i'm looking for some answers to help determine why my gt has suddenly become sluggish on acceleration from about midrange thru topend..i'll explain.. my 2002 gt has 65,000 mi. on it. i drive it daily back and forth to work, but u know as well as i that eversooften, someone out there wants to test u..my motor 4.6 is completely stock w/5-speed. i have changed the stock exhaust from cats back to an ARK exhaust, the company is 'arkspeedraceing' out of california. and i use a k&n filter in my stock airintake. when at idle after warming up.. u hear a nice rumble a slight miss 'this is what it sounds like to me' i've had it looked at and was told theres nothing wrong,they all do that, that its just the cam.... i was thinking of haveing it dynoed.... just to see if my rwhp is where it should be.i'm also running 5w30 at present should i change to 10w30 ? how can i find out what is causeing this sluggish performance? any help will be greatly appreciated........

You could have a dirty mass air senser,plugged fuel filter and possible plugged catylic converter.....5w30 is too thin 10w30 sythetic at least..is your gas milage lower then normal??

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Nicks Automotive
2334 Wyecroft rd unit 2
Oakville Ontario
L6L 6M7
www.nicksautomotive.ca

Could it be that the weather has suddenly become warmer and/or more humid? Cold air will allow the car to make more power, warmer and more humid air will make the car feel sluggish.
SS

I have to agree with the above response. the oil you are using is too thin.And if you are over filling the oil, it can cause crank lag, or basically slows the crankshaft down. I had both a 97 GT and a 98 cobra. I always used 10 W 30 in the smaller motor, but in the cobra I used 5 w 30 cause it had the four cams. It could be the type of gas you use, lower octane, but that wouldn't make much difference, maybe a little. Fuel injectors could be dirty, plugs dirty bad plug wires, etc... I had a 99 expedition and it had a similar problem, I changed all the plugs and wires, and used a simple fuel treatment and it ran great afterwards. If I were looking for some pep I would def. consider gears. you could get a set of 3.55 or 3.73 ring & pinion gears and still retain some gas mileage. I feel that the newer mustangs engines, I.E. the 4.6's like bigger gears. I had gears in my cobra, 3.73's and went with the 4.10's. huge difference in performance. I have 3.90's in my 07 GT and it is alot better off the line. Everyday driving is a concern I think for you, so maybe a mid pipe, and some gears after you determine the problem. I know what you mean with the sound your engine is making after it warms up and mine did something similar too. but if it is skipping, I would consider a tune up, or just maybe run a system (fuel) cleaner in your gas, and see if it helps.

If the cap says 5w20 why would you run 10w30? do we know more than the engineers at ford?

When was the last time you did anything the Ford engineers did originally? If that were the case, all of our cars would be stock!
As for the oil weight, it's really a suggestion and it's not what you have to put into your car. In winter time, I suggest to run the thinner oil but in summer time I always go with something thicker. The first numbers and one letter signify the oil's viscosity at a certain temperate in the Winter (cold start), hence the W, and the number after the W signifies the hot temp viscosity. Depending upon your application and location, a knowledgeable owner or shop can recommend the appropriate oil to use.
SS

JDM suggests using a 5-20 synthetic in thier motors because as engine parts move they create a wave, the thicker oil takes longer to fill back in and continue protecting parts compared to the 5-20....I thought the same thing too, thicker oil would be better for protection so I used to run 20-50 in most of my older cars...and because it helps restore compression temporairily lol.

Apperently there's been MASSIVE arguements over oil weights.

__________________
Black 91 Mustang LX Coupe
2.3L Auto

Denonford 8250Ti
Focal Utopia 165W
Kicker SoloBaric 15" (round)
Rockford 301S
Memphis 75X2
JBL CSX200.1

JDM??? As in Japanese Domestic Market?
And what is this wave theory you speak of? Never heard of it, maybe you misinterpreted something?
People dont use thicker oil specifically for more protection, most use it to keep oil pressure higher at high temps and high RPM. Not to mention the fact that 20W50 has a much higher viscocity index at hot operating temp, it also has a lower tendency to cause cavitation.
For the average joe who doesnt really know the difference, dont run a thicker/thinner oil because someone told you to. Unless you had an engine built, or know a thing or two about why you should be running a different oil, stick to what the manufacturer recommends (or engine builder).
Engine oil does not restore compression.
SS

lol not the Rice JDM, the guys that are famous for making power with the 5.4L mod motors, and 4.6L 's too.

JDM builds performance parts.

The wave I'm talking about has mainly to do with bearings....as the parts spins there is a "wave" of oil being pushed in the direction the part is moving, behind the part, there is less oil because it's been pushed forward, so the theory is that a thinner oil will take less force to move and less time to fill back in behind the part thereby making more power and protecting better. The reason they suggest Synthetic is because a thin oil tends to break down in high heat conditions, sythetic holds up better to heat.

That's basically what I was told and not in those exact words, but it seemed to make sense to me when I was told....I'll see if I can dig up a discussion about it.

__________________
Black 91 Mustang LX Coupe
2.3L Auto

Denonford 8250Ti
Focal Utopia 165W
Kicker SoloBaric 15" (round)
Rockford 301S
Memphis 75X2
JBL CSX200.1

I used to have a Park Ave with a 3.8 back in the day, it had 275K on it and it was getting pretty tired...was underpowered and had some compression loss on a few cylinders, I added 20-50 with the Lucas oil stuff, and it brought the compression back up to an acceptable level, thought it wasn;'t a HUGE jump like a sleeve and bottom end job but it was enough that it didn't burn a quart a week and I got some power back.

__________________
Black 91 Mustang LX Coupe
2.3L Auto

Denonford 8250Ti
Focal Utopia 165W
Kicker SoloBaric 15" (round)
Rockford 301S
Memphis 75X2
JBL CSX200.1