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So, I've been thinking about fuel pressure, tuning my car for higher revs, and such. I want more fuel pressure, but don't want to spend the money on an adjustable FPR. So, in my special, old school hot rod way, I'm going to modify my FPR. I don't know if this will work for cars with OEM ECUs, but, if it does, you could get better gas mileage. Someone more knowledgeable will have to say whether or not the stock ECU can handle the extra pressure.

Here's what I'm going to do:
I'll take note of the current injector pulse width at various RPM with MegaSquirt. Then, I'll push the top of the FPR in 1mm, and compare values. Pushing in the top of the FPR puts a preload on the spring, allowing less fuel to return to the tank, thereby increasing the pressure to the injectors. Then, I'll repeat this 2 more times.
Should I keep doing it until the car runs differently? I don't know at what point the extra pressure would wear on the injectors.
I could also buy a tool to measure the fuel psi coming out of it, and keep it under a certain psi, if anyone knows what would be a good limit.
If more fuel pressure is beneficial to cars with stock ECUs, I could find the sweet spot, and modify them for others, using a micrometer.

More fuel pressure wont do much for a stock ecu when it comes to milage... During closed loop/partial throttle the ecu is going to compensate and do what it can to stick to its programming.. It will help open loop fueling though if you are having problems running lean... Usually on a stock ECU with minor bolt ons that wont be the case... Most stock ECU's are actually programmed overly rich during open loop mode.. On an N/A motor you usually pick up more power by leaning it out...

You wont put much extra wear on the injectors, but stock fuel pumps can only out put so much fuel.. There will be a limit... With a fuel pressure gauge you can find the limit of your pump but running the motor and pinching off the return line... Also the fuel injectors will only be able to handle a certain amount of extra pressure.. at some point they will end up sticking open..

There is nothing wrong with doing this modification... Its a poor mans adjustable fpr... Every regulator will react a little differently though... You'll have to try and figure out a way to test the regulators before you ship them out if you plan to try and sell any..

This made me smile, because I was reading about exactly this the other day!

Thanks, crazycanadian. It's nice to have a modern mechanic look over my posts
What do you recommend, as far as how to find the limit?

I believe the stock pressure is around 35-40 psi, so I wouldnt go much further than 10 psi above that. Since you are using MS, you could narrow down the pulse width to the point that you still end up with the same or less fuel because the same pulse width at increased pressure will allow a larger amount of fuel into the cylinders and should lead to a better atomization of the fuel and a better burn. The better air fuel mix should make more power, but as far as finding better mileage with a stock ecu, you might be hard pressed to do so.

Thanks, redline. That is exactly what I am going for, and I am hoping to find a way to have MS do sequential injection. Hopefully, I can figure out if it would help on a stock ECU.

Redline322 wrote:I believe the stock pressure is around 35-40 psi

With FPR taking vacuum 30-38 PSI, fpr disconnected from vacuum 37-46 PSI (thanks Ryan)

fowljesse wrote:Thanks, redline. That is exactly what I am going for, and I am hoping to find a way to have MS do sequential injection.

There are a few options. There's code for v2 to do semi-sequential (sequential on 4 only, semi on more than) and Ms3 seems to support sequential.

I'm not sure what kind of shape your injectors are in, but if you have access to a good fuel injection cleaning kit (one that uses a spray can hooked directly to the rail) you can make sure you are getting the fuel at the pressure you want out of the injectors in the proper spray pattern and you dont end up with a lean cylinder and it'll take one variable and risk out of your experiment.

Thanks, fellows. I may upgrade to MS 3.
Dan, thanks for the specs.
I believe that my injectors are clean, because I ran Acetone for a few years, and, to pass emissions recently, I ran Acetone, mineral spirits, and 90% Isopropyl.
My car has pretty good low end grunt that I want to exploit, and I think with high fuel pressure, sequential firing, and a strong spark, I can get more torque out of it. I'm also planning to make a new IM, when I put in my Colt cams, so this will all add up.
What is the highest fuel pressure that you guys have heard of someone running on a KL?

You know a MSD adjustable FPR is only 50 bucks. I ran one for more than 3 years on the RS, worked great! But then it wouldn't be as fun

I didn't know. Thanks. The ones I looked into that looked reputable were over $100.

Ok after looking seem the price on these has doubled... WTH I payed less than 60 dollars total for mine several years ago. I looked online some odd months back and did not notice that they are now 90-100.... for the same one. Jesse if this does not work out for you let me know and perhaps I can pull this off of my RS for you

Well, thanks, Josh! That would be great. Perhaps I have something to trade. I don't remember all of what I have, though I haven't gotten around to squishing the OEM one, yet..

So what' the plan, put the fpr in a vise with a socket on one side and squeeze? Only trouble is the opposite side may give as well so how do you plan to ensure only one side collapses?