sn95_331_GT_ yellow

so aside from the other things that i know need sorted out, my motor is running like absolute garbage and i really have no clue...

its back-firing like a bastard all the time and it just feels like it either loading up with fuel or super lean if i try to feed in any power...

i have an 87 octane tune loaded in (due to the higher compression) and i selected 30# injectors on the tuner...

aside from setting the idle to ~800rpms and raising the limiter to 6600 i really have no ideas wtf could be wrong...

any help would be great guys this OBDII BS is kicking my a$$!!!!

i want my 302 back

cliffyk

• I assume you are running the return type fuel system;
• What MAF are you running?
• What tuning system are you using?
• Did you adjust the tune for the 170° T-stat--not just the fans, the ECT vs AFR tables too?

There's a bunch of other info needed too, but this will be a good start...

sn95_331_GT_ yellow

yep stock return style

stock MAF

SCT X3

didnt touch the t stat stuff, the car runs right at 178- 182*, and it does it whether its in open or closed loop, when it first starts for about a minute or so itll be fine then it starts back firing

cliffyk

It's going the run rich as heck with the 170° T-stat and no changes to the various ECT related tables and functions--put a stock 210° (IIRC) thermostat in there and then start to tune the new engine...

sn95_331_GT_ yellow

yeah but this problem is present basically when i first start it up, not just after it warms up...

im thinking theres something wrong with the injectors maybe?

oh, whats the fuel pressure supposed to be static? ~40psi IIRC?

i need to hook up the wideband and start seeing what it looks like and go from there

cliffyk

Above you said:

Which is it? Once you get that straightened out let me know--we'll work it from there...

sn95_331_GT_ yellow

start the car up and from anywhere from 20-60 seconds it will run ok, although sometimes the INSTANT the car starts it will backfire once... after that its starts to run like crap

once the car warms up the avg coolant temp is the 178-182*

if you hold the car at one particular rpm its ok, the minute you alter it up or down itll backfire again

when i drove it when i was driving at one particular speed it was ok but then when i tried to accelerate it would sputter and "load up" it felt like, closed throttle deceleration was fine no issues there

had no power, felt worse than the NPI motor

sn95_331_GT_ yellow

ill take a video for you tmrw and try to get an in-car view too around the block

cliffyk

One thing just occurred to me--Does the tune know you now have a 5.4L engine?

There is a scalar value named Standard Air Charge, used by the PCM to calculate engine load. The current load is one of the key ingredients of the fueling and ignition timing calculations.

If this is still set to the 4.6L value (0.001553) it needs to be changed for the 5.4L engine. The formula is:

2.701e-09 * pi * ((bore/2)^2) * stroke

Where:

2.701e-9 is the lbm/mm³ of air at STP;
pi = 3.14159
bore = the cylinder bore in mm;
stroke = stroke in mm;

So, for the 4.6L engine (90.2 mm bore x 90.0 mm stroke) we get:

2.701e-9 * pi * ((90.2/2)^2) * 90 = 0.001553 lbm/mm³

and for the 5.4 (90.2 mm bore, 105.8 mm stroke) we get:

2.701e-9 * pi * ((90.2/2)^2) * 105.8 = 0.001826 lbm/mm³

Bottom line--the tune needs to be modified to use 0.001826 as the Standard Air Charge value...

sn95_331_GT_ yellow

whaaaaa?...

no its still a 4.6, just with PI heads and the cams

i never got around to it today, my best friends dad just dies so im taking a break from the car for a week or so, ill let you know when i get back up to work on it, thanks again though