fuel pressure spike off idle

[channer]

Hi all
 
I am trying to figure out why I have a stumble/hesitation when I move from a stop position.  I finally got a fuel pressure gauge... and I notice that my fuel pressure spikes from 35PSI to 40 PSI as soons as I press the gas... and then it goes back to 35PSI.  it stays at a constant 35PSI... when I am cruising. 
 
It appears that I am flooding the engine for a second or two...and it causes that stumble/hesitation.
 
 
Does anyone know why I am getting this fuel pressure spike?  What can I do to fix.
 
 
I checked  and my fuel pressure 43PSI  with vacuum off.  I have an early turbotweak chip... and I don't think it is adjustable.  It's also the 2nd fuel pump that I have in the car.
 
 
any help is greatly appreciated.
 
dave

[earlbrown]

When you touch the gas pedal, vacuum drops and the fuel pressure goes up accordingly.

If you'd like to verify that it is or isn't out of whack, get a large face vacuum gauge and tape it to the windshield.  2" of vacuum equals right at 1 pound.   Example: You're idling at 18" and 35psi of fuel...  When you crack the throttle and are cruising at 10" you should have 39PSI of fuel. 

 When the throttle commands 0", the fuel pressure should be the same as the base setting. If not, you have a fuel delivery problem or a problem with the FPR, or FPR signal lines.

[channer]

thanks...

I guess I have to buy a vacuum gauge now... or find somebody with one!!!!

what do you mean by FPR "signal line"?

dave

[earlbrown]

the hose that runs from the throttle body to the fuel pressure regulator.

sometimes they can do really silly stuff like seal under vacuum and leak under boost...   or...   work fine under boost but a piece of trash acts like a check valve and keep the pressure high when it should be at the idle setting.

[Steve Wood]

As Earl said, it sounds like it is working exactly as it should



Instructions for your chip should be on the turbotweak.com site

[daveismissing]

Hey Dave, Welcome to Ihadav8

Checked the TPS and IAC settings?

How can a parts Ho like yourself not have a vacuum gauge?

( Channer is a close second to Just a Six in the parts hoarding catagory)

[channer]

Hey Dave, Welcome to Ihadav8

Checked the TPS and IAC settings?

How can a parts Ho like yourself not have a vacuum gauge?

( Channer is a close second to Just a Six in the parts hoarding catagory)

Dave

TPS = 42 IAC = 15-20.... not too crazy about the BLMs = 120...  all other numbers look good.

I finally broke down and got another fuel pressure gauge... why would I need a vacuum gauge!!  Now, I am on the lookout for an adjustable FPR...   do you have?

dave

[TWIN86GNS]

Channer,
 
I might have a spare Accufab FPR on the shelf in the garage.  If you still need to borrow one, let me know and I will grab it for you. 

[channer]

Paul

thanks for the offer... i need to somehow get up to your place.

I finally picked up a vacuum gauge tester... after stopping at two CTs and a Parts Source store.  Its a little dark to do anything tonite.

dave

[Scoobum]

Dave...you and I talked about this before. You threw a bunch of parts at that car all at once...correct? Was the throttle body one of the swapped in parts?

[channer]

Dave...you and I talked about this before. You threw a bunch of parts at that car all at once...correct? Was the throttle body one of the swapped in parts?

Brad... 

I would never installed everything at once... it takes me forever to install one part... but i did swap the stock TB for a 62mm TB.   The seller said it was a Steve Munroe TB but I don't think it is... after reading what he does with his TB.  I don't have another to throw in.

dave

[Scoobum]

I'll talk to Dan in the morning...we may have one at the shop you can try. I also have an AFPR sitting here.

[Scoobum]

We don't have a TB...but you can have the AFPR.

[channer]

Hi All

I tested with a vacuum and fuel pressure gauge today.  The car is on jack stand... so I did not do any real road testing... just throttling the from the throttle body.  I also found & install a stock 237 GM fuel pressure regulator... and tested with that also.

at idle, the FP = 35 and vacuum is 18
- when I give some gas... fuel pressure jumps to 40 & then drops to back to 35, the vacuum drops to around 5 & then climbs slowing back to 18.  I feel a bit of hesitation when I see the FP jump to 40.  This appears tp be close to the 2"of vacuum for 1lb of PSI

- when i give it a real quick jerk on the TB linkage from idle, fuel pressure jumps to 40, and the vacuum gauge looks like it almost hits zero.   This is where I see/feel the most hesitation... as the fuel pressure drops.  This is almost 3" of vacuum for 1lb of PSI.  What would this mean?


I took a look at the chip.  it says Eric / 50lb / ver B.  I went to the TT site... and Eric mention there should be a version on the upper left or else its a non-adjustable.

dave


ps: Brad... if I need the AFPR... I will let you know.