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Spring stretch mod - fuel return valve


 
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Beastrider
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Joined: 30 May 2019
Posts: 7
Location: Wales

PostPosted: Sun Feb 09, 2020 0:17    Post subject: Spring stretch mod - fuel return valve Reply with quote

My KZJ95 has an irritating whine/buzz which seems to come from the passenger footwell. The noise follows the engine revs but not causing any driving problems - just annoying. From reading this forum, it seems the spring stretch mod in the fuel pump return valve may be the thing to try first.

Some people stretch it just a few mm, others say up to double the original length. I have also read that the spring weakens over time. Does anyone know the free length of a new spring? Or the part number for a new valve?

Increasing the spring force presumably increases the pressure required to open the valve. Could there be a detrimental effect on the pump by increasing the back pressure?

How much fuel is likely to leak out when I remove the 14mm blanking pkug from the top of the return valve? Do I need to use a hose clamp somewhere?
Thanks
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diggerdave
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Joined: 03 Oct 2014
Posts: 339
Location: York

PostPosted: Sun Feb 09, 2020 0:50    Post subject: Reply with quote

If memory serves... I stretched it to about double its length. Everything has been fine (60,000m). I don't recall any fuel leaking at all, but keep a towel handy.
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1997 KZJ90 (narrowbody) 3.0d, 2" suspension lift, 235/85/16 Cooper STT Pros. 208k miles
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warwick lawley
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Joined: 11 Mar 2016
Posts: 15
Location: united kingdom

PostPosted: Thu Feb 13, 2020 0:08    Post subject: fuel return line vibrating. Reply with quote

At low engine revs, there was this irritating buzzing noise from the rear nearside of the car. I found that the fuel return line was resonating thus setting up this dammed vibration. I fitted a non return valve in the engine compartment and the buzzing noise was gone. The non return valve fitted opened at the slightest pressure so did not impede the return flow but was sufficient to dampen the fuel flow pulses and cut down the resonance.
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Beastrider
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Joined: 30 May 2019
Posts: 7
Location: Wales

PostPosted: Thu Feb 13, 2020 22:52    Post subject: Reply with quote

Hi - that's interesting. I was also researching about fuel pulsation dampers which i believe are used in the feed line on some engines. I suppose your NRV is acting in the same way in the return line. Can I ask exactly where you fitted it and where you bought it?

Meanwhile, I have stretched the fuel return valve spring from about 13mm to 16mm and it has definitely reduced the irritating buzz noise. Probably I need to stretch it a bit more.

I also read that a longer length of flexible hose can cut down the resonance.

For me, the noise mostly seemed to come from the passenger footwell but also would come from the rear nearside floor area.
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warwick lawley
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Joined: 11 Mar 2016
Posts: 15
Location: united kingdom

PostPosted: Sun Feb 23, 2020 0:58    Post subject: Fuel return line pulsations Reply with quote

The NRV was an aluminium bodied device obtained from my local Motor Factor for under £5. I fitted it on the NS wheel arch in the engine bay and ran an extra short pipe to the fuel metering/pump unit. A damping unit with an internal rubber diaphragm would have been ideal and would have got one had I not had success with the NRV.
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Beastrider
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Joined: 30 May 2019
Posts: 7
Location: Wales

PostPosted: Wed Feb 26, 2020 20:59    Post subject: Reply with quote

Thanks for the reply. OK - I know the ones you mean. I have seen those NRVs too. Good to know it worked for you. Iíll try that if the noise returns.
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