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Diesel Tech Questions: weird shifting, steering wobble and more.

Top Tech: You've Got Questions? We've Got Answers!

Bruce W. Smith
Jan 6, 2017
Photographers: Bruce W. Smith
Photo 2/5   |   Super Duty 4x4 front axles turn even when the hubs are unlocked. If a bound-up or rusted U-joint gets in the right position while cornering, it’ll cause the axleshaft to bind, which results in a violent shaking of the steering wheel.

Mystery Steering Wobble

I’ve got more than $1,000 invested in trying to chase down a steering wobble on my ’10 Ford F-250 4x4. I’ve replaced the ball joints and steering linkage, checked the front axle U-joints, and even replaced the steering box. But the wobble of death is still there when I’m going through a turn at speed in two-wheel drive. It doesn’t happen all the time, but when it does, it’s scary as hell! What have I overlooked?
C. Langford
Greenville, South Carolina
This is a problem that’s been cropping up more frequently on ’99-and-newer four-wheel-drive Super Dutys as they approach 100,000 miles on the odometer. How did you check the front-axle U-joints? Did you put a small prybar on each U-joint to see if it has any slack? That’s the typical old-school check. We suspect your Super Duty could actually have a frozen U-joint, so the joint will not move when you do the typical check.
GOS Performance has seen more than 20 Super Dutys in 2016 that have the same death wobble your truck is exhibiting. The cause of each one, according to owner Aden McDonnell, was a rusted U-joint.
“Super Duty front axles turn even when the hubs are unlocked,” Aden says. “If the frozen U-joint gets in the right position while cornering, it’ll cause the axleshaft to bind. The result is a violent shaking of the steering wheel. A quick way to confirm a U-joint is the cause is to lock the hubs, switch to 4Hi, and see if the cornering wobble gets worse. If it does, that points directly to a frozen front-axle U-joint.”
The fix: Replace the axle U-joints on both sides. Better yet, if room allows, replace them with ones that have Zerk fittings instead of the greaseless stock versions that created the problem.

All Locked Up

This morning, my buddy’s ’05 Chevrolet Silverado 2500HD’s automatic transmission suddenly locked in First gear. The first sign of trouble was the ABS warning light appearing on the dash, and a few minutes later the unit stopped shifting. All the fluid levels (oil, brake fluid, and transmission) are full. The truck has 370,000 miles on the odometer, so it’s not in great shape. Any recommendations or idea what happened to it?
Mark R.
Amelia, Virginia
When an antilock brake system–related code is triggered and the transmission is not shifting properly, it usually indicates there’s a problem with the vehicle-speed sensor. The ABS relies on communication with the speed sensor and the Allison transmission to function properly. Because both systems are exhibiting an issue at the same time, our first instinct would be to look at the common denominator: the speed sensor.
Photo 3/5   |   Sometimes, aftermarket EGR coolers on 6.7L Cummins engines will throw a P2457 diagnostic trouble code, indicating the cooler isn’t doing its job. In actuality it is—just not to the exact degree the OEM computer likes. One trick to overcome the code-throwing is to solder a ¼-watt 10 K ohm resistor (brown, black, orange, gold bands) to the brown and white wire that comes out of the EGR orifice temperature sensor.

Cooler Resistor

One problem fixed, another rises. At least that’s what’s going on with my ’08 Dodge Ram 2500. I replaced the plugged factory EGR cooler with an aftermarket version. Now, 200 miles later, the check-engine light comes on and a P2457 diagnostic trouble code is triggered, which appears to be “EGR Cooling Performance.” It’s a new cooler and the readouts on my Edge Products monitor show the air intake is between 195 and 220 degrees (where the exhaust gas enters the intake) and coolant temperature is 195. Those are normal. So, what’s the issue here? Nothing else was touched when the new cooler was installed.
Rodney L.
Colorado Springs, Colorado
The ECM doesn’t like anything temperature-related to be the least bit out of factory specifications. The exhaust gas being recirculated into the intake for a re-burn is too hot, according to its set of parameters. “Too hot” could be just a few degrees outside the limit that throws the code.
The reason the aftermarket cooler is causing the code to fire is it probably has larger exhaust passages and is a little too efficient on letting exhaust gas flow through its core. The downside of this is that the exhaust is not staying in contact with the cooler’s walls long enough to make temperature low enough to satisfy the computer.
Mat Johnson, one of the diesel technicians at Mobile Diesel Service (541-459-8939) in Sutherlin, Oregon, says they solder a ¼-watt 10 K ohm resistor (brown, black, orange, gold bands) to the brown/white wire that comes out of the EGR orifice temperature sensor. “The resistor lowers the overall temperature readings the computer sees by slightly lowering the voltage in the wire heading back to the computer,” Mat explains.
“We haven’t seen the hotter recirculation gas going back into the intake make a noticeable difference in overall engine performance,” Mat says. “It’s just enough to trip a P2457 code. The resistor solves the problem. It’s either that or replace the aftermarket cooler with a stock one.”

Quirky Allison

I’ve got an ’03 Chevrolet Silverado 2500HD with a 6-inch lift, 35-inch tires, ATS Diesel Performance Aurora 3000 turbocharger, and a Pacific Performance Engineering programmer. The truck is fast. But now the transmission is acting really weird, and I’m hoping it’s not toast. It has started to shift erratically, sometimes hanging, shifting really hard, or shifting too early. I pulled the pan off and the fluid looks and smells like new. The filters are new, and the screens are clean. The weirdness doesn’t happen all the time, and there aren’t any diagnostic trouble codes.
Zach Taylor
via the Internet
Having good tools and a technician who knows how to use them can save you a bundle of money. We suspect the problem isn’t with your Allison five-speed automatic, but rather with the ignition switch on the steering column. Yes, this sounds odd, but one of the mechanics a McDonnell’s Automatic Transmission Specialists in Livingston, Montana, says he sees this shifting issue frequently on older Chevrolet and GMC trucks.
Our ATS contact says the transmission control module in the Allison unit is very sensitive to any type of voltage fluctuation. When the contacts inside the ignition switch begin to wear out, they can intermittently cut power (drop voltage) to the TCM while the vehicle is being driven down the road.
This power interruption can be for a fraction of a second or last several seconds, and it has no impact on the operation of the rest of the truck, so the driver has no clue what’s happening. But that voltage drop/loss really messes up the TCM.
Every time the voltage to the TCM drops, even for a fraction of a second, the transmission goes into a full reload process and is relearning all the shift parameters. This results in the transmission operating normally for days or weeks. Then, all of a sudden, it begins shifting strangely.
A data logger will identify any voltage fluctuations between the ignition switch and the TCM.
Photo 4/5   |   Check the heater core return line on your ’04-to-’07 Super Duty to make sure the heater core hose/tube that crosses the firewall isn’t ready to pop a leak. It has a tendency to rub on the FICM. Rotating the hose/pipe slightly will provide clearance and stop the potential coolant leak.

Blown Heater Hose

I’m sitting here on the side of the road, waiting for AAA to tow my ’07 Ford Super Duty to the nearest shop. It puked gallons of coolant all over the engine and firewall—a total mess. It looks like the FICM rubbed a hole through the coolant hose running from the heater core. It never dawned on me to check it. I thought passing this along to DP readers could save them 100 bucks in lost time, coolant, and clean-up.
Richard Horner
Boise, Idaho
We appreciate the heads up. That’s one of those little preventive maintenance things that can easily slip by an owner. Anthony Youngblood says the heater core return line is one of the items Super Duty Service (816-548-6970) in Grain Valley, Missouri, checks on every 6.0L-powered Ford that comes into the shop.
“All ’04-to-’07 Super Duty owners should inspect the heater core hose/tube that crosses the firewall, because it’s prone to rubbing on the FICM,” Anthony says. “If I catch them early, I twist the hose on the coolant Y-pipe, thus giving a little clearance between it and the FICM. If the hose looks like it’s about to rub through and rupture, I will cut it at the rub spot and place a barbed hose connector there. If it's noticed during a cab-off job, I suggest the customer replace the hose because it’s easy to access.”

Persnickety Duramax

My ’95 Chevrolet Silverado’s 6.5L turbodiesel engine starts, runs for about a minute, and dies. Sometimes it will start right back up, run for hours, and then shut off, and it won’t start. Other times, it won’t start at all. There also are times when the engine starts and blows a lot of black smoke, which eventually clears out, then it runs great. I changed the pump-mounted driver and still have no results. It’s driving me crazy. Can you help?
Kirk Osterling
via email
Every engine, regardless of manufacturer, has an Achilles’ heel. The IDI 6.5L GM diesel’s nemesis is its wiring harness or the pump-mounted driver, according to Mark Gotchall at Oregon Fuel Injection. The company has a terrific diagnostic page on its website that covers diesel-related issues, including your Chevy’s intermittent stalling problem.
Here’s how the first part of the 6.5L PMD “No Start/Dies/Stalling” diagnostics reads: “This is often caused by a bad pump-mounted driver or fuel-control-solenoid driver. However, it is unusual to have multiple failures of the PMD. A bad fuel-control solenoid (part of the injection pump) can cause the same symptoms and codes. A bad EGR, EGR vent, wastegate control, and transmission solenoid are on the same quad driver circuit and can cause intermittent stalling.
“The PMD gets 12-volt power from a fuse when the key is on. The PCM then sends a signal to the PMD to close the fuel-control solenoid. When the solenoid closes, it sends a signal back to the PMD and that is relayed to the PCM. The response time of the closure signal is called C-time. “C-time should change slightly when the engine is accelerated or decelerated. A fixed C-time can indicate a bad fuel-control solenoid. If the C-time is erratic when the rpm is stable, that’s usually an indication of a bad PMD.”
Photo 5/5   |   Knowing if a turbo is functioning properly isn’t easy to tell unless you can monitor the boost—and know what pressure is normal and what isn’t for that application.

Weak Turbo

I have a ’98 Chevrolet Silverado 2500HD. This is probably dumb to ask, but I think the turbocharger is not performing. How do I test its performance or know if that is the problem? I bought the truck a few months ago for work, and now it doesn’t accelerate well.
Mark Ortiz
San Gabriel, California
No question is dumb. Knowing whether the turbocharger is functioning properly isn’t easy to tell unless you can monitor the boost—and know what pressure is “normal” and what isn’t. The best advice here is to take your truck to a local diesel shop and have technicians give the 6.6L Duramax engine a quick checkup with their diagnostic tools. They can tell right away if the turbo is working the way it should be.
It’s also good to have a way to monitor boost and EGT while you are driving, especially with a truck used for work and towing. There are several really good aftermarket monitors that provide real-time data. If you go that route, have the installer show you how to use and understand the different readings. Knowing what is happening under the hood pays big dividends down the road, including knowing if the turbo isn’t performing the way it should.

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