TBI Throttle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.

Hard timing dialing in fuel pressure

Old 03-03-2015, 05:38 PM
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Hard timing dialing in fuel pressure

Hey guys. So recently i did some mods to my stock 305.

So far i have an MSD blaster coil, mallory cap and and rotor, summit wires, and ac delco plugs set at .45 gap.

Throttle body spacer, injector spacer, and a jet performance adjustable fuel pressure regulator. Yes i know you can modify the stock one.

I have a custom chip and running 93 octane. Its a john wayne chip if anyone is familar.

I was told i could get a significant difference with a couple psi to the fuel pressure. I tightened the fpr a couple turns over what appeared to be stock using the old fpr as a guide. It feels like it has a noticeable amount of power at lower speeds, but on the highway when i floor it it just doesnt pick up like it did before the mods.

Before it had a good balance of power (the little it had). Is it the tb spacer or injector spacer? Or does the psi just need to be dialed in better, or is my fuel pump not sufficient?

It does run great! Its smooth all around and idles great, its just the feeling of being pushed back in my seat thats spotty and i cant quite pin point it. Any tips or ideas?
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Old 03-04-2015, 11:57 AM
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Re: Hard timing dialing in fuel pressure

What is your fuel pressure at idle, and at WFO/max RPM?
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Old 03-05-2015, 06:03 AM
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Re: Hard timing dialing in fuel pressure

It's the same all the time. Don't have a vacuum controlled fpr
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Old 03-05-2015, 09:45 AM
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Car: 1990 Formula Firebird
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Axle/Gears: 10 bolt, 3.42 & Torsen Posi
Re: Hard timing dialing in fuel pressure

Just because you don't have a vacuum FPR doesn't mean its holding proper fuel pressure at high RPM/high engine loads.

If you are reaching the fuel pumps limit you will see the pressure tapper off as you reach peak RPMs at WOT.

How do you like the John Wayne Chip? I've seen him post on the facebook groups in the northeast, but his claims of horsepower/torque/fuel efficiency improvements seem pretty outrageous on stock motors. And he claims his are may better than some of the big name brands, it all seems too good to be true, and he can be a real A-Hole if you even begin to question his claims.

Another possibility is you are giving her too much fuel and it is loading up on the highway. Get a fuel pressure gauge to dial it in instead of guessing on how much you are increasing the pressure.

Get a gauge
get a gauge
get a gauge
get a gauge!
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Old 03-05-2015, 10:33 AM
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Re: Hard timing dialing in fuel pressure

John Wayne's chip definitely made a noticeable difference. It allows me to run on 93 octane very smoothly as we'll with no pinging. I can't say how the other chips are but for the money I spent I'm very happy.

I'll definitely check out the gauge .

After researching though I realize what's going on, because it's static fuel pressure, even though it may be running rich at idle which for me is 600rpms doesn't mean it's not rich cruising at 1500rpms or at wot.

I realize what happened. Less pressure gave me optimal air fuel ratio at lower rpms but became lean at higher rpms explaining the loss of power at wot.

Running rich made my car feel sluggish at low rpms because it was just that, rich. But at wot I felt more power as it leaned out letting more air in.

So I just need to find the balance.
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Old 03-05-2015, 12:28 PM
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Re: Hard timing dialing in fuel pressure

You shouldn't have to find a balance with an EFI car. You should be able to dial in the air/fuel ratio to be just about perfect across the board. Sounds like you need a custom tune done by a reputable tuning shop, who will put the car on a dyno and get it dialed in perfectly.

If you are correct in your assumption, changing the fuel pressure to optimize low load vs high load is just a band aid to cover up a shitty tune.

Also, a tune isn't necessarily good because you can run 93 without pinging. 93 has a higher resistance to pre-ignition than lower octane fuels. I run 87 in my car all the time, but if I wanted to I could run 93 with no pinging, but with a stock tune setup for 87, running 93 would be like burning money.

None of what your saying is boosting my confidence for these John Wayne chips

Last edited by Formula 305; 03-05-2015 at 12:31 PM.
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Old 03-05-2015, 12:49 PM
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Re: Hard timing dialing in fuel pressure

Seems like you have something against john Wayne chips...

My car has more power no doubt, but I don't see what me fiddling with the fuel pressure has to do with it...
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Old 03-05-2015, 02:23 PM
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Re: Hard timing dialing in fuel pressure

Originally Posted by Video View Post
Seems like you have something against john Wayne chips...

My car has more power no doubt, but I don't see what me fiddling with the fuel pressure has to do with it...
I have no experience with John Wayne chips, so I have no opinion one way or the other, I'm just skeptical.

And just because your car has more power doesn't mean its a good tune. The point is you shouldn't have to fiddle with the fuel pressure to get it to perform better in the high or low range with the minimal modifications you have. Some guys have to run Vacuum fuel pressure regulators, but they have heavily modified cars.

Your car should run great both in the high & low range with a constant fuel pressure by changing the injector duty cycle. The whole tuning process and how the ECU calculates/delivers fuel mixture, if you want to know more about it ready some of the threads in the DIY PROM section.

And I don't doubt it has more power. By making a high octane only tune allows the tuner to increase the spark advance, giving you more power, but what I'm saying is that:
1.) either you goofed up the tune by monkeying with the fuel pressure
2.) the fuel tables in the tune need to be tweaked a tiny bit.

Any mail order tune is going to be imperfect because every car is unique, without doing in-car tuning your never going to get it perfect.
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Old 03-05-2015, 02:53 PM
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Re: Hard timing dialing in fuel pressure

Originally Posted by Formula 305 View Post
If you are correct in your assumption, changing the fuel pressure to optimize low load vs high load is just a band aid to cover up a shitty tune.
Thank you. Have already had this discussion on other threads of this forum. Fuel injectors TOO LARGE, using VRFPR as last-ditch effort to "fix" a problem they shouldn't have to begin with. TBI injectors don't fire into a vacuum like port injectors, which is why GM didn't bother to vacuum-reference them.

In this particular case, I suspect a failing fuel pump--it can supply enough fuel for low-to-medium load, but maybe the pump is "going away" and can't supply enough fuel to maintain pressure at high load/high RPM.

Until he tests and reports the fuel pressure at WFO-max RPM, we won't know for sure--so for now it's all guesses and suspicions.
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Old 03-05-2015, 03:00 PM
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Re: Hard timing dialing in fuel pressure

Originally Posted by Schurkey View Post
Thank you. Have already had this discussion on other threads of this forum. Fuel injectors TOO LARGE, using VRFPR as last-ditch effort to "fix" a problem they shouldn't have to begin with. TBI injectors don't fire into a vacuum like port injectors, which is why GM didn't bother to vacuum-reference them.

In this particular case, I suspect a failing fuel pump--it can supply enough fuel for low-to-medium load, but maybe the pump is "going away" and can't supply enough fuel to maintain pressure at high load/high RPM.

Until he tests and reports the fuel pressure at WFO-max RPM, we won't know for sure--so for now it's all guesses and suspicions.
I have seen this debate on other threads, and I don't have any experience with it. On highly moddified TBI units it may be necessary to run a VRFPR, GM never put one on a TBI motor, but then again, GM never tried to get 400HP out of a smallblock TBI motor either.

I didn't mean that to be a blanket statement, as I can't surely say that on highly modified TBI systems the VRFPR isn't required, but surely in this case his car is not highly modified and adjusting the fuel pressure regulator shouldn't be necessary.

Moving forward I would take 2 steps
1.) Get the gauge hooked up and monitor fuel pressure at varying operating conditions, confirm the pump is supplying adequate fuel for what you are trying to do.
2.) Contact John Wayne chips, see what fuel pressure they recommend, set it there and leave it.
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Old 03-05-2015, 03:17 PM
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Re: Hard timing dialing in fuel pressure

Originally Posted by Formula 305 View Post
I have seen this debate on other threads, and I don't have any experience with it. On highly moddified TBI units it may be necessary to run a VRFPR, GM never put one on a TBI motor, but then again, GM never tried to get 400HP out of a smallblock TBI motor either.

I didn't mean that to be a blanket statement, as I can't surely say that on highly modified TBI systems the VRFPR isn't required, but surely in this case his car is not highly modified and adjusting the fuel pressure regulator shouldn't be necessary.

Moving forward I would take 2 steps
1.) Get the gauge hooked up and monitor fuel pressure at varying operating conditions, confirm the pump is supplying adequate fuel for what you are trying to do.
2.) Contact John Wayne chips, see what fuel pressure they recommend, set it there and leave it.
^^^ Wisdom.

I'd only add:
3.) Verify that it all works and drives properly when you're done setting fuel pressure0--your short- and long-term fuel trim numbers should be reasonable, and your O2 sensor should remain happy under all conditions.
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Old 03-05-2015, 08:40 PM
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Re: Hard timing dialing in fuel pressure

Should have went with EBL!
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Old 03-13-2015, 10:50 AM
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Re: Hard timing dialing in fuel pressure

I have basically the same mods except a chip from tbichips.com and a fp gauge. I set mine to 13 and it to seemed like it was choking at higher rpms. My fix was that i had a drop base air cleaner which was still restricting air flow around the injectors. So i made my own tbi power charger ( search for it on jegs and you'll see) and cut the base of my air cleaner wider to sit on it, thus no more restriction. No more high rpm choking.
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Old 03-13-2015, 10:54 AM
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Re: Hard timing dialing in fuel pressure


Restriction
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Old 03-13-2015, 10:56 AM
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Re: Hard timing dialing in fuel pressure


No restriction
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