Mechanic Checks For Winter Operation

A Mechanic has to maintain vehicles accordingly depending on the conditions and adapt throughout the seasons which includes hot and cold weather. Since Winter is now upon us it's time to cover some preventive maintenance tips that experienced Mechanics are familiar with, but I want to share the basics with everybody.
Coolant Testing the coolant is of course very important and changing the coolant and thermostats should also be considered. Cummins promotes DCA (dry chemical additive) checks, to make sure the system is not overcharged or undercharged. DCA prevents liner pitting by reducing air bubbles forming in the cooling jackets. Changing the coolant (non lifetime brands) with the thermostats every 2-3 years isn't a bad idea since coolant eventually breaks down and the acidic build up that forms starts to eat up gaskets and castings.
Belts and Hoses who doesn't know the importance of these bad boys. They get the most abuse from constant tension, heat produced from driving the belts and hot/cold temperatures on the hoses. I always say "when in doubt change it out". Pulley bearings and belt tensioners need to be checked out and the cooling system should be pressure tested. School buses have 1 inch cooling lines throughout the bus interior and need to be observed for leaks and loose clamps.
Batteries batteries can either be load tested once a year preferably in the fall or changed when needed. Sometimes the latter happens at the most inconvenient time when it's cold, wind blowing ....a spare bus (in my case) needs to be fired up from a cold condition. So we generally do the yearly load test and go from there deciding what step to take next.
Block Heaters Most buses in our fleet have the conventional block heater system. Our plug-ins are timed in cycles to come on during certain ambient temperatures. We test them at every service to stay on top of  'no start' conditions in the cold. A couple dozen of our newer buses have diesel heaters that have timers so they come on a couple of hours before the run.
Tune Ups Mechanics know the advantage of keeping an engine tuned up. Easier starts less fuel burned is the main objective. Valve sets, fuel filters and air filters are all you can really do to a diesel engine especially with newer models. Checking for engine codes doesn't hurt, some codes do not light up on the dash and become inactive. Common sense helps in this area of maintenance and needs to be applied looking at everything that makes a highway vehicle function. The regular Mechanic or the 'Mechanic in you' can figure this stuff out.

Diesel Mechanic's Favorite Diesel Engine

This a rather boring video but just listen to that diesel engine purr! Sit back with your favorite beverage and enjoy... The Cummins C Diesel engine 250 HP running in one of our pusher school buses (early nineties model). This engine is one of my favorites in the fleet, one reason is it's mechanical fuel injection. For the Mechanic... much easier to work on compared to today's units.

I had one of the Mechanics from the Cummins dealership ask me if any of our buses with this engine model were coming due for auction, he was interested in picking one up because of the non-electronic fuel injection system. These are popular models mainly because of the basic mechanics involved when working on them. The Bosch fuel injection pump is straight forward and works off a mechanical linkage operated by an air throttle pedal. The fuel shutdown is controlled by relays and is a very basic hard wired electrical system.

I know I'm dating myself here but electronics just needs a wisp of condensation and you're going to end up with some trouble. The precise technology of today is amazing stuff and controlling operating systems with printed circuits can't be beat compared to older technology but I sure miss it. Let's just say for all of us modern Mechanics you've got to stay sharp!

Cummins N14 Injector Troubleshooting

I found this interesting video from a Mechanic named Daniel who posted an in-depth video on troubleshooting and repairing an injector miss problem on a Cummins N14 injector. This is an electronic diesel model that has solenoid controlled injectors pulsed by the engine ECM. It's an interesting video and very detailed for the aspiring Cummins N14 Mechanic.

Cummins N14 Injector Troubleshooting and Repair "With this particular injector the way it works is that the solenoid is in an always open position allowing fuel from the rail into the injector and only closes during the downward stroke of the metering plunger so as not to allow the fuel to go back to the rail, rather trapping it in the injector and metering it to the cylinder. Technically, with this particular injector it would be more that the injector fuel supply is “closed” electronically at the injector. danielresume 6 months ago The solenoid is the only aspect of this injector that is electronic and governed by the ECM. It has been my experience that when these solenoids get weak or fail completely the engine might still run at idle without a misfire but under power will miss and have no power. The injector also has a ceramic check ball and metering plunger which will cause the same condition under power if worn as they will allow fuel to escape under pressure rather than injecting to the cylinder." I hope this Mechanic tip has been helpful.

Mechanic Tips-School Bus Fleet Preventive Maintenance

Every Fleet Mechanic will have there own ideas on how to set up the best PM program for their equipment which will vary for different locations. With different climates, road conditions and power trains the procedures will never be exactly the same. Our shop likes to condense the annual PM since the regular checks are carried out every 5000 Kilometers (3000 Miles). Oil changes are done every 15,000 Km with an oil sample to be analyzed. Fuel filters are replaced at every oil change.

The Allison 2000 and 3000 Transmissions  are all running on TES-295 Synthetic oil which has drastically cut down on repairs. Right now we change the oil every 3 years, the newer buses have prognostics which tells us with a dash light indicator when the filter and oil needs to be changed. Air filters are replaced every year regardless of the mileage. Steering Filters are serviced along with changing the oil every 2 years. Valve Sets are carried out according to the Manufacturer i.e Cummins every 5000 Hours or 240,000 Km (Electronic Models). With the introduction to emission controls in 2007 we now have to perform manual regens if required and replace the DPF (diesel particulate filter) every 150,000 Km (90,000 Miles)

Air Dryers every 2 years with a new unloader kit and dessicant filter. Dirt is a factor on school buses so we service interior heater filters and the entire lighting system (Non-LED lights). We check the starting and charging systems including the battery pack. If necessary we will run tests on the batteries and alternator. years ago alternators and starters were removed for rebuild but the time and parts did not add up as an economic strategy so we decided to give these components a 5 year life span before determining if they would need replacement. The cost has come down so much on electrical reman units, it's feasible to go this route with the added bonus of a warranty period.
 
Spring brake chambers are replaced every 5 years regardless of mileage and condition. The Mercedes MBE 900 requires a coolant and thermostat change every 2 years, the other diesel engines in our fleet do not have a time or mileage limit but we're working on that to prevent antifreeze deterioration and thermostat failures. Our tires tread depth is measured every Summer and pressures checked during each service.

Common sense plays a role with any preventive maintenance program and we found the best way to set one up is to sit all the Mechanics down in one room and go through the fleet  figuring out the best program to cover all the bases. Breakdowns will quickly eat up your labor time and parts budget like wildfire so keeping on top of maintenance with a feasible program will pay you back 10 times over.                                                                     

No Start Cummins Diesel Engine

Cummins Diesel Engine
Here are a few tips and checks you can make when your Cummins Diesel Engine will not start. This information pertains to mechanical injection diesel engines.

Don't feel insulted with some of these checks because the simplest steps have been overlooked many times.

The rule of thumb is Check The Simple Things First!

1. When your Diesel engine cranks but will not start - No smoke from exhaust
2. Is there fuel in the supply tank? Always check the source on your diesel engine
3. Check electric or manual fuel shut-off.
4. Is the air intake or exhaust plugged?
5. Note: Remember, a diesel engine needs air and fuel to run
6. Fuel filter plugged / seperator full of water?-drain as required.
7. Your diesel engine injection pump not getting fuel or fuel is aerated. Check fuel flow or bleed fuel system.
8. Check inlet restriction to fuel transfer pump
9. Inspect lift pump operation. Remove outlet line and crank over engine
10. Worn or malfunctioning injection pump
11. Internal pump timing incorrect
12. Engine camshaft out of time

My experience with diesel engines has taught me to start from the source and work my way to the injectors.

Check the filters to see if they are still full of fuel, if not you've got a diesel engine that has run out of fuel - a no brainer. I went on a service call once and found out that the operator had filled the tank with gasoline, anything can happen!

Otherwise you have an obvious failure that you have to sink your teeth into. Replace fuel filters if the mileage or hours are excessive.

Check fuel lines from the tank to the primary filter [Fuel/Water Seperator]
Tip: I use a remote fuel container and slip the suction line before or after the primary filter. If diesel engine performance improves you know you have to start checking for faults back to the tank.

This procedure bypasses the fuel tank and lines up to that point which tells you if the problem exists in those areas i.e. restriction or split/cracked fuel line or bad pick-up tube in the tank.

Pull output line off of the lift pump on the side of the block and crank engine over and check for fuel output.

Prime fuel system with primer pump and bleed the injection pump, once primed crack injection lines at the injection pump and observe for fuel output.

In most cases you will find a problem up to this point, if not check injection pump timing or check to see if the camshaft gear is actually driving the injection pump. These failures are not common at all.

I hope these tips help you troubleshoot your Cummins Diesel Engine.

Cummins ISC Diesel Engine Fuel In Oil Repair.

The Cummins ISC Diesel Engine is a great performer, we have several in our fleet and they are a very durable diesel engine. As with any engine there are failures and in this case we experienced the oil level increasing to an over full condition. One test that told us it was fuel in the oil was the oil sample analysis. We took a sample and the guys at BTA in Kamloops faxed over a report to let us know it was in fact diesel fuel.

Another tell tale red flag was the oil pressure was dropping below normal along with a splatter of oil on the rear engine compartment door. The viscosity decreased making the oil thinner causing these conditions. We actually went through this repair before and the symptoms were exactly the same (that's what happens when you have a fleet with the same drive train).



The CAPS Fuel Pump has to be replaced to repair this condition since it provides the high pressure fuel and injection delivery. It runs directly off the accessory gear and is about the same size as a 2 cylinder air compressor. The fuel lines and accessories have to be removed along with the pump accessory drive gear. The first thing to do after this repair is change the engine oil and get rid of that thinned out engine oil.

Cummins Diesel Engine Drive Gears

If you were to remove the front cover off of any diesel engine you will come across a series of drive gears. No belts or chains here, you're looking at the timing gears that make this diesel engine run. Each gear is timed to each other with specially placed marks that must be lined up during assembly.

Enlarge this picture by clicking on it and you should see the timing marks on the crank and cam gears. They look like center punch marks one on the crank and two marks on the camshaft.

The crankshaft and camshaft gears are driven together to provide proper valve and piston timing for combustion to occur. Fuel injection timing on the Cummins C Model diesel engine (pictured here) is accomplished by inserting a pin into the injection pump drive gear (top right).

The pump in turn has a pin in the side of it's housing that has to be removed, flipped around & aligned into the injection pump shaft setting it for injection on #1 cylinder.

The oil pump is also driven off of the crank gear and idler gear. The air compressor is located lower right without it's drive gear installed.

Cummins Engine Repair - Camshaft Gear Noise

Here's an email I received from Jonah Barnes, Lead Mechanic for the School District in Sierra Vista, Arizona. He noticed a noise coming from the front end of a Cummins C Diesel Engine. It turned out to be the camshaft gear. The photos tell the story and I'm amazed how long this gear lasted. It just goes to show how durable a quality metal casting can be and how long it can take a pounding without blowing apart. This gear would have made a huge mess if it exploded inside the timing cover.


"Quote"

Hello John,
It really wasn't too noisy actually. When the compressor placed an added load on the cam gear it would actually rock the gear back and forth and "knock" against the front cover. It almost really did sound like a " bongo drum".

According to the other mechanics who have worked here longer than I the previous attempts of replacing the compressor would cause it to be quiet for about a week or so then it would go back to the intermittent drum beat. They were adament that it was the compressor again and they were just getting bad ones.

They even went as far as replacing the fan hub and alternator a few times with no luck. I used redneck diagnosis and used a piece of fuel line and placed one end in my ear and the other end I listened around until I was sure it was in the front timing cover.

It actually made the sound faintly using the hose when the compressor governor unloaded but it was not as pronounced as when the compressor was running. I have only been with the school district here just a few months but have been a mechanic most of my life.

I have run into a lot of different broken things but this gear being broken like this and the engine still running down the road and running routes without missing a beat (literally) is pretty amazing I think.

They said it has been doing this almost 3 years but no one really thought it was that serious. I contacted cummins here and they know of no recalls on the gear but they are available from cummins for about $350.00 US.

I am originally from Indiana and my dad was an engineer for cummins for several years and he was pretty amazed too that it was still running. I don't think it would have much longer though. I will be sure to keep you informed of other mysterious problems I encounter on my end.

The more information out there the more it can help other people who are sitting there scratching there head. We tend to get a lot of life out of a bus out here because of not having to deal with rust issues so there are several high mileage buses just waiting to keep me employed!

Thanks again for your help.

Jonah Barnes
Lead Mechanic
Sierra Vista, Arizona

"Unquote"

Thanks to Jonah for sharing!

I love to receive emails with Mechanic Information sharing experiences of real life repairs & troubleshooting. This is helpful for Mechanics & Truck Owners who always have new and interesting problems to solve.

Allison Automatic Transmission Wiring & Troubleshooting

The Allison Transmission Control Unit on the 1999 Saf-T-Liner is located under the floor directly below the driver. There are 3 plug-ins which is an easy way to tell this is a W-TEC 3 system [World Transmission Electronic Unit 3rd generation]. The Transmission vehicle speed signal enters here and exits at two different plugs, one for the speedometer and the other to the Cummins ISC ECU.



We will trace the exiting wire from the ECU that provides our Vehicle Speed Signal since that is the code and the speedometer is operating normally. Since we have speedo operation that gives us an obvious clue that the incoming signal to the Trans ECU is OK.[resistance should be checked regardless]
The wire we want to trace goes from the Trans ECU to the VIM [Vehicle Interface Module]
Removing the dash back cover makes this check MUCH easier.


Remove the cover from the VIM








The VIM is an interface between the Trans ECU and the chasis wiring. Various operations are accomplished through this module like the exhaust brake, back up lights, neutral start, high idle and of course our vehicle speed signal runs through here to the Engine ECU.
[Click the Pic to Enlarge]
Now we can check the continuity and see if we have a circuit. After checking this out there is no connection between the Trans. ECU and the VIM.
I'll run a new wire to repair the open circuit, an easy fix. It's nice to get a gimme once in awhile!

In the VIM you'll notice a series of relays and 2 fuses. If you experience a dead keypad and there is battery voltage to the VIM then check these fuses. One is main power & the other is ignition power.



The other vehicle speed signal wire [tan wire # 157] comes from the trans ECU directly to the speedo. The speed signal to the VIM is the same number [tan wire #157] since it comes from a different plug.




This is where it all begins from the output shaft housing of the transmission. The output sensor is a single coil unit that sends an AC voltage to the Trans ECU.
There is a toothed wheel rotating inside the housing that creates the signal to the sensor.
The Allison 3000 Automatic Transmission is a very reliable unit when maintained properly. The wiring problems come and go but are easy to trace and repair with the right tools and wiring diagrams.

B20 Biodiesel Approved for use by Cummins

{This is a from a recent article released by Cummins}
B20 Biodiesel
One reason for biodiesel’s popularity is its capability to reduce emissions. Biodiesel may also help to reduce reliance on imported oil, using renewable “homegrown” energy sources. Cummins has completed the necessary testing and evaluations to ensure that customers can reliably operate their equipment with confidence using any biodiesel blend from B2 to B20 biodiesel fuel.

The popularity and use of biodiesel fuel continues to climb. Recent studies predict that, by 2008, 1.2 billion gallons of B100 biodiesel will be produced in the United States. One reason for biodiesel’s popularity is its capability to reduce emissions. Biodiesel may also help to reduce reliance on imported oil, using renewable “homegrown” energy sources.

Pure 100% biodiesel contains no petroleum and is commonly referred to as B100. While it works in diesel engines, most manufacturers, including Cummins, recommend a blend with petroleum-based diesel fuel. B5 is a blend of 5% biodiesel and 95% petroleum-based diesel fuel and is the most readily available biodiesel today. Other blends that are also available include B2, B10 and B20.

All of these biodiesel blends up to B20 are now approved for use in Cummins diesel engines, including those in transit operations.

Cummins has upgraded its previous position on the use of biodiesel fuel for three key reasons: First, the American Society of Testing Materials specification ASTM D6751 now includes an important stability specification for B100 biodiesel; second, the availability of quality fuels from BQ-9000 Certified Marketers and Accredited Producers is growing rapidly; and third, Cummins has completed the necessary testing and evaluations to ensure that customers can reliably operate their equipment with confidence using B20 fuel.

“We have completed exhaustive analysis and test evaluations which enable Cummins to provide the necessary guidance and information to our customers for the proper and successful use of this fuel in our engine,” said Edward Lyford-Pike, Chief Engineer – Advanced Alternative Fuel Programs. “This will enable our urban transit fleets to have a choice that includes fuel made, in part, from renewable resources”. For more information, see the Cummins biodiesel FAQ.

Cummins ISC Electronic Diesel Engine- cranks over but will not run.

Cummins ISC Diesel Engines need to be analyzed using a laptop computer with Cummins Insite software.

Sometimes however you can troubleshoot a no run problem the good old fashioned way by looking listening and using common sense.

The fuel transfer pump mounted on the left rear of the engine is a vane type unit driven by an electric motor.

The first clue was the transfer pump motor was not running at all with the ignition key on, it will charge up the system every time you hit the ignition key with a very distinctive motor noise at high rpms.

So since the golden rule with electrical problems is to check the source I went to the battery and checked the multiple fuses that supply power to the engine ECU [electronic control unit]

I found 3 fuses had blown indicating a possible short or high amp draw. The first thing to do was hook up a jumper wire [with an inline breaker in case there was a short]

Once hooked up the fuel transfer pump started working but sounded very sickly! It was enough to limp the School Bus back to the shop.

Since the main problem was a overly high draw from a faulty fuel
pump motor, replacing the fuel transfer pump was our next step.

The fuel pump must be installed as a unit [do not just change pump and motor] and will not seal properly on the old housing. You are guaranteed to have a fuel leak once you start it up.

How do I know? because I tried it as a shortcut and instantly had a fuel leak between the housing and fuel pump/electric motor.

There is very little room to move in this Thomas pusher since it is a rear engine unit. Remove power steering lines and rear radiator frame brace to gain access to the pump housing fuel lines and mounting bolts.

Test the pump by cycling it a few times with the ignition switch.

Fuel filter replacement is recommended, we pre-fill the primary filter and install the secondary filter dry which allows incoming fuel to be pre-filtered instead of being poured out of a fuel container, this avoids contamination.

The new fuel transfer pump will do all the work priming the system.

Just listening to the uncharacteristic sound of the fuel transfer pump led us to this rather easy diagnosis. It's a gimme that doesn't happen too often.

The main tip here is to always check the source first when troubleshooting a problem. Electronic diesel engines like this Cummins ISC model still run off a 12 volt battery so things have not changed too much from a few decades ago!

School Bus Mechanic on my "Squidoo" Lens

Cummins Diesel Engine Turbo Failure

Cummins Diesel 'C' Models come with a Holset brand Turbocharger. The operator noticed a noise coming for the engine, it was the turbocharger compressor and turbine wheels making contact with the turbo housing.

When a turbocharger fails it's hard to guess how much damage has occurred and how much debris has gone through the system.
In this case on one of our "C" Cummins Engines the turbo shaft bearings failed and the oil which is fed from the engine under pressure entered the exhaust and intake system.





Once you get oil in the system and various particulates or even chunks from the failed turbocharger it is recommended to replace the air charge cooler as well.
This one was saturated with engine oil, we always have a rebuilt air charge cooler on hand since there has been problems with the aluminum core deteriorating causing turbo boost leakage and loss of power.

The turbocharger was sent out for repair and all the piping checked and cleaned out as required. This problem was caught in time by the operator who heard the noise from the engine as it happened.
If undetected there would have been much more damage. Once we replaced the turbo and the air charge cooler this bus was ready to go once again.

This is what could happen and most times cannot be avoided on a Cummins Diesel Engine.