Accumulator Bad - Now What

[JK McDonald]

I am helping another 928 owner get his 1983 started that's been sitting in his garage for about 18 months. After recharging the battery and checking off the typical string of storage related issues we had her running pretty well. But his car continues to be very difficult to start each morning. While troubleshooting everything was looking good until we got to the accumulator. When it was removed and 20 Psi of air pressure applied, we found that it's internal bladder was leaking badly. As a quick fix (he's been laid off because of the down turn in the oil business) I offered to add a simple relay to provide an alternate pre-start power source to the fuel pump. This will allow him to pressurize the fuel system as necessary so his car is ready to start even after he's been out of town for a while. A new $300 accumulator is pretty far down his list of priorities right now.

The new circuit worked so well on his car that I decided to install a similar relay on Miss Purdy (84 US auto). The only parts needed are a small Bosch relay, spring loaded ON/OFF toggle switch, 16 amp fuse and a couple lengths of wire with crimped on connector terminals.


Each 928 model year's wiring lay out will be slightly different but on my 84 there is a separate factory installed 16 amp fuse mounted on the fuel pump relay (XVII) housing to protect the fuel pump. I added an additional 16 amp fuse into an unused fuse position (# 22 on my car ) to provide the new power source to the fuel pump.


The reverse or back side of the # 22 slot has a Key ON B+ power bar connected along the bottom of the fuse terminal. The Top connection of this fuse slot (Reverse Side) has a single male spade terminal with no wire connected. From the Top Reverse Side spade terminal of the # 22 fuse terminal I connected and then routed a new wire to one of the Normally Open main terminals of my Bosch relay. The other Normally Open main terminal of the Bosch relay has an output wire routed behind the fuse panel and down to the Rectangular Clear Plastic "PLUG T" located along the bottom right hand edge of the fuse panel. To make sure the new power source to the fuel pump is reliable, this output wire from my Bosch relay is soldered onto the copper terminal neck of the Red/Green Stripe wire coming out of the Clear Plastic "PLUG T" . I found that it's easier to pull the complete rectangular plug away from it's socket, then use a small jewelers flat tip screwdriver to compress the spring finger holding the Red/Green wire terminal in it's socket. Once the Red/Green striped wire has been pulled out and into the open it will be much easier to attach the new wire using a soldering iron. A little solder flux on the Red/Green striped wire terminal neck helps to make the soldering process easier, more secure and a better electrical connection.


When you slide the original Red/Green and newly attached wire back into the # 4 position in the Clear Plastic Plug - make sure it snaps securely in place. Gently pull outward on the wires to verify that the terminal will not come out of it's small square hole. Once you're satisfied with the connection, firmly reinstall the Clear Plastic Plug back into original location of the fuse panel.


To supply a KEY ON +12 volt source and ground to the new ON/OFF toggle switch used to energize the Bosch relay coil I crimped a couple of terminals to each end of two wires (flat male spades to one end and female terminals to the other). I then plugged the two male spade ends into an empty fuse panel relay socket and the two female ends through the Toggle Switch and Bosch relay COIL terminals in series. A multi-meter can be used to find a good source for the relay coil power and ground. I placed the Toggle (Button) Switch by the driver's right knee and routed their wires behind the console back toward the fuse panel. The Bosch relay was mounted out of the way on the upper right hand back side of the fuse panel using a factory hole in the metal frame.


The factory fuel pump circuit is not triggered to run until the distributor begins to rotate. If your injectors are not pressurized from being parked for an extended period, it can take several additional minutes of cranking before the fuel rails are fully primed. The new circuit allows you to run the fuel pump and pressurize everything up to spec's before engaging the starter. The spring loaded Toggle (Button) Switch is released prior to turning the ignition key to the start position. At this point as the electronically triggered fuel pump relay begins to run the pump (distributor is rotating) the engine is able to immediately fire up with no delay. Under normal conditions I'm sure that I wont have to prime the injectors when everything works as advertised but - if the need ever arises. Obviously not a graphic artist


Just My 2 Cents - Michael

[JhwShark]

Nice contribution! Should be part of...."Up-Fixin der Porsche" as many of the contributions here fit.

[Plexus928]

Here is an easier fix.
my accumulator was a leaker, I eliminated it.
Fuel pump is running at 50 pound pressure plus. from the moment the key/starter is touched it is micro seconds at that pressure before the injectors are under max fuel pressure. instant start.
no accumulator, no problems.
put a length of (high pressure)fuel hose in its place and give it a try.

edit;
Back to your friends slow start problem, assuming the problem is fuel delivery, as the fuel pump (with no engine running) is at max pressure instantly , the problem has to be faulty injectors, or fuel pressure regulator.