fuel pressure test has thrown up some weird results
Turbo Mini Forums

finally had some nice enough weather to get out and test some more bits on 'monster' (recently better known by my girlfireind as gremlin due to all the problems its been having)

aaaaaanyway..i hooked up my fiuel pressure gauge with a t-peice and mounted it through the vent on the bonnet..took it for a spin..and not only was it jumping all over the place before i even started moving, when i was driving something even stranger happend..put my foot down alittle just to get it into some boost, and as the boost was coming on and what was indicated at literally 1 psi on the boost gauge my fuel pressure gauge was reading past 15 and at one point actually went off the clock ... now i have no reason to believe my gauge is shit..but ill try another out in the week to be sure...but WTF could be causing it be raising pressure that high and that irratically ..the fuel pressure reg is new and from avonbar, so i know its not a cheapo knock off.

sugggestions welcome.

thanks

check where the reg is getting its pressure feed from on the carb,

ie check its not fed from the manifold, it should be from the plenum IIRC

yeh ive got the feed fro mthe left hand side of the plenum going into the top left connection on the reg

Where are you measuring boost, and what is your maximum boost setting? The plenum is often at boost pressure when the manifold isn't.

sounds right,

Ok,

I would pull the return from the reg to the tank off and blow down it to see if theres any blockage.

whats size is the return BTW?

^^^ As above, sounds like a blocked return hose.

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1/4mile in 13.2sec @ 111 terminal on 15psi

Or is the regulator plumbed in correctly; Matty, care to comment

ive got 8mm hoses all round... ill run out now and see if the return pipe is blocked..im guessing it should be pretty easy to blow through it..hopefully thats what it is as thats an easy fix...oh and im running my boost gauge off the top of the inlet.

ive just gone out and blew down the return pipe, apart from abit of resitance to start with, it soon cleared and i could hear it bubbling away i nthe tank..ive got pretty strong lungs but i wouldnt say i had to blow down it that hard

bubbling? where does the return go?

Yes i moved to the darkside

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Ditto...

actually thats a good point..im not sure if its just the fuel left in the line bubbling alittle, but the return just runs up to the top of the tank as its always done

What pressure is the regulator set at? How much boost are you running? And what if any boost control are you useing?

Own the day

its set to 3.5 psi...and the cars running with a bleed valve, which at teh minute ive only got wound out a couple turns, should be running about 6psi but i cant rev it enough at the minute due to running issue

As others have said, is the reg even plumbed properly ?

the FP readings you are quoting, seem pretty impossible.

As for the return, if you can blow up it, its clear. You'd barely be able to manage 1psi or so blowing yourself.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

yeh im almost certain i have the fuel pressure plumbed in propely...but just to check.

i have fuel source going into the single pipe on the right side of the reg.

return pipe going out the bottom..then i have the fuel out coming from the bottom one of the 2 left hand side pipes..and the pressure feed coming from the left side of the plenum to the top one of the 2 left hand side pipes on the reg....and ihave to agree with you on the FP readings..i just cant see what could be causing it to read those kind of figures..or as irratically as it is

id try testing the fpr without driving it, pressure gauge plumed in to the carb feed and some method of pressurising the sensor pipe with the pump running just see what it does, then plum it all back in by the book, no bleed valve and take it from there

Yes i moved to the darkside

Instagram @jdm_brett

ok ill disconnect the pressure feed and hook it up to a foot pump, ive got an old alloy wheel valve i can connect the pump with..ill see what happens..ive pretty much admitted defeat that its not gonna be ready for the RR day on saturday

I haven't read the whole thread, but I'll bring a spare pressure regulator with me to the rolling road day incase yours is buggered.

Ben.

Having done the return line check, you also said the FPR was new.

For the sake of a few minutes, is it worth just separating the two halves by undoing all the retaining screws and checking the diaphragm and adjusting springs are seated correctly and free to move ?

Also, if I were you, I'd bleed your temporary windscreen fuel gauge line of air and try again. The erratic pressure could be due to this, but unlikely.

It's up to you how you bleed it but it'll either mean running the pump or the engine depending on how you have your pump wired. Necessary precautions for fuel under 3.5 psi pressure and all that.

At idle, do you have a nice steady 3.5 psi or is it fluctuating ?

For the sake of exclusion, is it worth taking this up to 4.5 at idle and repeating the drive by test after you've checked the FPR seatings ? I know 4.5 is a little high but you can always wind it back again after.

The only other thing fuel pressure related I can think is that the gauze filter in the carb might be blocked and its causing a restriction which is leading to lean out. It's a pain to check as its a carb off job again but it really does sound like something is amiss in your fuel delivery setup.

You'll crack it. Don't give up just yet.

When can you get the AFR sensor working ?

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
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cheers minimole itd be great to test another gauge aswell
Rich ive been busy again and tried to get as much accurate information/tests done as possible...firstly i closed the bleed valve compeltely so i know that regardless what the boost gauge is saying its only going to be running approx 3psi...then i disconnected the pressure feed and hooked it upto a foot pump ..and it seems to be raising the fuel pressure at about the right time..it didnt get near 15psi fuel pressure unti lthe foot pump was reading up towards 10psi which sounds about right ? and i could physically hear it squirting the fuel through to the carb .
after this i noticed that when i turned the fuel pressure down to 3.2 psi the needle was rock solid and didnt move , as soon as i slowly turned the pressure up as soon as it got upto 3.5 psi the needle was twitching alot, and even on the test drive monday the needle was rarely moving smoothly and was juttering all over the place.
i will def give the carb gauze filter a look as i need to take the carb off and replce the oil feed to the turbo as the leaks getting worse...its looking like ill be able to take the car off the road in a week or so as my girlfriends going to south africa for 2mths travelling so is lending me hers..that way i can get the exhaust off to mount the AFR sensor bung, and all the other jobs without worrying about having to use it for work the next day ...its obviously going to be invaluable once i do get it fitted tho.
Ben

Ben
I'm glad to see you are following a logical course of fault finding to try and narrow this fault down.

Something I would now recommend, is for you to rig up the fuel pump and return to a 1 gallon fuel can- that way you can eliminate any possibility that it is the suction strainer in your fuel tank that is causing your problem. Obviously do this with care.

thanks tom ill try that next , and i guess if the fuel flows nicley with a consistant pressure from the can then i knows its the suction strainer... ill borrow the old mans petrol can.
ill just unbolt fuel pump from the top of the tank and find some way of safely supporting it in the fuel can, obviosuly taking the battery out first..JUST incase haha

ben ,sounds a lot like your carb isnt holding over 3 psi odd .. try adjusting it to 3 where its a good solid needle ,and test drive then .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

well i had the fuel pressure set to 3psi and the boost still at the lowest setting and it does drive abit better higher revs...its seems ot be more if i only accelrate at half throttle it goes pretty good but really doenst like ful lthrottle...ive sorted out borrowing a petrol can for tomorrow, and will use the mrs car so i can take drag the petrol tank out. only 3 days till the RR day i might start trying to pray 3 times a day and see if that helps hahah