The 2.5L Performance FAQ! (Newbies: Read, Know, Love!)

The 2.5L Performance FAQ! (Newbies: Read, Know, Love!)

The NEW 2.5L Performance FAQ

What you've all been waiting for, I'm sure- It's the new 2.5L Performance FAQ!

What is covered by this forum:

Performance Modifications to the 2.5L Duratec V6. It is possible to swap the 3.0L Duratec from a Taurus, Sable, Escape, or Tribute, but that swap is out of scope of this forum. Please see the 3.0L Performance Forum. Questions pertaining to other vehicles or the Zetec (2.0L) Cougar do not belong in this forum.

What type of questions can I ask without getting flamed or locked?

There is no magic formula. However, common sense NEEDS to prevail. If you ask a question such as “I haven't really searched, but I wanted to know what the best intake for the V6 is?”, you're going to get flamed, and the thread will probably be locked in short order. The search button is your friend, and many answers are readily available by utilizing this feature. If you have searched, but still don't even have a place to start, ask the question. There are enough truly knowledgeable people on this forum to help out. That being said, do not simply throw away the advice given by the senior members of the boards as “stupid” or “I don't like that answer”. We're here because of experience, some of us dating back to the beginnings of the Contour platform.

Out of scope questions (F/I, 3.0L) will be locked, please go to the appropriate forum.

Road racing stories will be locked (even deleted) with extreme prejudice. You have been warned.

If you ask a question that is blatantly answered by this FAQ, it will be locked. Again, fair warning.

Excessive profanity, excessive attempts to get around the board's censoring program with “$”s or “!”s will not be tolerated. This is a family forum. Post with respect, you will be treated with respect.

Insults, bickering, and the like will not be tolerated. At least act maturely here.


Q: What are common problems with the Cougar?

A: By and large, the Duratec V6 engines in the Cougar are dead reliable. The major problems reported with our cars are the sunroof rails (not covered by this forum), fuel pump (see question below on return/returnless systems), and alternator failures. Alternator failures are the most common problem by far, and are difficult to replace yourself due to their position (tucked away under the firewall on the passenger side of the car) due to our top-heavy DOHC V6. There is also some speculation of “oil starvation” on the pre-2001 engines, which lack a third oil return passage in the block and heads. Those with pre-2001 Cougars (actually all as a matter of good maintenance) need to watch their oil level, and may want to fill the engine with 6.5 quarts instead of the perscribed 6.0 (with filter change) for an extra safety buffer.

Q: How much horsepower do I have stock? Why are people reporting lower numbers on a dyno?

A: The 2.5L Duratec V6 engine produces 170hp @ 6250RPMs, and 165 ft/lbs of torque @ 4250RPMs. The reason that people even with modified V6s do not report these numbers is because dynos record wheel horsepower instead of crank horsepower. Any vehicle has what is called driveline loss, or the amount of power “lost” as the transaxle operates to get power to the ground. Typical losses are between 15% and 18% for MTXs, 20% to 25% for ATXs. We have documented what we call “factory freaks” which for some reason or another are gifted with more power than the rated 170hp.

Q: My Cougar is slow. What I can I do to make it faster?

A: First off, “slow” is subjective. The Cougar was built by Ford to be an entry level sport coupe on a basically dead platform (even in '99). The Cougar was never meant to hang with the likes of WRX STis or Lancer EVOs. It is, however, quick and agile for a domestic given its size and weight. The 2.5L V6 is a good mix of power and reliability, and responds fairly well to modifications. The three most common upgrades (and the first ones you should look at) are Intake, Headers, and Exhaust (see I/H/E in the Glossary). There are a myriad of choices for intake and exhaust systems, and which is “best” will be argued until the cows come home. I won't get into them here in this FAQ. Headers have two choices, MSDS and Weapon-R. The latter manufacturer sold a direct copy of the MSDS headers, but with stainless steel, and may require welding depending on your application. Weapon-R headers are no longer sold since an injunction was granted against Weapon-R by MSDS because of the design copy. MSDSs also come with all gaskets, bolts, and MIL eliminators to prevent CELs.

Q: Can I put a turbo, supercharger, or nitrous system on my Cougar?

A: Yes, but those modifications are out of the scope of this forum. See the “Forced Induction” forum for more details. If you call nitrous oxide “NOS” (NAAAAWWWS!), prepare to get flamed- Nitrous Oxide Systems (NOS) is one particularly shameless brand of nitrous systems, and not the only one that will work on our cars.

Q: How about larger fuel injectors? Bigger injectors make more power, right?

A: This is a very common and very mistaken assumption. I have to break this down into several parts, all are important, all work together:

First off, Engines 101 states that you need to maintain a stoichometric ratio of air to fuel (14.7:1, closer to 13.0:1 under WOT, lower for F/I) in order for the engine to efficiently burn fuel and extract the maximum amount of mechanical energy from the air/fuel explosion. Your ECU knows this, your ECU is coded with an injector constant to tell how long the ECU should keep the injector open (because it knows how much the injector will flow over a given amount of time- In the case of stock, it's 17 pounds (17#) of fuel (at 40psi) per hour.

Now- Slapping in larger injectors without changing the injector constant in the ECU will cause the engine to run rich, because the ECU doesn't know you've put in larger injectors. The short and long term fuel trims will max out (35%) and the ECU will trigger a CEL for running rich. Woo. Fun.

Larger fuel injectors are available for the car (even 42#/hr SVT Lightning injectors will fit), but the $20,000 question is “WHY”? The 2.5L Duratec is a very small displacement 6 cylinder engine, and the 17#/hr injectors that come stock with our cars support up to around 200-210 crank horsepower before they have to be held open for longer than is recommended per cylinder event. This is why the SVT Contour (same engine, hotter cams) got 19#/hr injectors to give an additional buffer of safety. 19#/hr injectors support up to around 250 crank horsepower.

Unless your run on a dyno while logging injector duty cycle shows more than 80% at high-RPM WOT, (and if you haven't done any of this, get the thought of changing injectors out of your head!), then you don't need bigger injectors. F/I cars (including nitrous) may need bigger injectors, but again- Leave it to the dyno log or the F/I kit manufacturer to tell you for sure.

Q: Then what about a bigger MAF?

A: Same thing. Bigger isn't better! Larger MAFs claim to add power, support larger injectors, and claim they are “calibrated” for a specific size injector. This is snake oil at its worst. The injector size is a constant written into the computer program of the ECU. All a “calibrated” MAF does is augment the signal from the MAF to the ECU and fool it into adding more fuel to match this “magic” new amount of air coming into the engine. Trickery! The better solution (if you really MUST have a larger MAF) is an SVT Lightning MAF and a chip programed with the correct air/fuel tables and injector constant. Completely, utterly, and TOTALLY useless for all but the most radically modified 2.5L engines.

Q: I've heard that the Cougar is the same as a Contour, and that you can get better parts from the Coutour SVT. My Cougar is a Mercury. Is this right?

A: Yes. The Cougar is built on the same platform as the Ford Contour. Therefore, it is about 75% identical parts as the Contour. The Contour SVT is the performance version of the Contour, and its 200hp 2.5L Duratec V6 has many parts that transfer over directly to the Cougar V6. See the “SVT Upgrades – By Request” stickie thread.

Q: What spark plugs are the best for my engine?

A: Motorcraft AGSF32PP or AGSF32PPM (formerly AWSF32FS) Double Platinum spark plugs or the equivalent Autolite APP104 (APP764 is discontinued but will work) Double Platinums. Due to our cars' DIS, both anode and cathode need to be platinum or platinum plated. To reduce emissions (especially when cold) our spark plugs fire in pairs (one cylinder on the compression stroke and one on the exhaust stroke) to re-burn any remaining unburnt air/fuel mixture. Therefore, while one plug is firing anode to cathode, the other is firing cathode to anode. Use of non-double platinum plugs will greatly reduce the life of the plug and may lead to drivability issues and misfires.

Q: What do I gap my plugs to?

A: The sticker on the underside of your hood lists the specifications for spark gap. For normal double platinum plugs, gap between .052″ and .056″. My inclination is to gap low so that the plug can wear without immediately going out of gap tolerance.

Q: What is the difference between “return” and “returnless” fuel systems? Which do I have?

A: Cougars built before 5/9/1999 had two lines connected to the fuel rail- One supply line from the fuel tank, and a return line for any unused fuel. The fuel pumps in return-style cars simply supply a constant pressure to the line, and fuel rail pressure is controlled by means of a vacuum controlled diaphragm (the FPR). After 5/9/1999, Cougars were produced with only a single feed to the fuel rail, and a computer controlled fuel pump. Instead of a vacuum FPR, a sensor sits on the fuel rail and the computer commands the fuel pump to supply pressure under different load conditions. Because of the added stress of this system (and perhaps other filter factors, etc), fuel pumps in returnless Cougars have had reliability issues and may fail to keep up with demand first under WOT conditions, then gradually getting worse until the car runs lean and stalls.

Q: My CEL came on. What's wrong?

A: Hard to say. Your ECU has flagged an error, but you can't tell what's wrong until you retrieve the code from the computer. You can use any OBDII-compliant scanning tool (such as Autotap), or some auto parts stores like Auto Zone will scan the code for you for free. The dealer is also available to scan the code, but the expense of repeated diagnosis is usually prohibitive.

Q: Can't I pull CEL codes out of the on-dash diagnostics mode (Pressing “Reset” and “Units” together, then turning the key)?

A: Nope. The in-dash diagnostics mode does not pull DTCs from the ECU. It only displays various (and fairly useless) lesser codes such as the infamous DTC 9318 (low voltage) and 9201 (fuel sender circuit malfunction).

Q: My CEL started to flash and I lost power. What's wrong?

A: A flashing CEL indicates excessive misfires. Your engine should be turned off and the vehicle should not be driven until you seek professional diagnosis and repair.

Q: I keep receiving a CEL about “EGR flow Insufficient” or “EGR Flow Excessive”. The valve is working fine. What's wrong?

A: See DPFE in the glossary. The sensor that measures EGR flow is most likely bad.


ATX: Automatic Transaxle

CEL: Check Engine Light (see MIL)

Detonation: (see Pinging)

DIS: Distributorless Ignition System

DMD: Dual Mass Damper. A type of harmonic balancer that contains a second mass that is tuned to dampen harmonics at higher RPMs. The Cougars came standard with a single mass damper that can be replaced with a DMD available from Ford or Ford resellers. Many report improved N/V/H and may reduce wear of the engine over time.

DOHC: Dual OverHead Cam. Engine design in which pushrods are no longer used- Instead, the cams sit on top of the valve assembly and the cam lobes push down on the RFFs, causing the valve to open. A more efficient design, can take more revs, but lacks the pushrod “punch” you may hear about.

DPFE: Differential Pressure Feedback EGR. This sensor detects pressure differential across two points on the EGR feed tube to ensure the proper operation of the valve. Common cause of “EGR flow Insufficient” or “EGR flow excessive” CELs

DTC: Diagnostic Trouble Code. The error code flagged by the ECU and turns on the MIL

ECU: Engine Control Unit. The vehicle's main engine computer

EEC-V: The Electronic Engine Control, fifth generation. Our cars' ECU

EH: Extrude Honing. Process by which abrasive putty is pushed through an air passage (be it UIM, LIM, or intake ports on the heads) under high pressures to smooth out to imperfections in the inner surfaces. Allows for better airflow

EGR: Exhaust Gas Recirculation. Valve that allows the engine to control cold emissions and to moderate pinging in the event of cylinder overtemperature

FAQ: Frequently Asked Questions (You're reading it!)

FPR: Pressure Regulator

HLA: Hydraulic Lash Adjusters. Our cars' version of lifters. Takes up the slack in the valvetrain by means of an oil pressure controlled cylinder designed to ensure the cam lobe always fits snugly against the RFFs.

IACV: Idle Air Control Valve. Cylindrical valve mounted on the rear of the UIM. Controls idle air flow

IMRC: Intake Manifold Runner Control. Also called “secondaries”, this is the control system that opens up the second set of 6 intake runners in the LIM when the engine reaches around 3400RPMs. It allows the engine to breathe through the entire manifold, increasing power

I/H/E: Intake/Headers/Exhaust. The most common mods to our engines to net additional power

LIM: Lower Intake Manifold

LSD: Limited Slip Differential

MAF: Mass Air Flow. Term used for the Mass Air Flow sensor that sits between the filter and throttle body. Electronically measures the rate at which air is coming into the engine

MIL: Malfunction Indicator Light, also called the CEL. The ECU flags this light to come on if it detects an error while the car is in operation

Moosing: “Honking” sound caused by resonance in the vehicle's intake system at idle. Usually caused by a defective or failing IACV

MTX: Manual Transaxle

N/V/H: Noise, Vibration, and Harshness. Term used to show the effects on driveability, ride comfort, etc.

Pinging: Sound caused by the premature explosion of the air/fuel mixture, like the sound of a can of spray paint being quickly shaken. Also called detonation, a dangerous condition that can be caused by overheating of the engine and can lead to cylinder or valve failure

P&P: Port & Polish. Method by which the cylinder heads are reworked to allow additional airflow into the cylinders for more power

RFF: Roller Finger Followers. Our cars' version of rocker arms. The RFFs sit between the HLAs and valve stems and provide the opening motion of the valve when struck by the camshaft lobe

SVT: Ford's Special Vehicle Team. Ford's division for specialized higher-performance cars

TB: Throttle Body

UIM: Upper Intake Manifold

WOT: Wide Open Throttle

Please PM me for any additions or corrections you would like to see on this FAQ. Despite my many assertations to the contrary, I am not infallible, and may have missed something.