Is the 7MGTE J-tube a restriction?

[Van]

I think it might be my 7M's latest prob... :dunno: 1/6/11, I took the Supra to VIP Performance (Portland), to get the AFC NEO wired in and the JDM TCCS ECU hooked up. Today they ran the car on the Dyno and the car was leaning out, AFRs going from 11.3 to 12.7, going into WOT then w/i 1000RPMs (2500 -3500RPMs) AFRs would go back down, heading toward 11.3. This happened three times during the test. Adjusting the AFC had no effect.
The technician stated he has seen this happen before, when there is a restriction in the fuel system. My FP is running 47-50psi during cruise at 2500RPM, 70psi during WOT, and goes up to 90psi, (during testing of the FP in the car). The high pressure side works well, he thinks there is a restriction in the return side. He checked the banjo bolt and the copper washers on the return line, no restrictions there...
I read that the J-tube is a restriction, is that true; is the J-tube what could be the prob?
MODS: New 2JZtt Denso pump, new Denso 550cc inj, new 7MGTE FPR and damper, 12v mod, w/ new wires and relay.
Thanks.
Van

 

[Dirgle]

Well, I don't think the j-tube is causing your lean spot.

But if your going to run the 2JZ pump the j-tube will become a restriction due to the increased flow. However the real fuel issue I see here is the factory 7MGTE FPR. You need an adjustable fuel pressure regulator to correctly use the Lex/550 mod. The fuel pressures you're seeing are way high.

 

[Van]

What is/are the target pressure(s)?
Thanks.
Van

 

[Dirgle]

A good rising rate FPR with a ratio of 1:1 is recomended such as this one from driftmotion:
http://store.driftmotion.com/static/i-aeromotive13109.php

The also sell a full FPR kit for the 7MGTE


Next your baseline pressures should be set as per the TSRM:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=73

 

[IBoughtASupra]

The DriftMotion 7M fuel pressure regulator kit is highly recommended. It makes sense to run this setup with the fuel pulsation dampner feed line. I ran this setup in my 7M and had it set to the fuel pressure according to the TSRM for the stock injectors. If you are using aftermarket injectors, you will need to set it to what those injectors require.

Setting a fuel pressure regulator too low can cause it not to have enough pressure to flow through the injector and too high can cause it to leave an injector open.

 

[Van]

Thanks!

 

[Van]

So, the technician said the stock FPR is a RR of 1:1, and were getting what is needed for fuel pressure on the Denso 550s, monitoring the FP using a FP gauge, (attached at the FPR), he sees the FP rise as he steps on the foot feed. What he doesn't see is the gauge showing the FP rising when he snaps the throttle open then closed. He still thinks that is indicative of the restriction on the return line. He'll by-pass the J-tube Saturday and we'll see what happens...
I really don't understand most of what is being said in this regard. Thanks for your guidance.
I'll keep folks posted. Van

 

[Dirgle]

Not sure how your mechanic came to the conclusion a restriction on the return side would cause a lean problem. If anything it would go rich due to the higher pressures that are created due to restriction on the return side. Next, while yes the stock FPR is a 1:1 regulator, it lacks adjustability. Important to properly tune the LEX/550 mod. Third at idle with the vacuum line on you should be seeing no more then 30psi if you take the vacuum line off and plug it, you should see no more than 40psi. You are way over that. 47-50 psi is forcing a considerable amount more fuel through through those injectors.

At 50psi those 550cc injectors are behaving like 615cc injectors.

Now removing the j-tube restriction may relieve some of this, but you still really have an adjustable FPR for the Lex/550 mod.

 

[Poodles]

FP is only supposed to rise under boost (1PSI boost = 1PSI more fuel pressure), if it's not going down under vacuum, yeah, it sounds like the j-tube. Also, the jtube is a restriction on the return, it wouldn't cause it to be lean, it would cause it to be rich.

It sounds like the 12v mod in addition to the non-bypassed j-tube is causing it to be rich in the lower RPMs causing your tuner to try and lean it out causing the lean condition when flow through the j-tube no longer becomes a restriction.

The stock FPR may not be up to the task either. The j-tube's function is to supply fuel pressure in the event the FPR fails, so they're really a system...

 

[Van]

Not sure how your mechanic came to the conclusion a restriction on the return side would cause a lean problem. If anything it would go rich due to the higher pressures that are created due to restriction on the return side. Next, while yes the stock FPR is a 1:1 regulator, it lacks adjustability. Important to properly tune the LEX/550 mod. Third at idle with the vacuum line on you should be seeing no more then 30psi if you take the vacuum line off and plug it, you should see no more than 40psi. You are way over that. 47-50 psi is forcing a considerable amount more fuel through through those injectors.

At 50psi those 550cc injectors are behaving like 615cc injectors.

Now removing the j-tube restriction may relieve some of this, but you still really have an adjustable FPR for the Lex/550 mod.

I'll pass this on to him later today. Thanks. Van

---------- Post added at 02:26 AM ---------- Previous post was at 02:20 AM ----------

Thanks, Poodles. I'll add your comments too, when I talk with him tomorrow. Van

 

[djdvp]

The j tube is a restriction if you remove it and look the return is only the size of a pin hole if you drill it out and hook it back up you will no longer see changes in pressure of fuel. Or you can bypass it completly it will hold a more consistent pressure set on an adjustable regulater. Set between 36 and 40 on regulater when you get one thats adjustable that is the stack regulater causes lean condition though but j tube drill out or bypass is a must for consistent fuel pressure. History j tube was invented as a fail safe so that when your regulater shits you can limp home it causes a very rich and inconsistent fuel pressure though one of the many crap shots made by toyota oiling is another one but thats another story

 

[Sinistr]

Pretty sure the OP got this issue resolved over the past 9 months

 

[Supracentral]