A real test of the difference a fuel pump makes (dyno)

[Sean73]

I agree w/ Tony regarding AFR at stock boost. Have you ruled out a problem with your stock fuel system? I would run a dyno at stock boost, and see what happens. You could be compounding problems by messing w/ fuel pressure, adjusting the AFM, adding fuel computer etc., if your stock fuel system is not running right in the first place. By running a dyno at stock boost, you'll be reducing the number of variables, and have a greater chance of solving problems correctly.

 

Also, at 10 psi, your injectors are at the threshold of being maxed out (if not already). It's true that some people can run 10 psi or more on stock injectors, but not all stock injectors are perfectly equal, especially on higher mileage engines. I'd assume nothing about the injectors unless you have tested them. I have found a high degree of variability in the turbo injectors that I have tested personally.

 

If you still run rich in the mid-range at stock boost, then you'll know that you need repairs, not mods.

 

Good Luck

 

Sean

73 240Z: L28ET, 84 ECCS, NPR IC, Custom DP, 3" Ex., 3.7 R200

[Guest bastaad525]

what a difference a few gearteeth make!

 

After digging up some old threads from people who've installed larger injectors and 'tuned' their AFM's to match, I found that 18 teeth was a commonly used number for the amount to tighten the gear... so that's what I did... the car was not happy with that! Apparently this went from being slightly rich to WAY too lean... the car BARELY idled. So... loosen it by 9 teeth, and the car is still stuttering pretty badly. Anyways, in the end, I lessened and lessened the amount of adjustment from the starting position, and just leaving it tightened only 3 or 4 teeth more clockwise than where it started seems to have helped, though my light miss is still there. Idle smoothed out a tad. I was amazed that even such small adjustments would make such a big difference... on my N/A ZX they had nowhere near as much noticeable effect. Ah well, at least now I know that was pretty close to as good as it could get. Tommorow I'll experiment with it going the other way, just to see how it feels, though logic and the smell of the exhaust tells me richening it up is NOT what it needs, at the same time I look at the dyno charts and as super rich as it already is, it consistently makes a few more hp/ft lbs when it's running richer. Strange but true....

 

 

Ah but I'm getting sick of and FROM the car again, literally... spent all of the last two days chasing the smell of fuel inside the car... this just started as of yesterday... replacing hoses left and right hasn't helped... I just can't tell where its coming from.

 

Odd thing is, I only smell it after making left turns.... ?????

[Len]

Don't make left turns!!!!!!

I told you two or three teeth....Now WHO'S YOU Daddy!!!!!!!!!!!!!!!!!!

Just remember We get what we pay for A 1981 to 83 280 xzt n FMS you want more get a Haltec, SDS, Z31 FMS otherwise enjoy the ride! But it is fun to push the max on what you got!

[Vintage-TechZ]

Bastaad,

Regarding your fuel vapor in left hand turns,..have you had your fuel tank off and replaced the old hoses yet ? Well if you hav'nt do it soon before you get bad sick ,nerve damage or start talking in tongues !

The hoses on the top of the tank are most assured to shrink and crack and as you crank around a corner the splash and vapor will fallow the path of least...well you know !

Anyway, hope you find it.Nothing ruins a ride faster than that discomforting pungent smell (unles it's racing fuel ! )

...........Vince

[Len]

Vince is right!

I don't mean to make light of your fuel smell! I had the problem years ago with Volvo 122s. It ended up being the gastank having two leaks at the seam.

Check it out! People look at you weird if you talk in tongues and your not in church!

[Lockjaw]

I would have put a fuel pressure guage on it before replacing the pump, that would have saved you the money, but you will need the pump if you plan on further upgrades.

 

I can just tell you, I hate the stock injection since moving to the JWT stuff, and would encourage you to do the Z31 swap.

[jeffp]

First and formost that thing that needs to be cleared up is the requirement for a larger capacity fuel pump.

I have done mucho research on this topic with my ca, completed accurate testing of the system for my application, but this info applies to all fuel pumps.

Guessing when it comes to fuel pumps can be a VERY expensive guess.

In order to determine if you need a new pump, you really should take the time to see just what your pump will do.

You know how much the injectors will flow @ 3 BAR so that will be your flow rate of the pump minimum. The next variable is the fuel pressure. NOTE: a stock turbo fuel pump will crowbar @ 65psi meaning it will NEVER provide more then 65psi of pressure, so @ 3 bar (44.1psi) you will only be able to boost the car to 20 psi and the pressure will not rise anymore. Then you have the fuel requirements @ 65psi. For your injectors you will need 1554cc's of fuel per minute. So if the pump can run that kind of fuel delivery you are in there.

Injector size is also the determining factor as to how much hp the engine will be able of producing. I will refer you to RC engineering for flow rates and hp ratings of the injectors http://www.rceng.com/technical.htm#WORKSHEET

When you find out how much flow is needed to get the desired hp from the engine, then it is just a matter of seting up your system and testing it (not while running the car).

Start with the static psi (3bar or 4bar) add in the boost pressure (using a rising rate fuel pressure regulator) the rate should be 1:1 on the regulator.

so 43-44 psi plus the boost of 20 will give you 64psi. Then plug in the formula for the injector size to match the desired hp. for my car at 600hp 72lb/hr injectors @ 35psi of boost=79psi of fuel pressure the injector required will be 600cc/min to get 600hp, so the total flow of the system I will need is 3600cc's a minute from the fuel pump/lines/and rail.

 

To do a quicky real time test on your system what you will do is hook up a fuel pressure gauge to the system (feed side of the rail) and test the car under boost. The fuel pressure should rise 1 pound for every pound of boost. The gauge should NEVER lose pressure under boost through out the rpm range. If you do see a pressure drop in the gauge under boost you need a bigger fuel pump, no question about it.

Had you tested the system BEFORE you went and bought a fuel pump, you would have found that the stock Nissan pump was within operating requirements of the system and injectors.

I guess what I am getting at here is that all of this stuff is just simple math, there really is no guess work to the equation. Just plug in the numbers and see what you get. Then after you understand the requirements of the system, test it on the car real time with all of the system components installed and see if you get the correct fuel from the system. Just going on the advice of someone for me in my case was not good enough, why, well because I have not found ANYONE that has done the real time in life testing of my system, and even if they did, I still would test my own car and system, you NEVER know is something is screwy on your own car for some reason.

Come to find out, the 280ZXT system has a 4psi drop across the system from the fuel pump outlet, to the fuel rail. There is some restriction either in the fuel damper, or the line in some place is not the correct diameter(either through the bends, ir a ding in the line(it's the bends in the line) or the damper is the constriction.

Well according to the data on paper I should be able to run X amount, but try running 4psi of pressure low @ 30psi of boost one answer BOOM!

So My recommendation for anyone is to FIRST test the system before you buy anything. Save yourself the headache, the question of is it good enough and should I buy this or that. FUEL delivery components are NOT cheap, and replacing a component based on what who ever said will do this or that is just not good effective design, or rationalation for your particular situation.

[Guest bastaad525]

I would have put a fuel pressure guage on it before replacing the pump' date=' that would have saved you the money, but you will need the pump if you plan on further upgrades.

 

 

now you tell me. why is it that so much of the great advice I get here seems to come after the fact Anyways it wasn't much money lost really, more the time and hassle that came after the install. I only rushed to replace it because everyone here seems to agree that the stock one is 'no good' when it turns out it was fine for my car in it's current state. But the theories were kinda backed up by my first dyno results (the a/f ratio going lean above 5000rpm) so it just made sense. You're right though, another trip to the dyno with a pressure gauge would have told me that the stock pump was probably doing it's job just fine. But, you are also right about needing it at some point, a) because I know my stock pump was not long for this earth... I bet it would have failed within the next few months, and I do plan on further upgrades well, just my I/C installed and turning up the boost

 

 

Anywho... there are still a few vapor lines left that need to be replaced I know, the two that you need to drop the fuel tank to get to. A job I've been dreading. I dont think the tank itself or any fuel line is leaking though, I've looked under the car numerous times for a drip but dont see anything. The tank was also dropped, inspected, cleaned and recoated about a year ago. I had asked them to replace those vapor lines then but they conveniently 'forgot'. Just odd how this smell JUST started at the same time as I put in this new pump and swapped return lines and such... well I need to experiment a little... I guess pay closer attention to, if the smell only comes with the windows down (probably means it's a leak and the smell is coming from under the car) or even with windows up (those old vapor lines).

 

Question: where do I find such large size fuel hose? a couple of the hoses on the vapor tank are very large, 1/2" or more in inner diameter. Largest fuel line I've been able to find is 3/8". I dont think it'd be a good idea to use, say, coolant hose, as even the vapors would probably eat thru this pretty quick, no? Where can I find the right hose in the right size? please dont tell me it's gonna be 'dealer only'.

[Lockjaw]

You can use some tranny fluid lines I believe, thats typically what I use, something for higher pressures.

 

Well sorry about the late info, I don't check the board that often. I have just found from personal experience that replacing parts without testing is an expensive way to find the source of your problem. You may think one thing and go another direction to find the probelm.

 

I can tell you when my CAS was going bad in my Dizz, I was convinced it was the coil, the ignitor, whatever. Anything but that piece. Mentioned it to a friend, he says, check the CAS we are seeing that alot with 300ZX's. Funny thing is, I had a spare. Replaced it, and all was good.

 

So don't feel bad, I don't always heed my own advice either.