How much fuel pressure drop is "okay" during a WOT pass??

[Missouri T]

Hello again, all.

I put a test gauge (that I can see when I'm driving) on my T and went for a ride.

Here's what I found:
Hose off pressure: 45-46PSI (depending on which gauge)
(1) Base highway speed Cruise pressure was 38-40 PSI.
(2) Mat pedal to WOT, 14-15PSI boost: 60-62PSI
(3) First Shift, boost same, fuel pressure drops to 58 PSI
(4) Next Shift, boost same, fuel pressure drops to 55-56 PSI and does NOT drop.

Of course, by that time I'm going WAY too fast....speedo pegged and then some, so I backed out.

From what I've gathered in four good hard passes, the pressure drops to 55-56 PSI at it's lowest point.
That is "1 lb. per lb. of boost....".
The lowest the O2's got were 750-760 right before I let out.

What do you all think?
I'm thinking everything is A-OK.

I do have another issue but I'll post that in another thread.

Thanks a bunch in advance for taking the time to comment!

 

[RareT]

Based on line off fuel pressure being set at 45, and max boost at 15, "ideally" you should not see anything less than 60 psi throughout the run. It looks like your pressure starts out fine then is dropping as your run continues. What fuel pump do you have and is it hotwired? Fuel filter changed recently? Your "1 lb Fuel pressure for every lb of boost" is based on your at idle, line off reading, NOT your cruise fuel pressure reading.

Ed

 

[6SENSE]

Everything RareT said

Shouldnt have dropped below 60psi. Dont worry about 1st and 2nd gear, 3rd and on (high gear) is where you want to look. This is where you will get your highest boost and mostly likely to get KR. Even if your not getting KR now, something is not right. You could probably be running more boost if things were right. Gotta' match boost with FP pound for pound. I say try swapping the filter out. Could have been some gunk that went through the lines........ Ive been there before, years ago .

 

[Missouri T]

I replaced the fuel filter immediately before the testing....

The fuel filter is BRAND NEW/AC-Delco.

Possibly?
Fuel Pressure Regulator? It is almost 5 years old.
Possibly the sock on the in-tank pump?

FUEL PUMP:
I have an ATR Superpump (single) and it IS hot-wired.
I also have a voltage booster.

Thanks for all the input, folks.
Bill

 

[RareT]

Simple/cheap things to check first......

verify fuel gauge is accurate (although it does correspond to your O2 readings)

fuel filter installed with arrow pointing in direction of flow.

check voltage going to pump, and at connector by gas tank.

plenty of gas in tank

fuel sock may be collasping at WOT

pump may be weak, cavitating....due to age, or how often it has been run low on fuel causing it to overheat. ( I'm not insinuating that you've run it low on fuel, maybe previous owner did. I see people all the time post how they put in 16, 17, 18 gallons of gas in their tank )

Ed

 

[Missouri T]

Will do...

I tried two fuel pressure gauges, they were within 1 lb. of each other.

Fuel filter is right direction.

Plenty of fuel in tank.

Fuel sock collapsing? Your guess is as good as mine on that one.

I spoke with ATR and they said the regulator could be bad, it is almost 7 years old now.

I HOPE the fuel pump is okay.

I'll check the voltage right away.

Thanks again,
Bill

 

[RareT]

Another thing I thought of....the pulsator was re-used when the ATR pump was installed and it may be leaking.

did you replace the fuel pump? How old is the pump?

Yea, the regulator could be bad too, do you have one to swap it out with in order to check?

Ed

 

[Missouri T]

Learned a bit....

I have 13.9 volts at the fuel pump wire at the rear of the car with the car running. Perfect.

The previous owner replaced the whole sending unit with the ATR Superpump assembly almost 7 years ago.
Should've been a new pulsator in that unit??? The pump is not "loud" at all.
By the way, where is the pulsator? On the sender/pump unit?

My interesting-looking regulator:
My adjustable regulator has, what appears to be, an aluminum "cap" on top of a Bosch 237 base?!?!?!
What in the world is that?
Some old no-longer-manufactured design?
I can't find any of that type in any of my books/catalogs.
The cap appears to be held on with three or four allen set screws to the Bosch top.
Could this arrangement be leaking under 15PSI? QUITE possibly.

No, I do not have another regulator to swap out.
DRAT!
And I do not really have the money to go get the new Billet Unit I'd LIKE to have from Poston or Kirban this week.

Thanks again!
Bill

 

[RareT]

Normally the pulsator is not re-used when replacing the pump with a performance pump. It is replaced with a short piece of fuel line (2"-3") The pulsator "connects" the fuel pump to the fuel line inside the tank. It's purpose was to reduce noise and something else that I've forgotten.

The regulator you have is a good popular unit. It's a billet top that was attached to a 237 bottom. That's not to say that it isn't going bad.....

Volts look good

If it was me, and I had a 7 year old pump and regulator in there, I'd replace them both. (old technology + age) That pump is probably just a TTA/Syclone pump. I believe that's what ATR was using "back then". Not to mention that sock may be the old design that was prone to collasping.

However, if you're content with a max of 13-14 lbs. of boost.....leave it as is. (I wouldn't run more than that, myself) Proper fuel delivery is critical on these cars, especially if you plan on turning the boost up.

Ed

 

[RareT]

Another "simple" thing....

How tight does your rubber L vacuum line fit onto the regulator? 2 small zip-ties at each end of it will help ensure it doesn't leak under boost.

(I'm running outa ideas! )

Ed

 

[Missouri T]

I hear you loud and clear....

I would feel a lot more comfortable with a Walbro 340 in there with a new design sock.
Finances will not allow that.
The Regulator?
I may look into that, seeing as all I have to do is replace the actual Bosch unit and not go to a full billet.
I think I can con the wife out of $40 or so.

Which is "better"?
The Bosch 233 or 237?
The 237 is GN and the 233 is TTA, right?
The TTA is the "good for 60 psi" I've read about.......

My vacuum hose is VERY tight.
I only have zip ties on one end, since I've been doing all the testing and tuning.

Thanks for all the input, folks.

 

[RareT]

233 = GN ..... 237 = TTA The 233 "roughly" would give you 33 psi line on(40 line off).....the 237 would roughly give you 37 line on(44 line off)


Now you're going somewhere I haven't been before....taking one of the stock ones apart and putting the billet top on it...you're on your own now!

Ed

 

[m233roller]

Fuel Pressure?

I had the same exact thing going on and it ended up being Reds latest XP pump with less than 1000 miles on it.

 

[Missouri T]

Man, I hope not....

Whatever is bad, I'll sure replace it.
I want to start ENJOYING this car, instead of perpetually working on it.

I keep telling my wife that it HAS to run consistently right SOMETIME.
Why? Because I've replaced everything imaginable.....except the fuel pump and regulator.
Guess I'm cursed?

The car runs like a raped ape now, I just want it to be A-100% dead-on, so I can finally go out and hunt some 5.0's and LS1's.