Drilling out the J-tube?

[LordLo]

So does drilling out the J-tube lower fuel pressure since it no longer restricts the fuel flow?

If that is so, couldn't I build myself a ball and spring type of AFPR kind of like the MBC? So it would restrict fuel flow up until the tension on the spring is met, but the spring tension could be controlled via a knob?

Also would I be able to run it in conjunction with the stock fpr?

 

[iamshawn]

only way to know what your fuel pressure would be with any turn of a knob would be a gauge. when you doing the ball and spring thing you won't know when you are getting boost and would run lean.. = boom bam clank clank

Fuel is something i wouldn't mess with homemade stuff... not worth having a blown engine just by trying to save a few bucks.

 

[IwantMKIII]

No, j-tube is a safety feature for mostly stock cars.

You could build one with the right know how and parts but i would NOT recommend it at all, don't forget vacuum plays a big part with feul control. Feul is also very corrosive.

Yes but, if you build one or buy one then there is no need for the stock FPR.

 

[GrimJack]

No, j-tube is a safety feature for mostly stock cars.

Agreed. This is just to let your car limp home if your FPR bites it on the road.

The reason many people have bypassed / drilled this out is because they are pushing a LOT more fuel through there, and therefore this starts to becomes a serious restriction. Furthermore, the failure rate on aftermarket AFPRs isn't really something you need to lose any sleep over.

 

[Datsrboi]

Ok my question here is how common is it for the stock FPR to go bad? I have a walbro installed on a stock motor basicly since my stock one is old and dont want to drill out that Jtube unless I am sure the stock FPR dont go bad as fast.

 

[jetjock]

Such a regulator wouldn't maintain the constant delta P required across the injectors with varying manifold pressure.

 

[Datsrboi]

Such a regulator wouldn't maintain the constant delta P required across the injectors with varying manifold pressure.

So do it right and install an aftermarket FPR with the walbro or dont do it at all?

 

[jetjock]

Well, whatever you use has to correct for manifold pressure. You just can't regulate fuel pressure to a set value and leave it there. That'd work only as long as the pressure at the injector's outlet remained the same ie; at atmospheric or some other level.

A little thought experiment:

1) Put injector with 30 psi of fuel behind it into open container.

2) Energize for exactly 1 second. Measure fuel delivered.

3) Put injector into vacuum cleaner hose and repeat experiment. Is more or less fuel delivered?

Note: For illustration purposes only. Do not inject gasoline into vacuum cleaner or spontaneous disassembly of cleaner will result

 

[Piratetip]

There has to be a video of this somewhere.

Ah here we go.
http://www.youtube.com/watch?v=t2K42GbDN1Y
http://www.youtube.com/watch?v=Xj5M-nHIKXM

 

[LordLo]

Reason I ask is because after I drilled out my J-tube the car can no longer hold a decent AFR anymore. It used to hold a decent 11.5ish AFR, but now it jumps all over the board... 11.5....12.5....14...13....12.....13.5. This is at 80%-90% throttle.

Before hand, I would go 80-90% throttle and it would hold a steady 11.5 afr.

Maybe my stock FPR just crapped out on me?

 

[IwantMKIII]

Reason I ask is because after I drilled out my J-tube the car can no longer hold a decent AFR anymore. It used to hold a decent 11.5ish AFR, but now it jumps all over the board... 11.5....12.5....14...13....12.....13.5. This is at 80%-90% throttle.

Before hand, I would go 80-90% throttle and it would hold a steady 11.5 afr.

Maybe my stock FPR just crapped out on me?

do you have a wideband?

 

[LordLo]

do you have a wideband?

Zeitronix ZT-2. I can email you the file if you want. It's looks pretty bad.

 

[IwantMKIII]

what are your mods?

 

[LordLo]

T61, RC 550cc, 3in system (no cat), 9-10psi, and stock AFM. In theory I should be running somewhat rich.

 

[Poodles]

stock fuelpump?

 

[Datsrboi]

I see all his mods and nothing to control his fuel like SAFC and all.. Yet he has bigger injectors. Shouldn't that be dumping more fuel causing the rich outcome?

 

[LordLo]

stock fuelpump?

Yep, stock fuel pump.

 

[LordLo]

I see all his mods and nothing to control his fuel like SAFC and all.. Yet he has bigger injectors. Shouldn't that be dumping more fuel causing the rich outcome?

I did have an SAFCII a few months back, but the device is so primitive IMO. I'm going to go maft in blow through mode instead.

 

[IwantMKIII]

mistake 1, 550's with no lex AFM, mistake 2 not feul tuning device

 

[Poodles]

no, he'd be very rich, but he's on the stock fuel pump...

get a walbro, your fuel pump is tired...