CP4 Fuel Injection Pump Preventive Maintenance

Original design CP4 fuel injection pump.

There has been a lot of discussion about the 2019-2020 Ram 6.7 CGI Cummins Turbo Diesel trucks that were equipped with the Bosch CP4 fuel injection pump. A few people have “the sky is falling” attitude, while most others are not concerned at all about the new for Cummins pump choice. When we were in Columbus for the Cummins 100th anniversary celebration in 2019, we were told by the engineers that the reason for the change was to reach the higher fuel pressures required for stricter emissions. This sounded reasonable, but as I have told my students and many of you at technical sessions during May Madness events, manufactures generally make changes for one of three things: emissions, fuel economy, or cost. I have to think that Cummins and Ram engineers were looking at all three. If you look at TDR issue 111, pages 34-39 the editor dude did a nice job of relating the experiences of former Chrysler engineer Steve Albu from an article in Hagerty Drivers Club written by Editor-at-Large, Aaron Robinson reminding us the tightrope auto manufacturers must walk when it comes to emissions regulations. The laws are essentially forced on them, and it then falls on the manufacturer to make a technology work, or pay the price.

CP4 Preventive Maintenance

Back to the question for the TDR audience that own the 2019-2020 6.7CGI engine: What preventive measures/best defense can you do?

1. DO NOT RUN THE TRUCK OUT OF FUEL! Yes, I’m yelling at you. Lack of fuel (no lubricity at all) can lead to certain disaster? Data is trending in that direction.

2. Keep the pump cool. Any engineer will tell you that as temperatures go up, lubrication is even more important to keep metal parts from scuffing. Try NOT to continually run the fuel tank near to empty before filling it. The more fuel in the tank, the cooler the fuel will be, and the cooler the CP4 fuel pump will run.

3. Lubricity. This is much talked about, and many of us just run clean #2 diesel. If you have a ’19-’20 CGI 6.7 Turbo Diesel engine in your truck it can’t hurt to add one of the commercially available lubricity additives to every tank. Just a little insurance to stack the odds in your favor.

4. Keep the fuel filters changed. Just like any other HPCR system, clean fuel is a must. Do your part and change the fuel filters at least every 15,000 miles. From my last filter change (Issue 111, page 107) you can see that the engine mounted fuel filter looked brand new at 15,000 miles. But I will continue to change the filters, regardless of what they look like, at the specified interval.

5. Keep the water out. Do yourself a favor and drain the filters once in a while. In TDR Issue 111, page 107-108 you can see the hoses I added to my truck to keep the mess down, and to easily capture a sample to check for water in the system.

As I pointed out in TDR Issue 106, page 111, only time will tell if the Bosch CP4 pump will prove reliable. It seems to have proven to be reliable in the EcoDiesel based on my unscientific dealer survey, but since Cummins has decided to switch back to the Bosch CP3 pump in late December 2020, it appears they believe it might be better for their customers to use the very reliable “old” pump.

All 2021 trucks are now shipping with a CP3 pump installed. A rumor floating around the internet is that a retrofit is coming for 2019-2020 trucks equipped with CP4 pumps, but I can find no credible evidence of that happening.

CP4 Examination

I was at a northern California dealer in December picking up some donation parts for the college when they asked me if I wanted a 6.7 CGI Cummins Turbo Diesel CP4 pump they had replaced. I figured this would be my chance to see for myself what kind of failure was happening, so of course I took it. When I got home, I promptly started taking it apart to check out the problem. The first thing I took notice of was it was one of the old style pumps as identified by the six drilled spots on the pump housing.

Original design CP4 fuel injection pump.
The multiple drilled dots indicate the original design pump.
The revised design from TSB 18-060-20 REV. A will have a single drilled dot in this same location. The number of dots on the old style pump is not significant, just that any pump with more than a single dot is not the latest style.

The Tear Down

As soon as I pulled the fuel control actuator, I noticed it was perfectly clean, but it smelled of gasoline. I kept a sample of the “fuel” from inside the pump, and tried another unscientific test. I put some on the bench and tried to light it. If you have ever tried to light diesel fuel, it is very difficult to do when not on a porous surface. The fuel from this pump caught fire quite easily. This appeared to confirm the pump was replaced because it was contaminated with gasoline.

You can see that there is no metal debris present, especially on the screen on the fuel control actuator where you will first notice metal debris when the pump is coming apart.

I continued to disassemble it and as you can see from the photos it was in perfect condition. I do not know how long the truck ran with gasoline mixed with the fuel, or the concentration, but it did not seem to harm this pump, which is alleged to be so easily damaged from lack of lubricity. I will leave it to you to draw a conclusion about the design of the Bosch CP4 pump but, personally, if I had one, I would follow the suggestions above and just drive it.

CP4 fuel injection pump cylinder show no scoring.
The cylinders showed no abnormal wear or scoring.
The pistons and rollers show no abnormal wear from lack of lubrication.

Stan Gozzi
TDR Writer

This article originally appeared in the Turbo Diesel Register, Issue 112.

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