pulls hard part throttle, power drops at WOT

[5.0Torx]

hey all

as the title reads, im having some issues with my recent P head swap. Heres the list, from air filter to tailpipes. Car is a '93 LX, 5 speed.

1) K&N filter, cleaned and oiled not too long ago. Id guess 2000 miles / 5 months.
2) 94 mustang GT MAM with the F2VF electronics.
3) STOCK INTAKE TUBE
4) professional products 70mm TB and EGR. new TPS - .9xx volts.
5) cobra/explorer intake. The early kind that doesnt require moving the ACT and all that jazz
6) 99 explorer GT40P heads. Did NOT get them cleaned up or valve jobbed. I lightly wirewheeled the crud out of the combustion chambers. They werent in that bad of shape to begin with, i think.
7) trick flow double valvespring kit
8) cobra 1.7:1 RRs. Stock cam. stock pushrods. New lifters. New timing chain set at stock orientation.
9) BBK non-P headers. Had to flip the spark plug wires on 6, 7, and 8 due to tight clearance.
10) catted X pipe, SLP LM1s, and 2.5"s tails. 2.5" the whole way.


Anyways, it seems to run like it should at part throttle, but when i go to the floor, it really flattens out. As a point of referance, the car was neck and neck with my dads '00 GT. Now its not even close. my butt dyno isnt lying.

Whats going on? sorry so long.

TIA

 

[cenok is family]

have you taken it to get tuned yet? you're a/f could be way off or it could be a vacuum issue. put it on a set of rollers and see where you're at.

 

[TechSteele]

For a second opinion,
Hes right, its Bogging.
It cant handle that much Air or Fuel, or both.
It needs some major adjustments.
You first need to know if it needs more fuel, or less.
Check the plugs for a hint after stomping on it a bit.
If your Old man can drive behind you, he May see some black smoke when you floor it.
I would go through the entire ignition system too ("spark") Distributor, cap rotor, plugs, coil, wires, and so on. if ANYTHING is worn or even maybe old, replace it. The more or best spark the better too.
If its AIR, spark wont help.
hope that all made sence.

 

[5.0Torx]

I have a 255 lph fuel pump and an AFPR waiting to go on the car, but i have held off because i dont have a fuel pressure gauge yet.

would "tuning" on the dyno entail dialing in more/less fuel pressure, and advancing/retarding the dizzy?

thanks

 

[5.0Torx]

oh and i checked the #1 plug last week (after about 2000 miles of driving) and it looked great. golden brown, like toast.

 

[TechSteele]

Im not totally an expert on EFI systems yet.
Im wondering if there is a vacuum leak somewhere.
The words Vacuum advance came to mind, but i was thinking more along the lines of the throttle body, not the distributor.
In an old carb, we would check the butterflys/choke linkage/float.
(i am so used to the old systems, i try to think in terms of carbs)
I know there are a couple vacuum lines in there for the fuel/air.
Worth a look.


A 255lph might be a bit much for you.
The one good plug just means that cylinder is/was good at the time you checked it. I dont think its in the ignition system, i would bet its in the Intake/Throttle somewhere.

It just sounds like adjustment in the throttle body/top end somewhere.
Have you checked for any codes yet?
There is a sensor, or solenoid, or vacuum somewhere not opening during WOT, but im not good enough to say where exactly to look. I have to differ to someone more knowledgeable about such things.

I know what im thinking, but its hard to put into writing, hope this dribble makes sence.

 

[87AODGT]

have you ever changed the fuel filter? that would definately cause the car to nose over at wide open throttle if its not flowing what it should, happened with my car.

 

[67coupe]

Are you using the right spark plugs? Looks like GT40P heads take a different plug than stock E7's.

http://www.stangnet.com/mustang-forums/749277-help-wrong-spark-plugs-gt40p-heads.html

 

[5.0Torx]

Im using the plugs that autozone has listed for 99 explorers. I forget exactly, but i think its AP25's.

Fuel filter changed 2k miles / 5 months ago. Could there be sludge in the fuel tank? i'd clean the tank out when i change the pump.

 

[67coupe]

Might want to double check. Autozone is showing the 764 as standard on 99 exploders.

There is a difference in thread reach btw the two. 0.460" for 25's vs. 0.702" for 764's.

 

[strtrcr50]

Torx, did you check for codes?

 

[5.0Torx]

i will double check the plugs

i checked codes a few days ago and it gave me 67 and 11. 67 because i had it in first gear, not neutral. 11 is system pass, i thought. ill double check those too

 

[Cjfoxbody13]

I know this might sound weird, but I had a problem similar to yours with mine. I was running good under normal conditions but during WOT it felt like it was getting enough fuel or something. So I changed my fuel pump and filter, spark plugs and wires, and even the cap and rotor. And come to find out it was the alternator. ( My volt gauge wasnt working...)

 

[Dachipsta]

I was dealing with the same problem with it flattening out after mashin down the throttle past half way. Turned out it was a tired fuel pump. Replaced it with a 155lph and it was like a different car. It pulled hard throughout the entire throttle range. I know you have a new pump ready to go in so you may as well go ahead and change it out now......my .02

 

[TechSteele]

Alternator?
Do tell
Like to hear that story.
How did the Alt effect performance?

 

[Cjfoxbody13]

Well the Alt wasnt drawing enough spark. So, when I would have the lights, radio and a/c and went to WOT it had a hesitation. A 4,000RPM's it felt like I was hitting a rev limiter. It was the orig from 91 I believe 75amp. And the plug wouldnt set well. So I replaced it with a 160amp and yellow top. And everything had been good ever since.