UPDATE!! Upgraded fuel pump issue SOLVED but some more Q's

[Guest bastaad525]

Got my MSD fuel pump put in yesterday (many thanks Tim240z for the very clean install... hope you're enjoying that St Pauli Girl!) and right off the bat something aint right. The car is stuttering a LOT really really bad misfire at idle and cruising. Brought the car back to Tim immediately, and he just did a simple test where he clamped down on the fuel feed hose, lowering the pressure in the system, and voila the car ran perfectly. So it's definately an issue of the new fuel pump is putting out way too much pressure. Tim believes this is due to the fact that I'm running the stock 240 feed and return hard lines, and I can see how that might be, as the stock return is smaaaaaaaaaaaall and probably is creating a restriction and building up pressure. But I do know that a lot of guys on here have upgraded their pumps lately... am I the only one running the stock feed and return lines? Did anyone else run into any problems with running too rich after installing an upgraded pump? Are there any other solutions other than making a new feed line and putting the return onto the stock feed? Would an adjustable fuel pressure regulator be able to take care of this?

 

I ask that because I came across this statement made by Sleeper Z in an olllllld thread:

 

It should be possible for a higher flowing pump to overwhelm a stock regulator, especially at idle. If you can monitor fuel pressure while driving, you can confirm that problem by checking the pressure goes down under moderate loads, or verifying once under boost that your pressure is 37 psi plus your boost pressure.

 

Which makes me think it may be more a problem with the regulator and possibly not be my fuel line setup. Also, and I know this is real mickey mouse... but I gotta ask. As I said, Tim did clamp down on the fuel "IN" line right after the fuel filter, and as he did so the car smoothed out and ran much much better. Now, if I got a pressure gauge installed to see EXACTLY what was going on, could I do something like this on a more permanent basis? I had to ask... I do agree with Tim though that this may cause the car to run too lean under boost, but I also think if this pump is supplying SO much more fuel (enough to handle up to 600hp!!) that even clamping down on it's flow wouldn't keep it from supplying enough for my much more meager setup at the top end. Again... I know it's cheesy, but please keep an open mind and give me real reasons why this would or would not work!!! All I can say is when he did this the car idled and revved much smoother than it ever has even before the fuel pump!

 

Anyways my first step after this is going to be getting a pressure gauge on there and seeing exactly what it's doing. Next will be an adjustable FPR (not a rising rate unit)... if that wont fix it then I guess it's new fuel lines.

 

 

Anyways... did anyone else run into any problems like this and if so what solutions did you find worked?

[yo2001]

time for an adjustable fuel regulator.

[Tim240z]

time for an adjustable fuel regulator.

 

Please feel free to correct me if I'm off base here, but wouldn't the restriction in the return line hamper the regulator. From what I can gather, the small return line is acting as a pressure regulator and is increasing the pressure too much. The fuel pressure regulator would just be unable to decrease pressure because it would need a free-er exit for the fuel. If the fuel can't get back to the tank quickly enough, the regulator will never be able to be functional.

 

Tim

[yo2001]

if the regulator is working, then the FP wouldn't be too high and won't be outflowing the return line. That's what I think. Could be wrong. though

[Tim240z]

It's my understanding that the regulator works by allowing flow to the return line (lowering pressure), or blocking flow to the return line (higher pressure). If the return line is the restriction (high pressure), then there is no way for the regulator to lower the pressure further.....no?

[Tony D]

I could not even run with the stock N/A fuel pump through the stock 240Z return line. I am amazed you could run at all!

Very common problem, and is usually solved by running fuel return through the vapor line from the tank to the crankcase.

You have to do some jiggering with how you get the return line to that vapor line, as it runs along the left side of the engine / fender well, but is a full 1/4 or 5/16" I.D., and worked just fine as a return line for me---and several other people.

 

Easy way to check it is to loop some EFI line back to the line and hook it into the tank out back. I had a return fitting in my filler neck from somethign else, so that is how mine is currently tubed up out back. If you already have a 280Z tank with the big pickup line and 1/4" return line, then you can run the vapor line to the tank return fitting.

 

That should solve your problem.

 

Good Luck...

[Guest bastaad525]

Tony - was thinking of doing that exact thing. Reason I DIDN"t think that would work is that vent line goes to the vapor tank, not directly to the fuel tank, couldn't this create problems with fuel building up in the vapor tank? Now that you mention it though, it IS possible that the small return has always been a problem, hence why my car has always seemed to run a bit too rich at idle and had a slight misfire/stutter problem.

 

Tim - I can definately see how both the FPR and the return line COULD easily be the problem. On one side I can see how the restriction could be caused by very small return line. On the other side I think that the stock FPR was set to regulate pressure to a certain psi, but it was also set to regulate to this psi ASSUMING a level of pressure about what should be provided by the stock pump. Now, the only input that controls the FPR's function is the boost/vacuum reference, right? So if you suddenly increased the amount of fuel pressure being supplied to the FPR by the fuel pump, but obviously vacuum pressure has remained the same on the FPR, it's still only opening so far allowing so much fuel to divert back to the return line. It has no way of 'seeing' the increased pressure being provided by the new pump. So being as it's still allowing only that same amount of fuel to bypass to the return, it's not allowing the additional fuel provided by the new pump to bypass, hence the increased pressure. But me, I really dont know enough about how the stock FPR works... will it compensate for a higher flowing fuel pump and allow more fuel to bypass on it's own?

[Guest bastaad525]

by the way I did pick up the pressure gauge and fittings today... was going to install it and see where the pressure is at but it's raining out and hence all my errands for the day got slowed way down... barely making it out the door on time to get to work. I may take my car to the dyno tommorow and see how it's running exactly the way it is now with the new pump... I will say that it definately feels too rich across the board, even on boost, and would like to verify this before I mess with anything. I think the fuel curve may give more of an idea as to what the problem may be or how to best solve it.

[Tim240z]

Fix the problem first!!! You'll be pissing $$$ away running it on the dyno with known issues. IF you really want to test the return line issue, get a 4 foot section of fuel hose and run it from the manifold return line to a 'jerry can' (no stock oem 240Z return line causing restriction) and see if it clears up any. At least then you will know.

 

Tim

[Guest bastaad525]

now THAT is a good idea!! Definately a great way to know for sure without/before running all new lines. Tim don't get me wrong I know sometimes it seems odd that I will try to dodge one fix and try to take the 'easy route' but that's not really the case at all. It's just... look at my options... if it's anything that involves me getting under the car then I am assed out on being able to do it at home, and I really dont want to ask you if I can come over to your place every time I need to get under there to fix all this piddly stuff!!! That's why I'm trying to find solutions from above the car first... I can spend 5 days putting in an adj FPR if need be and no one cares.... for some reason my apt. manages associate a car on jackstands as a mess-in-progress *shrug*. LORD I can't wait till I move outta this place.... Anyways I do have some fuel cans here, I'll run the return to one of those and see if the car runs better that way.

 

Only reason I wanted to dyno it the way it was was to see if the fuel pump is creating a rich mixture across the board or see if it's only running rich at low rpms off boost as you anticipated. I was also most likely going to pick up the adj FPR before hand and have it ready to go. But I will try your idea before I do anything.

[Guest 81na ZX]

This doesn't help this problem, but heres some additional info:

 

On DSMs, upgrading the fuel pump leads to FPR overrun. Stock, it runs abour 36psi fuel @ 0psi. With a stock FPR and a new pump, you could see up to 60psi @ 0psi... The problem there is not the lines but the regulator itself. The opening into it is about 4mm, way too small for increased flow.

[Clifton]

I have run a Paxton pump and my current 255l Walbro pump with a stock L28ET FPR on the 71'. With both pumps the pressure was a little higher at idle by a few pounds from the volume, even with a larger return. It hasn't caused any problems though as it drops to normal as the revs pick up a little. On the 73' I run a 255l Walbro and used one of the emissions lines for a return line. The pressure is 36 psi at idle, right were it should be. I wouldn't even bother with a guage or after market FPR until you get a real return line on there.

[Guest bastaad525]

Okay first off props to Tim240z you were right dude. I'm very glad you suggested running the return hose into a can like that to see if it changed anything. Very good idea that saved me a lot of time and some money, and put to rest any question or doubt as to what the problem was, very quickly and easily.

 

Also props to Tony D and Clifton, I think you guys were on the same page for a quick, working solution, using a hard line that is already present on the 240 and really not serving any purpose in a turbo swapped 240, and I picked up from there.

 

 

 

So here's what happened. First I tee'd in my Home Depot pressure gauge and left everything else alone (the hoses routed the way they were before the pump swap). Started the car and let it warm up and checked the pressure... was at a nice rich 60PSI!!!! A wonder my car would idle at all like that. Disconnecting the vacuum hose from the FPR didn't affect the pressure (clue #1 that Tim was right and that the FPR was not in any way the cause of the problem, and that an adjustable FPR wouldn't help to solve it). So I got a fuel can, disconnected the return line hose from the small stock return line and ran it into the can, restart the car and now it's idling right around 35-36psi, and disconnected the vacuum line from the FPR brings it up to almost 40psi. So no doubt that Tim was correct, the return line was just too restrictive for the new pump.

 

So I did as Tony D suggested, ran some 5/16" fuel hose from the return line of the fuel rail to the hard line that opens up right under the coil, the one that goes back to the vapor tank. The pressure stayed where it was supposed to so that hard line is fine, as far as size goes. But now it sounds like a waterfall running in my car constantly as you can hear the returned fuel getting poured into the vapor tank, and there were occasional fumes as I drove around... no good. So I took it to a shop where I have a friend, he lifted the car up and I did a little more rerouting out back.

 

First, the hose that comes out of the top of the vapor tank, and disconnected it from the hard line that I now had the return hooked up to, and just left that vent hose hanging (so it is still attached to the top of the vent tank, and passes out thru the right rear fender, and just hangs down open in front of the fuel tank)... since nothing but vapors come out from there and it wasn't routed to anything before anyways, I figure it shouldn't be a problem. Worse comes to worse I can always hook that hose up to the stock small return line that is no longer being used. I then attached a new fuel hose to that hard line and connected it to the stock 240z tank fuel feed nipple (The fuel is now fed from the bottom middle of the tank as is so commonly done on turbo swapped 240 tanks)... was going to connect it to the stock return nipple on the fuel tank, but I noticed that that nipple is also very small, the same size as the stock return line, and figured it may still be a restriction. The stock feed was just sitting there plugged and unused... so now that is my return. Fuel pressure stayed where it is supposed to be, however, I do noticed the the needle fluctuates, very rapidly, between about 35-37psi. If I grasp the feed hose and squeez it a bit it stops, but goes back to jumping when I release it. Tim did leave the stock ZXT fuel damper in place back by the tank, but it seems that the gauge is reading some pulsing. Should I worry about the needle twitching? Will this affect the way the motor runs?

 

Also, I really wanted to ask, is it okay that I have the return plumbed in to the stock 240 feed nipple on the tank? The nipple sits a good 3-4" from the very top of the tank... and I worry that when I full tank it (been running at about half tank all day today) the fuel in the tank will 'block' the returning fuel and will cause the fuel pressure to increase... do I need to worry about this? I couldn't think of any better place to route it to...

 

Anyways... problem is pretty much solved... car running back the way it was... dont really notice any increase in top end performance from the pump. Was going to dyno today after fixing all this stuff, but the shop was pretty busy, so I'll probably go back tommorow morning and see exactly what effect JUST UPGRADING TO A BETTER FUEL PUMP had (and of course a bigger return line)... good research

 

If you guys see ANY problems with my setup the way it is please let me know!

[mobythevan]

Don't people with sumps on the bottom of the tank feed from the bottom and return to the bottom all the time? Just asking another variation of Bastaad's questions, does it matter if the return line is in the top, bottom or middle of the tank?

[Guest bastaad525]

You know I may be wrong but I think Tim240z's own car is setup like this. He has a fuel cell installed, and I know I've seen two braided lines plumbed into the bottom of that... one of them may be the return? I hope that having the return in the middle will be okay... getting tired of stressing it!

[Tim240z]

Don't leave open lines anywhere. Fumes are way more explosive than liquid fuel. Someone walking by with a smoke can BBQ your car...

Tim

[Guest bastaad525]

Don't leave open lines anywhere. Fumes are way more explosive than liquid fuel. Someone walking by with a smoke can BBQ your car...

Tim

 

 

 

!!!!!!

 

 

knew there was going to be some catch with that... okay I'll route that somewhere.

 

Tim - is it okay to have the return 'dumping' into the fuel tank about 1/3-1/4 the way from the top? Will this cause any backpressure when the tank is full and restrict flow, causing pressure increase? Is your return line plumbed into the bottom of your fuel cell?

[Tim240z]

You can put the return anywhere on the tank. Yes, my return and feed lines are next to each other.

BTW....I won't say"I told you so"....lest you doubt me anymore!!

 

Let us know how the dynomometer goes....

 

Tim

[JMortensen]

Someone walking by with a smoke can BBQ your car...

 

As someone who has thrown a lit cigarette into a jar of gasoline to prove that it won't catch fire, I can tell you that walking by gas fumes with a lit cigarette will not start a fire. There MAY be some ideal set of circumstances, ie you just took a drag and the cherry is as hot as it is going to get, and the fumes are at just the right density, but under normal circumstances it won't happen. LIGHTING a cigarette near fumes can. And yes, even though I knew it wouldn't catch the jar of gas on fire, I still winced when I threw it in. It's that whole self preservation thing, I guess.

 

Jon

[Tim240z]

Jon,

I did mean that tongue in cheek, and the phrase was merely for analogy value.....bottom line is: it's not safe....but your point is valid nonetheless...