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Popped The Vacuum Line Of The Fuel Pressure Reg N Got Detonation...

jjman

By jjman,
in Engines & Forced Induction

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jjman Mentor

jjman

Posted
Posted

Hey people.

So on the weekend i was giving my car some WOT. 2nd gear wound out fine but just after i got into 3rd it pinged- 1/4 of a second's worth, i got off the gas straight away. Sounded like 5 or so audible knocks before i got off the gas.

Turns out the vacuum line off my fuel pressure regulator popped off... Im putting it down to deteriorated vacuum line and a tune at a new boost level (18psi).

Since then iv reconnected the vacuum hose.

Car seems to start, run and drive fine still so Im assuming that the momentary detonation didnt do any damage... (tho i havent given it any WOT yet till i replace the vacuum lines)

any thoughts on what would have caused this? deteriorated line not holding the 18psi or something more sinister?

any thoughts on whether i would have done damage and how to check for it? im thinking that if i had done a ringland or a head gasket id know about it? (there is not smoke or anything coming out the pipe and no oil etc in the coolant)

cheers

J

GTScotT Grand Master

GTScotT

Posted
Posted

The problem is that audible ping isnt always what kills the motor, its inaudible ping thats happening when you least realise it..

My concerns are if the fuel pressure would drop enough to actually make it lean out and detonate... Or if the tune is just on the edge as is....

My recommendations are that you do a comp test (and leakdown if you want) to gauge if the motor is in as good health as it was prior, then run the car up on another dyno and have the opperator monitor knock and the AFR's.

If all is good then dont worry and press on.

TiTAN Grand Master

TiTAN

Posted
Posted

you would have bigger issues with the car leaning out massively when the line comes off the pressure regulator, once you take into account 18psi of boost the fuel pressure difference is only ~27psi instead of the 45 it should be (as the regulator adds 1psi of fuel pressure for every 1psi of boost to keep the difference in pressure at ~45psi)

as long as you didnt keep thrashing it without the reg connected to vac/boost the chances of it having melted something is fairly low.

GTScotT Grand Master

GTScotT

Posted
Posted

Isnt it that its 1psi added to the base pressure for every psi boosted?

Meaning he would have more like 65psi rail pressure at 18psi boost?

zebra Grand Master

zebra

Posted
Posted

yeah, I think titan was referring to you have to subtract the amount of pressure in the inlet, so 65psi rail pressure - 18psi boost pressure = 47psi effective rail pressure

GTScotT Grand Master

GTScotT

Posted
Posted

Something like that, I wonder if the riser is for failsafe or if it actually needs it to run the injectors right...

Either way I am not convinced the vac hose is all that made it ping, sounds like the tune is either pretty hard or too close to the edge.

zebra Grand Master

zebra

Posted
Posted

it is needed to keep the fuel flow linear(ish) to injector opening time, otherwise, say you have 45psi rail pressure and 45psi boost pressure, no fuel will flow out of the injector due to no pressure differential

jjman Mentor

jjman

Posted
  • Author
Posted

cheers peeps.

Im going to replace the lines today and then take it for a drive and see if there are any anomolies indicating problems/damage. All feels fine so far so god damn are my fingers crossed...

Harey Veteran

Harey

Posted
Posted

Yeah as said the difference between 27psi and 45psi relative fuel pressure is a lot and definitely something I would expect to cause it to run lean.

Hopefully it was brief enough to not cause any damage!

As far as a cause for it, yeah just old or crappy vacuum lines. Definitely replace them, I really like the Turbosmart range of vacuum hose as its nice and soft and seems to hold on really well.

Also make sure there is enough length in the hose so that when the engine twists/moves that its not putting too much tension on the hose.

Is there already a clamp on that vacuum hose? If not get one.

jjman Mentor

jjman

Posted
  • Author
Posted

Yeah as said the difference between 27psi and 45psi relative fuel pressure is a lot and definitely something I would expect to cause it to run lean.

Hopefully it was brief enough to not cause any damage!

As far as a cause for it, yeah just old or crappy vacuum lines. Definitely replace them, I really like the Turbosmart range of vacuum hose as its nice and soft and seems to hold on really well.

Also make sure there is enough length in the hose so that when the engine twists/moves that its not putting too much tension on the hose.

Is there already a clamp on that vacuum hose? If not get one.

cheers mate.

yeah going to go and get those blue silicon ones. Also def going to put a clamp on it! f*kn hell. Such a small thing that can have disastrous consequences...

MrStabby Grand Master

MrStabby

Posted
Posted

cheers mate.

yeah going to go and get those blue silicon ones. Also def going to put a clamp on it! f*kn hell. Such a small thing that can have disastrous consequences...

Go OEM unless you *know* the brand is good. There's a lot of crap silicon hoses out there.

GTScotT Grand Master

GTScotT

Posted
Posted

takes a lot more pressure. remember we are talking pounds per square inch..... not a massive amount of force in that little hose, a cable tie done tight will hold it.

but I agree nissan could have tried harder there (however Evos are the same - i think they all use JECS items?)

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

just cable tie it up with a small black one..

I cabled tie all the hoses up tight just in case any decide to come off.. I replaced all the spring clamps with screw clamps (yeah I am anal aye?)

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