While checking for a leaky fuel injector, I recently performed the Fuel Pressure Test on page F-97 in the FSM. With a jumper between F/P and GND terminals, and ignition to ON (car not running), fuel pressure was somewhere around 41-42 psi. The FSM states the spec for this test is 36-38, anything higher indicates the pressure regulator is bad.

Here are my questions: My system pressure is only slightly higher than the spec (about 3-4 psi). Is this enough pressure to warrant replacing my pressure regulator? Or should it really not make much of a difference.

My car is sometimes hard to start, and it has been known to flood while trying. I originally thought it may be a leaky fuel injector, but could 3-4 psi higher fuel pressure while cranking be a cause for this? If so, can I tune this out by decreasing the Cranking Inj Time in the PFC?


Here are my relevant mods:
Power FC
Supra fuel pump
New fuel filter
Rest of fuel system is stock


Thanks for the help,
Rob

 

The extra preasure will not cause your fuel injectors to leak. Send your injectors off to RE engineering and have them test them, they will tell you if they are leaking or not, and clean them if they arn't. If they are leaking you will need to replace them. This was one of my problems when I was replacing things in that area and they helped me find out why my car was flooding.

 

no, I know that extra pressure will not cause them to leak. My question really isn't about leaking. After performing these fuel tests, I don't think my injectors are leaking (the system passed the Fuel Pressure Hold test with flying colors, which indicates little to no fuel is leaking out of the system). Thanks for the thought though PorscheGuy.

But since injectors are run via duty cycle, won't excess fuel pressure lead to more fuel injected into the motor? Correct me if I'm wrong.

Since, the system passes the pressure hold test, I don't think the injectors are leaking. So, I guess I was wondering if the extra pressure could cause the motor to flood while trying to crank it over? Should the regulator be replaced even though my system is only 4 psi over the spec?

 

Unless you changed your fuel pressure regulator, it's still a 1:1 for the pressure no matter how big the pump is...

 

From personal experience, installing walboro pump increased my fuel pressure which in turn made me run rich(according to my wideband O2) so saxyman990 is correct. An increase in fuel pressure WILL increase fuel being dumped into the motor. The ratio of fuel pressure to boost does not change, but the overall amount of fuel dumped into the engine does change.

I know lots of guys running 45 psi static fuel pressure, but I ran out of injector duty(running 99%~) so I turned my fuel pressure from 45 psi to 52 psi and then went into the Power FC and had to retune to get my a/f's back into the 11.2~ with better injector duty numbers(80%~)

 

That shouldn't happen. If that were the case, you wouldn't need to use larger injectors, a larger fuel pump would do the same trick as long as you could measure the output.

Are you sure something else wasn't done at the same you changed the pump?

 

Fuel pressure regulators have long been referred to as the "poor man's fuel computer" because raising fuel pressure will indeed cause more fuel to be injected at a given injector duty cycle.

Even if the stock fuel pressure regulator was not touched, the volume of fuel being delivered by a new pump can overwhelm the capacity of the regulator or return line to handle the excess fuel and increased fuel pressure would be the result.

 

Yes, I'll agree that the stock FPR could be overrun. However, that's not "by design", but "by malfunction" as it's no longer able to do it's job.

 

It's not by design, but its a common issue with highflow pumps on otherwise stock fuel systems. The honda guys get lumpy idles with big pumps and stock regulators, its just not big enough to bypass enough fuel at idle to keep the fuel pressure at factory spec. But I seriously doubt a few psi of increase alone would cause the problem described. Hard starting and flooding can be caused by tons of things, and if you try a few times to start a rotary they tend to flood out just because of the volume of fuel we use.

 

I'm positive nothing else was done, as I do all of the work on my car. The regulator/injectors/lines/etc are all stock. Only fuel mods are pump and PFC.

 

Jim, this was kind of the point that I was trying to get at. But, is the excess pressure that I am seeing a result of a bigger pump, or is it a sign that my regulator is going the way of the dodo bird?

Would this small amount of extra pressure actually warrant changing regulators? I was kinda thinking along the lines of BMike: It doesn't seem like only a few psi would make a big difference. Maybe I'll try tunning out some cranking fuel in the PFC and see if that makes a difference. Thoughts on this?

 

I've never heard of anybody having problems with the Supra pump running rich at idle, but I know that the walboro pump does. I've tried a GT-R R33 fuel pump and even that made my car rich at idle, but when I installed the Supra pump, I didn't have problems with flooding.

What does your fuel pressure look like right now?

 

my car has the same problem but I am in the process of checking the injectors if they are leaking. I am too wondering if the power fc can tune the FD to where it wouldn't flood once the car is off.

I got my plugs changed and drove it for about 2 days and it got flooded again. The car is running really really richer than other FD's that is what a rx7 mechanic told me. That is why the FD gets flooded. Anybody have a clue?

Will the pfc fix this problem once the injectors are checked and cleaned?

Mike

 

Might even be excessive ignition advance at low rpm, it'll cause the car to run pretty bad and would lead to flooding if your cranking time is excessive. I'm not sure how the PFC handles cranking timing but if its adjustable it may be too far advanced. It sounds like short of a bad part you've just got something bad in your cranking mixture or ignition timing causing the car to be hard to start which is leading to flood if you crank too much without a start.

 

saxyman990 and Kitsune, are your idle goes up high when you turn you light on or off? my idles go up to 1400 rpm if i turn on the light, if it's off it goes back down to 1000 rpm.
i have pfc and supra tt pump and most my parts on fd is stock. i was thinking maybe bad injectors, too.

 

Nope, I have no problems with my idle. I have set my PFC to idle at 950rpm (1050 with EL and 1100 with AC). The actual idle is pretty much dead-on with that.

Check the settings in your PFC, and also check the idle speed control (ISC) solenoid.

 

Dear Uncle Bobbert,

YO

Anyways, I don't think that the increased fuel pressure and efficiency of the supra pump is your problem. Yes, increased fuel pressure with the same injectors will give you more fuel in the chamber, but if your settings are even relatively close, the car will idle and start up without flooding. In fact, it seems to get screwy if it's too lean at idle rather than too rich. I have run a map for 550cc primaries before with 850cc put in their place and it started up and ran. Granted this is with a hotter spark than you're probably using and it wasn't too terribly pretty, but it didn't flood either. I think that your problem is definitely a setting in the PFC somewhere though. IIRC you are running a "tuned" map - you might want to question whoever tuned the car and see if they changed the cranking/start up settings from what apexi gives you to start with (I don't remember what settings it lets you mess with). Taking a first glance at this, 4psi of increased pressure shouldn't be creating these flooding problems you're having on its own, something else is wrong. If you get rid of the FPR, I'd go with something aftermarket.