2nd Over boost switch failure

2369488 · 08-23-2007, 07:10 PM

Back in april I had a problem with the engine not starting thru this web site and the help of a number of other users I was able to determine the cause was the over boost switch being bad (OEM93060610100). I determined this by going thru the process of grounding the wire and the engine started fine. I ordered a new switch from our host install on 4/27 and 950 miles later the car wouldn't start one morning. Their was no prior indications of a problem.

I suspected the switch again. Sure enough I grounded the wire and the car started right up. When I hooked it back to the switch is fails to start.

Has anyone else run into this problem. I don't want to continue to replace this switch if something else is causing this problem.

By the way I am still waiting for a call back from our Host as to whether they will cover this under warranty.

Thanks, Steve

Tinker · 08-26-2007, 01:51 PM

I have also had issues with boost switches and ended up filling the switch with solder.

I noticed the wire that connects to the boost switch (it is a ground) was getting pretty warm / hot. This causes the diaphragm in the switch to melt / fail.

I THINK my problem was caused by either a bad relay or the older fuel pumps that might be near the end of their lives and may be drawing extra amperage. You can run a volt meter from the relays in the trunk to get a gauge on how the 2 pumps compare.

I don't think it is a switch issue.

Tinker

2369488 · 08-26-2007, 02:52 PM

Thanks Tinker for the reply.

So I am a little confused.

You mentioned filling the switch with solder. What was the purpose of this and did this action by itself correct the problem.

Regarding the relays or fuel pumps possibly drawing extra amps creating heat at the switch and melting the diaphram. Did you every measure specific draws/voltage to determine if you had a bad relay or if your fuel pumps were drawing more amps than specified.

What was the final fix? Did you replace any pumps or relays?

thanks again.

Steve

Tinker · 08-27-2007, 09:45 AM

So I am a little confused.

You mentioned filling the switch with solder. What was the purpose of this and did this action by itself correct the problem.
Simply by passes the boost switch. It is a ground.

Regarding the relays or fuel pumps possibly drawing extra amps creating heat at the switch and melting the diaphram. Did you every measure specific draws/voltage to determine if you had a bad relay or if your fuel pumps were drawing more amps than specified.
I did measure the voltage, but I can't recall the specific load as this was about 3 - 4 years ago. I emailed a few 'experts' who couldn't provide an acceptable draw for the pumps.

What was the final fix?
Soldering the switch (rendering it useless) and replacing the relays is all I did. Cured the symptoms, but probably didn't fix the cause. If there is any chance of an 'over boost event', you need to fix this correctly. One of my front relay sockets appeared to have gotten hot in the past and that might have caused a connection issue with the relay.

I would recommend examining the fuel pump relay sockets in the front trunk. I would bypass the pump relays with a voltmeter to get a draw to determine if one pump is worse than the other. Ground the boost switch at the motor and see if its getting hot.

Tinker

911boost · 911boost's Garage

You can also just ground the overboost switch out with a jumper, but I do not recomend not running the ob sensor/switch.

Mark Crowe · 08-27-2007, 03:34 PM

Steve, can you send me your previous thread, I am also having some issues with fuel pump relays in the front and the over boost switch, and would like to check the wiring and amp draw , and specifically which wire on my 3 litre turbo activates the overboost cut out. The wires have discolured from age so it is making life a bit interesting.

WERK I · WERK I's Garage

This is a good one!! These switches should never really wear out from over current through the contacts. The switch acts as ground path for the windings of the fuel relays, which is a much lower current. It does not act a path for the current through the fuel pumps. Not unless the wiring had been modified by some fool who had no idea what does what.

Make sure your ground strap from the transmission to the chassis is secure, clean and well grounded. If this connector is not grounded well, you will have other circuits using ground seeking the path of least resistance, which very well could be through the IC pressure switch.

Porschephd · 08-28-2007, 06:45 AM

These switches are known for being all over the place and failing. You can also use an adjustable Hobbs switch which does the same thing but allows you to dial in the overboost you want. They are a lot more reliable.

2369488 · 09-02-2007, 03:16 PM

Thanks everyone for your input.

I checked wires for overheating -none were hot or even warm. Also could not find any discoloration in the wire insulation for the relays.

I did recheck the ground strap and made sure it was clean on the contact ends

I have another pressure switch on it way and let's hope this last longer other wise next step might be to go the Hobbs switch approach.

Steve