fuel pressure?

[86grdnatl]

Okay so i hooked up a fuel pressure gauge and with the car running at idle with the vacuum line on it reads 31 lbs. With the vacuum line off, it reads 39 lbs. Are these numbers within the perameters for a completely stock 86 grand national?

 

[SHADOWII]

Negative, 43#s line off. Do you have an adjustable regulator? if not, it would behoove you to purchase one. A rebuildable one is a good investment along w/a hot wire kit. It will aid in tuning and h/g failure. Note: I believe my f/p was 33/39 before I swapped to the above.

 

[mikestertwo]

Okay so i hooked up a fuel pressure gauge and with the car running at idle with the vacuum line on it reads 31 lbs. With the vacuum line off, it reads 39 lbs. Are these numbers within the perameters for a completely stock 86 grand national?

For a completely stock GN with the 233 regulator those numbers sound right.

 

[Ttype6]

Okay so i hooked up a fuel pressure gauge and with the car running at idle with the vacuum line on it reads 31 lbs. With the vacuum line off, it reads 39 lbs. Are these numbers within the perameters for a completely stock 86 grand national?

Yes.

 

[86grdnatl]

Thanks for all of the replies everyone. The reason i ask about the fuel pressure is that when accelerating the car stumbles and bucks and falls flat on its face. After replacing the coil pack, ignition module, spark plugs, and spark plug wires, im pretty sure its a fuel delivery problem. I did replace the fuel filter and the fuel pump not too long ago, but i am pretty sure the fuel pump sock may be clogged because of the amount of grunge in the tank when i replaced it. If my fuel pressure is off, would that explain the bucking when accelerating? Ive been trying to research as much as possible about fuel pressure, but i could not find anywhere that gave me a definite answer in regards to lbs.

 

[84BuickGNYorkPA]

For all your stock questions on the fuel pump pressure read Steve's web site here is a link http://www.vortexbuicks-etc.com/basics.htm#Fuel_Pressure_Regulator

I would be giving some thought on upgrades to the fuel system and chip. Like say hot wire kit with Walbro pump, set of fresh fuel injectors, say 60lb'ers with a turbo tweak chip to match the new injectors, and a billet regulator to adjust the fuel pressure.

Chuck

 

[86grdnatl]

Thanks a lot for the link. Do you think I have a fuel delivery problem in your opinion? I see that my car is meeting the #'s described in the article, but I'm not certain that it is my problem

 

[Ttype6]

I'm pretty sure its a fuel delivery problem.

I am pretty sure the fuel pump sock may be clogged because of the amount of grunge in the tank when i replaced it.

Ive been trying to research as much as possible about fuel pressure.

You say you're pretty sure. You can be 100 % sure if you remove the schrader valve from the end of the fuel rail,connect a hose,that's long enough to reach the wind shield,to the fuel rail,and connect a pressure gauge to the other end of the hose so you can observe the gauge while driving.
The only fuel pressure you need to research is your fuel pressure with a gauge you can see while driving.

You say your fuel pressure is 39 with the hose off. This is what it should be.

After you install a gauge,drive the car. If you make 15 lbs of boost you should see 54 lbs of fuel pressure.
I'm gonna guess you can't make any boost because the car is running so bad.
When you first open the throttle ,the gauge should go from 31lbs up to ,something close to,39lbs. Then if you make any boost,the gauge should rise 1 lb of fuel pressure for every 1 lb of boost pressure.

If it acts in any other way than this,you have a fuel delivery problem.
If it acts like this,you don't.

You need to inspect every hose from the MAF,in and out of the turbo,out of the intercooler and into the throttle body.

You also need to follow and inspect every vacuum hose that is connected to the vacuum block on the top of the throttle body. Don't forget to follow and inspect the hose that goes to the MAP sensor on the inside of the passenger side fender.

Your problem sounds more like a MAF problem,but you must do these things first.

Tell us what you find.

 

[86grdnatl]

ok so heres an update. I hooked up the gauge and it reads 31 lbs at idle, vacuum line on. then i floor it and i get up to about forty miles per hour before the bucking and backfiring starts, so i let off of the gas. The gauge reads 38-39 lbs when i let off the gas. The boost lights come on on my dash (digital dash) so i feel as tho the boost is kicking in. Plus i can hear it. But for some reason the lbs wouldnt go above 39 lbs. I then stopped for a couple minutes and got the fuel pressure to stabilize at 35 lbs before i accelerated again. Only this time i took it up to about 40 mph (where it bucks) and the pressure gauge stayed pegged at 35 lbs the whole time. What do you guys think?

 

[RmvBfrFlght]

Definitely a fuel delivery issue.

> I did replace the fuel filter and the fuel pump not too long ago

Double check that the fuel filter arrow (flow direction) is toward the front of the car. If the pump was one of the infamous '0169 Walbro's, good bet that it is bad.

RemoveBeforeFlight

 

[86grdnatl]

Thanks alot. I checked and the arrow is toward the front of the car. I am pretty sure that my pump is bad because my filter is brand new (replaced it a week ago). Is there a brand of fuel pump that is the most trusted and reliable? Also, do you know of anything that i could use to really clean and degrease the fuel tank while i have it removed?

 

[RmvBfrFlght]

I'm not sure on what to use to clean out the tank. Gasoline is a good solvent, it may be better to get a new one. Although if it is just particles of stuff, hang it upside down and give it a good spraying with a garden hose. then hang the tank in the sun to dry it out.

As for a pump, the Walbro 340M is commonly used. Like others have mentioned a hot wire kit is also a good idea. Can get the pump & install kit along with a hot wire set up from Racetronix.

See the G75 Fuel Pump Assembly and the G77 Fuel Pump Assembly, need to check the connector by the back of the tank to see which is the right kit.

RemoveBeforeFlight

 

[grey racer]

For a few dollars more you can get a Reds XP pump which is a modified Walbro and much higher quality.

 

[Ttype6]

I hooked up the gauge and it reads 31 lbs.

Did you perform the inspections I described?

 

[Ttype6]

The gauge reads 38-39 lbs when i let off the gas.

When you let off the gas,you should see 30-31 not 38-39. This makes me think you have a vacuum leak.

The boost lights come on on my dash (digital dash) so i feel as tho the boost is kicking in.

You need a gauge to know how much boost you have.

I then stopped for a couple minutes and got the fuel pressure to stabilize at 35 lbs before i accelerated again.

The pressure shouldn't have to settle to a number.It should go right down to 31-35 immediately.
When you saw 31 lbs,was the car warmed up and in neutral?
When it settled to 35,was the car in gear?

 

[Ttype6]

Also, do you know of anything that i could use to really clean and degrease the fuel tank while i have it removed?

Are you talking about the outside of the tank. If so,a clean tank is more prone to rust. You shouldn't have to clean the inside.

 

[86grdnatl]

Ttype6- yes the car was warmed up and it was in park when it read 31 lbs at idle. Then i took it for a spin and could only get the gauge to get up to 39 lbs max. when i slowed down and stopped i looked at the gauge at it read 35 lbs. At this point the car was in drive (the d with the circle around it). i wasnt sure if it was going to go to 31 lbs again so i waited. But after 3 minutes of waiting i came to the conclusion that 35 lbs was the lowest it was going to go. As far as the inspection, i did check and i forgot to let you know, sorry about that. I replaced the rubber vacuum lines at the vacuum block (all of them) and i also replaced the pcv line going to the pcv valve. I also replaced the vacuum line and check valves going to the egr and fuel vapor canister. The only line that i didnt change was the line from the egr to the egr solenoid (couldnt figure how to get that one off) but it didnt look to be in too bad of shape anyways. I also did not change the two rubber connectors 1) going to the fuel pressure regulator, and 2) going to the map sensor because i am going to have to go the auto parts store to grab those.

 

[Ttype6]

But after 3 minutes of waiting i came to the conclusion that 35 lbs was the lowest it was going to go.

That's because it was in Drive. The motor makes less vacuum then. You need a boost gauge to determine if you're making boost. If it's making boost and the fuel pressure isn't rising with the boost,you have a fuel delivery problem. check to see how much voltage you have at the fuel pump connector at the back of the tank.

It's possible that you have a fuel delivery problem,but I don't think it's the cause of the bucking.

 

[86grdnatl]

Would I be able to check the voltage of the fuel pump connector with my multimeter? And I do have a boost gauge, am I correct when I say that I need to tee into the black line going to the map sensor for the gauge? I think it is the second line from the back of the vacuum block. And I couldn't find where the boost line could go through the firewall. Any ideas? Thanks for all the help I really appreciate it

 

[Ttype6]

Would I be able to check the voltage of the fuel pump connector with my multimeter?

Yes,with the car running. I like to pierce the 12 volt wire with a safety pin. You can get good contact to it with an alligator clip. You could also back probe the correct terminal at the connector with a safety pin.

Am I correct when I say that I need to tee into the black line going to the map sensor for the gauge?

Yes. I tee in where it connects to the metal line by the heater control valve.

And I couldn't find where the boost line could go through the firewall. Any ideas?

There's a grommet,on the firewall,where the throttle cable comes through. Insert the line through it,along side the throttle cable.