35. After finishing the installation, Derks fills the transmission with TranSynd fluid and road tests the truck to verify that everything is operating properly.

Fuel Filters & Cold Weather

As you’re probably aware, it’s been cold here in the upper Midwest this winter. My truck began setting the trouble codes P0089 and P0093 during the most recent cold spell that included below zero temps, and then it would barely move. My question is, does the cold weather affect the fuel injection system? What can I do to prevent these sorts of problems?


Ralph Brown
Green Bay, WI


Thanks for your questions, Ralph. While this column is appearing in the magazine just as the spring temperatures arrive, it would he helpful to re-read this some months from now as we all prepare for another winter.

First the codes…

P0089 Fuel Pressure Regulator (FRP) Performance
P0093 Fuel System Large Leak Detected (2001 model year or P1093 for newer trucks).

Both of these codes are related to a problem with fuel rail pressure. The difference between the “commanded” and “actual” rail pressures must not exceed 20MPa (Mega Pascals), which is about 2,900-psi, or a trouble code will set and “limp mode” will occur. When limp occurs, the accelerator pedal will feel somewhat dead and vehicle speed will be limited to something in the 20-30 mph range. All of this is designed to limit damage to the engine and drivetrain when a significant problem occurs.

Not achieving the desired fuel pressure could be due to any one of several fuel system components. Here’s a list of the most likely suspects:

-Simply out of fuel.
-Restricted fuel supply, such as a blocked fuel sock in the tank, kinked fuel hose or plugged fuel filter (debris, gelled fuel, etc.).
-Defective rail pressure relief valve that bypasses too much fuel.
-Defective rail pressure sensor.
-Fuel pressure regulator.
-CP3 fuel pump.
-Bosch high-pressure pump.
-Worn out injectors, which bypass too much fuel back to the fuel tank. This is why the diagnostic trouble code indicates a large fuel leak. It’s not about an actual leak that might produce a puddle beneath your truck.

Always change your truck’s fuel filter when any rail pressure related codes appear. While manufacturers currently recommend a 15,000-mile replacement interval, you can get a contaminated tank of fuel at any fuel stop. Be prepared to change your truck’s fuel filter while away from home by carrying a spare filter along with any tools you might need. Your truck’s owner’s manual contains a fairly complete set of instructions for changing the fuel filter. I recommend practicing at least once when the weather is nice and you have plenty of time.

The above list in arranged from the least expensive fix to the most expensive. Always eliminate the cheap and easy before suspecting something more serious or expensive. If this is an out of warranty repair, insist that the mechanic follow this advice.

Somewhat like motor oil, the viscosity of diesel fuel will vary as a function of temperature—thinner when hot and thicker when cold. A P0089/93 code that occurs when it’s cold outside is not duel to worn out parts. On the other hand, if these codes appear only on hot summer days when you’re working the truck you can assume that the cause could be due to worn-out parts.

Cold diesel fuel can have a harder time making its way through a partially plugged fuel filter, and is why changing the fuel filter should be your first step in the troubleshooting process. Do it in the fall when it’s still relatively nice outdoors. It’s a tougher job when the thermometer is below zero. I know this from experience…

Bigger Intercooler = Less Torque?

I’m currently considering installing a larger aftermarket intercooler in my 2002 F-350 7.3L Power Stroke. Being a performance gas engine builder for many years, I fear that a larger intercooler might shift the power curve to a higher rpm like what happens when a high-rise manifold is installed on a gas engine. Plus, I’ve heard about a loss in low-end power when equipping the truck with a larger intercooler.

I use my truck almost exclusively for towing and wish to maintain the low rpm torque curve. If the larger intercooler does move the torque curve to a higher rpm, perhaps a water-methanol injection system would be a better choice.


Phil Watanabe
Via Email


Phil, most diesels run without a throttle restriction plate that gas engines have. Diesels are able to inhale their cubic inch displacement in intake air every second revolution. Gas engines don’t unless they are run wide open. So… this means that many performance rules for gas engines don’t necessarily apply to diesel engines—including changing the air intake volume.

For a diesel, increasing the volume of the intercooler does two things, all else being equal. 1- More volume slows the boosted air transit speed through the intercooler system, which can make the turbo a little less responsive and a little slower to produce boost pressure. If your truck is used primarily as a town vehicle, the minor increase in turbo lag could cause a little more smoke in a stoplight-to-stoplight situation. 2- Slowing down the turbo boosted air transit speed through the intercooler will improve heat transfer and make it more efficient. This should provide a slight increase in towing performance while on the highway—just what you’re looking for.

In reality, the various performance-oriented intercoolers now being offered won’t seriously affect around-town performance, but you should experience a noticeable improvement while towing heavy trailers up steep grades. In general, every additional 10 degrees F you lower the turbo-boosted air, your truck’s engine will produce an additional 1 horsepower. A factory intercooler can reduce boosted air temperatures by up to 200 degrees… that’s 20 horsepower. A performance intercooler will give you a few more horsepower when you need them most.

I’ve experimented with water and water-methanol injection as a way to augment an existing air/air intercooler in a diesel pickup I once owned. By itself, water or water-methanol can be as effective as a good intercooler in reducing the turbo boosted air temperature. When combined with an air/air intercooler, water/water-methanol doesn’t lower temperatures much at all. The downsides to water/water-methanol injection are the required daily maintenance, the cost of the water-methanol solution and a loss in bed storage space.

There are exceptions, but in general only those truck owners who use their truck for competition or equip their truck with multiple turbochargers will see a worthwhile advantage when using water/water-methanol injection when compared to a simple air/air intercooler. In short, engines running with extraordinarily high boost pressures can benefit from additional methods that cool that boosted air. Most trucks closer to stock just won’t see a performance benefit that justifies the effort.

6.0L Head Gaskets

Guys, I need some advice. I have a Ford F-350 equipped with the infamous 6.0L diesel. Unfortunately, the engine’s head gaskets have failed yet again. I’m running a Banks SpeedLoader, cold air intake and 4-inch exhaust system. I replaced the original factory gaskets quite some time ago using ARP studs and Hypermax gaskets. Now, the head gaskets need replacing yet again. Is there a modification I can perform to avoid this? Like most, I’m on a budget and need a little help keeping costs within reason.


William Rencke
Via Email


The 6.0L Power Stroke has had its share of head gasket problems, mostly due to owners adding power and the engine’s use of just four head bolts per cylinder. To help improve head gasket durability, Navistar incorporated 14mm bolts, but larger bolts by themselves may not be enough when increasing power above stock. The aftermarket ARP 14mm head studs usually produce an improvement for most owners.

We’ve learned that some problems diagnosed as a bad head gasket were actually due to a cracked EGR cooler. The EGR cooler is cooled by engine coolant, and can become clogged with soot over time. A cracked EGR cooler can allow exhaust backpressure to over-pressurize the cooling system. This allows soot to contaminate the coolant, which might be incorrectly diagnosed as a leaking head gasket. Aftermarket stainless-steel EGR coolers are available that help reduce the likelihood of an EGR failure, and would be recommended.

I’ve had lengthy discussions with Ford performance people about stock 6.0L head bolts and head gaskets. They say that the factory parts usually survive most modest performance programming as long as that programming doesn’t advance the injection timing. Advancing the injection timing allows for a longer injection pulse-width to increase the fuel-rate and engine performance, without producing a late injection (more smoke). Unfortunately, advancing the timing puts more stress on the heads, head bolts and head gaskets. This also applies to the Duramax and Cummins, to one degree or another. So, my advice is to stay away from programs or devices that aggressively add timing and stay close to the Ford 6.0L power specs.

Included in the above link is a clickable list of Diesel World magazine stories that walk owners through a long-lasting repair for failing 6.0L head gaskets. Keep us posted about progress and ultimately how you resolved this most recent problem.

Diesel Backfire?

I have a 2001 2500 Dodge Cummins, which I acquired used with nearly 200k miles on the odometer. The first problem I had with the truck was due to a faulty throttle position sensor. I replaced that sensor, but for some reason it seems to produce a backfire when accelerating in second gear. I have noticed that the fuel lift pump doesn’t seem to function normally, such as when first turning the ignition key. Is this backfire due to not getting enough fuel?


Lee Mallory
Via Email


While it may not seem possible, a diesel engine can produce a backfire. I actually have a video showing a backfire at a diesel event, where the truck was running with nitrous oxide. This happens when raw diesel fuel mist injected into a cylinder doesn’t ignite until it reaches the hot exhaust manifold. A backfire can damage the turbocharger, so taking care of this problem should be a priority.

The electronically controlled Bosch VP-44 rotary fuel injection pump used by Dodge from 1998 through 2002 is somewhat sensitive to inlet fuel pressure. The stock electric fuel lift pump should supply approximately 8-12 psi of fuel pressure. A lift pump failure can affect both the reliability and life of the Bosch pump, as well as a symptom that could be interpreted as a backfire. Many owners have equipped their truck with a fuel pressure monitor to help them catch a lift pump problem before it results in a failure of the fuel injection pump.

A number of companies offer a way to monitor fuel pressure. One such vendor is U.S. Diesel Parts. These kits are fairly easy to install, and will illuminate a dash-mounted red LED at pressures of 5-psi or lower.

In addition, either the FASS fuel filter/lift pump combo or the BD lift pumps are popular alternatives to the factory lift pump. The FASS system incorporates a fuel filter as well as a lift pump. Additional fuel filtration can be a good idea for folks who have experienced contaminated fuel. Good luck. DW

If you like the Q&A series, here’s the previous post in the series: Tech Q&A Part #6

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