Another petrol tank

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Another petrol tank

Post by philhoward » Tue Jun 30, 2020 8:11 pm

So it holds pressure - when it can actually build it up.

Is your filter between pump and engine blocked?


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Another petrol tank

Post by philhoward » Tue Jun 30, 2020 8:15 pm

Test:

With pressure at zero (vented), temporarily restrict the return line (coming off the regulator in the fuel rail / crimping it with Mole grips will do for test purposes), then give it the priming pulse but no more. Do not attempt to turn the engine over. Any pressure reading to report?

It does look like a sticky fuel pressure regulator -


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Another petrol tank

Post by DARK STAR » Tue Jun 30, 2020 8:33 pm

Thanks Phil, I'll try that tomorrow.
Filter is before the pump, I haven't checked it yet but it really shouldn't be blocked again, the cars has only done about 20 km since I cleaned it (months ago) and the hoses are new.


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Another petrol tank

Post by philhoward » Tue Jun 30, 2020 8:36 pm

You should have a post-pump filter too?...


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Post by DARK STAR » Tue Jun 30, 2020 8:38 pm

Why, if the petrol is clean going into the pump it will be clean coming out ... :?:


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Post by philhoward » Tue Jun 30, 2020 8:48 pm

It’s the level of cleanliness - how many microns does your pre-filter remove down to?

Hypothesis is some muck keeps getting stuck in the pressure regulator. Concern is if it’s got into the regulator it’s likely in the injectors too.


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Post by DARK STAR » Tue Jun 30, 2020 8:53 pm

That's a good question, I'll have to ask Mr Sytec ...


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Another petrol tank

Post by scimjim » Tue Jun 30, 2020 9:09 pm

DARK STAR wrote:
Tue Jun 30, 2020 8:38 pm
Why, if the petrol is clean going into the pump it will be clean coming out ... :?:
not if the pump disintegrates :D


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Post by DARK STAR » Thu Jul 02, 2020 6:06 am

After 24 hours residual pressure 1,2 bar

Pressure released, exit hose clamped as suggested
Fuel pump primed = zero pressure
Fuel pump primed several times = zero pressure ... :(


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Another petrol tank

Post by scimjim » Thu Jul 02, 2020 8:12 am

Bypass all of the fuel pump wiring and see if it builds pressure?


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Post by philhoward » Thu Jul 02, 2020 8:17 am

Taking the rule that pressure is resistance to flow, you’ve either got no flow or no resistance. If you’ve clamped a hose, it isn’t a lack of resistance so must be no flow. In that case either insufficient fuel getting to the pump (your Sytec filter) or the pump isn’t pumping (insufficient electrickery or unhappy pump).


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Post by DARK STAR » Thu Jul 02, 2020 12:49 pm

Y e s ...
That sounds logical but it is only when starting that the problem exists.
When the engine is running pressure is stable at 2,4 bar.
And why does the damn thing start only AFTER the residual pressure is released?

Hot-wiring the pump +ve (so bypassing the ECU) solves the problem.
Hot-wiring the earth (+ve from ECU) does not.

Anyway I'll take the pump and filter cradle off yet again and have a look in every orifice.


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Post by philhoward » Thu Jul 02, 2020 12:58 pm

DARK STAR wrote:
Thu Jul 02, 2020 12:49 pm
Y e s ...
That sounds logical but it is only when starting that the problem exists.
So the issue is getting from partial pressure to full pressure - at which point it can maintain it until you turn it off again?
When the engine is running pressure is stable at 2,4 bar.
And why does the damn thing start only AFTER the residual pressure is released?
No idea - that's the bit that makes no sense because:
Hot-wiring the pump +ve (so bypassing the ECU) solves the problem.
So that suggests the bits you bypass (Relay I assume) appear to be at fault
Hot-wiring the earth (+ve from ECU) does not.
Unlikely to be the earth then :D
Anyway I'll take the pump and filter cradle off yet again and have a look in every orifice.
Something still doesn't add up - so it will start if a) you vent the pressure (mechanical intervention), b) bypass the relay (electrical intervention), or both operations are needed? The only place mechanical and electrical join is the pump.


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Post by DARK STAR » Thu Jul 02, 2020 1:09 pm

This has been going on so long I can't remember if both operations are needed.
I think not because it has always started after venting the pressure.
I'll try hot-wiring again without venting ...
Err, do you think the system is currently 'pressurised' after priming :?: :roll:


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Another petrol tank

Post by philhoward » Thu Jul 02, 2020 1:15 pm

It should be pressurised after priming - that's the purpose of it. I'm totally lost why venting that pressure (then running the pump constantly) makes it work as that's totally the opposite?


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