5 Symptoms of a Failing CP4 on a 6.7 Powerstroke

5 Symptoms of a Failing CP4 on a 6.7 Powerstroke: How to Fix

The CP4 high-pressure fuel pump is a known problem for various Ford Powerstroke and GM Duramax diesel engines. 

In this article, we are going to help you narrow down the symptoms which lead to a failed CP4 and help you fix the problem for good.

If you come across the symptoms listed below, you will need to first do a few check-ups such as testing your Powerstroke standard fuel rail pressure and then proceeding to replace or rebuild the CP4. 

Many specialists believe that the best thing you can do is replace the CP4 and the rest of your entire fuel system, which could cost you upwards of $10,000. 

Moreover, if you are only getting a few of these systems, be sure to stop the car immediately before your CP4 fails completely 

As this is a rather complicated repair that involves extensive mechanical and diagnostic experience, it’s best to leave it all to a professional. 

All in all, the quicker you get to the bottom of the problem, the better it will be for your car and your bank account.

What are the symptoms to detect a failing CP4 on a 6.7 Powerstroke Engine?

  1. Sputtering At High Speeds, Stalling & Power Loss
  2. Reduction of Fuel Efficiency & Gas Mileage
  3. Engine Starting Difficulty
  4. Engine May Surge Or Fail To Fire Up
  5. Rise In Temperature & Rattling Noises

Sputtering At High Speeds, Stalling & Power Loss

As the high-pressure fuel pump fails to deliver the correct amount of fuel into the engine, the engine starts sputtering. 

This can most easily be felt at high speeds as the engine pulling power becomes inconsistent and unnatural. 

This will also likely lead to significant power losses throughout the rev range, especially at higher RPMs, while towing, or going up a steep slope. 

If the fuel pressure becomes really low, there is a great deal of chance that your engine will cut off and the car will stall.

A CP4 failure is also linked with transmission fluid leakage which can occur due to problems with the fittings on the transmission fluid filter.

Reduction of Fuel Efficiency & Gas Mileage 

The high-pressure fuel pump is not just there to pump gas uncontrollably into the engine as it is also tasked with making the entire fueling process more efficient, which leads to better fuel economy.

As such, if the fuel pump isn’t able to operate as it should, it is likely going to lead to subpar fuel efficiency and a much lower estimated operational range.

This problem typically leads to the fuel pump pushing more and more fuel into the engine and thus creates a significant disbalance between the air and fuel entering the combustion chamber.

Understandably, pushing more fuel into the engine can create all sorts of problems, which is why this should be dealt with as soon as possible. 


Engine Starting Difficulty 

An engine not starting is a dead giveaway that something is terribly wrong with your Powerstroke, but the problem here is that there are numerous reasons why that could take place.

Regarding the CP4 pump, if it isn’t able to provide fuel into the engine at all, or in really minimal amounts, there will be no combustion, which means that the engine will fail to even engage at all.

Even if the engine does kick into life, it is not likely going to run smoothly or evenly and could stall and refuse to kick in, which could repeat this entire circle until the amount of fuel entering the engine becomes negligible. 

Engine May Surge or Fail to Start Up

Engine surging caused by the CP4 pump is also fairly common and can be most noticeable while accelerating, such as entering an on-ramp or while overtaking. 

If you happen to be towing or going up a steep slope, even minor acceleration inputs will be met with stark resistance. 

Once again, issues such as these are backed by, or will eventually be backed by all the other symptoms of low fuel pressure such as engine stalling, sputtering, or not wanting to engage at all.

Rise in Temperature & Rattling Noises

The last two symptoms we are going to mention are rattling noises followed by a potential rise in engine temperature. 

The lift pump (low-pressure fuel pump) sends fuel into the CP4 pump. 

If the CP4 is malfunctioning, you will be able to tell if you just listen to the lift pump.

If you hear the lift pump sounding inconsistent, loud, or not at all, it obviously isn’t able to do its job properly and is likely pulling air.

Also, if you see your engine temperature rising, it could also be due to problems with the CP4 pump not being able to provide the correct amount of fuel and thus leading to changes in the combustion process.

What causes a CP4 to fail on a 6.7 Powerstroke? 

  • Lack of Proper Lubrication and USLD Fuel Usage
  • Air Bubbles Inside the Housing
  • Bad Fuel Additives
  • Low-Quality Fuel

Lack of Proper Lubrication and USLD Fuel Usage

According to a recent CP4 fuel pump class action lawsuit, the main problem that’s causing the CP4 pump to fail is the lack of lubrication and ultra-low sulfur (USLD) fuel that is currently available across the USA. 

USLD fuel is much better for the environment, but it isn’t optimal for the CP4 pump as it does not enable it to lubricate itself as well as with fuel mixtures with higher levels of sulfur. 

As the CP4 lubricates itself with diesel fuel, if the supply of high-quality diesel isn’t consistent, it is going to lead to problems with the pump. 

Air Bubbles Inside the Housing


When diesel fuel is pumped out of the tank to the engine, really small air bubbles are worked into the viscous liquid itself. 

Inherently, diesel fuel is higher in viscosity compared to gasoline, which is why these bubbles can’t reach the surface as easily. 

When the low-pressure pump starts pumping diesel from the bottom of the tank, it sucks those bubbles as well, which in turn interrupts the flow of fuel entering the CP4 pump.

Bad Fuel Additives 

Using improper fuel additives could also lead to CP4 problems, especially additives such as DEF (Diesel Exhaust Fluid). 

DEF is denser than fuel, which is why it travels to the bottom of the tank almost immediately. As the low-pressure fuel pump sucks fuel from the bottom, it is going to suck in these additives.

This can be salvaged if you clean the tank, and do everything in due time. 

However, if you fail to do so, DEF is going to start crystalizing and clogging the injectors, which can cause major damage including the CP4 itself.

Low-Quality Fuel

Low-quality fuel is brimming with all sorts of contaminants, including water, small metal shavings, asphaltenes, dirt, and whatever else finds its way into the fuel.

If such fuel starts entering the CP4 pump, it is going to prevent lubrication and will likely lead to issues down the line, especially if some of your fuel filters become clogged or partially clogged along the way. 


How to Fix 6.7 Powerstroke CP4 Failure

When you encounter any of these symptoms, you first need to do a few check-ups to see what is exactly causing the problem. 

Therefore, be sure to follow our guide listed below.

Check Your Fuel Levels

Well, none of this makes no sense if the actual problem is down to low fuel levels, so be sure to have at least ¼ of the tank filled with high-quality diesel fuel before doing any of this.

Inspect the Fuel Filters & Replace the Filter, If Required

Low-quality fuel, improper additives, or USLD fuel can all lead to clogged fuel filters, which is why you should first look at your fuel filters for any signs of contaminants, especially small metal shavings.


If that is indeed the case, you will have to replace the fuel filters and try again after priming the fuel system correctly. 

After replacing the fuel filters, turn the ignition on and wait for 20-25 seconds before the system primes itself, and then start the car up.

Do a Data Reading Test With the OBD Testing Tool

Be sure to acquire a decent OBD-II scanner or take your car to a  workshop in order to diagnose it for any faults and improper fuel system delivery readings.

Crank the car up, and check the standard fuel rail pressure, which should be between 4000 PSI and 5000 PSI. 

If your actual readings are much lower than that, your CP4 is struggling to provide enough fuel to the engine. 

Fix Your CP4 Pump

If the readings show that your CP4 pump isn’t working, you will have to either rebuild it or replace it with a new one. 

If the CP4 pump on your truck isn’t too old or too beat up, you can go for a CP4 pump rebuild kit, which includes all the stuff you need to get it done. 

However, it is often better to go for a brand-new CP4 as the differences in price aren’t huge.

But newer CP4 pumps use ceramic for the components that fail most often, which means that these are more dependable and should last longer.

The big kicker here is that most specialists recommend replacing the entire fuel system as even a thorough clean isn’t going to get rid of all the contaminants, especially the metal shavings.

This means that even if you replace the CP4 pump, there is a good deal of chance that the issue is going to return soon enough.

It is recommended to replace all of these components:

  • Fuel Rails
  • High-pressure Lines
  • Injectors
  • Overflow Valve
  • Return Lines
  • Fuel Tank

How much does it cost to replace a 6.7 Powerstroke CP4?

The costs of replacing just the CP4 on a 6.7 Powerstroke will cost you around $1,500 to $2,200, while a rebuilding kit typically costs between $1,500 and $2,000.

Replacing all of the fuel components, as recommended by most specialists, could raise the total bill (with labor costs included) up to $10,000 to $15,000 which sure is extremely worrying as that can sometimes be more than the truck itself.

How do you prevent 6.7 CP4 failure?

After familiarizing yourself with how immensely costly it can be to repair this problem, you should focus all of your attention on preventing it from ever taking place.

We do need to mention that you can’t permanently solve this problem as most mechanics deem it to be an inherent issue of the CP4. Either way, if you do take proactive action, you might avoid the brunt of the impact. 

Only Stop at Reputable Fuel Stations with Higher Grade Diesel Fuel

Low-quality fuel is the silent killer of the CP4 pump, which means that the longer you use low-quality fuel, the higher the chances of a premature CP4 pump failure.

Change Your Fuel Filters Frequently 

Skiping on your regular fuel system maintenance is not recommended for a wide variety of reasons, but skipping on replacing your fuel filters whenever needed can lead to a premature CP4 pump failure. 

Also, even if you do replace your fuel filters in due time, make sure to always use OEM or a quality aftermarket filter. 

Use Quality Recommended Diesel Fuel Additives 

One way to countereffect low-grade diesel is to use a high-quality fuel additive that is specifically designed and tested for the Powerstroke engine. 

Granted, this also isn’t a guarantee that your fuel pump is not going to fail, but it has been proved that a quality diesel additive can only help your CP4 to better lubricate.

CP4 Bypass Kit 


One of the best things you can do is to invest in a reputable CP4 Pump Bypass Kit or a so-called disaster prevention kit, which is used to redirect the fuel back into the tank for it to be flushed by your filters twice before entering the CP4 pump.

This will help with trapping all the notorious little metal shavings within your fuel filters as opposed to some of your more critical fueling components.

Even if you go for the world’s most effective CP4 Bypass kit, it won’t do you much good if you don’t replace your fuel filters regularly. Some even believe that you need to replace your fuel filters even more regularly if you go for a bypass kit.

CP4 to CP3 Conversion Kit


One of the more expensive things you can do is replace your existing CP4 pump with the older CP3 pump, which many believe is two times more reliable at the very least. This makes sense only if your truck is out of warranty.

Lift Pump

A high-quality lift pump (low-pressure fuel pump) can help alleviate most of the issues the CP4 suffers from as it excels at removing air from the system.

This not only provides a steadier stream of fuel but also minimizes the chances of contaminants getting stuck anywhere within the system.