and turns off, it's the turning off part that sounds bad... when you turn the key off the engine putters out for one to two seconds and then pops a porsche fart out before its all the way off.
the cooling fan comes on sometimes and goes off in less than 5 min. But this little pump with the hose stays running for hours or days or untill the battery is dead. I have a picture but i guess i have to find a photo hosting site before i can post it... BRB

There's the bastard. Now what is that thing....

http://i735.photobucket.com/albums/w...te951/prob.jpg

The problem is that the DME relay thats in there doesn't seem to be shutting everything off when you shut off the car. And a new DME relay was not letting the car start at all. whatever thats about...

I'll try the clarks garage fix/diagnos, can you send me a link to the site or to the post?

Thanks so much in advance guys, i'm going to like it here. I just hope i can help somebody someday...

and just so you know, i've copied this post on one other website but Rennlist is where i hang my hat.

quinnfiske

Here is a link to Clark's Garage. Great site with much info. You will find people are anxious to help because all of us have had problems solved here and want to pay it back.

http://www.clarks-garage.com/

Bri Bro

Look at clarks and find the section on bypassing the fuel pump. The pump doesn't run with just the ignition on, it only runs while cranking and when the engine starts. If it starts with the bypass, it points to the problem.

That hose is to the idle controller. The connector that is circled is to the turbo water pump sensor.

Monte951

Mother@##$*$ Sonova$@#^ I found the problem....

I really want to thank everyone on this little problem but were about to see whos on their game!

I will follow up tonight with pics once i get my camera back.
The DME relay that is in the car has been modified. poorly i might add.
The new DME relays are perfect.
Only problem is: only the modified relay will make the car go.

The modified relay has a small peice of paper wedged between the lower switch inside the relay.
The circut is always complete. This is why my idle controller is always humming and my battery is always dead. It's essentially a DME jumper that never comes out.

My riddle now is why the hell would somebody do that? (ok stupid question: to make the car work)
Why the hell would you HAVE to do that?
Seems to me: providing the 12v to the leg of the relay that closes the switch at position 2 (accessory position) would solve the problem.

Now what do you guys think? The car has been working fine with the constant 12v to that relay while in operation so it seems. And which leg needs the juice?

the leg labeled 30 seems to operate the magnetic coils in the relay that close the switch. 12v to that one?

I'll send pics soon

Off to clarks garage... pics and more to this story soon to follow.

951Porschiste

Describe how the car will not start with a good DME relay in place.

Does the engine turn over, but does not fire?
Does the engine not turn over at all?
If the engine turns over, does the tach needle bounce?

Bri Bro

The first DME relay gets the voltage from the ignition switch but it goes through the alarm system. My guess there was a problem with the alarm system and this was the band aid fix. The alarm also goes to the alternator so you might also have a patch on it. To start the car, you need 12VDC on pin 86 of the DME relay and that 12V comes from the alarm system. To bypass the alarm, do this:
http://www.clarks-garage.com/shop-manual/elect-23.htm

Also look under DME relay on FR Wilk site. He also has a link to the manuals at the bottom.
http://www.the944.com/

Monte951

WHOOOOO HOOOOOO!!!!
OK Brian Broderick, I need you to send me a PM with your address and phone number! I'm buying you a Pizza at the very least!

It worked like a charm.

Now i'm going to leave the alarm jumpers in place a make em permanent. looks like the battery drain has gone away cause the idle controller is not running anymore when the cars off so i think this is the solution!!
Any reson i shouldn't leave the alarm jumpers on and if i do leave em on does that render the alarm useless? I wasn't going to use it anyway, just good to know and hopefully this thread helps somebody else!!
Thanks all that helped, I couldn't have done it without Rennlist!!

(i'm dead serious about the pizza Bri!)