daveo90s4

Hi all,

1986 928 'twin distributor' LH model (ROW RHD, Australia).

I last drove this car a year or so ago, no problem. It's been up on my 4-post hoist since then. Decided to drive it. Cranked over fine, wouldn't fire.

I have:-
1. Put 12v power direct to fuel pump terminals. Pump buzzes fine, and with power direct to fuel pump terminals engine starts and runs fine, tachometer works. So fuel pump etc all good.
2. I have removed fuel pump relay and put multimeter across pin holes 30 and 87. With ignition on I get good battery voltage.
3. I have bridged pin holes 30 and 87. Fuel pump does not run. I think it should with these two pin holes bridged.
4. Then, just to be sure, I have removed the bridge and re-applied 12v power direct to fuel pump. Spins over properly and engine starts and runs fine.

So...... I am thinking that I have a break in the 12v wire that runs from pin 30 (or 87 - I need to check) to the +ve terminal of the fuel pump.

I think I can check that for continuity:- ignition on or off, there should be continuity between fuel pump 12v+ terminal and fuel pump relay socket pin 30 (or 87 - as above I will first check which of these two pins carries current from relay to pump).

And if that is the case, how best to fix? I am very reluctant to remove the CE board and 'play' around behind that. But I think if I were to:1
a. Get a new fuel pump relay socket;
b Make up four short wires with spade terminals to plug into the OEM fuel pump relay socket;
c. Make one new long wire to run from the fifth pin on the relay socket (12v+ ignition on ***) direct to fuel pump;

Then I would simply be effectively using all the original circuitry - apart from the believed-broken power dire to the fuel pump - and avoiding 'playing' behind the CE board.

And I think this would be a cheap and easy solution, easily documented for any future owner.

(*** I am deliberately not dealing with the 30 second ignition on fuel pump prime OEM stuff. Bridging pins 30 and 87 takes that out of the equation I think).

Many thanks in advance for any wise advice / suggestions.

Regards

David

FredR

Dave,

With the relay removed check pin 30 for voltage to earth [not terminal 87] - it should show battery voltage. Then check terminal 87 for resistance to earth - I suspect it will indicate infinite resistance- i.e. a circuit break.

daveo90s4

Dear Fred and all - I AM OFFICIALLY STUPID!!

Two things in my previous post that I did not mention.
1. I was playing with relay position XXII (because that is what my printed relay chart said was the fuel pump relay position), and
2. My reversing lights were permanently on, with ignition on (which I thought was just yet another unrelated problem).

Stumped by the fuel pump no run issue, I spent some time thinking about the reversing lights on problem. Decided the most likely problem was a stuck relay. In my lounge, not in my workshop. So I looked up on line the 928srus relay position for reversing lights. Eureka - position XXII. So I had been bridging the reversing lights (no wonder they were on with ignition on) and had not been bridging fuel pump relay pins 30 and 87 after all.

Too late tonight to go back out to the workshop to remove position XXII (reversing lights) jumper and install jumper in correct position for fuel pump.

I guess I should not be too hard on myself - the printed relay position diagram I had initially used is clearly wrong. Aaargh!!

Stand by, I will report back!!

(Just explained all this to my wife Fay. She says she was right all along, she had said it was probably an electrical issue. Precious)

Cheers

DaveO

FredR

Dave,

The only people who do not make mistakes are the BS merchants who do nothing but talk- welcome to the human race!

When I first got into DIY spanner work with my motorcycles back around 1972 a friend of mine had a BSA Bantam two stroke. Asked me if I could decoke the cylinder head- no problem said I cockily - dead easy - 4 bolts and the head was off. Quick wire brush and clean and back on with the head. As I was tightening the head bolts [no torque wrench of course in those days] something felt wrong so I removed the head again and bugger me- there was a washer over one of the studs! How the hell such happened I have no clue to this day.

daveo90s4

So....

Snuck out to workshop without darling wife knowing.
Climbed up ladder to access car atop 4-post hoist (to avoid incriminating myself by moving car parked below)
Into driver's seat, leaning down to passenger footwell
Removed bridge from reversing lights relay position, refitted that relay, tested reversing lights. Wonderful, they now illuminate in reverse only. Progress.
Removed fuel pump relay - correct one this time ha ha. Bridged pins 30 and 87. Fuel pump operates. Great. Not a wire-to-fuel pump problem after all.
Got back inside. While typing this wife says "For a minute I thought you must have gone back out to the shed. But you can't have" I stayed silent, neither confirming nor denying.

Should have it all up and running with little effort tomorrow. Now I can sleep without pondering it any more.

Good night from me Down Under

DaveO

FredR

So half asleep you fall off the ladder and break both legs!!!

By the way when I had the pleassure of your company last year you may remember that when we took that little spin in my 928 I was having some difficulty with the kick down not working. Later that evening after we had dinner and parted ways I sat down in the TV room and glanced over to the side table - dozy sod here noticed the kick down relay laughing its nuts off at me!!! I forgot to put it back in after doing some testing.

daveo90s4

So Fred. Q. How to fix a kick down switch problem?
A. Stick the relay back in!!

nice when the fixes are so simple. And we can laugh at ourselves.

cheers

Dave

daveo90s4

..

Bertrand Daoust

Don't worry Dave, we all make mistakes like that once in a while. I did few times...
The best thing is that you found the problem quite fast.
I really laughed when I read: "For a minute I thought you must have gone back out to the shed. But you can't have" I stayed silent, neither confirming nor denying...

Mrmerlin

If you can`t fix it with a hammer,
then its an Electrical problem.
Carry ON !

daveo90s4

Wee correction Stan

”If you can NOT fix it with a hammer then it is an electrical problem”. Ha ha.

i should have known this at the start of this little saga, when the original fuel pump would not run with 12v applied direct to it - even when I did hit it with a hammer!

Onward and upward

Dave

Mrmerlin

Fixed