Dyno day

Published in the June 2009 Issue June 2009

Dmax Tech Ballooned Up Pipe

A chain is only as strong as its weakest link, right? So is a modified diesel engine. It seems that no matter how much you do to an engine or powertrain, something else will fail when you increase power output. This expanded up pipe from a Duramax LLY engine shows what can (and most likely will happen) when cylinder drive pressures become too high to be contained by factory parts. To prevent this from happening (which you shouldn't ever run into unless you're shooting 300-horse nitrous shots into an 800-horse engine), you need to address engine rpm and turbo configuration.


Cummins Tech Injector Deals

There are two things that can cause a normal injector nozzle swap on a late-model 5.9l or 6.7l cummins to go horribly wrong.

Overtightening the electrical connector nut to the terminal post on the top of the injector can cause the post to break off. On the 6.7l injectors, there is a small metal puck between the nozzle needle and the injector internals that can come out with the removal of a nozzle and then fall off at the worst possible time. There is no fix for a broken terminal post and there's no part number for the small puck. If either of these scenarios happens to you, well, it sucks to be you. you'll have to buy a new injector, which retails for just less than $1,500 at your local Dodge dealership.

Dowever, don't make the drive to the parts counter just yet. You can order the same replacement injector from Cummins through an over-the-road truck service center, often found near large truck stops. These centers often service and sell parts for peterbilt and other Cummins-Powered Heavy-Duty diesel trucks, but can order parts for any Cummins engine. with a core exchange, you're looking at closer to $500 for a new injector. That's a lot of cash to fork over for a stupid mistake, but it beats paying a thousand more for the same part at a dealership.

If you need to order a new injector, you'll need the engine serial number and the bad injector for the core exchange. How do we know all of this? Don't ask.

PSD Tech

How about a crash course in how to test your 7.3l power stroke's glow plug relay?

It may be late spring or early summer when you're reading this, but now is the perfect time to test that glow plug relay before cold mornings come back around and you find yourself with a truck that won't start.

The glow plug relay is found atop the engine on the passenger side, mounted just above the valve cover. On the late 1999-2003 trucks, there will be two relays that look identical. The glow plug relay is the one on the backside, closest to the firewall. You'll see two large posts and two small posts on top of the relay, each with some wires attached to them.

The large post on the passenger side of the relay should be seeing 12 volts at all times. It is connected direct to your batteries. So it is the "hot" side of the relay. The large post on the opposite side of the relay will be the "relayed" side, which is the side that is connected to the glow plugs. When the key is turned on, the relay should send power to this post, which in turn sends power to your glow plugs, allowing them to warm up and heat your cylinders.This side of the relay should see the equivalent voltage the "hot" side is seeing, for anywhere from 30 seconds to two minutes. It will then click off and power will no longer be sent to the glow plugs.

Testing the relay to see if it is functioning properly is simple. it can be done with a voltmeter or even a test light; however, we prefer to use the voltmeter. Ground your voltmeter to the truck and test the "hot" side of the relay with the key off. You should be seeing 12 volts or whatever voltage your batteries are storing, while the "relayed" side should not see any voltage at all.

Now, have someone turn your ignition on (don't start the truck) and test the opposing side of the relay. It should now be seeing the same voltage as the "hot" side. If the voltage is lower or there is no voltage at all, you've got a weak or bad relay and it will need to be replaced.

You should be able to find these relays at just about any parts house.


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