What are some causes for low high end power?

mark0101

mark0101

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My car isn't that good on high end, could you guys tell me what are some causes. I am guessing that its my fuel pump. The car has 91,000 miles. which fuel pump should I put and how much does it cost?
Thanks in advance
 
could be any number of things - from valve seals , oil pressure,dirty fuel injector,fuel filter etc,spark plugs/wires.What makes you think it is the fuel pump? I believe it pumps or maintains the same pressure at any speed-I am sure somebody that realy knows here will correct me:)
 
well having searched the forum, most people replace their fuel pumps to get better high end power.
 
true, higher volume /pressure fuel pump to deliver more fuel-I am not sure I understand what is going on -your car is running fine you just want to add a little extra kick in the top end?
 
2nd on fuel filter. IMRCs stuck closed would also cause it. as would a bad fuel pump.
 
Before you go changing a pump, run a fuel pressure gauge through the door and do a couple pulls winding out 2nd gear while someone keeps an eye on fuel pressure..
 
Ditto on the gauge. Check pressure. But I want to add that low fuel drop out at WOT almost always results in either cutout - literally the engine shuts off for a second and as pressure comes back it comes back too, its a very jerky motion - or a result is pinging (detonation). Detonation could be happening and if so the knock sensors are retarding timing which would result in a loss of power.

And like said, in a working system fuel pressure is maintained at a constant level - thats what the pressure regulator does. Adding a better pump wont do anything since pressure is a result of flow and in the end everything comes down to the injectors. However, a increase in pressure via the regulator will force more pressure through the injectors so an adjustable injector can help a little...

BUT, top end power loss could also be just one faulty COP. If the car seems slow under load (slowly accelerating in third up hill for example) then a COP it may be.

If you want to help narrow it down, check the fuel pressure and unplug or pull the fuse (if there is one) for the knock sensors.

I guess what I am getting at is down throw a pump in there just yet.
 
unity said:
Ditto on the gauge. Check pressure. But I want to add that low fuel drop out at WOT almost always results in either cutout - literally the engine shuts off for a second and as pressure comes back it comes back too, its a very jerky motion - or a result is pinging (detonation). Detonation could be happening and if so the knock sensors are retarding timing which would result in a loss of power.

And like said, in a working system fuel pressure is maintained at a constant level - thats what the pressure regulator does. Adding a better pump wont do anything since pressure is a result of flow and in the end everything comes down to the injectors. However, a increase in pressure via the regulator will force more pressure through the injectors so an adjustable injector can help a little...

BUT, top end power loss could also be just one faulty COP. If the car seems slow under load (slowly accelerating in third up hill for example) then a COP it may be.

If you want to help narrow it down, check the fuel pressure and unplug or pull the fuse (if there is one) for the knock sensors.

I guess what I am getting at is down throw a pump in there just yet.
Click to expand...



a single cyl miss would be felt and throw a cel after a while. a lack of pressure on an older obd2 system would only throw lean codes at the extreme. (not gonna happen at wot though)
 
"a single cyl miss would be felt and throw a cel after a while. a lack of pressure on an older obd2 system would only throw lean codes at the extreme. (not gonna happen at wot though)"

A full mis-fire, yes. I had a faulty coil pack causing a mis-fire, yet no CE and no codes. There are several others who had the same failure - where the coil still sparks or something, but its weak and seems to come out when the engine is under load.
 
Last year I was running 15.1- 15.3 1/4 mile times with only a trap speed of 88

I was told a tune up blah blah blah. and I did all of it. Then I replaced the fuel filter, Put a 255LPH fuel pump in, and now I ran a 14.8 witha trap speed of 95
 
unity said:
"a single cyl miss would be felt and throw a cel after a while. a lack of pressure on an older obd2 system would only throw lean codes at the extreme. (not gonna happen at wot though)"

A full mis-fire, yes. I had a faulty coil pack causing a mis-fire, yet no CE and no codes. There are several others who had the same failure - where the coil still sparks or something, but its weak and seems to come out when the engine is under load.
Click to expand...



if you cant feel a cyl drop out at wot then youre not paying enough attention.

im well aware of how it can fail. ive been working on performance concerns and CELs on fords for 7 years now.
 
Nitrobasher said:
Last year I was running 15.1- 15.3 1/4 mile times with only a trap speed of 88

I was told a tune up blah blah blah. and I did all of it. Then I replaced the fuel filter, Put a 255LPH fuel pump in, and now I ran a 14.8 witha trap speed of 95
Click to expand...

And I ran a 16.7 @ 87, then a 15.9 @ 90 with NO changes to my vehicle at all, just a change in density altitude. :rolleyes:
 
Ok, How would you check your fuel pressure guage? Do I have to buy a special tool for this.
Plus know I am leaning towards what Unity said about the knock sensors. When I take my Continental or my Town Car to 100+ they feel strong but with my mark VIII, it struggles to get there.
What are COP, and how you go about checking them?
 
Nitrobasher said:
Then you need to change your density altitude again because that is one slow lincoln:eek:
Click to expand...

My point was that other factors can affect track times.. that it wasn't necessarily your fuel pump change that had the effect.

My 15.9 was at 6500' density altitude - corrected to 0' DA that should be a 14.46 @ 98.45. Even just correcting for track altitude to sea level that's a 14.79@96.6.
 
"if you cant feel a cyl drop out at wot then youre not paying enough attention.

im well aware of how it can fail. ive been working on performance concerns and CELs on fords for 7 years now."

Yet you clearly DONT understand the ignition system in a Mark VIII. If FOUR Ford dealers and over 1k later in diagnostics can not pin-point a mis-fire and thats after going through the forums and using the collective intelligence of the community first. I even had my car's data sent to Ford including emissions readings, etc... The "wasted spark" system can "fire" a dead coil. We are NOT talking about a "cyl drop" here, a full blow failure is easy to feel and detect. I finally found the problem when I put the no longer, but new, coil packs and wires from my 96 into my 95 - suddenly the 95 acted the EXACT same way. I replaced one coil pack at a time with wires to follow. I did not get to the wires, the first coil pack I swapped fixed the problem. It bench tested fine, no CE light and it was only an issues under load or WOT. I was happy I found the problem, but pissed that is was something a simple as a coil.
 
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