95maxrider

iTrader: (32)

Here's the situation. Over the last year I've noticed my car pinging pretty badly in certain situations. It's most noticeable when I drive by a wall or something that the sounds can bounce back from, usually at 50% throttle. Once I hear the noise I don't go WOT, so I can't say what it sounds like at WOT.

I installed a used Walbro (190 LPH I think) a little over a year ago, and I really don't think the car ever ran right after its install. I have a NISMO AFPR and my AFR is good at idle/part/WOT. Last week I replaced all O2 sensors, spark plugs, etc. Even so, my car was pinging like crazy at my last auto-x event.

My mechanic ran an "EKG" on my fuel pump, and this is what he found:

Can anyone elaborate on what this tells you?

Apparently the line is supposed to be a lot smoother, which indicates that pump may be on its way out. He said something like if you use a FP that's too large, you will force your system to return excess fuel, or use fuel that has gotten too hot waiting to be used, which could cause detonation. We will be doing more tests this weekend hopefully.

I've searched for the LPH flow of the stock 4th gen FP, and I can't seem to find anything. Does anyone know what it flows? I would normally just go buy a OEM FP, but the car is setup for a dry 65 shot with the JWT program. I'm pretty sure I need a 190 low pressure FP to spray a 65 shot, but I'm not positive. How do you calculate what flow a 65 shot needs? I want to go with the smallest FP possible to eliminate any problems associated with a larger one. I'm also confused about the 190 low pressure v. high pressure. Which do most people use and why?

The car isn't throwing any codes for a KS or coils, so I'm just about out of ideas as to what could cause this much pinging. Any help would be appreciated. Thanks guys!

95maxrider

iTrader: (32)

anyone?

hacim105

iTrader: (6)

Well I'm not sure but here's my opinion. First of all I fail to see how the amount of fuel returning to the tank matters in anyway, or how a higher rated fuel pump would cause excessive fuel to return to the tank. As for the fuel being too hot, I think that's always been a concern on a return system, but again I doubt that would have anything to do with the pump itself.

Just out of curiosity have you swapped the original fuel pump back into the car to see if you're having the same problem? Perhaps you need to replace your fuel filter. Are you using colder plugs for you car since you run nitrous, perhaps that could be the reason?

As far as pressure goes your AFPR is determining that. The LPH of the fuel pump is just a number that shows the maximum amount of fuel it can pump through the system if needed. I don't believe it's the actual fuel amount flowing through the system. In fact that's why you need the AFPR so that it can make sure the proper pressure is there.

So perhaps your fuel pump is dying. Sometimes that just happens to be the case. Or perhaps your injectors aren't performing properly. From all the problems I've seen it usually seems like pinging is caused when timing is bad or if the car is starved for fuel.

GeoKohler

I know this is an old post but I've seen so many people getting confused about our fuel systems I figured I would share some of the information I gathered over the last 30 years or so wrenching.

Our Maximas use high pressure low volume fuel pumps that flow 190 lph stock and can deliver well over 100psi though we run 35 to 50psi depending on modifications and varying engine load. When the vacuum pressure in the intake manifold drops due to the opening of the butterfly in the throttle body the vacuum line leading to the fuel pressure regulator transfers that low pressure condition to the diaphram in the regulator which in turn raises the fuel pressure proportionaly to meet the demand of the engine. Alternately, a carbureted sb or bb type engine uses the high volume low pressure type pump and generally only produce 6 to 10psi and are capable of 100 to several hundred gallons per hour. As correctly mentioned above the main and only purpose of flowing that much extra flow is to flush the fuel rails or float bowls continously ensuring a cool fuel supply to the engine. Introducing hot fuel into the cumbustion chamber causes pre ignition knock. Say you have a 10:1 compression engine and for simplicity it happens to be 100 degrees out. When the 100 degree latent heat in the fuel air charge is compressed to 10 times less then it's original volume it is now 1000 degrees. Thus adding hot fuel is a bad thing. Same goes for super chargers and turbos explaining the need in most cases for an intercooler to cool the air after it has been compressed. A good example of gases heating from compression is your air compressor. Fire it up and see how long you can hang onto the pipe coming off the jugs...not long...
Many backyard tuners also neglect the need for more fuel after adding headers, Y-Pipe and porting leaving the stock fuel delivery system to attempt to handle the new overly lean condition only by the action of the O2 sensors reporting the lean condition. This inturn will eventually cause the MIL light to trip due to the long term fuel trim to be off. Once in closed loop operation there is enough adjustment range in the system to compensate to where the engine will run but you're not going to produce any significant power until you jack up the fuel to match the air. The simplest way to add more fuel is to install an adjustable fuel pressure regulator and crank it up a little at a time until you dial in the sweet spot. Fairly accurate tuning can be achieved without a dyno simply by knowing the exact wieght of the vehicle and a USB to consult adapter. Using the data logging function of a laptop/netbook interfaced by way of the consult port actual HP can be be interpolated by timed acceleration of mass data but that is beyond the scope of my rant.
Anyway, If I read one more post about somebodys new Walbro 255LPH pump being way to powerful for their setup I'm going to punch myself in the junk for wasting my time reading it trying to figure out how they managed to get online. (Not refering to this post). In this case I would install a fuel pressure gauge unit and log the pressure during a test run noting the exact time of the annomaly each time it arises during the run then go over the log(Never tune on the road! Staring at an LCD barreling down the tar is a good way to make the Darwin list.) If the problem is constant you could just stand there and look at the gauge while the RPMs are fluctuating and see if it's a fuel regulator issue though I've never ran into such an issue with a regulator. There's no way even a stock regulator couldn't handle the flow from a Wahlbro. Once the manifold pressure is achieved the excess fuel simply flows unrestricted back to the tank by way of the 5/16ths return line. Hook your Walbro up to a 5/16ths fuel line fitted with a T'ed in fuel pressure gauge and leave the other end open. Start up the pump and you will see 0 PSI, maybe 1/2PSI in the actual fuel return line in the vehical due to the internal resistance of the hose. With 5/16ths" in and 5/16ths" out how could there be too much back pressure to allow the return? There's even less gasoline exiting the manifold then coming in due to the fuel consumption. Maybe if you were using a commercial 20HP Honda Pressure washer for a fuel pump! I better not give anyone any ideas...lol
Oh well, 7am, off to another fun day in my Laptop/PC/Electronics repair shop....RAW joy!
Peace....

sergofast

iTrader: (22)

NIce...thats some good educated info right there!