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I'm experiencing a slight rich issue and need the groups help.  

Its an l28et running a JWT 550 kit in a 71 240z. Using the stock l28et fuel rail, Aeromotive FPR with psi gauge, upgraded to bigger fuel line (still using the oem return line), and an unknown in tank pump.  Prior owner says its a 300zx turbo pump, but I have yet to drop the tank.  I have seen it go to 65 psi with no pressure drop at all.  11.5 AFR until boost crosses the 10 psi mark, then fuel pressure shoots up 5 psi too much (relative to boost )and stays that way.  At idle, fuel psi is correct. Cruising, it's correct.

The problem shows up only after 10 psi of boost, thats when my AFR's go to 9.5-10.5. Myself and other can't see any smoke from the tail pipe during acceleration.  I believe there is an restriction thats not allowing the fuel to return fast enough. Maybe the oem fuel rail? I don't see any pinches in the rail that would cause such a thing.  Maybe its my setup.  Any ideas where the restriction might be?

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Edited by Timecode
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65psi is really a lot of fuel pressure. You might be maxing out the flow on the lines already. 

 

Factory says maybe 36 or something if I remember correctly. The only reason I would see to turn up the pressure was if you didn't have enough flow out of your injectors and you wanted to force them to spray a bit more fuel.

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65psi is really a lot of fuel pressure. You might be maxing out the flow on the lines already. 

 

Factory says maybe 36 or something if I remember correctly. The only reason I would see to turn up the pressure was if you didn't have enough flow out of your injectors and you wanted to force them to spray a bit more fuel.

Normal for a lot of boost though, that was 27 psi of boost. At idle fuel is at 29-30 psi. 40 psi at 10 psi. Just after that fuel pressure ramps up, +5 psi too much no matter what psi I stop at.  

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Return line is too small by the sounds of it. With high volume pumps and big boost you normally require at least a 3/8 return line.

 

OEM fuel rail suspect. I believe it's only 5/16 on the return side. Plus it has lots of bends and each bend restricts fluid flow. Order a Pallnet fuel rail and run the FPR on the return side. - 6AN Hose  both inlet and return.

 

May also be a restriction at the tank. Make sure no hose is pinched at tank. You may have to modify the return line at the tank if it is too small. 

 

Edit: Check the return line under the chassis. Pretty sure it's only 5/16". Too small. 

Edited by Chickenman
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Where do you have the Fuel Pressure Regulator plumbed in? To the Inlet side of the Fuel Rail or after the return side of the Fuel Rail. Can't really tell tell from pictures. 

 

That is a bypass regulator and should be plumbed to the return side to operate correctly. This gets more critical the more Boost you run. 

 

As per Aeromotives instructions:

 

https://www.aeromotiveinc.com/tech-help/faqs/faq-efi-regulators/

 

 

 

3.) I’m trying to plumb an Aeromotive, stand-alone EFI regulator but don’t know where to put it, before or after the fuel rail(s), and which ports should go where?
Unlike a standard or “dead-head” carburetor regulator, which controls pressure between itself and the carburetor by stopping flow, the bypass regulator controls pressure between itself and the pump by bypassing flow.  The optimum EFI regulator location is after the fuel rail(s) when possible.  All pump flow, minus engine consumption, must always run to the regulator, wherever it is.  Putting it after the fuel rail means all fuel must run through the fuel rail, and over the injector inlet, at all times.  This ensures full flow is available to the injector in any instant.  Most Aeromotive EFI regulators have two inlet ports, one on each side, and one bypass port, on the bottom.  Either inlet may be used with a single fuel rail engine, both inlets with dual fuel rail engines.  Any unused inlet ports must be blocked with the appropriate port plug. The ideal flow-path is: out of the fuel pump, into one end of the rail; out the other end of the rail, into the regulator side port(s); out the regulator bottom (return) port, back to the top of the tank.  Dual rail applications should employ a Y-block to split the supply line before entering the rails, then individual lines are run from the opposite end of each rail into each inlet port on the regulator.

 

I think you may have more than one issue. 

 

BTW, do you have a voltage Booster hooked up to the Fuel Pump. Like  Kenne Belle Boost-A-Pump? You need big return lines with those.  

Edited by Chickenman
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A small return line won't cause issues on boost that aren't worse at idle, at least not by itself.  Remember the return is a bypass that the regulator uses to drop pressure by bleeding fuel - the more fuel you need to flow and/or higher pressure you want to maintain, the less you have to dump through the return line.  If the line were too small and you have a single pump running at constant speed you would be seeing too high pressures at idle LONG before seeing issues at boost.

 

Do you have any other hardware in your fuel system, like a non-linear FPR (these were very popular in the 80's and 90's), a second pump on a Hobbs switch, Boost-a-pump, etc?

 

Also, 

 

 

11.5 AFR until boost crosses the 10 psi mark, then fuel pressure shoots up 5 psi too much (relative to boost )and stays that way.  At idle, fuel psi is correct. Cruising, it's correct.

 

I'm assuming that when you say "stays that way" you mean that it stays too high until you are off boost, and then returns to normal.  Is that correct?

 

And...

 

 

 

Normal for a lot of boost though, that was 27 psi of boost. At idle fuel is at 29-30 psi. 40 psi at 10 psi. Just after that fuel pressure ramps up, +5 psi too much no matter what psi I stop at.

This doesn't sound right either.  The 29-30 value sounds about right for idle with the pressure reference connected and the stock base fuel pressure (zero vaccuum) of 36.3psi (2.5 bar).  The regulator's job is to always maintain a (in this case) 36.3psi difference between the fuel rail pressure and the intake manifold pressure.  So, 10psi of boost should yield 47psi of fuel pressure (not 40).  65psi fuel pressure would be appropriate for 29psi of boost, but way too much for 10psi.  

Edited by TimZ
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1: A small return line won't cause issues on boost that aren't worse at idle, at least not by itself.  Remember the return is a bypass that the regulator uses to drop pressure by bleeding fuel - the more fuel you need to flow and/or higher pressure you want to maintain, the less you have to dump through the return line.  If the line were too small and you have a single pump running at constant speed you would be seeing too high pressures at idle LONG before seeing issues at boost.

 

Do you have any other hardware in your fuel system, like a non-linear FPR (these were very popular in the 80's and 90's), a second pump on a Hobbs switch, Boost-a-pump, etc?

 

Also, 

 

 

 

2: I'm assuming that when you say "stays that way" you mean that it stays too high until you are off boost, and then returns to normal.  Is that correct?

 

And...

 

 

 

3: This doesn't sound right either.  The 29-30 value sounds about right for idle with the pressure reference connected and the stock base fuel pressure (zero vaccuum) of 36.3psi (2.5 bar).  The regulator's job is to always maintain a (in this case) 36.3psi difference between the fuel rail pressure and the intake manifold pressure.  So, 10psi of boost should yield 47psi of fuel pressure (not 40).  65psi fuel pressure would be appropriate for 29psi of boost, but way too much for 10psi.  

 

1: I agree with that for the most part, but you can have situations where an electric fuel pump has higher voltage applied to it at higher boost. Kenne Bell " Boost-A-Pump" and PWM controllers in EFI ECU are just two examples. Since we don't know all the details in the engine I thought I would mention that.  Asked about that in post #5. Return lines need to be at least -6.

 

3" OP mentioned in Post #3 that he pulls 27 lbs of Maximum boost.  10 lbs boost was only starting point .

 

OP. why don't you give Aeromotives Tech line a call. See what they say? Bit of a head scratchier. 

 

Edit: Notice you are using an electrical fuel pressure sender off the AFR. Do you have a secondary sending mechanical unit plumbed from the fuel rail to confirm pressure readings? Not the first time I've seen instrument failures drive you crazy. 

 

Don't use a Liquid Filled mechanical gauge. Inaccurate due to temperature fluctuations. Unless you buy a high dollar Liquid Filled gauge with a dial pressure bleed. 

Edited by Chickenman
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Goodness 27psi, what power territory are we talking about? What turbo out of curiosity?

 

Do you have your duty cycle on the injectors?

 

We might definitely be in the territory where you are maxing out your injectors and they are basically just dumping fuel instead of injecting. 

 

That does seem quite a bit to be running through the factory fuel rail with the bends and the hoses and things like that.

 

Have you had the car tuned to try and lean out the map? Or is this more of a sudden occurrence?

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Just a flyer - are the reference port for the FPR and the port for the boost gauge in the same spot, or close?  Just to be sure.

 

The boost pressures is "helping" the regulator spring close the FPR return port.  Hard to imagine a step-type increase in pressure, of 5 psi.  The return line would only seem to come in to play if you were on the edge with the pump output and extra voltage caused more pump output.  Maybe your voltage regulator is bad.  Another flyer.

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Let me clarify.  TimZ, You are correct I meant to say 46 psi at 10 pounds of boost. It's an Aeromotive #13129, 1:1 FPR hooked up as per Aeromotive, fuel rail return piped to the FPR's inlet, output to the cars return line.  The smaller of the two fuel lines was replaced with a line the same size, if not a little bigger than the bigger oem line, I need to measure next time I'm home.  Nismo 555cc injectors, came with the JWT 550 kit. I haven't had time to see if the Z31 computer controls the pump or not but the pump is activated via a relay on the fire wall. No special pump boosters as far as I know.  The pump screams, too.  Not too loud with a full tank but at 10 gallons remaining, it gets loud.  At half tank its quite loud. Its been like this for 2500+ miles though.

I called Aeromotive and they said that the issue is weird. I think Chickenman is on the money, some restriction in the return that doesn't allow the bypass of enough fuel, but what.  The 240z tanks oem feed/return lines are plugged and the whole 300zx turbo pump assembly was bolted to the topside of the gas tank with everything plumped to that.

 

Chicken man, I could tap a mechanical gauge to the rail where the oem one was to confirm my readings are correct, which brand would you recommend?  I don't think the gauge is inaccurate though.

 

All engine components are tied to a vacuum block.  Maxed out injectors would lean out the mixture but thats not happening, plus I get the issue right after 10 pounds of boost, nothing is maxed at those pressures.  Turbo is a Turbonetics T3/T04b with a T04B compressor housing and V trim compressor wheel. It's a Ceramic ball bearing unit with a 57mm turbine wheel. The turbine housing is a .63 a/r.  

Edited by Timecode
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You're not really using the way a fuel pump works correctly.  All it produces is volume.  The FPR creates pressure.  Assuming the same voltage, you'll get maximum volume at idle or engine not running.  Because the injectors aren't bleeding off volume.  Assuming the same voltage again, if the return line was a restriction, you'd see the problem when you were running the pump without the engine running because the volume would be the greatest.  Nothing bleeding it off.

 

I'd check your pressure with a mechanical gauge.  Could be that you just have a rich tune on your JWT ECU, everything's fine with the FPR, and you just have a funky transducer on your pressure gauge.  The one in your pictures.  You might be on a wild goose chase, from bad data.  Pretty common.

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I confirmed 40 psi with pump on, engine off. The car goes rich as soon as the fuel pressure ramps up excessively, otherwise it runs perfect afr's under 10 psi.  If the tune was too rich I don't think I would see 11.5 afr's up to 10 psi.  JWT don't mess with the Nissan ECU as much as people think. Most issues people have with their tune usually lies within their own cars setup, including mine.  I won't rule out what you said at all. Thanks for the collective brainstorming all.

Edited by Timecode
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You're not really using the way a fuel pump works correctly.  All it produces is volume.  The FPR creates pressure.  Assuming the same voltage, you'll get maximum volume at idle or engine not running.  Because the injectors aren't bleeding off volume.  Assuming the same voltage again, if the return line was a restriction, you'd see the problem when you were running the pump without the engine running because the volume would be the greatest.  Nothing bleeding it off.

^Exactly.^

 

I'm thinking this whole fuel pressure thing is a red herring - the two data points that were given were _not_ off by 5psi - the corrected value given for 10psi was right where it should have been, and the fuel pressure stated for 27psi boost was maybe 2psi too high.

 

If you do the math for this, getting ~10AFR when you expected 11.5AFR requires ~15% increase in fuel delivery.  9.5AFR would take ~20% more fuel.

 

The 2psi extra fuel pressure stated for 27psi will only account for about a 3% increase in fuel delivery.  Even if you did have 5psi too much, it would only account for about a 7% increase.  

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Is the fuel pump controlled through the ecu? I'm not sure how complex the control system is but it seems to have a hi/low setting with a stock ecu. 

I know at trackdays I'll hear my walbro whining away much louder than if I just do street/daily driving. But i could be wrong, the one thing i don't know much about is how the fuel pump control works. 

But if the pump is run 100% all the time, and the return line was undersized you'd have the opposite problem. Too much fuel pressure at idle and lacking (or maybe correct) at full load or high rpm. 

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Well not that you run out of injector, but if the injectors stuck open like a really high duty cycle you wouldn't be injecting as much as hosing. I've seen dyno runs where that happens and they just basically run pig rich when it sticks open although that is usually accompanied by fluctuation at the FPR, usually solved by going to an uprated injector and running a lower duty cycle or turning down the boost.

 

It sounds like your FPR and your fuel pump are working if you aren't loosing fuel pressure in boost within a certain margin of error. 

 

Have you tried to lean out the tune? 

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So data points from what I can see on the video:

 

30psi fuel pressure off boost

 

62psi fuel pressure at what I am guessing is 30+lbs of boost, tapering to 61 psi as boost tapers down to 30psi (hard to tell on the gauge)

 

The only thing that seems odd is that when you hit what looks like 34-35lbs of boost your fuel pressure gauge does not go all the way up to 64psi it stays at 62 psi. Suggesting maybe you are maxing out your fuel pump or as mentioned above you are dumping fuel. 

 

Have a duty cycle table we can look at?

 

The pressure seems correct for the level of boost you are running assuming you are running a RRFPR or a FPC.

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