TPI BOY

car turns over, but wont start, smells rich. looked at my fuel pressure
gauge it reads 80 psi. turned car off and it stayed at 80 psi, pressure
didn't drop with key off. will not go lower then 80 psi. this is a tpi

TPI BOY

Any thoughts

NavAir

Sounds like a bad fuel pressure regulator to me.

ctmccloskey

NavAir is right on that one.
As well I would check your FPR. It is easy and fast to do as you simply unhook the rubber vacuum line connecting to the FPR and smell for gasoline. The smell of gasoline indicates a bad diaphragm in the FPR. The ethanol in gas literally eats holes in diaphragm. Fortunately their are not too hard to replace and the parts is about $100 now days. The new ones are tolerant of ethanol so they should last longer.

I have never seen pressure that high in an L98.

TPI BOY

jf the diaphragm had a hole, would not the fuel pressure go down. mine is holdin at 80 and it should be at 42psi

NavAir

The FPR diaphragm could be stuck, that would result in a higher pressure...

TPI BOY

anyone know where to get a good adjustable one

aklim

I'd go with the stock one unless there is some good reason to up the fuel pressure.

KyleF

I have one from South Bay. Nice unit, required some clearance sanding on my plenum... no big deal. 2min with a dremel.

KyleF

Insurance that you can hit 43.5 on the dot. That is why I have done it before.

This time around it is because I have a Supercharger, supporting mods, and I am going to start doing a custom tune soon so I may choose to run a higher pressure. With that said, if you put an adjustable one in, there is always the option to adjust your FP if needed later. If not, it can be set to factory spec and left alone as well. Prevents possibly needing to do the job twice later.

If I have ever replaced one, I have always went adjustable. The cost difference didn't matter as much as the time to take the plenum out and put it back on again.

aklim

Definitely will use an adjustable on forced induction. Is there much more to be gained with higher pressure? I just let the tuner set the pulse width based on the sensor readings. I'm sure he could set it for higher pressure but is the gain significant? Unless you have injectors that are smaller than should be?

JoBy

If you double the fuel pressure you only get 41% more fuel.
To double the fuel you need to increase base fuel pressure from 45 psi to 180 psi. Then add pressre from boost on that.

So if you have 15 psi boost you should need about double the fuel. To do that with pressure alone you need to go from 45 psi to 195 psi. ( what the pump see )

When increasing fuel pressure you also reduce flow from the pump.

When more fuel is needed larger injectors is the way to go.

aklim

So why do people crank up the pressure? Supposedly they get better atomizer effects but not sure how much improvement they can make from the combustion

KyleF

Just like timing, different combos will like different settings TBH.
Just like playing with the timing, one or two PSI isn't going to make any significant difference.

It isn't supposedly, injector spray pattern can be observed.

To know for sure, you would really have to get on a dyno and adjust it and see the results on your car and find what works best. In the end, Fuel Pressure alone can't be your only means to increase fuel flow capabilities of your fuel system.

From my research, it's best to think in terms of MAP. If your injectors idle at 38psi... or in Absolute pressure that is 262Kpa into a manifold at 40Kpa. There is a 220kpa pressure differential, but when you crack the throttle to WOT and hit a near 90Kpa or so in the manifold you need the Fuel pressure to step up to match that differential. Even more so if you are boosted. Essentially trying to maintain a linear pressure differential. Hence why the regulator references manifold pressure. Im more simpler terms, if you have 45PSI in your fuel rail, and when the injector opens there is 10PSI in the intake manifold, there is actually a net 35PSI pushing on the fuel. Doesn't matter is you are FI or NA, there absolute pressure in the manifold changes and different combos will run different manifold pressures.

In my particular case, I am boosted, non factory pump, and non factory injectors on my L98. While there is a possibility factory fuel pressure may be the right setting, but there is probably a real good chance it is not.

This link should help.

Also... and Ford related, but its the best reference I could find quickly - Kenne Bell tech tips for Mustang Blowers. Good section on fuel pressure.

However, even if the pressure differential changes, based on feedback the ECM can make pulse width adjustments but the differential can start affecting the spray pattern.

KyleF

Do you have a reference for this. The formula I have doesn't exactly solve this way.

vader86

If its a lot of fuel, then injectors. If you need to tweak at the strip or track or whatever without doing a retune of the chip, the AFPR. I have both, mine is a TPiS.

KyleF

This is a very simple way of stating what I detailed out. It doesn't replace proper tuning or proper sized injectors. It allows you to find the right spot for your combo and tune to run.

At less that WOT, in closed loop, the additional fuel flow will be adjusted for by the ECM in the BLM/INTs to still hit the target A/F. The better automization here would most likely show up in MPGs rather than power

At WOT you will see it richen the mixture more, but this shouldn't be your means to tune you fueling only.

aklim

I agree that on a flow bench you can see the atomization difference. What I am curious about is what is the effect of this atomization change? The peddlers of the AFPR tell us all kinds of things. Better MPG, more HP, etc, etc. I kinda suspect that unless you really go very radical, the difference might be useful if you are running in a competition for a big payout? Thoughts?

I would definitely agree with that. I would rather not increase fuel flow by cranking up pressure. I'd prefer to work on the pump volume and injector size and of course, pulse width but I suspect that the improvements are used to sell AFPR units and more placebo than actual gains.

That is a whole different animal than what most people will run though. Kinda why I wondered if there is any real gains. I would be looking to do it if I could see something concrete that would pay for itself in either mileage or power.

I'd probably say that at that point, maybe the entire program should be re-written or at least heavily revised?

KyleF

You would see it in MPG and Reduced emissions, but not much. In general port fuel injection (even batch fire) does a pretty good job of getting the air and fuel to mix well.

I am a big supporter of installing them for previously mentioned reasons, but I don't think they do much more than bumping your base timing a degree ahead or adjusting tire pressure. I don't think it can correct a bad tune, lack of injector size, or lack of pump. I do believe every combination is going to have a base fuel pressure it will run best at and show a few hp increase or decrease when adjusted. However, we are probably talking 1-2%. Otherwise I would be looking at getting the tune corrected if it had more of an effect.

I disagree, we are talking about a $100 part. A $100 part that would have very little use on a completely factory engine. What do you really expect to get out of a $100 bolt on? I suspect, as stated above, about 1-2% improvement when you find the sweet spot.

I really do link this to a similar situation as asking what base timing does my engine run best with? +/- a few degrees isn't going to make a huge improvement but can definitely show up. If major changes in timing need to me made, it needs to be made in the tune.

Same for fueling. Based off manifold pressure (s) your combo runs at, the injectors will probably like to be in a certain sweet spot and can show some improvements, but anything major needs to be addressed in the tune or components. The 22/24lb stock GM units, pump, and tuning are not going to support a Heads/Cam/Blower car making 500hp no matter what you set your pressure at.

JoBy

One example:
https://instrumentationtools.com/flo...-root-delta-p/

End statement:
The injector, when open, is a flow restriction with a delta P. Flow is proportional to Square root of delta P.

When doubling fuel pressure, you double delta P. Flow increase = sqrt(2) = 1.41 = 41% more.