Fuel Pump Maintenance

[bpossel]

Hello All!

I am thinking about doing some fuel pump maintenance.  In particular, I am thinking about removing the filter and cleaning it.  From what I have read, it seems that I need to remove the pump in order to get a good grip on the nut to remove the filter.

George, and or others...  here are my questions:
1.  Do I need to remove the pump in order to remove and clean the filter?
2.  Is cleaning the "correct" way to go, or should I replace the filter?
3.  Who sells the filter?
4.  What other things should I watch for?  Tips and tricks?

Thanks All!
Bob


bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[George Des]

Bob,

I've only removed the inlet and outlet fittings with the pump removed, but I'm sure if you are very careful in not destroying the pump rubber mounts that you can get to them off with the pump still mounted. I find the pump much easier to grip and easier to apply force to the fittings with the pump out. I have not been able to find the inlet screens new. I have it on my list of things to check out with SLS and others to see if they can source from Bosch--not sure they (Bosch) will sell directly. The same inlet screen is used on both style pumps. I have not seen many screens that are so bad, though, that they actually need to be replaced. They are fairly easy to clean. All that being said, I have damaged some of these screens beyond repair in the process of trying to remove them from the fitting preparatory to glass beading the fitting and mounting plate. I suspect others have damaged them in much the same way.

George Des

[ja17]

Hello Bob,

The screen is part of the intake fitting of the fuel pump. Follow the line from the gas tank to the electric fuel pump. The fitting which the hose is clamped on is the one with the filter screen. Early version 230SLs with their original electric fuel pumps may not have these screens.

Be prepared to clamp off fuel lines to prevent a major spill.  You man need to unfasten the metal schroud around the fuel pump.  I use a air impact to remove the fitting while the pump is on the car. This is about the only way without removing the pump.  The problem is the pump is suspended by those little rubber mounts and you'll break them all up from the strain of removing the fitting with a wrench. An air impact works good. Do not use an electric impact!  Too much chance of fire!

You can clamp off fuel lines to prevent spills with needle nose vice grips if your fuel lines are in good shape. If your fuel lines are old and brittle be prepared to change them, they will not survive the trama. Make sure to have something to hold fuel, something to soak up spills,  some new fuel line and clamps and a fire extinguisher.

Its best to do fuel work in the well ventilated outdoors. Be even aware of static electric discharge.

Joe Alexander
Blacklick, Ohio

[bpossel]

Hi Joe, George!

Thanks for the information.  Looks like I will remove the pump and simply (and carefully) clean the mesh filter.  I replaced my tank and IP Pump a couple of years ago, and am now really curious if any "crud" is on the mesh.  Something I should have looked at when the tank was out. I will try and take some photos and post.

Hope everyone has a wonderful upcoming holiday weekend!
Bob


bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[hands_aus]

quote:Originally posted by bpossel

Hi Joe, George!

Thanks for the information.  Looks like I will remove the pump and simply (and carefully) clean the mesh filter.  I replaced my tank and IP Pump a couple of years ago, and am now really curious if any "crud" is on the mesh.  Something I should have looked at when the tank was out. I will try and take some photos and post.

Hope everyone has a wonderful upcoming holiday weekend!
Bob


bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

Hey Bob,

Before removing the pump, take the hose off and use an artists brush to probe around in the inlet connection.

Take it out and if it is covered in gunk then you know it will need cleaning.

Here is a pic of the fitting on the old style pump.
Maybe you could remove the whole fitting with the 4 screws. Then when the filter is clean use a new o-ring to seal it.

Download Attachment: InletOutletConnectionPointsTextAdded.JPG
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Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[ctaylor738]

I just cleaned the inlet filter on my 280SE.  Removed the pump and clamped it in a vise using 1/2" softwood pads.  Removed filter fitting.  Hard to see how any gas got to the engine.  Soaked it overnight in carb cleaner and hosed it off.  Looked good as new.

Chuck Taylor
107 Addict
Falls Church VA

[bpossel]

Finally got around to remove my fuel pump today.  Pump was easy to remove.  Clamped all hoses, etc. and removed pump shield, then pump.  With the pump in a vise, took a bit of force to remove the filter.  WOW!  I could not believe how much "crap" was in the small filter.  Not sure how my car even ran.  See attached pics of before and after.  It was similar to cleaning a coffee filter full of coffee granules.  Note: I purchased my car over 2 years ago and replaced my gas tank w/new at that time, and also had Hans rebuild my injection pump.  Also, at the Tech Session last summer in Ohio, Joe tested my fuel pressure and it was on the low side, but as I recall, still within spec. Overall, car has been running very well.
I am currently in watching the shuttle launch (count down) and have not put the pump back on, but very anxious to re-install and see if engine starts, runs smoother.

Even if I don’t notice any difference, this is still a very overdue maintenance item on my car...

Regards,
Bob


Download Attachment: before.jpg
49.4 KB

Download Attachment: after.jpg
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bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[George Des]

Bob,
 
Your picture give a pretty good idea of how this build up can block the fuel flow. It also gives a strong hint on what can cause the older pumps to go bad, especially the ones that do not have an inlet filter screen and I've come across many. My guess is that early pumps on all the FI models came this way and that DB may have received a lot of complaints so the inlet screens were added later in production by Bosch. This same crud gets between the sealing surfaces of the main bellows seal and wears the surfaces so they don't seal anymore. Also the build up can "lock up" the vane and when power is put to the pump it overheats and burns out the windings. Trying to "unfreeze" the vane often leads to breaking the small tang on the seal driving washer which leads to the shaft spinning in the bellows seal with attendant leakage though the main shaft o-ring. Point is, this crud is very bad for the fuel feed pumps--old or new. I'll leave it to Hans and others to describe what it can do further down stream if it gets past the fuel feed pump.

George Des

[Jazn]

My fuel pump has no such screen, very early 230sl.

[lurtch]

Hello Bob and all others - - I think I need to go on record here and suggest a quick REALITY CHECK !

Bob, you would not be seeing that kind of crud accumulation in the filter unless your tank is well along the way to being completely  rusted through.  When you see rust scale like that, think of  the old cliche goes " - -  there is more where that came from - - ". You are not fixing the problem and eventually  you will start smelling gas fumes because the top of the tank will finally rust through. I know this because it happened on mine. I urge you to drop the tank and have a look at the interior of it.

Regards, Larry in CA

[bpossel]

Hi Larry,

I agree!  However, in my case, I replaced my tank, with a brand new MB tank shortly after I purchased the car.  I should have performed the fuel pump filter cleaning at that time, but I didnt know there was a filter in the pump at that time and have put this maintanence off for too long!  When I replaced the tank, I also had my fuel injection pump rebuilt.

The reason that I replaced my tank is that the previous owner did the tank re-liner route, vs replacing.  When I went to fill up the tank for the 1st time, I noticed a "skin" like material peeling at the opening of the tank, by the fill area.  I knew that if I didnt replace the tank w/new, that I would be fighting the rust, crud issue and never being pleased with the perfomrance of that car.

So, I agree, if you see this much "crud" in the fuel filter screen, you have bigger issues...  basically, need a new tank at a cost of 800-900 bucks.

Regards,
Bob


bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[ja17]

Hello Bob,

Nice photos of the electric fuel pump and fuel pump screen! Yes it is amazing what you find in these fuel systems. They seem to be very resilient! The three layers of screening and filtration work well. Water in the fuel then left to set, seems to do the most damage to the system.



Joe Alexander
Blacklick, Ohio

[ja17]

Hello Bob,

Nice photos of the electric fuel pump and fuel pump screen! Yes it is amazing what you find in these fuel systems. They seem to be very resilient! The three layers of screening and filtration work well. Water in the fuel then left to set, seems to do the most damage to the system.



Joe Alexander
Blacklick, Ohio

[waqas]

Sorry to resurrect this discussion, but I'd like to join the fray!

I've been cleaning out my fuel lines and filters this weekend. Specifically, the tank screen (was fairly clean), replacing fuel filter (gunky!), blowing air through the feed and return lines (forward-to-rear), and passing some old guitar (bass-E) strings through the internal fuel-tank lines to/from the "flower-pot" (with kind permission of the Dr Benz). My last task was to clean out the fuel pump screen, and I discovered I had the old-style fuel pump. Is it true that NO old-style pumps had screens? Can a screen fitting from a new-style filter be used on an old-style filter inlet? (do the threads match?)

I removed both inlet and outlet fittings to look inside the lower housing. Upon closer inspection, the outlet fitting (connected to engine side of pump) contained some kind of loose metal plate or mesh (I couldn't tell). Is this normal? I tried to take a picture, but it's not quite clear. Any ideas?

http://www.sl113.org/forums/uploaded/Waqas/200692542223_old-style-fuel-pump.jpg

WAQAS in Austin, Texas

[George Des]

WAQAS,

Many of the earliest large style pumps did not contain the inlet screen. I'm not sure when Bosch started adding these to these pumps, but I have noted that most of the ones with a screw type inlet fitting do not have it. The screen is exactly the same for both the large and small type pump, so if you're lucky enough to find a screen in good shape on a salvage small style pump, it is a simple press on fit to the inlet side fitting. I took a look at your picture and what you have off is the outlet side fitting. I think what you are calling a metal plate is actually the check valve that prevents fuel from flowing back into the pump.

George Des

[waqas]

Of course! A check valve makes perfect sense... thanks!

The picture was indeed of the outlet fitting, and I was trying to show the newly-identified check valve. The inlet fitting did not have a screen attached to it, but I was wondering if there was some other screen within the pump...... I gather not, from your post....

So on to my next question: assuming I can find a salvage new-style pump's filter screen/fitting (which is unlikely at the moment), once attached to the old-style pump inlet fitting, will the screen interfere with anything (impeller, etc) inside the old-style pump? I haven't opened my pump... no reason to...

Thanks for sharing all this valuable info!

WAQAS in Austin, Texas

[George Des]

WAQAS,

No, the screen is a direct fit to the inlet fitting and will not interfere with the impeller which is actually in a separate chamber from the inlet and outlet fittings.

George Des

[waqas]

Hi George, it's kind of you to have a 'live chat' with me regarding 40-tear-old fuel pumps at 5:40am CST!  

So, do you know if this screen (or entire fitting w/screen) is available separately from D-C?

Thanks again,

WAQAS in Austin, Texas

[George Des]

If available, I think it would be directly from Bosch. I have not contacted them so I don't know for sure. The inlet and outlet fittings are available from SLS. The outlet fitting  w/integral ck valve is fairly expensive. I've purchased the inlet valves--fairly cheap-- and they come w/o the screen. I have not asked SLS if they can supply the screens, but it may be worth a try if you cna't find one otherwise.

George Des

[waqas]

Thanks for the lead... I'll send SLS an email (I don't see it as an extra part in their online catalogue). If available, this would probably be a much better solution than trying to place a non-standard in-line filter between the tank and the old-style pump... avoiding any issues with fuel flow etc.

Kind regards,

WAQAS in Austin, Texas

[Ben]

I have a pump that has blown its fuse (8a) twice in quick succession !

I thought I had an ammeter hgere but it seems someone borrowed it and never gave it back (again !). Anyway I was about to remove it and open it up to check the brushes and the commutator, and repair/replace as neccesary, also checking the bearings for smoothness along the way !

Anybody had this problem or can throw any further light on it ??

Do you guys reckon the above repairs should sort out the problem ?

BTW the car starts and runs fine but dont trust it to drive anywhere but around the lot ! Also I removed all fuses and cleaned the corrosion and cleaned the connections at the pump and the fuse has been okay since but..........

Regards,
Ben in Ireland.
'64 230SL 4sp.

[waqas]

Hello Ben,

You might want to test the fuel pump by itself before you start opening it up. You can do this by placing a fuse directly in series with the positive terminal and the battery. If the fuse never blows, then it might be a temperamental short-circuit somewhere else in the wiring from the fuse-box to the fuel-pump.

Be careful when working around fuel vapour while messing with loose wiring, as sparking may occur. Make sure wiring is secure before applying power.

I hate tracking down temperamental short-circuits, as they never appear when you're looking.... :evil:

WAQAS in Austin, Texas

[hands_aus]

quote:Originally posted by Ben

I have a pump that has blown its fuse (8a) twice in quick succession !

I thought I had an ammeter hgere but it seems someone borrowed it and never gave it back (again !). Anyway I was about to remove it and open it up to check the brushes and the commutator, and repair/replace as neccesary, also checking the bearings for smoothness along the way !

Anybody had this problem or can throw any further light on it ??

Do you guys reckon the above repairs should sort out the problem ?

BTW the car starts and runs fine but dont trust it to drive anywhere but around the lot ! Also I removed all fuses and cleaned the corrosion and cleaned the connections at the pump and the fuse has been okay since but..........

Regards,
Ben in Ireland.
'64 230SL 4sp.

Hey Ben,
The Problem may not be with the pump but the wiring.
I would disconnect the wires from the pump and test by replacing the fuse and switching the ignition on.

Alternately use a multimeter to test if the pump +VE terminal has a direct short to earth.

If the coils of the pump are burnt out they can be rewound by a motor rewinding company. This has to be a lot cheaper than a new fuel pump.

It could be that the brushes are badly worn.

When I rebuilt my pump (with sage advice from guru George Des) I did not replace the brushes because they were still about 25mm long.
The local Bosch place had replacement brushes for about $25.00 a set.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[George Des]

Ben,

When everything is operating correctly with these pumps under load, they draw anywhere from 3.1 to 3.5 amps. Check yours out with an amp meter. If the circuit is drawing more than that make sure you don't have any other consumers drawing through that fuze--the pump should be the only consumer (radio or other accessory)-- or a possible short someplace. If the load is heavier than 3.5 and you can't find a short or another consumer, you may have a pump with possible seized/tight bearings, worn brushes or crud in the vane chamber that is causing some internal resistance--this you can rectify by dismantling the pump and replacing the bearings, brushes, etc. There are many posts on the board on how to do this. With age, these pumps also tend to have considerable carbon build up in the motor section from the wearing of the brushes. This combined with any fuel leakage into the motor chamber forms a thick black paste that really plays havoc with the lower ball bearing. Hope this helps.

George Des

[Ben]

Thanks guys for the help and advice...........I should tell you where I am at........this car had its feul injection system removed completely some years ago, and has been running on Gas ( not petrol) for some years. The current owner asked me to convert it back, so having amassed the various parts required, I removed the fuel tank and had it boiled & sealed, replaced the fuel pipes and clips, fitted the injection pump and built up the WRD.

I also repaired the CSV and removed the electric pump for cleaning & testing. I opened the end plate and was surprised to find a very clean impeller. I ran diesel through the pump and tested the output and pressure which were all very good. Because of this I decided not to open the pump any further so I fitted it to the car.

The car starts and runs fine but as I said, I drove it about 1 mile and returned and whilst idling it stopped and the fuse was blown. This happened once again after a similar drive.All the fuses looked bad so I changed some and cleaned them all.

Since I am in the electric motor business pulling the pump and replacing the brushes and bearings wont be a problem so I think I'll do that tonight and rule it out properly.

If it happens again all I can do is run a fresh wire from the original fuse back to the pump !

Regards,
Ben in Ireland.
'64 230SL 4sp.