Ipohboy

iTrader: (1)

I have an Aeromotive FPR that came with the kgparts fuel system kit when I bought it about 1.5 years ago. I frequently check the base fuel pressure at the gauge after driving the car with vacuum hose off when the car still running or by jumping the fuel pump connection at diagnosis box with the key on.

For the past 1.5 years it held base pressure that I set it to 40 psi perfectly.
but last week, the base fuel pressure started to drop to 29-30 psi. I raised it back to 40 psi immediately.

Then next day before I started my car, I double checked the base pressure using the diagnosis box and it still held 40 psi. Then I drove my car for a little while and came home , check the base pressure, It drops again to 29-30 psi!

I tried 4 times already raising back the base fuel pressure to 40 psi but the same thing happened , it will drop back to 29-30psi after driving the car.

Anyone with similar experience or experts want to guide me on where to start troubleshooting this problem?

Thanks.

spoolage

iTrader: (2)

Do you mean that the fuel pressure will drop once the engine has been shut down and the fuel pump is no longer running?

The first thing I would check is the rubber o-ring that is used to seal the fuel pump to the metal hard line on the pump housing. This is a possible culprit and easy to check. If you are still using the o-ring to seal, I recommend getting a piece of fuel line and connecting it to one end of the fuel pump nipple and the other end to the hard line of the fuel pump housing.

proz07

iTrader: (6)

or your fuel pump is dieing

z

Ipohboy

iTrader: (1)

Nope , I mean after driving, I check it with the key on and jumping f/p and ground at the diagnosis box. but sometimes I just took the vacuum hose off to check the base fuel pressure while the engine still running.

and forgot to mention, after I shut the car down, the fuel pressure will drop to 20 psi and slowly decreasing to 0 psi and it took just a few minutes to do so. It has been in that way for 1.5 years. I red in this forum that the fuel pressure should hold long enough (about an hour) before dropping flat to 0 psi. Is this true?

Ok, I know what you mean. I will check that later on when i go to my friend's workshop.

Maybe... but the fuel pump I am using is the new sard 280 lph along with the sard pump harness kit and only have been using it for about 1.5 years.

Dudemaaanownsanrx7

iTrader: (23)

ever Aeromotive FPR i've ever seen drops pressure rather quickly when car is shut down. so this isnt an issue.

Maybe your filter is getting more and more clogged. When was it last changed?

2007 ZX-10

29-30 psi is a good static pressure, 40 psi is too high...stop screwing with it

thewird

iTrader: (8)

Fuel pressure at idle should be 36-40 PSi. I run it 38 PSi. When the car is off with the key on, the fuel pressure is usually higher then with it running at idle, mine is 40 PSi with the engine off and key on.

Try checking your wiring to the pump or temporarily connect it directly to the battery with a switch you can turn on and off.

When was the last time you switched your fuel filter?

Also, since it the pressure drops after driving the car, check the vacuum hose that goes to the FRP.

thewird

Ipohboy

iTrader: (1)

The fuel filter is about 2 years old. I seldom drive the car, averaging 3 times a week on a short distance. I premix the fuel with Motul 510 2T oil, only 100ml per full tank. I don't know if this 2T oil could clog my fuel filter. I don't think so.

I still use the fuel pressure regulator solenoid on the black box (99+ fd3s). I don't know if this solenoid can contribute to this problem.

I will check my fuel pump tomorrow, the o-ring, the small plastic thing on top of the fuel pump assembly (I remember someone on this forum said this plastic thing could crack and cause low fuel pressure).

2007 ZX-10

unnecesary...puts more stress on the injectors, and opinions on this are like, well, you know...I've been running 30-32 for a loooong time with no issues (and low 11s AFR at 15 psi)

2007 ZX-10

Pre-mix oil won't damage/obstruct the filter, but you may want to change it out after two years just to be safe. Consider going with a relocated Aeromotive 10 micron, it's a nice upgrade from the stock pos

Sammy Built

iTrader: (18)

If fuel presure drops could mean you have a fuel leak in your fuel system like the following fuel line hose, injector o rings ,even loose connection some where.

Dudemaaanownsanrx7

iTrader: (23)

A stock FD's fuel pressure is between 36-40 psi. The FSM even states it should be in this area with the car off key on and the diagnostic f/p pin shorted to ground. I run my base pressure 40 psi @ 0 vacuum. Some people run base pressures in the 50's or more. Higher fuel pressure helps atomize the fuel better. A low fuel pressure will cause the spray pattern to be drippy and weak. Running normal fuel pressure is not hard on injectors that's what they are designed for. The main problem from high fuel pressures is finding a pump that can keep up with the high pressure without dropping off.

2007 ZX-10

I'd like to see a source for this tidbit

dripping is a separate issue, and indicates a bad injector...as far as "weak", how low is "too low"? 30 psi is still alot of pressure

Dudemaaanownsanrx7

iTrader: (23)

A friend of mine worked at a place that cleaned injectors and had these systems setup with several injectors in a line mounted in a fuel rail type thing. It had a regulator that allowed adjustment of the pressure in the rail for the cleaner they ran through them. When it was turned down real low you could see the pattern of the injectors get weaker and at a certain point they more dribbled the fuel rather then having a nice fine mist. The higher the pressure the prettier the mist was. Below are some sites that mention the advantage of running higher pressure. There are also some people on the forums that indicate running higher pressure helped with atomization, i posted a couple from the forum, but i couldnt find the one i was looking for that runs like 60 psi base pressure. EDIT:here it is https://www.rx7club.com/showthread.p...=base+pressure (rice racing runs 70 psi base pressure see post #24)

Other sites indicating the higher pressure helps with atomization.
http://www.msdfuelinjection.com/fuel_pressure.html (good read on increasing fuel pressure by MSD)

http://www.kinsler.com/page--EFI--4.html (look for the part that says GROUP FIRED and go to the 3rd paragraph)

http://www.densomediacenter.com/PDF/SAE03.pdf (this is regarding diesels but still applies look halfway down on the PDF file)

http://www.mwfi.com/VP44.htm (look under the discription for VP44 Fuel Injection Pump)

http://www.seatcupra.net/forums/showthread.php?t=45714 (post 2)

http://www.cadillacforums.com/forums...ector-mod.html

https://www.rx7club.com/showthread.p...ht=atomization

https://www.rx7club.com/showthread.p...ht=atomization

https://www.rx7club.com/showthread.p...ht=atomization

2007 ZX-10

key point, which I already addressed...read my post again instead of posting 50,000 links

Dudemaaanownsanrx7

iTrader: (23)

Reread my post again then read the 50,000 links too, cause i did read what you wrote and you asked for a source on fuel pressure and atomizationi did exactly what you asked except gave you more then just one source.

And if you're going to quote me you should add the part where i said increasing the fuel pressure caused a prettier mist, indicating better atomization (smaller particles of fuel)

You also have to take into consideration that these systems had no pressure fighting against them as in a forced induction combustion engine. Maybe if they did have additional pressures fighting the fuel it would start to dribble at 30-32 psi instead of whatever it was.

I honestly have no issues with the amount of fuel pressure you run, i'm just stating that running what Mazda recommends is not going to damage the injectors, and that it will help atomize the fuel running higher pressure, not to mention your duty cycle will be lower which may even help extend injector life. So while running less then what the professionals recommend works for you, it does not make it optimal.

Ipohboy

iTrader: (1)

Checked the pump today, o-ring , small plastic cap , all are ok.

but the pressure still drops. maybe the original pump relay is the culprit??

Ipohboy

iTrader: (1)

Update:

Problem solved.

It's just the liquid filled gauge that came with the kit. The pressure built inside the gauge forced the needle to indicate low/wrong fuel pressure due to expansion of the liquid with temperature change. I never noticed the gauge has small rubber cap to release the pressure built inside the gauge. Opened the rubber cap , some liquid squirted out, and the gauge reading came back to normal again. I might soon change it to electronic fuel pressure gauge.

cewrx7r1

iTrader: (2)

That is what you get for trusting a cheap gauge.

fendamonky

iTrader: (6)

He is correct. The shop I have all my tuning/major work done at has injector cleaners/flow bench and are certified/proficient in this arena. I am running 850/850 injectors @ 50psi and have no problems what-so-ever (hitting 85% IDC at 17.5-18psi with high 10/low 11 AFR). The spray pattern of 850's at higher pressure is *much* better then at a lower psi.

In addition to giving a better spray pattern, increasing the base fuel pressure (pressure shown at 0psi/0vac) will allow your injectors to flow more fuel, essentially becoming larger (850's @ 50psi = flow rate of 1000's @ 38/40psi)

As always, don't ask a question if you don't want to hear the answer ;-)


Just my un-educated guess here... but if raising the fuel pressure increases the injectors flow rate, and provides a better spray pattern then lowering the fuel pressure will decrease injector flow rate, and result in a sloppy spray pattern.

I'm thinking you're selling yourself short here Mark!! I'd turn your pressure back up and re-tune, you'll probably see better results ;-)