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Trouble with Bosch Pump


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Hi, I have just acquired a 1971 TR6, have been relayed home twice already. The pump overheats and starts sucking in air making a terrible noise. Petrol tank full. It has a new tank and all new Bosch ancilliaries. I think it could be the filter that is connected to the tank. The pump runs for about 40 miles, and gets very hot, also the pressure relief valve. It is in the garage at the moment in disgrace. Hopefully I will take the filter out soon and have a look at the innards which can be changed. The AA man seems to think it is the pump. I was talking to a mechanic who said that the pump was probably changed first and that didn't work, so then the petrol tank was changed, but the dross from the old tank was in the new system. Have not checked out the voltage output to the pump.

 

All very annoying, don't get this with the 500SL.

 

Some cowboy firm have been playing with the car who should have known better, ran rough at first with injectors 1 and 2 connected wrongly, after that goes like the clappers, no misfiring.

Any thoughts from the experts would be great.

 

Thanks a lot lads.

 

Regards,

 

Roy Jackson

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All very annoying, don't get this with the 500SL.

 

 

Yes, but you won't need to remortgage your home to pay the repairs cost! (ex 350SL owner)

 

It's probably not sucking in air, what you're hearing is cavitation (fuel vapourisation) and vapour doesn't pump too well. I'd start by replacing both the pre and post filters and checking the fuel pressure at the metering unit to check the fuel supply and operation of the pressure relief valve. Also have a look in the tank to see (or hear) if fuel is refurning to the tank. It might be a faulty pump, but in this application the Bosch pump is operating at the margins of its capacity so more likely the sound of it protesting as it struggles to do its stuff.

Edited by badshead
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Agree with Badshead - cavitation caused by a suction restriction. This could be caused by the wrong type of filter, blocked filter or the lines being too small.

 

Remember that the Bosch pumps have a much higher rated flow than the original Lucas. This means greater flow through the suction line pipes and filter and also greater flow through the relief valve and return line as the engine will still be using the same amount of fuel.

 

On modern car fuel systems, designed for Bosch pumps, you'll usually find no pre-filter (proper Bosch branded pumps have a built in gauze strainer), with a high pressure filter after the pump. I tend to use a strainer as a pre-filter and then a high pressure filter afterwards, but this is for EFI, so the pressure regulator is up front leaaving many choices of filter location. I know that people do run successfully with the Bosch pump and original configuration so start by checking the filter and fuel lines. Remember that any flexihose on the suction side may suck flat or partially flat while the pump is running (especially once warm) and then return to normal when switched off! I have also read that when using the original filter housing, it's important to get the right filter element for petrol use as there are similar sized elements for diesel use which do strange things when used on petrol.

 

Might also be interesting to measure the fuel pressure. If the relief valve can't pass sufficient flow then fuel pressure will be increased, possibly considerably. This won't bother the metering unit much but it will bother the pump! There are uprated relief valves available.

 

Good luck....

 

Nick

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hi have you got a power supply to the pump from the existing wireing loom . ?? if you have run a new supply powered from the battery via a relay as the bosch pump needs a good power line . check the voltage at the pump ?? if the voltage is low the pump will run hot . i had this on my 6 change the power line now its fine hope this helps rod

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The Bosch pump needs about 12 amps I think, much more than the Lucas pump.

 

As well as the power supply there is the question of position. You do not say where the pump is placed. The standard advice is that it should not be in the same position as the Lucas pump because, unlike the Lucas pump, it cannot suck the fuel up to itself effectively. The pump should be below the level of the bottom of the tank. So they are often in the corner of the spare wheel well. If it's wrongly placed that is likely to cause or at least contribute to your problems.

 

Regards,

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Roy,

 

You say;

 

The car has had 'new ''Bosch'' ancillaries fitted. and ........

 

'' after 40 miles the pump gets really hot, starts to make a bad noise and then the car stops''

 

Seems to me that it still has a ''Lucas'' pump and that is the reason for your troubles. I reckon the brushbox assembly is arced out, or the oilite bearings have had it, either way its getting far too hot resulting in the 'cavitation' that the other respondents are referring to.

 

I've not seen a Bosch pump that gets really hot unlike a Lucas one that can become too hot to touch......just before the car stops normally !

 

If you could positively identify the pump to the contributors I'm sure you would get a fix for your problem without wasting a lot more time (and money).

 

regards,

 

Chris

Edited by Chris Mountford
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I have always understood cavitation to mean air in the system, vapour is lighter than petrol surely and should remain at the top of the tank. Cavitation by restriction would also mean air in the system, although a good pump would be needed.

 

The Mountford road would be the one to navigate, unless you prefer the TR4 route! sorry only joshing.

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I have always understood cavitation to mean air in the system, vapour is lighter than petrol surely and should remain at the top of the tank.

 

 

Too much heat due to inlet restriction, worn pump etc causes the fuel to boil/vapourise in the pump assembly, there it remains and creates the vapour lock aka 'cavitation'.

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  • 2 weeks later...

Thanks for all the replies Lads.

 

Have written quite a lot about the trials and tribulations of the pump, but it has not been excepted three times.

 

Fed up with wasting time.

 

The whole thing has been changed for a Revington set up. Fine so far.

 

Regards Roy

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