KiLLJ0Y

for some wierd reason, when i hit 4000 RPM under WOT the engine bogs down and will not go past that at all.. in fact it wants to stall out until the RPMs come back down.

now this only happens once the car is warmed up to 175*... if the car is cold(100*-160*) i can hit 5200 at WOT with no problem and no bogging.


now the odd part to this is that if i only have the throttle part way open, and im at 180*, i can go past the 4000 RPM .. but as soon as i nail it.. it bogs hard!!

car has a custom chip from Dyno Don... see sig for upgrades to the car..

anyone else have this problem? or know how to fix this?

KiLLJ0Y

no one knows hu?

vortec305

did you ever find out what was causing you problems

robsgta

check your fuel pressure not just at idle but with out vacume as well..

CashMunson

iTrader: (1)

what is your air/fuel reading when it bogs?

robsgta

If it falls any where in the 30's on down then theres your problem

GTA matt

iTrader: (1)

id check the fuel filter, when was it replaced last? also the cat. converter may become clogged when it heats up. drill a small hole in front of the cat, let the car warm up, at idle or when u rev it up there should b very little exhaust coming out of the hole

KiLLJ0Y

still havent found out whats up..

fuel pressure @ idle is 38..

now someone mentioned checking it without vacuum? how do i do that?

one of my friends at work suggested changing the ignition module.. should i do that? i bought one but have no opened it.

fuel filter was changed last year, but i barely drove the car all last year, in fact the total mileage i have put on since i owned it is 3000. so the fuel filter has about 2500 miles on it.

my fuel pressure guage is attached to the fuel rail so i cant check it when im driving.

a recap... i cant pass 3700 RPM now even if i have 1/4 throttle down. if the engine is warmed up.. you cant make it go past 3700 RPM..

someone else suggested the MAP sensor vacuum is too great when at WOT.. but i cant imagine that happening

CaptPicardsZ28

Change the ignition module? Why? It sounds like a chip issue to me. Could be a faulty knock sensor or CTS sensor as well. You mentioned how it runs at different temps. Check the CTS.

robsgta

When ever no vacume is presnt your fuel pressure should jump up 10 psi when people say to check it with out vacume they mean by removing the small vacume hose to the regulator.

rgarcia63

psi at idle should be between 30.5-44psi, 38psi is good. With FPR vacuum disconnected the psi at idle should be 40.5-47psi. If your gauge is on a long hose tape it to the windshield.

The FPR (fuel pressure regulator) has a vacuum port like the EGR valve, on my 88' it's connected to one of the two ports at the passenger rear side of the plenum forward of the distributor. Disconnect it there and cap the plenum port, this should cause the FPR to run at 40.5-47psi.

The ECM can increase the fuel pump voltage, thereby increasing the pressure when needed.

The ignition module either works, or it doesn't.

Vacuum is at it's greatest at idle (15-22in. hg) So, vacuum is adversely porportional to rpm i.e. WOT = zero vacuum. The best place to check vacuum is some point close to manifold center.

KiLLJ0Y

ok sports fans... problem found

there is a plug some where before the fuel filter.. and we suspect its either the bag on the pump or the pump itself.. pulled the line off before the filter.. turned the key.. gas barely trickles out..

so, once we get the new rearend in.. we will pull the tank and pump and see whats up..

the pump is a Walbro 255L i think this time i'll just go with a stocker.

thanks to everyone who put in their guesses.

robsgta

5 bucks says its the fuel pump...:lala:

affliction1

ive got a bad knock sensor and thats what mines doing.falls on its face under heavy load but is fine in neutral.

hellz_wings

iTrader: (2)

woah this was from 2004.. old thread.

affliction1

lol i realized after but said screw it its out there