Bosch Fuel Pump / Filter

[Athomas]

Looking at the different Bosch Fuel Pump conversions on the market, there are two approaches in respect to the position of the Fuel Filter.

 

Some use a Bosch Filter pre-pump, others use the Filter post pump.

One supplier uses two filters, one either side of the pump.

 

Also, one kit promotes running a larger feed from the tank, increasing the tank fitting and the fuel line to 3/8"

 

Does anyone know the benefits of one approach against the other?

 

My car has had a Bosch pump for many years, but used the old Lucas Filter, the associated plumbing wasn't the best, so either option is possible for me to follow.

 

Any ideas folks?

 

Thanks Andrew

[TR NIALL]

Cannot say what benefits are but most Suppliers will recommend increasing the the Fuel Line to 3/8". A Pre and Post Filter are also used, the Pre can be any type but the Post must be a HI Pressure type, an upgrade to the wiring supply is also recommended.

[Dave K]

Had problems with the usual "hot day, long journey" misfire. I tried a new pump kit which had the Bosch Filter pre-pump but no joy, misfire still persisted.

 

Eventually went the whole hog and fitted a set up as per the "Prestige Injection" kit. Enlarged feed from tank, small pre-filter, main filter after pump, new style PRV, and uprated wiring to pump via a relay..

 

Touch wood, so far no misfires....

[Athomas]

Many thanks Dave, Niall.

 

Whats involved with the enlarged tank outlet, did you need to solder a new outlet boss to the base of the tank?

[Les Pettitt]

Malcolm at Prestige fitted his enlarged tank outlet when he installed my Bosch pump. He merely unscrewed the old outlet and screwed the new one in. The tank was around half full with petrol and only a small amount escaped into the spare wheel well. His familiarity with the job made it look so easy.

regards

Les

[TR NIALL]

Hi Andrew,Mine also came from Malcom at Prestige,give Him a Call im sure He can sort you out with whats needed.

[Dave K]

Many thanks Dave, Niall.

 

Whats involved with the enlarged tank outlet, did you need to solder a new outlet boss to the base of the tank?

 

 

Managed to swap the pipes without draining the tank aided by two of these little clamps.

 

http://www.frost.co....hose-clamp.html

 

One on the old outlet pipe, one on the new. Unscrew old fitting with pipe attached, swap for new fitting with pipe attached... You do get a bit of petrol splashing around, so take the usual precautions....

Edited April 19, 2012 by Dave K

[Guest ntc]

There is not and never been a need to fit a larger fuel outlet pipe

[Andy Moltu]

Interestingly one of the suppliers who eulogised about fitting a larger outlet from the tank, for years fed that to a glass pre-filter that had an internal bore less than the standard tank outlet.

[jobster]

bigger outlet here, feed to original filter and from filter to Bosch both with bigger diameter fuel lines. Works fine.

[Grabea]

I wondered when someone was going to spot the fact that the bullet filter favoured by lots of people on here has 1/4 npt connections so no matter how big you make the tank outlet it'll be limited by the size of the filter connections

Graham

[Mk1PI]

Agree CAV filter works fine - if you are paranoid the alloy can be relieved/drilled out slightly where the unions screw in I did the same with my tank outlet and then went up a union size 5/16" ID > 3/8" from memory

[Jersey Royal]

I wondered when someone was going to spot the fact that the bullet filter favoured by lots of people on here has 1/4 npt connections so no matter how big you make the tank outlet it'll be limited by the size of the filter connections

Graham

 

Graham,

 

Depends what size of Bullet Filter you go for , you would have to have a brain the size of a pea to go for the smallest as you say 1/4 npt.

Fillter i use has 10 and 12 mm fittings a A5 or A6

 

http://www.fuelsyste....uk/filters.pdf

 

The filters that do offer a restricted flow in my opinion, and having had one originaly and taken it apart are those

glass ones with chrome ends.

 

Like these

http://www.ebay.co.u...er&geo_id=32141

 

Cheers

GUY

Edited May 1, 2012 by Jersey Royal

[Alec Pringle]

If you really want to know how to fuel and filter a Bosch pump, have a good look at the installations on the German cars that used K-Jetronic and L-Jetronic systems as original equipment in period. Unlike some TR specialists, the German engineers actually understood what they were doing, and why . . . . as opposed to bullshit baffling brains.

 

Cheers,

 

Alec

[badshead]

The filters that do offer a restricted flow in my opinion, and having had one originaly and taken it apart are those

glass ones with chrome ends.

 

 

Maybe so, and perhaps I'm just lucky, but I've been using one for 8+ years (Revington kit) without any problem whatsoever. Why spend £60 when £6 plus an annual element change does the job?

 

Bill

[Jersey Royal]

Maybe so, and perhaps I'm just lucky, but I've been using one for 8+ years (Revington kit) without any problem whatsoever. Why spend £60 when £6 plus an annual element change does the job?

 

Bill

 

 

I too didnt have any problem with the Revington jobby.

 

I changed to the Bullet when i fitted an aluminium tank, which had a larger outlet than standard,the bullet has a larger filter area.

 

Heres my Revington filter,

 

 

The ID of the central tube is 5 mm, the outlet or rather hole in an original tank is 7.7mm, then i suppose it depends on what fittings

/ pipework you use to connect the two. So the supply has a maximum size of 5mm. The thing for me though was the small filter area.

I seem to recall on my set up, there always being air in it , as if the pump was moving the fuel faster than it could refill.

 

But yes it worked and didnt give me any grief.

 

Cheers

GUY

[Grabea]

Graham,

 

Depends what size of Bullet Filter you go for , you would have to have a brain the size of a pea to go for the smallest as you say 1/4 npt.

Fillter i use has 10 and 12 mm fittings a A5 or A6

 

http://www.fuelsyste....uk/filters.pdf

 

The filters that do offer a restricted flow in my opinion, and having had one originaly and taken it apart are those

glass ones with chrome ends.

 

Like these

http://www.ebay.co.u...er&geo_id=32141

 

Cheers

GUY

 

Thing is Guy that the Sytec bullet filter only comes in one size with a 1/4 NPT female thread at each end, yes you may have a 15mm push on connection but it's screwed into the 1/4 NPT thread in the end that was my point, for this reason I am fitting a swirl pot into which the return from the PRV feeds, this has a 1/2" outlet to the Bosch so lots of fuel available for the pump to draw from.

I'm also fitting a non return valve to the pump delivery before the outlet filter to prevent any debris collected by the discharge filter finding it's way into the pump when switched off.

Graham

[Jersey Royal]

Thing is Guy that the Sytec bullet filter only comes in one size with a 1/4 NPT female thread at each end, yes you may have a 15mm push on connection but it's screwed into the 1/4 NPT thread in the end that was my point, for this reason I am fitting a swirl pot into which the return from the PRV feeds, this has a 1/2" outlet to the Bosch so lots of fuel available for the pump to draw from.

I'm also fitting a non return valve to the pump delivery before the outlet filter to prevent any debris collected by the discharge filter finding it's way into the pump when switched off.

Graham

 

 

With all this talk about pumps and pipes i have taken the bullet apart to change the filter, whilst at it i measured the brass fitting,

 

 

One end has an Internal diameter 9.5 mm and the other into the bullet casing 7.92 mm ( near as dam it 8 mm)

 

 

I have always thought of a 1/4 to be the equivalent of 5mm, so in this case it aint.

 

Anyway you can have all the largest pipework in the world, i would think it wont make a jot of a difference

if your tank outlet is standard size. But i dont have a degree in Fluid Mechanics so cant comment.

 

Cheers

Guy

[roy53]

Graham i would advise you to sent the return fuel back into the tank and not the new swirl pot,this is so used hot fuel from the prv goes to the tank and fresh cool petrol is then fed to the pump.Look at the diagram for the later 6s,this was always one of the early solutions for 5 & early 6s to help over come hot pumps.

ROY

[Grabea]

Graham i would advise you to sent the return fuel back into the tank and not the new swirl pot,this is so used hot fuel from the prv goes to the tank and fresh cool petrol is then fed to the pump.Look at the diagram for the later 6s,this was always one of the early solutions for 5 & early 6s to help over come hot pumps.

ROY

 

Thanks for that Roy, this was a concern but I'm going to give it a go anyway as the surplus fuel will still be returned to the tank via the vent on the swirl pot, if it proves to cause problems it's a simple matter of plumbing to change it.

Once I get it done I'll post the results, busy painting the doors for now.

Thanks

Graham

[Andy Moltu]

Does the swirl pot have a vent to take any air that gets drawn in back to the return at the top of the tank?

[smizgals]

 

One end has an Internal diameter 9.5 mm and the other into the bullet casing 7.92 mm ( near as dam it 8 mm)

 

 

I have always thought of a 1/4 to be the equivalent of 5mm, so in this case it aint.

 

 

Cheers

Guy

 

 

1/4 NPT thread has outer diameter of 13.72 mm and with a wall thickness of 2x 2.235 mm gives a 9.25 mm bore, with a wall thickness 2x 3.023 mm gives a 7.67 mm bore. See http://en.wikipedia.org/wiki/National_pipe_thread & http://en.wikipedia.org/wiki/Schedule_40 .

[Jersey Royal]

1/4 NPT thread has outer diameter of 13.72 mm and with a wall thickness of 2x 2.235 mm gives a 9.25 mm bore, with a wall thickness 2x 3.023 mm gives a 7.67 mm bore. See http://en.wikipedia....nal_pipe_thread & http://en.wikipedia....iki/Schedule_40 .

 

 

Thanks for the above clarification.

Cheers

Guy

[roy53]

Thanks for that Roy, this was a concern but I'm going to give it a go anyway as the surplus fuel will still be returned to the tank via the vent on the swirl pot,

Thanks

Graham

 

But Graham that was the exact problem with the early plumbing,the surplus warm fuel was returned into the filter thus depriving the pump of cool fresh fuel from the tank/filter/swirl pot.

roy

[006]

8 mm will be ok for standard low HP engines, but will not only starve the engine of fuel at top end, high revs/high load.

but will also cause pump to cavitate, as its sucking fuel too fast thru too small a pipe.

which leads to bubbles forming in the fuel, which then leads to even less flow.

that why you need a pree filter, and also an after filter, these stop the minute frothed up fuel going down the line, into the pump first,

the the pump its elf makes bubbles, so these then go into after filter, and dissapear thru the filter material, and come out as good fuel.

not the frothed up stuff that most of you lot with inadequate supply / filters will be getting.

 

Any one of you actually had a look at the stuff coming direct from the pump, its not a pretty sight.

then put it into a big filter, and then see what comes out, much better.

 

I honestly think this is why folk dont get the HP they think they have got, because the fuel is full of air.

how many folk keep saying, my injectors are playing up, got air in them,

where the air come from,!!!!!!

 

some one said , look at the German cars set up, a good bit of advice .

 

You really need a big outlet / feed if you wanting good HP,

 

R