recommened fuel pressure

[Dillon79scotts]

today, my brother brought over his AUTOTAP and we couldnt find any issues at all, which is good, but its not good because it was acting up with me day before...

Hooked fuel pressure gauge up, about 44 to 45 at idle, with the fpr vacuum line unhooked(full fuel flow) was about 54 psi. it has good flow also.

when i drive it, it seems VERY DOGGY, feels like a 350 way to far ignition retarted.

Bleeding the brakes ATM so i couldnt hook up pressue gauge and drive it, but when i put it to the floor, it doesnt seem to take off very fast at all. i know its got more, because my stock 350 had more power.

if anyone can help point me in the right direction, or any input would be great

[Clyde65]

Pardon my ignorance but what is a Autotap?

[Shon]

Is this an LSx (4.8/5.3/6.0/5.7/6.2) set up? if so it needs 58PSI and normally there is no vac line hooked up.

Originally Posted by Dillon79scotts

Hooked fuel pressure gauge up, about 44 to 45 at idle, with the fpr vacuum line unhooked(full fuel flow) was about 54 psi. it has good flow also.

[clinebarger]

Shon, 99-03 4.8,5.3,6.0 truck engines had vacuum operated fuel pressure regulators.

Dillon79scotts, Fuel pressure specs with the vacuum unhooked is 55-62 psi, 54 psi is close enough....The gauge can be off anyway.
Have you scanned it for codes?

[Shon]

do remember there being a vac line on the fuel lines...we change the fuel lines at times DOH.
been a tough few weeks.

[Dillon79scotts]

yes ive checked for codes, nothing. 02 sensors are reading just like they should.

AUTOTAP is a laptop program, to pull codes and live data.

it seems to kinda have a small studder/missfire under full throttle, just every few seconds.

but i dont get why its so boddy and gutless, under full throttle. this is what makes me wonder if fuel pressue isnt high enough for it.

either that or brakes are dragging, but that would be a huge drag and i would smell it.

[Dillon79scotts]

Originally Posted by Dillon79scotts

yes ive checked for codes, nothing. 02 sensors are reading just like they should.

AUTOTAP is a laptop program, to pull codes and live data.

it seems to kinda have a small studder/missfire under full throttle, just every few seconds.

but i dont get why its so boddy and gutless, under full throttle. this is what makes me wonder if fuel pressue isnt high enough for it.

either that or brakes are dragging, but that would be a huge drag and i would smell it.

1979 chevy scottsdale 3/4ton (2000 5.3l truck motor) th350/203 t case.

Im wondering if torque management was left on my ecm, tuned by brandon at LT1swap

[BR3W CITY]

Im gonna actually venture out and say thats a definite possibility.

Torque management can be kind of a pain, when my truck was tuned (the "just get it running" tune) it would stumble around because of the cam and tq management would dog it out around town, almost like it was on6 cylinders. Once I had a full real-world tune on the dyno, those problems all cleared right up.

[Dillon79scotts]

Yeah, it came to mind about the last thing i could think of, i emailed the guy who did my tune, no reply yet.

but im assuming it would be tooken off, does a 2000 ecm even have it? its tunned for a manual trans, no egr, not vats, no evap,2002 chevy silverado

[Dillon79scotts]

only thing is it will run all the way up in rpms, but it just is down on power at full throttle, feels like limp, or lack of fuel pressure at full throttle.

if i am going fast enough to downshift it to about 3k rpms, its better but its still not it

[Shon]

Just depends on what he did when tuning it. I would be more than likely think its just the timing tables, the trucks do not have any timing in the upper RPMs, sometimes they are negative.
TM could be it but if its as bad as you describe its the main timing tables.

[BR3W CITY]

lol Shon, thats true. My truck had a whopping 1* of timing on the first run. I think we had to try 4 more times to bump the timing up were it really made some power.

[Dillon79scotts]

i have live data on my scanner, the timing alters like it should i believe. i know its moving around. cant remember numbers

[BR3W CITY]

the issue isn't the timing moving around (unless its going to retard)
What Shon is talking about is that the stock truck's tune has almost no timing in the higher rpm's. The tuner may have to try a couple times to get the timing to come up to where its actually making power.

What fuel pump are you running? You said that you check pressure at idle, but what about at full throttle, where the problem seems to exist. I'm wondering if the pump is having a hard time moving fuel at full throttle.

And this is kind of a long shot, but on previous vehicles I have had a plug wire rub-through and arc against another metal piece. It only happended when the engine came under load and moved a bit in the mounts. The wire would arc and feel like a missfire, no code thrown.

[Dillon79scotts]

Originally Posted by BR3W CITY

the issue isn't the timing moving around (unless its going to retard)
What Shon is talking about is that the stock truck's tune has almost no timing in the higher rpm's. The tuner may have to try a couple times to get the timing to come up to where its actually making power.

What fuel pump are you running? You said that you check pressure at idle, but what about at full throttle, where the problem seems to exist. I'm wondering if the pump is having a hard time moving fuel at full throttle.

And this is kind of a long shot, but on previous vehicles I have had a plug wire rub-through and arc against another metal piece. It only happended when the engine came under load and moved a bit in the mounts. The wire would arc and feel like a missfire, no code thrown.

havent gotten to check full throttle fuel pressure, its the walbro255lph. it flows great.

my wires are fine, ive looked them over

[DavidB]

Normally if I'm working on a car thats low in power the first thing I do is scan it if no codes still look at your data ECT, IAT temps being off would throw your timing and fuel curve off, TPS make sure your getting 100% if not linkage might not be right expecially since this is a hybrid. In my experiance(stock vehicles) Low power is usually: fuel pressure, clogged up exhaust or dirty air filter. If this motor is modified I would double check valve lash, valve timing- Some aftermarket cams are ground 3-4 degrees off. Good luck

[Dillon79scotts]

Originally Posted by DavidB

Normally if I'm working on a car thats low in power the first thing I do is scan it if no codes still look at your data ECT, IAT temps being off would throw your timing and fuel curve off, TPS make sure your getting 100% if not linkage might not be right expecially since this is a hybrid. In my experiance(stock vehicles) Low power is usually: fuel pressure, clogged up exhaust or dirty air filter. If this motor is modified I would double check valve lash, valve timing- Some aftermarket cams are ground 3-4 degrees off. Good luck

the IAT temps are very close to what it is outside, like 1 degree off when its been sitting overnight. TPS will read 100%.exhaust is new, air filter is new.

[Dillon79scotts]

Originally Posted by Dillon79scotts

havent gotten to check full throttle fuel pressure, its the walbro255lph. it flows great.

my wires are fine, ive looked them over

54 to 55 psi at full throttle in park

[Ackattack]

are you getting any KR?

what gearing and converter are you running?

[Dillon79scotts]

Originally Posted by Ackattack

are you getting any KR?

what gearing and converter are you running?

sorry, but what does KR stand for?

4;10 1500 stall, (need a 2k) 38.5 tires. i know its big but you would definely understand if you drove what i mean

[Shon]

KR=Knock Retard

[Dillon79scotts]

Originally Posted by Shon

KR=Knock Retard

yeah i remembered after i sent it. but i dont remember if it is or not

[Street Smart]

Originally Posted by Shon

Is this an LSx (4.8/5.3/6.0/5.7/6.2) set up? if so it needs 58PSI and normally there is no vac line hooked up.

100% agree, i had a fuel pressure issue when i first got it running. i "tempt" it out with a used fuel pump that i had. started and idled ok, no power popping in the intake. You need the press at about 58

[Dillon79scotts]

Originally Posted by Street Smart

100% agree, i had a fuel pressure issue when i first got it running. i "tempt" it out with a used fuel pump that i had. started and idled ok, no power popping in the intake. You need the press at about 58

58 at idle? or WOT. because with me having the 5.3l truck motor it has the vacuum regulator on the fuel rail controlling this

[usmcchevy]

Originally Posted by Street Smart

100% agree, i had a fuel pressure issue when i first got it running. i "tempt" it out with a used fuel pump that i had. started and idled ok, no power popping in the intake. You need the press at about 58

If he has a 99-03 with the regulator built into the fuel rail he will get less press at idle. 04+ should have 58psi at all times.