Standardized Test Procedure

Trucks years affected: 1997-2002, perhaps earlier.

Symptom

Broad band noise related to engine speed. The problem is caused by the diesel engine injector module and varies with engine RPM.

Basic Navistar truck history and evolution of the diesel injector module

Model year 1997 (perhaps earlier) had a diesel injector module that was separate from the engine block, and was connected to the diesel injectors using a cable. This was called the three box system. It was composed of an Injector Drive Module (IDM), an Engine Control Module (ECM), and a Vehicle Personality Module (VPM). The fix for this system was the bolt in filter between the IDM and the injector harness. A second party vendor (Spectrum Controls) supplied a special IDM filter that was effective in suppressing the noise. The 1997 Navistar had the IDM located just below the windshield in the center of the engine area. This is where the IDM filter was inserted in-line between the IDM and the connecting cable. The Navistar International name for the IDM filter is: IDM RFI Filter Part number 1807378C1. I saw this work effectively on four inline 6 cylinder 1997 Navistar trucks with the 466E engine.

Starting in 1998, Navistar used the consolidated engine controller. This box took the place of the three boxes listed above. This system utilized the case of the engine controller module called the Navpac or Diamond Logic Controller for part of the circuitry, thus necessitating that the module be isolated from the engine block. It was housed in a die cast aluminum enclosure, and was electrically isolated from the block using rubber mounting spacers. These trucks also had large amounts of RFI energy. The solution to this problem was deceptively small. International supplied a 5 1/2" long piece of wire with a 1000 pF silver mica capacitor in series with two mounting lugs. Heat shrink tubing surrounded the capacitor for protection. Instructions were to connect this "filter" between the floating aluminum IDM housing and the engine block ground. I was skeptical about this working. However, It did bring the noise down to acceptable levels in most trucks tested.

Important assembly note

For maximum performance, this bypass capacitor assembly must be installed so that the capacitor is closest to the engine block, and that the short length of wire must then extend to the Navpac case. Also the mating surfaces must either be free of paint or have a star washer that can cut through the paint to make a good connection. I also use "Penetrox", "Noalox", or similar aluminum to copper electrical paste to give good long term corrosion protection on these electrical connections. This is available at many hardware stores.

The capacitor values supplied with this simple "filter" changed with the model years 1998, 1999, 2000, and 2001. The value supplied during the last year was 2200 pF at 500 VDC. They were all effective in noise reduction. Not perfect, but a big help. A very few trucks that would not respond to the application of a 1000pF capacitor are fixed by an assembly made out of a 2200pF and a 680pF capacitor is parallel, which gives a value of 2880pF.

I recently tested a number of new model year 2002 Navistar model 7400 trucks. This integrated design has an aluminum box on an isolated rubber mount, but the die cast housing is much closer to the cab. It is relatively hard to see because of other engine components. The newer 7400 Next Generation Vehicle (NGV) has the Navpac located further back on the engine which aggravates noise issues since it requires longer circuitry to the injectors. Thus it provides a longer antenna for the injector circuit. Despite the possibility of additional noise, my testing revealed that the noise levels measured at 47 MHz are consistently low, averaging around .6 uVolts of broad band noise. These numbers were obtained without any kind of external filter. I expect that no International support will be required for RFI issues with these trucks when used in the VHF Lowband region near 47 MHz.

Additional model information

The following data was sent to me by International. It discusses the single bypass capacitor. However, good information on engine RFI solutions for the 8 cylinder diesel trucks is also included.

For DOT trucks that have the I-6 and the consolidated engine controller located at the top of the engine block (Qsp's), they need to install the Int'l service part number 1833127C91 1000pF capacitor kit. For DOT trucks that have the I-6 and the consolidated engine controller located near the bottom of the engine block (NGV), there in not yet an approved fix.

For DOT trucks that have the V-8 and the consolidated engine controller, they need to install the Int'l service part number 1833127C91 1000pF capacitor kit. They need to invert the heater hose clamps that are near the engine controller so that the heater hoses do not ground out the floating controller. Also they need to install two ferrite beads at the valve covers to keep the injector noise from radiating out of the engine on the glow plug circuits . The cost for 500 pieces of part#0431173551 is $2050.94/K. They can be purchased from Fair-rite corporation. You will have to get with Engine group for the ferrite beads. There is also another part number for a type 44 ferrite that has a slightly larger center diameter for easier installation. For DOT trucks that have the V118 V-8 we are working on a quieter controller and harness set.

The T-444E engines have lower volumes in the Department Of Transportation (DOT) vocation and therefore have only provided a couple of complaints. Recommended fixes are similar on these engines. Adding the 1000pF bypass capacitor, reversing the mounting clamps for the heater hoses that are routed over the Navpac bracket so that the hoses do not ground the controller, and possibly the addition of a large ferrite bead at each valve cover to filter noise off of the glow plug circuits (coupled from the injector harness and re-radiated).

The newest engine in the International lineup is the V-118. This engine will use a new two box system consisting of a new IDM and ECM, and digital injectors. The injectors are digital and have two coils instead of their analog predecessor having one coil. They also operate at lower voltages and higher currents.

5/11/2002 RFI update

I received an email from Barry Coe, N9BNB at International regarding a hint:

" Hello Bill,

I just wanted to pass along a little helpful hint. If you are having problems getting an International Truck with the T-444E engine to pass the 1 micro-volt SINAD test, one should relocate the heater hoses by moving the P-clips to a plastic insulator that does not conduct. We have seen up to 300 ohms of resistance between the engine controller and the engine block (with the two connectors disconnected). This reading needs to be infinite to allow a bypass capacitor (typically 1000pF or 2200+680 in parallel) to function when it is placed between the engine controller and the engine block.

The key point is to disconnect both connectors to the engine controller and measure the resistance from the case of the controller to the engine block. The bypass cap will not work if the resistance is significant. We are seeing around 300 ohms contributed by the heater hoses with P-clips. I would expect that one can either use metal stand-offs from the lower bracket, or some insulator material from the bracket that the engine ECM is mounted on to support the heater hoses."

Barry Coe
N9BNB -. ----. -... -. -...
Development Technologist
Electrical Test / Electro-Magnetic Compatibility
(260) 428-3140
(260) 461-1653 fax

International Truck and Engine Corp.
Truck Development and Technology Center
Mail Bin 18
2911 Meyer Road
P.O. Box 1109
Fort Wayne, IN 46801-1109

Credits

Over the years, Navistar customer support and service regarding these RFI issues has been excellent. My thanks to Ed Pierce, National Account Business Manager - Fleet East, and friendly associates Art Fuller and Henry Gantner for their timely good local service and product support.

Special credit is due to Barry Coe for providing updated technical information and for correcting my misconceptions on the International trucks and their electronic controller modules. He is a licensed Amateur Radio operator (N9BDB) and is well informed on the issues. Barry is a development technologist for International Truck and Engine Corporation in Ft. Wayne, IN. He does EMC testing of International trucks and their components.