fuel pressure

[Joeld]

used test guage from autozone and taped to windshield
idle with vacuum was at 25-26
built up about a pound per pound if boost to approximately 35 i did not go to wot
from what i read these numbers appear low
i had no knock through progresive throtle
thoughts?
stock other than vacuum brakes
joel

 

[Wld87GN]

Seems low. Mine is 43 at idle, I have a gauge under the hood and on A pillar. I was under the impression that there is a formula that its supposed to raise so much for every pound of boost but I dont recall exactly what that is.

I would be concerned that you are not getting enough fuel, if you are starting that low, you are not going to jump to the desired amount quickly enough. Do you have a stock regulator? With stock injectors and stock pump, this still seems low, but I am still in the READ READ READ phase myself.

 

[Bescurred]

That is really low, should be between 42-44 when you pull the vac line off of the regulator.

Do you have a adjustable regulator?

 

[Joeld]

Stock regulator, stock injectors.
I have hotwire kit and new fuel pump and adjustable fuel regulator all in the box ready to install.
I'm surprised that my numbers were as low as they are, while not getting knock under acceleration.
if I hammer the throtle then I get some knock (jump out of throtle quickly when I see it), but if I accelerate smoothly to say 3/4 throtle or so, no knock, I've not had enough room to go all the way to WOT gradually.
I will first install the hotwire kit and see what my numbers do, i did not test without vacuum hose to regulator, I will do that at idle also and see what I get.
Joel

 

[Ttype6]

Stock regulator, stock injectors.
I have hotwire kit and new fuel pump and adjustable fuel regulator all in the box ready to install.
I'm surprised that my numbers were as low as they are, while not getting knock under acceleration.
if I hammer the throtle then I get some knock (jump out of throtle quickly when I see it), but if I accelerate smoothly to say 3/4 throtle or so, no knock, I've not had enough room to go all the way to WOT gradually.
I will first install the hotwire kit and see what my numbers do, i did not test without vacuum hose to regulator, I will do that at idle also and see what I get.
Joel

Use some locking pliers to pinch the rubber fuel return line,down by the steering box,and see what you get for pressure.

 

[Chuck Leeper]

AIRC, the stock reg never did run at 42....
Some triks for early-on fuel control consisted of:
Mashing the reg body to compress the spring.
Tapping the vac nipple and running a hollow allen screw down onto the diaphram.
Cutting the reg apart and adding an epoxied on top w/ adjuster.
Hot rodders are a cleaver group!

 

[DavzGN]

Yes the stock regulator should be at 37lbs with the vac line off. And drop 8 or 9 lbs with the vac line on.

David

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[RmvBfrFlght]

I just may be that the gauge is off. I've been down that road before. Even more so since it is a lender from an auto supply store. Doesn't take much of a jar to throw them off (BTDT too).

RemoveBeforeFlight

 

[Joeld]

Hadn't thought about the gauge being off, always good to get other's thoughts. I'll try again this time with the vacuum hose off and see what I get. I can see why so many run the hood mounted gauges and the like. Does seem to be very important info for these cars.

 

[GullsGN]

I would not worry about it. If there is something wrong the fix is likely the parts that you already have and plan to put in. Just install them and then check your numbers. Don't over think it.

 

[Joeld]

you are right gully wasted time really if i plan to replace the typical trouble points

just looking for the best stock tine i can get

joel

 

[CGASTON]

Seems low. Mine is 43 at idle, I have a gauge under the hood and on A pillar. I was under the impression that there is a formula that its supposed to raise so much for every pound of boost but I dont recall exactly what that is.

I would be concerned that you are not getting enough fuel, if you are starting that low, you are not going to jump to the desired amount quickly enough. Do you have a stock regulator? With stock injectors and stock pump, this still seems low, but I am still in the READ READ READ phase myself.

1:1 ratio

Sent from my iPhone using Turbo Buick

 

[Ttype6]

Hadn't thought about the gauge being off, always good to get other's thoughts. I'll try again this time with the vacuum hose off and see what I get. I can see why so many run the hood mounted gauges and the like. Does seem to be very important info for these cars.

Remember,if you think your gauge is off,the O2 numbers on the Scanmaster will give you valuable data.

 

[Joeld]

I tested again tonight I ran almost wide open throttle and skan master shows me about 847 and i got about 3.5 knock on a run where i accelerated agressively could it be the temaining fraction of old gas?

without vacuum i had 35 psi about 25 psi with
i get a pound increase per pound of boost

joel

 

[GullsGN]

I tested again tonight I ran almost wide open throttle and skan master shows me about 847 and i got about 3.5 knock on a run where i accelerated agressively could it be the temaining fraction of old gas?

without vacuum i had 35 psi about 25 psi with
i get a pound increase per pound of boost

joel

How much boost?

 

[HighMileage]

Fwiw,its a good idea to have 2 fuel pressure gauges. That way you can see if they both agree. Then,chances are your readings are correct.

I've had hand held FP gauges be inaccurate before. One of which was a Craftsman.

Now I've got 3. The small one mounted on a fenderwell,an Autometer 2 5/8 one in the radio-hole,plus a handheld one that gets used now and then. I make sure they all agree.

 

[Joeld]

Thanks for the responses.
About 10-11 pounds of boost, I just got VDO yesterday, will install this weekend. For now I had to go by digital.
Joel

 

[1KWIKSIX]

I tested again tonight I ran almost wide open throttle and skan master shows me about 847 and i got about 3.5 knock on a run where i accelerated agressively could it be the temaining fraction of old gas?

without vacuum i had 35 psi about 25 psi with
i get a pound increase per pound of boost

joel

I believe that chip is designed for around 42 pounds of fuel pressure, with vacuum line off should be around 37 pounds. If you're not getting this reading & you have the stock fuel pressure regulator, get rid of it & grab an adjustable FPR so you can adjust it Both Accufab & Kirbans offer adjustable fuel pressure regulators that will work well. Until you have your fuel pressure stabilized & under control, it would be wise to stay outta boost....otherwise you will be at risk of doing some damage to your engine due to it running lean. When this is corrected, be sure that your boost is rising 1:1 with your fuel pressure readings. Do you have an upgraded fuel pump & hot wire kit installed yet? If your car does not have this installed, this should be your very first purchase & installation.

 

[Joeld]

I have stock chip, stock injectors, stock fuel regulator. I was hoping to get her tuned prior to replacing fuel pump, installing manual regulator and hotwire kit. Maybe not possible? Or maybe my injectors are dirty?

Joel

 

[turbo nasty]

If you dont have a hotwire and known good fuel pump tuning is the LAST thing you should be doing.