hesitation and o2/rpm drop. whats goin on?

[Mephisto]

took my sy out for some mild DM runs tonight... no WOT runs or anything like that...

cruisin around with DM on, goin maybe 35mph and 20% throttle when i got this engine hesitation... i went back and looked at the DM file and my rpms went from 2600 to 1900 and then back up. the o2mvs were in the 900s and dropped to less than 100 and then went back up... later on when i was driving home on the freeway, i got on the gas a lil bit to make a lane change (making about 8psi) and same thing o2s dropped and rpms dropped... i checked the fuel counts and theyre both at 128, intake temps at 100*, about 3* of knock on the boost run but i dont think thats the cause...

could it be a bad o2 sensor? one thing i did notice the other day was that the vacuum line coming off the front of the EGR is disconnected... but i dont know if that would effect anything if the egr disabled when the ultimate is set to t1-16 or higher right?

 

[Ian Turgeon]

My first thought is fuel pump, when they start going bad they can cause similar effects at low rpm, and work fine under all other conditions.

Adam's ty did the same, gun it and it would drive like a bandit. accellerate from a stop and arond 1800-2500 rpm it would feel like your coasting down hill.

 

[Mephisto]

ok well this problem has gotten worse... now it does it at low speeds and when i get on the gas i.e. getting on the freeway...

any other possibilities than fuel pump? its a walbro with less than 30k on it.

PS im also gettin a lot of knock now too, i have my fuel psi at 53... maybe if it is the pump could it be leaning out under boost causing knock? im sure shitty 91oct doesnt help but knock was never this bad... (18* @16psi)

TIA

 

[bezerk]

could also be your O2 sensor

 

[Ian Turgeon]

If you dont have a fuel pressure gauge in truck, I'd resort to taping auto-parts-store mechanical fuel pressure gauge onto the windshield and going for a drive. I'd guess the fuel pressure it dipping very low when you put any demand on it.

 

[Mephisto]

i have an autometer electric gauge in the cab, and ive been watching it when i drive. when im in boost its not rock solid it kinda wanders but doesnt make any significant drops.

could the o2 sensor be misreading, telling the computer to cut fuel psi?

 

[0966Sy]

You are in closed loop so if the ECM reads that the 02 is out of range it will store a code. Any codes? Take a look at your TPS Voltage and look to see if it drops under the condition your describing. I would say your fuel pump is fine, I wouldnt rely on the 02's dropping as being lean at a specific time. Look at your Injector DC during your condition and see if it drops some.

Dont just assume that it could be lean, look for some clues. You cant rely on the 02 in closed loop while cruising. It's going to keep crosscounting trying to keep the AFR at stoich.

If i where you i would lower my base FP down to 50psi and try to get it to do the cut out again. If it still happens then it's not doing it because your dumping to much fuel. I would look into Ignition wires, plugs, cap n' rotor. Hard to tell if it could be fuel/ignition related. GOODLUCK

 

[bezerk]

i have an autometer electric gauge in the cab, and ive been watching it when i drive. when im in boost its not rock solid it kinda wanders but doesnt make any significant drops.

could the o2 sensor be misreading, telling the computer to cut fuel psi?

get datamaster

 

[Mephisto]

im gonna pull the ultimate out go back to stock w/ 2 bar, and do a full ignition tune up and see if it still does it... im sick of this POS not running right!

theres nothing more frustrating than getting messed with by some punk ass kid in a vr6 and not being able to teach him a lesson cause your truck runs like poop :x

 

[Mephisto]

im gonna pull the ultimate out go back to stock w/ 2 bar, and do a full ignition tune up and see if it still does it... im sick of this POS not running right!

theres nothing more frustrating than getting messed with by some punk ass kid in a vr6 and not being able to teach him a lesson cause your truck runs like poop :x