82 930 is bucking....

galileo · 11-09-2011, 04:23 PM

While cruising seems like car is losing fuel pressure, and load buzzing noise coming from the rear. Fuel filter is new(did full tune up).
Fuel pump?

Thanks

mooney265 · mooney265's Garage

There are 2 fuel pumps... one between the front tires [by steering rack] and the other by left rear wheel...

You could turn on key, unplug blue/green connector at rear of CIS metering plate [plate sensor] and walk around car listening for both fuel pumps...

Let us know...

galileo · 11-09-2011, 04:40 PM

Rear pump buzzing really loud? Anyone here have detailed instructions on replacing rear pump.

Thanks

DSPTurtle · 11-09-2011, 04:51 PM

Tap it with a hammer and see if it will start pumping.
Oh yeah, to answer your question... take off the left rear tire. Grab a 10mm wrench and unbolt the two nuts holding the pump in. Lift up, twist and slide the pump towards you and use a 15mm (I think) and take the two fuel lines off (on one the back and one on the front). You need a 7mm and 8mm to pull the wires. Installation is reverse of removal. Should take you all of 1/2 hour. Most of the time spent taking the tire off and back on.
Oh yeah, make sure you have the new fuel pump in hand before you start

galileo · 11-09-2011, 05:05 PM

Thanks you very much!

galileo · 11-16-2011, 07:54 AM

Replaced rear fuel pump and still having same problem. Any thoughts?

Thanks

mark houghton · 11-16-2011, 10:07 AM

Allow me to do a listening check on this. Your words "a loud buzzing sound from the rear", and we jump to the conclusion that it must be the rear fuel pump. Galileo, did you confirm that it was indeed the rear pump that was buzzing, or just assumed and replaced it anyway...and still hear the buzzing? Maybe it's not the pump at all.....

Other things that buzz - well, I can think of one. If your car has the oxygen sensor/Lambda control system for emissions control, there is a frequency valve that oscilates in response to the signal it gets from the O2 sensor and computer. That freq valve is located behind and at the base of the fuel distributor (toward the front of the car...almost inaccessible). They make a constant buzzing sound that can clearly be heard without the engine running (but not so easy to hear with the engine running). Just a thought, probably not your issue, but if you had something odd going on with that control loop or it's components, it would mess with your mixture and may cause the poor running you're seeing.

So why would a brand new fuel pump buzz like a bee hive? Hmmm...

MBruns · 11-16-2011, 11:34 AM

If the car is running and the rear pump is noisey the problem may be that the front pump is not running and causing the rear to cavitate and not produce the pressure it should.

Mike Bruns JBRacing.com

Alan L · Alan L's Garage

Quote:

Originally Posted by MBruns

If the car is running and the rear pump is noisey the problem may be that the front pump is not running and causing the rear to cavitate and not produce the pressure it should.

Mike Bruns JBRacing.com

And it may not be the pump, but the relay.
One might hope the area of the buzzing could be narrowed down a bit by following the audible trail. But you could try swapping the two fuel relays in the fuse compartment up front - swap them over and see if the noise moves rear to front. Or goes away - as the front pump kicks in and the rear remains silent.
Alan

mark houghton · 11-16-2011, 12:52 PM

Quote:

Originally Posted by MBruns

If the car is running and the rear pump is noisey the problem may be that the front pump is not running and causing the rear to cavitate and not produce the pressure it should.

Mike Bruns JBRacing.com

THAT is a very good point and possibility!

galileo · 11-16-2011, 02:26 PM

Looks like it was the relay after all! You guys are great, thanks!

Leo

Alan L · Alan L's Garage

Quote:

Originally Posted by galileo

Looks like it was the relay after all! You guys are great, thanks!

Leo

Rather late in life, I have concluded that is why Pelicans were put on this earth. To serve a purposeful life up fixin der Porsche.
Alan

mark houghton · 11-16-2011, 06:07 PM

Well that's a pisser....spend the $$ on a new pump only to find that a fraction of the $$ for a relay fixes things.
I've got spares rattling around in my glove box - amongst other "just in case" things.

DSPTurtle · 11-16-2011, 06:23 PM

Hey Leo,
Send me your old pump so I can test it

jrogers · 07-23-2013, 08:46 PM

A bit of an old thread, but it helped me out. I was teaching my daughter to drive my 87 930, and the next day I had this exact problem. I think it was all of the on and off of the key that must have caused the relay failure. I was able to replace the front pump relay with the AC relay which was the same, and the problem was solved.