need help!!

[661gn]

just bought a gn
stock engine besides air intake. the car starts and idles good. only problem is that once i pass 1/4 throttle the car starts to bogg out/sputter...drives good as long as i dont step on the gas too quick....i seem to loose boost and nose falls once this happnes i let off the throttle and problem stops and boost builds up again.but this continues to happen...
any ideas to what it can be..

 

[bmackinnon]

Could be several things, but sounds like the fuel pump may be dead/dying. The very first thing any new owner should check is that the fuel pressure is rising 1:1 with boost. This will require a fuel pressure gage on a hose long enough to tape to the windshield so you can see it while driving/getting into boost. The (base) fuel pressure should be approx. 43 psi with the engine idling and the vacuum line removed from the fp regulator, and (with vac. line replaced!) should rise 1 psi for every pound of boost..... ie... 43 psi base + 15 psi boost = solid, steady 58 psi fuel press. (Substitute your boost #) Anything less, and you are going lean and are begging for a blown headgasket. Also, make sure the fp doesn't begin to rise and then fall off as the boost comes up.... a sure sign of a dying pump....

Make sure you don't keep beating on it, making it 'nose over', etc until you have this figured out.... if it is indeed leaning out, catastrophe is just around the corner.... :wink:

 

[661gn]

thanx for the help
i wil be getting into it this weekend...
i have a new stock fuel pump might instal and chek if that is the problem then install a upgraded one...
any members near bakersfield california???

 

[87TurboRiviera]

It could also be a build up issue... I came across a problem like this with my hybrid. Turned out to be a clogged cat, And heavy "scum" buildup on Idle air valve and Throttle Position sensor. The easiest thing to do would be a can of brake Kleen on the intake... see if that solves your problem... If not go for Fuel Pressure. BTW is it 43# base or 47# base? I have heard conflicting numbers.

 

[bmackinnon]

Stock fuel pumps were marginal at best for a bone stock car when brand new.... do yourself a favor and purchase an upgraded pump and hotwire kit without thinking twice... it's an essential upgrade for ALL TRs. Like I said above, you MUST verify the fuel pressure is correct and RISING properly with boost.

It's not 'buildup' , not the IAC, not the TPS.... nothing to do with them.... (although it could be a clogged cat).... with your symptoms, 95% chance it's either the fuel pump, the maf, or an ignition problem (coil pack/ignition module).... probably the pump....

Fuel pressure is set to the chip maker's spec.... 43 psi is the norm....

Check your fuel pressure under operating conditions first and foremost....