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post #1 of 9 (permalink) Old 11-16-2008, 02:26 PM Thread Starter
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Fuel Pump Function: one man's opinion

Symptoms, debugging info, whys and hows from my experience. In pondering the mysteries of the Bosch fuel pump in our 164 cars, I have found some information and come to some conclusions. I hope these will be of some help to others in identifying what and where to fix.

The Bosch in-tank fuel pump has an integral 1-way valve at its outlet to prevent loss of fuel pressure when turned off, thus delivering fuel more swiftly to the injectors when the car is once again started. As instant a response as can be hoped for. But the fuel line between the pump outlet and the exit fuel port may (and in our Alfa 164s _does_) have a rubber fuel line connection which can split. This can cause decreased fuel flow and decreased fuel pressure to the regulator. If too much fuel is diverted from the main line, the pressure can be too low to cold-start the engine. However, this was not the problem I experienced.

I had just cleaned up a fuel pump assembly and replaced the rubber "skirt" bushing Alfa uses to mount a plastic cage with fine fabric filter around the input port of the pump. The pump skirt has one penetration at its top which is used for a "soda straw" tube providing a suction port to the head space at the top of the fuel tank. This was described to me as an anticavitation measure by Paul, a senior Alfa mechanic at DiFatta in Baltimore. I had installed this the best I knew how, but I was finding that the fuel lines in the car had a mix of fuel and air in them, making for very irregular metering of fuel into the cylinders and consequent very rough running.

When I topped off the fuel in the tank, things ran better, but never well. This reminded some of the split in-tank hose issue, but the pressure in the fuel line appeared uniformly high, and seemed not to decrease with time after shutdown. Even days later, I'd still see a huge volume of air mixed with fuel coming from the fuel supply line when I disconnected it at the fuel rail.

When I pulled the pump again, its inlet filter screen was plugged with rust dust and sealer film from the fuel tank. I thought about what had happened and decided that Bosch/Alfa wanted the fuel pump to suck air instead of unfiltered fuel from bypassing the screening, so they provided the fuel strainer "soda straw" path to the top headspace. When the screening gets too dirty to allow sufficient fuel to the pump, the pump starts delivering a mix of fuel and air. Some fuel gets through to provide lube for the pump, so it doesn't self-destruct, and the pump doesn't suck on the blanked-off fuel strainer to tear the strainer and suck in a sudden and enormous amount of crud and destroy the pump that way. Sort of a best outcome solution, if you ask me. It tells the operator that there is a problem without destroying anything.

So I got some clear 3/4" od x 5/8" id vinyl tubing and a 2 gallon fuel can. I siphoned out the bottom of the fuel tank through the fuel pump mounting port until I could get no more rust and crud. I cleaned off the pump, rinsed the rust dust off the filter, reassembled everything paying attention to which of the four identical looking holes in the top of the fuel pump skirt (alfa part number 60801387, "seal gasket") actually penetrated to the pump inlet area. Only one does, and if you put the straw in the wrong one it will do nothing and the pump will pull unfiltered fuel through the correct hole. The car will continue to run for a while, but it may destroy the pump and you won't get much advance notice.

In hopes that this helps someone. I thought about the possibility of a split fuel line (high pressure side) and decided there was only one way it could cause air intake: if the unintended fuel jet caused a fine spray of fuel to inject bubbles into the fuel where it is taken through the filter, then one could get significant air into the pump. This seems not to have been my problem, but which seems to be plausible. I did look at the rubber fuel line connection when I took the pump out the second time. The first time it looked intact, and the pump had been running before its host car was totaled, so I put off replacing it. It turns out to have been aged and a little bulged, but it was intact. But it needed replacing, as a pre-emptive rather than corrective measure.

I looked up a picture to post below. I have another car which just now is giving hard starting behavior after sitting overnight. I _suspect_ this means it actually has a split in-tank hose and not just a crudded up filter. We'll see soon.

Michael

Last edited by MrT; 11-17-2008 at 09:29 AM.
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post #2 of 9 (permalink) Old 11-16-2008, 02:38 PM
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Good write up Michael. Bottom line is fuel pump will work well in a clean environment and with good check valve and rubber hose(s) depending on VIN. Early VIN's have one hose later have two above check valve and below tank cover outlet. Later VIN fuel pumps also have added filter screen added to bottom of pump to prevent trash from inside filter bucket from flaking rubber bushing pump mounts in or trash sucked in through soda straw. Cleanliness is next to good running Alfa!

Ciao, Alfisto Steve
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Alfa Semi-Daily driver: USA model - BB2 1991 164S Black Beauty II ALFISTO [U]

[U] BB1 1991 164L w/S engine and A/T now excess to inventory [U]

Daily driver and parts hauler but not car hauler 2004 Jeep Grand Cherokee Overland 4.7L H.O. V-8

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post #3 of 9 (permalink) Old 11-16-2008, 07:37 PM Thread Starter
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More info

I found an updated number for the rubber skirt (seal gasket) that had spilled over onto the next page of the parts list I had. The "new" number is 60572049 and refers to a pump change with the addition of a pre-filter on the pump. This would be the change to which Steve referred above. But I'm not certain what the change really, really is and whether there is really a change in the rubber seal.

I also found an image (posting a png for now):

Item 18 is a hard plastic tube attached to fittings on the early cars, but the fittings are modified for the later cars so the plastic tube can be replaced with ~8mm rubber tubing shown as item 31. Item 31 is the longer 3-3/4" or so hose that I have actually seen split instead of just bulging. Item 21 is the 1-3/4" or so rubber tube that lots of folks mention. The stock items are rubber hose without internal reinforcement but with a fiber jacket bonded to the rubber for strengthening. As the jacket de-bonds over time from the rubber, the rubber is left weaker and it splits. These are the items which are recommended to be replaced with Gates' submersible hose (Viton lined and Viton coated with internal fiber reinforcement).

Item 12 is the "seal gasket" I've mentioned. It has an orientation on the pump to align with some tabs on the pump body, and is attached in place on the pump with hose clamp item 22. Item 2 support arms are asymmetric, and Item 27 appears to be the "soda straw". The through hole in the seal gasket into which item 27 goes should be coming up at approximately the edge of the cover plate item 1, assuming I remember correctly and actually got the item in place properly. Unfortunately, the orientation of the gasket was an afterthought for me because I didn't have such a write-up as this for reference. Maybe your life can be improved in that regard.

The pump basket is a fiddly fit through the gas tank port. When removing it, you may do well to rotate the whole pump flange a few times to get the plastic bucket #3 oriented correctly so as not to break the fixturing for the arms #2. Take your time. It's possible. I broke one side of the first one I removed, but the next two times I removed pumps, everything survived.

Michael
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Last edited by MrT; 11-17-2008 at 08:36 AM. Reason: clarity and correcting the error Steve noted re: item 18 vs. item 31
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post #4 of 9 (permalink) Old 11-17-2008, 07:57 AM
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In your second paragraph second sentence change item "18" to 31 (longer hose in later models). Item 18 is early model rigid hose with banjo fitting that 31 hose replaces in later models.

Maybe new rubber seal gasket is supposed to hold up better to gasoline and not come about and clog pump intake. If you have metal mesh pre filter screen cap on base of pump rubber bits can't get in pump anyway. Bosch part number on pumps seems to be the same though with or without prefilter cap. Maybe Alfa part number for pump is different though.

Ciao, Alfisto Steve
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Alfa Semi-Daily driver: USA model - BB2 1991 164S Black Beauty II ALFISTO [U]

[U] BB1 1991 164L w/S engine and A/T now excess to inventory [U]

Daily driver and parts hauler but not car hauler 2004 Jeep Grand Cherokee Overland 4.7L H.O. V-8

"A day without an Alfa whine is like a day without sunshine"
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post #5 of 9 (permalink) Old 11-17-2008, 06:54 PM
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Cliff notes questions...
1) Can the later style be easily retrofitted to an earlier car?
2) What's required to do so?
3) What's the approximate change-over date?

Brad
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post #6 of 9 (permalink) Old 11-17-2008, 07:06 PM Thread Starter
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The pump assemblies are fully interchangeable. I used an older style ('89 production) single rubber hose assembly with no inlet screen on the pump proper in a '91S with no problem, and the '91S assembly (crudded up with liquefied rubber in the pump) looked no different from the dual hose jumpered '92S assembly I refitted for my wife's car. The seal gasket also seems fully interchangeable. It is my take on it that the older plastic hose assembly #18 could be exchanged transparently for the later fittings and rubber hose as in #31. It _could_ be as simple as removing the plastic tube and adding the rubber hose and clamps, but I can't just now guarantee that the actual fittings are the same from #18 to #31.

The changeover date is another question. I know the late '91 production '92S has the two-hose setup, the late '90 production '91S has the single hose with pump inlet screen, and the late '89 production '91L (not a typo) had the early no-screen pump with the single hose jumper.

Michael

Last edited by MrT; 11-17-2008 at 07:09 PM.
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post #7 of 9 (permalink) Old 11-17-2008, 07:21 PM
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Ahh, so there's actually three different setups! I've never dropped the tank on my 3/90-built car, so I can't contributute any data point. I bet your '89-built car has that extra brace behind the glove-box, right? (The one you have to cut when R&Ring the stepper motors). But I digress.....

Brad
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post #8 of 9 (permalink) Old 11-17-2008, 07:31 PM Thread Starter
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Quote:
Originally Posted by DPDISXR4Ti View Post
Ahh, so there's actually three different setups!
As I see it, there were two changes made along the way, each of which was plug-compatible (to mix metaphors a little) with the previous ones.
Quote:
Originally Posted by DPDISXR4Ti
I bet your '89-built car has that extra brace behind the glove-box, right? (The one you have to cut when R&Ring the stepper motors)....
I'll probably find out next spring.

Michael
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post #9 of 9 (permalink) Old 11-17-2008, 08:37 PM
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Quote:
Originally Posted by DPDISXR4Ti View Post
Cliff notes questions...
1) Can the later style be easily retrofitted to an earlier car?
2) What's required to do so?
3) What's the approximate change-over date?
1. Yes
2. Nothing but if you use two hoses you need banjo fitting item 32 or possibly cut old one off item 18 Rilsan feed pipe.
3. Production year 1991 all ZAR164000*06215000 - ZAR164000*06253900

Pump with pre filter screen VIN/chassis 6246085
Second rubber hose item 31 started with VIN/chassis 6250454

Ciao, Alfisto Steve
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Alfa Semi-Daily driver: USA model - BB2 1991 164S Black Beauty II ALFISTO [U]

[U] BB1 1991 164L w/S engine and A/T now excess to inventory [U]

Daily driver and parts hauler but not car hauler 2004 Jeep Grand Cherokee Overland 4.7L H.O. V-8

"A day without an Alfa whine is like a day without sunshine"
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