Hitachi Zaxis 470 | Lack of power - diagnostic process

Have you ever been in the position where a customer calls up to say ‘the machine is down on power and we think it’s the hydraulic pumps so can you replace them?’ You respond by saying ‘of course but wouldn’t you rather we look at it first?’ ‘No, just price it up, it needs to be fixed.’ Looking at the price of the part and to do the job you ask the customer, 'Are you sure you don’t want it looked at first?’ Strangely enough you find yourself with another job to do!

Approaching the machine, it could only be described as something that resembled a prehistoric animal. Its sole purpose in life is to crush large pieces of concrete as it tears down buildings. It has had a hard life but according to the owner he can’t buy anything else that matches this machine's performance which is why it is important to find out what is going on and keep it going. 

The customer complaint is that there is a lack of power which gets worse when warm, it’s been losing around 5l of coolant a day, running hotter than normal and seems to play up during warmer weather. The customer interview has given us some real direction to start our action plan which will help speed up the process. 

Whenever I attend a machine with lack of power concerns, one of the first things I like to perform is a relative compression test. Whilst not foolproof, this simple test can give you some quick direction. Relative compression results seemingly ok with one cylinder marginally lower but not enough to warrant immediate attention.

The next easiest measurement was to measure crankcase pressure using WPS500X. The settings were loaded from the Automotive Guided test menu where the time base, scaling and probe are set for you, again speeding up the process. Ensuring the WPS500 was charged and connected as per the test was all that was needed.

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At this point we are looking for something out of the ordinary. Uniform patterns that repeat consistently such as the above indicate things are even. Nothing out of the ordinary so onto the next test.  

Exhaust pressure waveforms can be extremely useful when looking of combustion issues as the exhaust output pressure is the result of everything. Air, fuel, compression ignition will all affect the exhaust pressure waveform. Again, we are looking for a uniform pattern as exhaust waveform characteristics cannot be accurately predicated without exact knowledge of engine and exhaust design.  

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Just by looking for a uniform pattern we can see that the exhaust pressure shows some inconsistencies. The exhaust pulsation is enough to warrant to dig deeper.

When moving to the next test, we needed to choose measurements that can give us an overview of the engine during operation. Looking at the crankshaft sensor, a trigger using Piezo clamp and rail pressure would give us a lot of information as to fueling, crank speed and cylinder identification. These signals were chosen based on accessibility.

Using math and scaling we were able to graph the crankshaft speed using a math channel. For more information on Math channels please see our forum post.

The math formula for the following capture is crank(A,60) which is listed in the default list of the math channels. If you are not too fussed on having the RPM value then creating the math channel freq(A) will see a similar pattern. You can then adjust the range of the math channel to zoom in on the trace. For more information on math please see the forum post. 

We can use these math channels direct in Pico to visualize the crankshaft acceleration and deceleration which is ideal when looking for combustion anomalies. This is similar to how manufacturers look to carry out misfire detection.

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As we can see there is a repeating change in the crankshaft speed and when we look closer at the rail pressure signal, there doesn’t appear to drop as much as the others. If the rail pressure isn’t dropping as much and the engine speed also doesn’t increase then it would be safe to say we are looking at a possible fueling issue. 

By adding in the firing order, we can determine which injector is the one of interest.

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What we do know is that we have gathered enough evidence and direction to give the fuel delivery system closer attention with particular attention on injector 6 which is likely to partial blocked or sticking. Using the non-intrusive tests at the beginning meant we could quickly focus our attention on problem areas without needing to take anything apart. With a clear action plan and a good interpretation of the results means we had all of this wrapped up in the golden hour. This means that downtime is reduced as if the machine is in a condition to continue to work then it can be put back in service whilst parts are ordered or arrangements can be made for a further investigation. Things are made easier of course by the level of accessibility that this machine gave but this is a great example of how combining channels to give you a picture of the vehicle operation can point you in the right direction whilst giving you evidence to back up any repair.

Another example of how non-intrusive measurements can be used is from a Renault C460 with a D11 engine. This vehicle had a lack of power and a vibration but no warnings were on the dashboard and no trouble codes where stored. As before, a relative compression test was carried out using a current clamp around the starter motor cable and preventing the engine from starting revealed straight away something wasn’t right. Using the guided test and the BNC+ current clamps meant setup was done in seconds.

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Immediately we can see that there is an issue and more importantly it is repeating. By using the rotation rulers, we can see that there is a lack of current associated with a cylinder. We know this because each time a piston comes up onto a compression stroke, the starter motor requires more current in order to keep turning the engine. If there is less or no current required during what would have been a compression stroke, then we must focus on this cylinder to begin with to determine the cause. Next challenge is then how to identify the cylinders. 

We tend to say to people practise using Pico on known good vehicles. If it’s just capturing say injector 1 and a camshaft signal, great! If it’s a fuel pump current from inside the fuse box, perfect. What this does is starts to build the confidence in order to start using Pico on the trickier jobs when they come in. Not only this but you’re also starting to build a nice collection of known goods! Uploading these to the waveform library also means you have a secure place to store them but also others can use them for their own diagnostic purposes. The other options for when there isn’t a known good is to refer to the technical information. 

The easiest way to identify cylinders is to use an identifier for a known cylinder, or sync. For Petrol engines this could be an ignition trigger, primary or secondary ignition pattern but for diesel you only really have an injector. We pick this as they tend to fire around TDC during the compression stroke. Petrol engines tend to be less picky about whether or not they spark during cranking but diesel engines tend to want to see a certain amount of fuel pressure before they will send a signal to fire an injector. During a relative compression test, we need to engine not to start so the quickest way is to stop the fuel or disconnect the injectors. This means though we lose our sync, what now?
 

A look through the waveform library found nothing for Renault C however, Renault and Volvo trucks use the same powertrain. Under Volvo we filtered by using same basic information in order to broaden our search. We kept the filter to make, primary fuel and capacity. The D11 is a 10.9L of which removes a lot of the passenger vehicles! Unfortunately, though there were no waveforms we could use. We had found through the technical information that that the timing for both the D11 and D13 engines are the same so we could use a capture from a D13. Amending the engine size to 13L we found the one we were looking for, Injector 1 with the camshaft signal. Looking at this capture using the Camshaft signal and an injector meant we could use the camshaft to determine cylinder 1 and then using the firing order, associate the other cylinders. We do have a presentation on this technique which can be found on our YouTube channel.

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The next capture to make then was to perform another relative compression test using the same setup but to add another channel, in this case the Camshaft sensor. We knew from the known good that cylinder 1 fires first after the double pulse reference on the camshaft sensor. As we had the option to add another channel, grabbing the exhaust pulse is always a nice addition. Remember the exhaust pulse is the result of everything, intake, combustion and exhaust. We would expect a nice, uniform, waveform if all things are equal.

Clearly, that isn’t the case. We’ve used the camshaft to now identify the cylinder with the lack of current draw during compression. We know that the cylinder 1 is first to fire after the double pulse on the Camshaft and so using the firing order we can identify the remaining cylinders. What we notice in the exhaust pulse is that it is not even and to be honest, at this stage of the diagnosis that’s all we need to know. We could spend another 30mins trying to work out what is going on but ultimately that’s not going to fix the truck. From everything we have gathered so far, we need to be looking at Cylinder No.3. Removing the rocker cover things become clear relatively quickly. 

What we are looking at here is Cylinder No.3 exhaust valve. As you can see the adjuster has moved out much further than the others and in doing so was partially holding open the exhaust valve. What had happened was the lock nut had come loose and in doing so the adjuster had wound itself in. 

Removing the adjuster to make sure there wasn’t any damage to adjuster you could see how close it was before the locknut was about to fall off completely.