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VQ35 fuel problem......car spits and sputters


angry_dave24

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Hey guys, its been a long time since I have been on here, but I don't know where else to go to get a good answer to my problem, and I am tired of pulling my hair out.  I have a 72 240z that I had a vq 35de out of a 2003 350z installed into by a company that specializes in z cars down in Tampa Florida.  They dynoed the car and it put down 273 to the wheels using their tune.  It ran great for the short spurts that I drove it in front of the shop.  This company also deleted the NATS, and used the stock computer.  This supposedly gets rid of the need to use the standalone engine management, and it retains the VVT.  What the car is doing is every time I drive the car it drives fine under little load.  When I accelerate moderately hard after it has been running for a while, or if I have been driving in traffic for a bit and try to accelerate, the engine almost completely cuts out.  The engine dies out until I lift off the throttle, then it idles fine.  If I kill the ignition and restart it, it runs like a raped ape for about 1-2 minutes and the problem restarts.  Upon investigation I have found that the fuel pressure slowly drops off from the required 50 psi, down to about 10 psi.  I figured ok, well it must be the fuel pressure regulator.  I installed a new aeromotive regulator and got rid of the craptacular regulator the people installed with the engine (no name e-bay special)  The one I installed has 1 input, 1 output, and a return port.  It also has a port that allows a guage to be installed.  I plummed it all up, and went for a drive and alas it does the same thing.  The pressure slowly drops off at the upper rpm range.  I installed the regulator back by the tank, not my first choice, but this is where the original was, and I was just trying to get it hooked up to see if it fixed the problem.  Would having the regulator back there somehow effect the fuel delivery to the engine, and potentially cause this problem?  I am using a wallbro 255 fuel pump, fully capable of providing ample pressure and flow.  I am using the stock fuel tank, drawing fuel from the original port.  I would love to run a fuel cell, and nice AN lines with an internal pump, but money is tight.  Any ideas would be really appreciated.  NSDQ!

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Well your first problem (from what I understand from many people, not personal experience) was using Z fever to begin with.  Seems like all I hear is horror stories from that company, especially anything involving VQ swaps.  Secondly just because you replace the regulator does not mean that the regulator is getting proper fuel pressure to begin with.  Walbro is a reputable company but that does not mean the pump is not defective or clogged, especially since you are using a tank that is 40 years old and probably wasn't properly cleaned out and setup to run F.I.  I would also check the voltage the pump is getting under load and ensure that you are getting proper voltage. 

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According to the guage on the regulator it is getting 50 psi until under a load, then a few seconds after the load is put on the motor the pressure slowly drops off.  Could it be that it provides adequate pressure, just not enough volume to keep the pressure up?  The tank was boiled out and professionally cleaned.  I have seen the inside of the tank. What would I have to do to set up the tank for fuel injection?  I have verified the pump is getting about 13 volts.  I have also verified the pump is getting plenty of amperage.  I was trying to avoid mentioning the company by name, not trying to cause a commotion, I just want it to run right.  For the small amount of time it runs right, it is stupid fast, when I get traction ( no lsd swap yet). Forgive me if my knowledge is not where I would like it to be when it comes to cars, but you are dealing with a novice. 

Edited by angry_dave24
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Well its good to know that it was cleaned out properly.  The main difference between carbed and FI tanks is a baffling system.  You have to realize that when you are cornering/accelerating and your pickup starts sucking air the carbs are still getting gas from the float bowls, with an FI system if the pickup is ever not submerged then you are going to have issues.  Are you checking the voltage after load has been put on the motor?  It seems to me your problem is originating after you are driving it, not while it is sitting still.  You need to recreate this.  Otherwise you are correct in your assumption that there is some sort of blockage where you are getting enough PSI as long as the volume requirements are not too high.  Did you use AN fittings or barbs?  Either way it shouldn't be too much trouble to disconnect the lines and blow them out along with putting some air pressure in the outlets of the pump and filter and blowing back to see if anything comes out.  Sorry its taken me so long to respond, the new forum system does a horrible job of email notifications.

Edited by Zman0690
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He specified he was using a Walbro 255 which should provide more than adequate volume for what he is running.  I do agree that an improperly sized fuel filter could be an issue.  Although Angry_Dave hasn't posted a reply to this in a while so this may be another thread which has no conclusion.

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Well, you're fairly certain the Pump is doing it's job.  But  it's hard to say. 

 

Maybe try this: Take the return line off and connect a hose to it to a gas can and start the pump. There should be a steady flow into the can without a lot of bubbles. The regulator should be still showing the full pressure.

 

If that's the case, then put back together the lines, pull loose the line BEFORE the regulator, before the engine, and into the gas can you should have a pretty high velocity flow, if not, go back and temporarily remove the fuel filter, bridging the line with a tube, hosebarbs etc.  You should have a good flow then. 

 

If none of these do you have a good flow as you'd expect, replace the pump.  If w/o the filter you have a good constant flow, Replace the filter.

 

What it sounds like to me is that the Pump builds the needed pressure, but soon as the engine drops that pressure, the pump can't replace it. Sounding like a weak pump to me. 

 

If the filter is clogged, then it could be that the pump is able to draw enough to build the pressure, but the pump can't pull enough through the Filter fast enough to replenish.

 

Try these tests and see what you come up with. Basically We're just pulling parts out of the system to see what's not working well.

 

You said you saw the inside of the tank, Was it shiney new , or coated?  if they cleaned and painted, you could be sucking paint chips in, which is a nightmare.

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Sorry guys had to go out of town for work, I will try what pharaohabq said in the near future and let you guys know how it turns out. I would love a way to just insert a 350z fuel pump with the built in regulator into a fuel cell and call it done, but that is way more than i can afford right now. Anyone got a good pump on the cheap?

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Good pump on the Cheap. Well sure there's a ton of them on Ebay, but you get what you pay for. 

 

A better idea would be to go to the Junkyard and pull a pump from any v6 or V8 EFI engine'd vehicle.  the volume shoudl be there and since it's an OEM it should be pretty bulletproof.  If you gut the whole assy, you can cut open the top of your S30 tank,  put in the whole assy from the top and seal it with rubber and bolts.  Assuming it'll fit.  If you get it from a Nissan with the VQ (Quest, Pathfinder, 350/370z, 3.5 maxima/altima) it's likely that the plugs will line up, and it'll already have the  right pressure set.   you can tack in some baffles while you're at it. (just make sure the tank is empty and cleaned of fuel before you start weling in there)

 

Good luck, and let us know what you figure out.

 

Phar

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I just ordered a 350z gas tank with pump and all for $100 shipped. I'm gonna try to cut out the flange and weld it into the 240 tank I've got. I'm a little worried about the depth being correct, but we'll see when it gets here. 

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  • 2 weeks later...

I'd love to see pictures of this flange swap.  I think it'll work great. if anything a little plastic modification and bending of the float arm should sort it out.  Please post some pictures along the way.  :)

 

 

I 2nd this. Getting those parts isn't too hard really. It's just be good to see how you do this and then how it's all connected up and working...

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So money is no longer as tight as it was.  Paid off a lot of bills with taxes :icon47:   I am just waitiing to see how the 350z pump swap works out.  Please post lots of pictures, and ample explanation.  I think that this pump setup, if it works properly, will be a great asset to the vq swap community.  If it works, and the write up is good I vote sticky. 

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  • 1 month later...

I posted these in my thread but I figured I should share them here too. Here's my progress on the pump swap. After welding it up I used a smoke machine to find the inevitable pinholes. I also ordered some tank sealer  that I'm going to coat the inside of the tank with. My harness should be back next week so I will be able to test it out soon. 

 

IMG_4810%5B1%5D.JPG

 

IMG_4816%5B1%5D.JPG

 

IMG_4811%5B1%5D.JPG

 

IMG_4818%5B1%5D.JPG

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  • 4 months later...

So I figured out my problem, its the tank.  I heard the 280z tank is baffled.  Anyone confirm?  I think I would like to go with that tank, then run a hard stainless line to the engine.  I also plan on installing a pickup that sucks full from both sides of the tank.  Any thoughts on this?

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Hey Dave,  Yes the 280Z tank has a couple baffles, but would hang lower in the 240Z, due to the larger spare tirewell. But I think its probably the pickup more than anything.  Does it have the issue when the tank is full?  A full tank should be keeping the pickup under the level the whole time.  I'm not sure if you tried any of those other tests.  it could still be your fuel filter. A 240Z filter is too low flow and would certainly cause that. You might try a 350Z filter if you haven't already.  Zero's tank looks awesome.  I want to do that with my VQswap.

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