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1988 XR3i MFi Fuel Pump Problem

Old 27-06-2019, 04:45 PM
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meridian
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Default 1988 XR3i MFi Fuel Pump Problem

Hi all,

I have a lovely 1988 XR3i with MFI K-Jetronic, and have a strange fuel pump issue

The car will start, run and perform faultlessly, under all conditions, whether hot or cold etc

However, after driving the car for around 5-10 miles, the fuel pump becomes noisy. I'm convinced it is sucking in air as the noise will come and go erratically, and when grabbing the high pressure line out of the pump between my fingers when the noise is present, you can feel high frequency vibrations. Those vibrations are not there when the noise isn't. The noise is significant, and spoils an otherwise fabulous car, but has no effect on performance, fuelling, or starting. Just an annoying noise

For what it's worth, I have done the following

1) New Bosch fuel pump
2) Re-built mounting cradle with 3 x new rubber mounts, so pump fully floating and insulated and no chance of any resonance
3) New low pressure fuel pipe from tank to pump
4) Checked all tank vents are clear, and of course the fuel cap
5) Brimmed the tank to see if it has any effect, but none evident

Worth mentioning that removing the fuel cap has no effect, and so there is definitely no vacuum within the tank

When the noise is present, I have dropped the pump from it's mounts and 'moved around' No pulling or moving of the pump itself or squeezing the inlet fuel pipe has any effect on the noise

Leave the car an hour or so, the noise will subside until driven a few miles again. Even running the car static until the fans cut in will not cause the noise to happen, leading me to believe it's related to expansion and pressure/vacuum changes in the tank that occur through temperature changes

Out of desperation I am likely to try another pump on it, but don't hold out much hope !

Any suggestions

TIA
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Old 27-06-2019, 08:14 PM
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haz87
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Was it definitely a genuine bosch pump? There are far too many fakes about and unfortunately the 3i style external pump is one of the easily replicated types.

2 other things i'd check - the non return valve on the pump itself, did you install a new one with the new pump or swap over the old. I've had one of these make some odd noises before, tho admittedly drive time/heat didnt impact, it was there from start.
Secondly, the fuel accumulator - this irons out pulses and most definitely has influence on things such as vapour lock etc.

Lastly voltage - have you checked to see what voltage is at the pump? The current draws on these are high, the wiring breaks down, and heat will only exacerbate that, it could be struggling with low voltage
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Old 28-06-2019, 06:52 AM
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Hi Haz,

3 very good points

Definitely a genuine Bosch pump, but no non return valve supplied with it, and so not replaced. I think this is a very good point and is something I'll look at straight away

Yes, accumulator is something I've considered but I would think problems here would manifest themselves further upstream, metering head' for example with a distinct effect on running. As I say, it runs perfectly

Will test voltage at pump with problem evident, but you don't here it slow down at all so don't think there is a problem. Any voltage drop can be heard, for example a small effect on the pump when the fans cut in

Thanks

Last edited by meridian; 28-06-2019 at 06:57 AM.
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Old 29-06-2019, 04:28 PM
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Pretty sure it's the accumulator. Noise is in the pipe, and up at the accumulator where it comes up from the pump/car underside, the pipe is almost dancing with vibration. You can feel 'turbulence' in the pipe when squeezed between your fingers. Nothing on the outlet side where it goes to the filter though, which is clearly a good thing. Amazed it doesn't have some effect on starting and running, but car is super sweet

For good measure, it's had a new pump non return valve and also an in-line filter from tank to pump

Anyway, new Bosch accumulator ordered from eBay. Easy job, so fingers crossed

Pic attached for good luck !
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Old 29-06-2019, 06:53 PM
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Glad you sussed it
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Old 02-07-2019, 09:00 AM
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New Bosch accumulator fitted. Sweet as a nut !

Thanks for your help Haz
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Old 02-07-2019, 01:05 PM
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