Livio928

I have had three go in my two '89s. Once in the middle of nowhere farm country where the nearest property was about 1 1/2 miles away. The other was at Watkins Glen and I had to be towed back home to Ontario (3 1/2 hr). I have been thinking to keep a spare with me as well.

jcorenman

Sorry for the confusion. But the question I posed was why an original pump with relatively low miles would show so much wear. I am still clueless...

The commutator was not machined that way, both the brushes and commutator were badly worn. There was no mechanical binding that I could find, the rotor and pump turned freely and the pump ran quietly. These things run immersed in fuel, and we almost always fill with Chevron or Shell 92-octane.

It is particularly annoying since these things are sealed cans-- there is no way that I know of to open them for periodic inspection and then put them back in service. Other than taking it down to the clinic and trying to talk them into an x-ray, I don't know of any way to identify this sort of wear before it fails. And at $200-250 a pop it's kind of painful to just add a fuel pump to the every-60K-mile list. (But that's probably what the clinic would charge for an x-ray, if they could be talked into it).

Cheers, Jim

Glen McCartney

Wonder if the resistance of the windings on the armature/rotor of this particular pump was causing a higher than normal current draw but not enough to have a fuse blow could have been the cause of the premature wear of the commutator and brushes. Only thing that may make sense as others have had original pumps for 100,000's miles.

123quattro

I'd bet they got a batch of spring from a different supplier that were stiffer than spec. Thus the extra wear from the brushes. Quality control has improved leaps and bounds in the last 30 years.

That said, nice work on the actual pictures.

Livio928

The mechanic I use, who was from the factory and trained in Stuttgart in 70's and 80's asked if i used the octane boost in my fuel. I did when I would go on the track. He mentioned that many of the pump failures he had seen, seemed to have a correlation with added octane boost in the fuel and the pump failure. Not sure exactly how that could lead to failures in the pump itself, but I do have to say that it occurred with me three times over the years. Could the extra octane/acetone or whatever they use contribute to this? Just something else to ponder.

CraigL

How are brushes made? Does anyone know?
Is there any chance that something hard (an impurity) was embedded?

jpitman2

My guess would be some resistance somewhere lifting the current - check the new pump's draw, and see if its higher than normal. My 83 CIS pump pulls 7-8A - now. I have chewed through 2 pump relays in my 10 years with the car. Last time it failed I had to jumper the relay to get home, and while I was checking things I saw a spark out of the corner of my eye - the the pump fuse (early bullet style)! Poor contact. Now I have made some adapters so I can fit blade style fuses for the high current show stoppers. The pump fuse on mine is a 16A (IIRC?), so there is some room for the current to rise before blowing the fuse.
jp 83 Euro S AT 55k

Mike Simard

What can you tell about the commutator construction, is it machined copper or press formed from some kind of mix?
This really deserves some effort to find the cause.

Gasoline formulations have changed alot and have caused mysterious degradation of lines in the aviation industry that nobody could understand.

If the commutator is solid copper though, that rules chemical attack out.

Could the polarity have been reversed?
In electrical discharge machining, changing polarity can have a huge effect on the wear of the electrode or workpiece.

Lizard928

I've opened a number of these pumps up, high miles too, and have NEVER seen wear like that on any of the ones I've opened....

docmirror

After hearing about the octane booster additives, I'm leaning toward a chemical issue. The additives are supposed to be high in Oxegenates. Wondering if there is some aggressive chem reaction between the O2 in the booster and the pure or nearly pure copper of the commutator. If the car sits with the commutator in a bath rich in O2, I think it might make a lot of surface Cu2O, or CuO? Chemists?

Just an idea, but I don't have much to back it up.

John Speake

IIRC the pump is straight after the tank, the filter after the pump. So fuel contaminated with fine (abrasive) particles could get into the pump and cause the heavy wear you have found ?

It would be interesting to see what's inside the filter...

WallyP

Octane boost?

If you are talking about the standard parts store octane boost, you are just wasting money. They do a fair job of doing exactly what they say that they do...

The problem is that adding $5 to $10 worth of octane boost to increase the octane of the fuel four or five points is pretty silly. They are counting on you thinking that a "point" is one octane number - it isn't. An "octane point" is actually 0.1 octane number, so your fuel goes from 89 to 89.5 octane, or 91 to 91.5. Whoopee.

waynestrutt

"And at $200-250 a pop it's kind of painful to just add a fuel pump to the every-60K-mile"
Jim
I am using this.
http://www.ebay.ca/itm/390476309080?...84.m1423.l2649
The volume is 228L/Hour
At this price I can keep a spare. If anyone is concerned about volume this puts out 228L/hour or 60 gal/hour.More than any 928 requires we hope.
From the WSM
1979 1360 CC/30 SEC

FOR K-JETRONIC

(1981/1982 Models)

Engine M 28.09 and M 28.10 1120 CC/ 30 SEC

(1980/1981/1982/1983 Models) L JETRONIC

at least 1150 cc/30 sec.

Beginning with 1984 Models

Engine Type M 28.21/22 1350 CC/30 SEC

85 on 1350 CC/30 SEC. M28 43 44 45 46

As from Model 87

Englne type M 28. 41/42/47/49/50

87 on 1250 CC/30 SEC

At 6300 rpm the fuel pump is turned off at the relay

228 L/ hour or 1900cc/ 30 sec so we are well covered. If you need more pressure put a restrictor in the return line to the tank but more than likely the pressure regulators will take care of that.

jcorenman

The commutator should be solid copper, but is badly discolored as well as worn. That would suggest surface oxidation of some sort, e.g. chemical contamination. Which could be related to rapid wear (i.e. heat and arcing where the brushes meet the commutator). I'm no expert but folks who are, worry about clean commutators.

No additives except occasional techron, years ago. No octane booster, ever (no need...). The tank was clean when I had the sender out last year (intermittent fuel gauge). I'll check it again as soon as I get the GT put back together... And filter pic's coming...

hb4

Jim,
Here's some info from the web....



[URL="http://www.gulfelectroquip.com/technical.php?technicalname=commutator"]Here's another site with more info, including photos of types of brush wear and causes.URL]