92ZR1WANNABE

Do LT1s have a "service port" to check fuel pressure?

If not , where the heck to I check it at?

What is the fuel pressure I should be running on a 92 ? 40-42?


Thanks

toptechx6

Yes, the knurled cap (just left of the vacuum lines in the picture below) is on the underside of the right fuel rail located by lifting straight up on the plastic cover. You are correct concerning the pressure spec.

92ZR1WANNABE

Heh, dunno how I didn't see that there last night.

Thanks!

Pressure / regulator check out ok, next is the road test with the gauge taped to the windshield.


45 psi key on / engine off
40 psi engine on / idle
45 psi at the crack of the throttle or the unplugging of the FPR.


Thanks for the help!

scotth48

I think the FSM is 41-47 psi with vaccum off, 38psi engine and line on. I have put in a new Aeromotive adjustable FPR and have Bosch 3 injectors in (24 lb stock replacement) and when I set for 43 psi I get only 25 mpg. I have been playing with pressures and as I increase pressure I am getting better mileage. Right now pressure is set at 72/64 and mileage is 29-30. I am going to try next to plug vaccum line so the pressure would remain at 72 to see if there is an increase. This is on a '93 LT1 stock. The fuel pump is about topped out as far as pressure as it is a stock replacement dephi model. I took the one out that came with the car as it had higher pressure and thought that was causing problems originaly. I don't understand why the higher pressures would give my better mileage other than it is atomizing better due to finer spray into the manifold. Anyone have similar results with higher fuel pressures???

Wathen1955

Curious - what is needed to measure the pressure (i.e. fittings etc)?

aboatguy

Standard fuel pressure gauge

Usually they come with a couple of different sized fittings.

dogfish246

Cant you just use the fuel pressure port on the incoming line that goes into the fuel rail? It has the black screw on protector cap (like a tire valve cap)... Thats the one I use, didnt even see the one under the fuel rail...

92ZR1WANNABE

I don't believe mine has that port, only the port mentioned above.

Which is why I had to ask were in the heck it was... (didn't see it buried under the vaccum lines under the fuel rail cover)

As far as what fittings and things of the such needed to connect to it? Just your standard $35 fuel pressure gauge should be all thats needed. Its all I used.

If you want to go one better, The new fuel rails on my 355 actually use that port for a small screw in accel fuel pressure gauge so you can always / easily know how much pressure your running.

I will post some pics when I get home from work.

dogfish246

I got this one last week and for the price, I love it! It has a bleed valve too which is good. It has a rubber gauge cover so you dont damage anything and it has a long line so you can rest it on the windshield. I reccomend it!
http://www.amazon.com/KAL-EQUIP-KAL2...5557905&sr=1-5

Zabman

Scotth48....It only seems as if your MPG has increased. With the higher fuel pressure, the injectors flow more fuel for a given pulse width. When the PCM is in "closed loop" the pulse width must therefore be reduced to get 14.7:1. Since the PCM calculates the MPG on the calculated fuel flow, which is derived from the pulse width (which is less), the calculation is incorrect, resulting in the apparent increase in MPG.

Wathen1955

Thanks for the recommendation and link. Nice price.

scotth48

But it is also reflected at the pump when I fill up. And I do top it off, takes a few extra minutes to do so, thought of drilling a larger hole in side of neck for it to vent quicker when filling.

82CorvetteCE

Putting a drill to your gas tank nozzle will send you to the next world with an explosion and your beloved Corvette will be up in smoke- better to just take your time when filling gas into your tank.

Charles.rogers1

my fuelrail doesnt have that valve, atleast a quick look I didnt see it. where else could they be??

Cliff Harris

Changing the fuel pressure affects the flow rate of the injectors. The ECM can compensate when it's in closed loop mode because it uses the O2 sensor to tell what the AFR is. If you don't change the injector flow rate parameter in the tune then your AFR will be AFU in open loop mode.

Injector atomization is greatly exaggerated in importance. If you look closely at the injector firing sequence you will find that the injector fires against the back of a CLOSED intake valve. Been meaning to do an article on that...

Klyde

You have to be careful with how high you push the FPR pressure. As stated the ECM will shorten the injector pulse width to achieve the best fuel mixture depending on your O2 sensor feedback. The pulse valves in the original injectors are a little slow reacting compared to modern injectors and with the shorter pulses you can get variable sprays from each individual injector. Also the ECM can only shorten the width so far and with your pressure too high you will get to much gas per pulse driving your mixture too rich. Some where I read an article about this when I installed an adjustable FPR and it stated 50psi as the maximum pressure for my 96' LT1. I also use the Bosch III injectors and they tolerate the shorter pulses a lot better then the original ones. They also have a better spray pattern then the ones that come with the car. That being said I believe setting up your fuel pressure to the maximum for your car will give you better gas mileage and much quicker throttle response.

I use a Bluetooth OBDII reader and an Android program called "Torque" that lets me read my fuel mixture and I get the best results at 47 psi with the Bosch III injectors. Total cost for the reader and the "Torque" program was less than $35.00. It allows you to monitor almost all engine sensors in real time on your phone or Android tablet. Well worth the investment to see what's going on with your engine. Just plug it into your ECM port and link it through Bluetooth to the Torque program and set up a display for any engine sensor you want. I just setup displays for my O2 sensors and fuel mixtures then adjusted my FPR till I started to drive my mixture rich then backed off a little and tightened the adjustment nut. So far the car works really well and I've gotten 33 miles per gallon on the flat highways here in the Midwest. I've driven to my parents house in Hershey PA from my home here in Indiana on one tank of gas (609 miles - 30.45 mpg average).

DrDyno

I'm with Klyde... I followed his lead with the Bosch III's from FIC and an Aeromotive adjustable fuel pressure regulator. Jon at FIC told me to adjust the FPR to 44psi with the vacuum hose on, which is where I've left it.

Also followed Klyde with Torque for my HTC-One Android phone and a BAFX Bluetooth reader. Phenomenal!
Do yourself a favor and get an OBD extension cable so you don't have to find the OBD socket all the time!

Klyde

DrDyno:

My FSM states that the car may run lean below 42 psi and rich over 47 psi. Watching what happens in real time I would say they are right on with their numbers. My car starts to run rich at 48 psi. The FSM states the pressure should be between 42-47 psi. If 47 psi is ok for the old style injectors then the newer BoschIII's should easily handle it. You should try the extra 3 psi. It makes throttle response just a little quicker and helped my overall gas mileage.

DrDyno

Thanks, Klyde... Will do!

sissond

Just a little curious as I have many more pressing issues to sort before entertaining anything like this...but what injectors are you referring to?
Is it these:
http://fuelinjectorconnection.com/sh...?productid=206