Cat 3116 Troubleshooting No Power

The problem with this 3116 Cat Diesel Engine was no power. The funny thing was it felt like someone stuck a banana in the tailpipe. There was no engine miss or hesitation what so ever. I checked for excessive back-pressure and that was normal.

One thing that seemed curious was the rpms in neutral went to the maximum without any problem but as soon as you put a load on the engine the rpms stayed at around 1200 rpm with no torque at all.

The Cat 3116 Governor controls the fuel rack which in turn decides how much fuel to allow to the injectors according to engine load and speed. The operator controls the throttle and the load is read off of the turbo boost pressure. The boost line goes directly to the governor air fuel ratio control. The more boost, the governor moves the rack for more fuel.

I tested the air/fuel ratio diaphragm with a regulator on the bus and it was leaking into the housing meaning the diaphragm had failed. Once I replaced the diaphragm it was a no-brainer to retest the new assembly and check for leaks. The new diaphragm was holding nicely.

NOTE: Don't test diaphragm over 20 psi

Here is a picture of the old diaphragm with a split in it. I remember the red flag that popped into my head when I called the Cat dealer for this part and they had 3 diaphragms on the shelf. Perhaps a recurring problem?

The 3 allen head screws are removed to pull the cover off to replace the diaphragm. This is an easy procedure once the governor is removed from the engine.

The governor linkage must be unhooked from the fuel rack before removing. Here you can see the pin which slides into the linkage and secured with a C clip.

The governor does not have to be timed and is fastened to the engine with 3 m8 bolts. Not much to it once all the fuel lines and piping is removed. This was a case of a smooth No Power situation. There was no white or black smoke, the engine did not miss or do anything really obvious. Testing the diaphragm with the air regulator is just another way for a diesel mechanic to troubleshoot a Cat 3116 Diesel Engine.

Delco Remy Starter - Troubleshooting Noisy Engagement

Usually when a starter is noisy during engagement you will have to remove it and check it over. Other things to check is the flywheel teeth that mesh with the starter drive gear. When the starter continually spins at high speed while starting then either the drive gear or the flywheel teeth are badly worn. What causes this is the operator engaging the starter while the engine is running. The starter below has a worn groove where the snap ring is positioned.

The machined groove should be as thick as the lock ring. You can see the groove has been worn lengthwise from the constant pounding of the drive gear during normal starting. The lock ring fits inside the washer on the shaft and locks the two together to provide a stopping point for the drive gear when the starter is engaged.

The only way to repair this condition is replacing the starter or the armature shaft. Either way the shaft itself cannot be repaired. The Mechanic has to decide which route to take in this situation.

Spring Brakes - New Long Stroke Models

Spring Brakes are the safest (since the new design) and most powerful parking brake mechanism available for highway & industrial trucks and equipment. The spring itself could knock a whole in the wall if unleashed from the spring brake chamber.

Years ago there used to be a removable clamp on the spring brake section so the diaphragm could be replaced. This was soon changed to a permanent solid clamp because of the numerous accidents and deaths that occurred from inexperienced people unclamping the spring assembly. without spring brake tool for caging the spring.

The spring brake tool or Caging Bolt as it's called comes with every spring brake chamber and must be left on in case the time arises for spring brake caging. This tool hooks on to the spring inside the brake chamber. The tool is inserted and turned too the right in a "T" shaped orifice then screwed tight on the outside of the pot with a 3/4 inch wrench.

Today spring brakes come in a Long Stroke version that allows more travel and less chance of going over the slack adjuster travel limits. The Long Stroke has 1/2 inch more travel at 2.5 inches maximum. The total stroke is 3.0 inches which is strictly to allow extra movement if the 2.5 inch stroke is reached.

Every Long Stroke spring brake chamber comes with square threaded fitting ports and a stamping and/or tag attached to the brake chamber body. The body itself is much longer than the original 30 Series brake chambers. Every Mechanic and operator should know the limits of these and other spring brake models.

Spring Brakes are the most important part of any highway vehicle operating on the road today.

Troubleshooting Electronic Diesel Engines

Troubleshooting electronic diesel engines can be a headache if you don't have the troubleshooting software required to check for codes. This is the first step when there is a amber or red code indicator light on the dash.

Once you rertrieve the code you can get a general idea what part of the electronic system to start focusing on. It may be a lost signal from a sensor or an innacurate signal that the computer (ECM) picked up.

Computers being as logical as they are will pick up on anything that is not within parameters according to the way they were programmed. This is a grreat advantage to your troubleshooting process.

Don't rule out the basics. A poor connection causing resistance will fool the ECM on the amount of resistance or voltage a sensor relays back to home. Always check connections both positive and ground starting at the battery.

There have been several instances in my shop where a poor ground has been the root of many electrical problems especially with electronic systems. So the first step is to check the electrical source thoroughly and then hook up the laptop.

If you send me a question about an electronic diesel engine with a code on the dash, I will tell you to follow the sequence in the above paragraph. It's reality now, every shop running or servicing electronic diesel engines need to have the proper software to get by with day to day operations.

How To Troubleshoot Air Brake System ABS Code .

This ABS system is by Meritor Wabco found on most highway transport vehicles. An ABS light on the dash indicates a problem that has to be repaired since an ABS fault is a fail according to Motor Vehicle Inspection criteria. The ABS system does not operate normally when there is an active code.

The code description reads "Right Front Wheel Sensor - Open"

When looking at the Right Front wheel the sensor looks like it's intact. The first thing to check is to make sure the sensor is pushed all the way into the housing. The sensor reads a tone wheel on the hub and sends a signal to the ABS Control Module.

According to the troubleshooting specs the resistance of the sensor should be between 900 and 2000 ohms. When I checked it out there was no continuity causing an obvious open circuit as indicated by the fault description. The first step is to check the wiring itself for any damage or the possibility of a faulty sensor. Most times exposed wiring to the environment is at fault when troubleshooting a circuit problem.

Further inspection shows a spot on the sensor wiring that has rubbed through on the brake pot assembly. One of 2 wires has been damaged and caused the open circuit condition. I use heat shrink butt splices since they seal very nicely from the environment.

Once the wiring was repaired I moved the bus in a forward direction & the ABS warning light went out. This was an easy fix and it was nice to stumble across the bad wire in an easy to reach location. This conventional school bus is a only a year old but you never know what can happen to wiring and components when operating on a daily basis. I hope this mechanic information has helped you out and maybe you will have it as easy as I did with repairing this failure.

School Bus Power Steering Pump Front Seal

This is a Haldex 2 stage Power Steering Pump removed from one of our 1998 Pusher School Buses. The problem found was the power steering level was rising on it's own. No, it's not magic but a front seal allowing engine oil to enter the pump suction side.

The power steering pump is bolted in tandem to the rear of the air compressor which has an open crankcase with lots of engine oil being splashed about. Since the suction side of the pump is facing in this direction, if the seal is faulty engine oil will enter the pump and end up in the power steering reservoir.

One quick check to confirm this is the engine oil is black as usual from hydrocarbons while P.S. oil is standard 10w30 engine oil so there is a noticeable difference from the normal appearance.
To change the seal the pump must be removed and the front housing taken off. Always mark the pump stages before dis-assembly for easy reassembly.

With the end housing taken off the seal snap ring can be removed then the front seal can be easily replaced. This pump operates not only the power steering but the hydraulic fan motor as well. There are 2 output ports on the pump which supply pressure oil to run the 2 systems. This pump is mainly found on the 3116 cat Engines in our fleet & work very well in normal day to day operations.

Mechanic Troubleshooting - Allison Transmission Wiring

Our fleet has absolutely zero manual transmissions, school bus drive trains are unless requested differently come standard with Allison MD 3000 electronic transmissions. Once they get a few years use there are electrical glitches that occur.

In this case the code pointed to the C3 pressure switch. This switch reads the clutch pack #3 oil pressure in the transmission module. It activates at around 37 psi when pressure is operating the clutch release and engagement.

If it fails, a code 32 will pop up. Most times the wiring is at fault so we will check the continuity from the ECU to the Trans. Module. (shown in the photo above)
At the front end the blue connector has to be disconnected from the ECU where the appropriate terminals have to be probed and checked for resistance. The Allison troubleshooting manual is a "must have" for this procedure. For newer units the WTEC 3 is required(world transmissions electronic controls). These manuals are available at an Allison dealer.

You can tell if the system is in the 3rd generation from the 3 connectors at the ECU. In this case the ECU is located under the driver side floorboard attached to the body(Thomas 1999 Saf-t-liner).

The resistance read 25 ohms which is excessive. As with other codes replacing wiring has become a common occurrence. We use shielded wiring which we run front to back to eliminate the defective wire. Many times if transmissions act up and shift awkwardly in wet weather there's a good chance you have a wiring issue.

How To Manually Check for Transmission Codes

Press the 2 arrows on the shift pad with key on and read the 4 digit code that comes up. Record the first 4 number code then press mode which will bring up a second code(if any) . I hope this mechanic information has helped you out.

Replacing Power Steering Hoses on a pusher school bus

Replacing power steering hoses on a pusher school bus involves bypassing the original steel power steering lines. This school bus is almost 12 years old, the pipes deteriorate over time from rust and vibration. They are clamped to the underside and usually start to leak in that area.

To make the job quicker we replace the pressure and return lines with high pressure double wire braided hoses. The ends are pipe thread and can be easily adapted to fit properly. The factory piping needs to be flushed out after and plugged since it will drip oil for days after and appear to look like the power steering is still leaking.

The hoist makes this job much easier running the new lines and securing them to the body. Once the lines are installed, the filters in the reservoir should be changed and 10w30 engine oil added. We found on occasion that 15w40 is too heavy an oil and creates a backup in the reservoir causing seepage.

The hoses are approximately 40 feet long and can be made up at a hose shop. They have all the tools that a mechanic shop could not justify to have since this is not a regular failure. This mechanic fix isn't hard to diagnose since oil leaks are pretty obvious to the naked eye.