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ELECTRICAL INTERFERENCE: Diagnosing Radio Frequency Interference Symptoms
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By Mighty Auto Parts
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link hidden, please login to view appeared first on link hidden, please login to view. Troubleshooting today’s technology can be challenging for even the most experienced technician. Making an accurate diagnosis, rather than throwing a lot of expensive parts and labor at the symptom can be a challenge. How would your shop handle the following customer complaints? a) Crank but no-start b) Hard starts c) Long crank time d) Misfire […]
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By Counterman
Engine misfires are among the most common issues that a technician must diagnose. However, the biggest problem – from a diagnostic standpoint – is that it’s almost an automatic reaction to blame misfires on the ignition system. Understanding why this is a problem, and the reason it happens, can help you differentiate between ignition-related and non-ignition-related misfires.
There are a couple deep-seated reasons for the blame. To begin with, years ago, before fuel injection and distributorless ignition, the majority of all noticeable misfires were caused by an ignition problem – either a bad spark plug or plug wire. Note that I said noticeable misfires. On today’s vehicles, ignition problems indeed are a common cause of engine misfires … but also a common misdiagnosis. This is where it starts to get interesting.
Carburetors, distributors and plug wires got us through the first 80-plus years of the automobile, and did a great job at it. But the bottom line is that they were simply inefficient fuel and ignition systems. Compared to today’s vehicles, they ran terrible! Once you had a few miles on them, they idled rough, maybe had to warm up a little longer to avoid a stumble, and most cars had their own little idiosyncrasies for starting.
This was the type of performance we were used to, so nothing registered to us as a misfire until it was a “dead” miss. This is a term we as technicians use to refer to a misfire that renders a cylinder completely ineffective, or completely “dead.” These types of misfires shake the entire vehicle to the point where even the most absent-minded of vehicle owners knows something is wrong.
It Was Easy Once
Back in the day, spark plugs had relatively short service intervals – around 10,000 miles – and plug wires were wide-open to abuse and wear. So, not only were they the frequent cause of misfires, but it wasn’t uncommon to open the hood and see a spark jumping from a plug wire to ground, or between wires. This made it easy to diagnose, and if there was no visual cue such as this, a common trick was to use insulated spark plug wire pliers and pull off one wire at a time to see if it made a difference. If you got no change, you found the suspect cylinder. If you got the daylights knocked out of you, you needed a new set of insulated pliers!
This was a sloppy yet effective diagnosis, but by no means an insult; I’ve done it a “million” times. Now, let me get back to the diagnostic problems of a misfire. For complete and correct combustion to occur, you must have the proper amount of air, fuel and spark; you must have the correct amount of compression; and the ignition timing must be correct. So, the possible causes of incomplete combustion could be too much or too little air; too much or too little fuel; lack of or not a strong enough spark; spark at the wrong time; or a mechanical problem that causes insufficient compression.
On old cars, incomplete combustion was common (one reason emissions were so bad), but there was no computer, no electronics to tell us, and as I mentioned, we were used to engines that ran a little rough and didn’t have the best drivability. On today’s vehicles, complete combustion is critical for emissions and fuel economy. This is why the engine control module (ECM) continuously monitors for complete combustion, and while there’s a lot to that, we’ll just focus on the misfire monitor.
The operation of the misfire monitor is primarily based on crankshaft pulses. The ECM continuously monitors crankshaft speed via the crankshaft sensor, and if it sees even the slightest deviation, its logic deduces that some form of incomplete combustion (i.e., a misfire) has occurred. Since any type of incomplete combustion will cause an increase in emissions, a diagnostic trouble code (DTC) is stored, and the “Check Engine” light is illuminated.
While the driver of the vehicle might not have noticed anything wrong, the ECM did, and now there’s an annoying light glaring at the driver, enticing them to seek service. As a technician, when we pull the DTCs on a vehicle that seems to run fine, it’s not even a slight surprise to see misfire codes, which are always P0300 for random misfire, or P0301 and up (the last number indicating the cylinder from which the misfire occurred).
When You Assume …
With all of that said, now let’s focus on the diagnostic problem of assuming that a misfire is caused by ignition. Problems such as the slightest pinhole vacuum leak or the slightest loss of fuel delivery from an injector will be detected by the PCM, storing a misfire trouble code. If we allow ourselves to automatically blame it on ignition, a percentage of the time we will be wrong. However, since we know that ignition problems still are common, there are certain signs we look for and certain things we can do to determine if the problem is ignition-related.
To begin with, one telltale sign of an ignition misfire is the flashing “Check Engine” light. As part of emission control, all ECMs will store trouble codes when a misfire is detected. But, when the ECM determines there’s imminent danger of damage to the catalyst, it flashes the “Check Engine” light to get the immediate attention of the driver. This occurs when it picks up a “dead” misfire, with the logic that quite possibly there is excessive unburned fuel coming out of the dead cylinder, which will damage the catalyst.
These “dead” misfires again can be felt by the driver, so a shaking vehicle and a flashing “Check Engine” light go hand-in-hand. While not always, this is usually an ignition problem, and quite often the engine will idle smooth, but under acceleration begin to misfire and flash the light. Most misfire monitors are accurate with the reported cylinder, and a common practice for diagnosis is to swap the coil and plug from the suspect cylinder with those from another. More often than not, the misfire will move, and while it feels the same, the ECM will instantly report the misfire from the other cylinder.
Rolling back the clock again, even in the age of the carburetor, technicians knew that misfires could be caused by multiple factors aside from ignition, and if a car had a misfire that wasn’t blatantly obvious, we relied on an oscilloscope to be able to “look” at the operation of the ignition system on a screen, which allowed us to compare the efficiency of all cylinders and deduce whether the problem was ignition-related, or caused by another factor.
These tools and techniques still are relevant today, but there are more special-tool requirements for more vehicles, as opposed to one set of test leads that you could hook up to any make or model. As technicians, we always take into account all of the factors that can cause a misfire, so as not to misdiagnose it. However, we may not always have the required equipment to view ignition waveforms, so we continue our inspection with more signs that can indicate an ignition-related misfire.
Spark Plugs and Critters
Naturally, worn spark plugs can cause a misfire. If you know the mileage on them, it can help you decide whether it’s time for replacement. Once they’re removed, excessively worn electrodes are a good clue.
It’s always important to look for wiring damage. Coil wiring can be inviting for rodents, so a close inspection always is a good idea. Carbon tracking is another tell-tale sign of an ignition misfire. The high-voltage spark produced in the coil finds its path to ground by jumping across the gap of the spark plug. Electricity always takes the easiest path to ground, and if it finds an easier way than the spark plug gap, it’ll go there.
Spark plug wire or coil boots are designed to insulate the high voltage, but problems can cause the spark to travel under the boot and ground to the base of the spark plug. Carbon is a byproduct of an electrical spark, and a high-voltage spark traveling between the wire boot and plug will leave its “footprint” via a carbon track.
Carbon tracking also can be visible inside a distributor cap, and where you find it, you can be sure of an ignition misfire. A final visual indicator of an ignition misfire can be oil in the spark plug wells. Many of today’s cars are designed with spark plugs in the center of the combustion chamber. It’s common in these designs for the well seals to leak, and oil can work its way up underneath the coil boot and cause a misfire.
During any type of diagnosis, we always use sight, sound and smell as our most important tools. Even if you can’t see it, you get used to the sound of a jumping spark, and this can be an indicator of an ignition misfire. You also might smell excessive fuel at the tailpipe. There are other indicators with scan-tool data that can give you a clue as to whether you have an ignition misfire, but you have to be careful.
If you have an ignition misfire and excessive fuel is being introduced into the exhaust, the engine-management system will recognize this as well and make adjustments to fuel delivery, which can alter engine data and the smell from the exhaust.
As you can see, this is a really deep hole, and the bottom line is engine misfires can be difficult to diagnose at times due to the sensitivity of modern engine-management systems. However, a thorough inspection and careful mindset will allow you to head off an ignition misfire before getting too deep into additional diagnostics.
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By NAPA
Some automotive issues make themselves known instantly and in a big way. But signs of a bad water pump aren’t always so brash. A bad water pump can wreak havoc on your engine and should not be taken lightly. But how does a water pump go bad? Here’s a few bad water pump symptoms that can help you deduce if repairs are in order.
Leaking Coolant
One of the most common symptoms of a bad water pump is a link hidden, please login to view from the water pump itself. Many water pumps are constructed with a weep hole below the pump drive shaft. Normally this weep hole is dry as the pump drive shaft seals keep the coolant at bay and away from the water pump bearings. But if the seal fails coolant can then seep past harming the water pump bearings and dripping out of the weep hole. The driver may notice a sweet smell of coolant cooking off the hot engine or a small puddle of coolant under the vehicle when parked. If the coolant is dripping on the accessory drive belt system there may be damp areas under the hood. If your vehicle develops a coolant leak or you find yourself adding coolant to keep it filled, check the area around the water pump just in case.
Overheating
One of the common signs of bad water pump functionality is link hidden, please login to view. The pump may not leak coolant, but the pump mechanism itself may have failed. Over time the fins of the pump can actually wear down to the point where they are no longer moving coolant. Cavitation can eat away at the metal pump vanes and pump surfaces. Plastic water pump vanes can disintegrate over time as the plastic ages. This all adds up to coolant that is no longer moved through the engine block and into the radiator to be cooled, leading to overheating.
Bad Noises
Water pumps have bearings that have to stand up to not only engine heat but also tension from the drive pulley. If you start to hear a grinding noise or high pitch squealing from the front of the engine, the water pump may be trying to tell you something. Try and rule out squealing belts by double checking belt condition and belt tension. Once you are sure the belt isn’t the cause try to pinpoint the source of the bad water pump noise. Be careful to not place any body parts near that rotating accessory drive system or the engine cooling fan. Simply stand in front of the running engine with the hood open and observe for a few minutes.
Oil Contamination
How to tell if water pump is bad can sometimes depend on the design of the engine. Some water pumps are buried inside the engine which makes it difficult to observe any problems. For example Ford Duratec V6 engines have the water pump located behind the timing cover. A leak from the water pump will allow coolant to mix with oil around the timing chains but the leak will not be visible on the outside of the engine. Checking the engine oil regularly and looking for an increase in oil level (due to coolant collecting in the oil pan) or a milkshake-like oil appearance are signs of possible symptoms of a bad water pump. Unfortunately these can also be signs of a bad cylinder head gasket, so further investigation will be required.
Any of these symptoms should be taken seriously and further investigation as to the source of the problem. If a bad water pump is diagnosed, it should be link hidden, please login to view. Don’t risk ruining an engine by putting off a repair that is relatively minor.
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link hidden, please login to view on link hidden, please login to viewor trust one of our 17,000 link hidden, please login to view for routine maintenance and repairs. For more information on how to know tell if your water pump is bad, chat with a knowledgeable expert at your link hidden, please login to view The post
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By Mighty Auto Parts
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link hidden, please login to view appeared first on link hidden, please login to view. Customer complaints of rough idle, misfires, crank but no start or long crank time symptoms can be a challenge with today’s technology. Random or multiple misfire codes may be stored in memory. Symptoms that seem like an ignition related issue may actually be fuel related, carbon induced, or in some cases a normal characteristic. Fuel […]
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By Mighty Auto Parts
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link hidden, please login to view appeared first on link hidden, please login to view. Low voltage conditions or the integrity of an electrical connection can pose some challenging events for the technician attempting to make an accurate diagnosis. In the world of automotive diagnostics, electrical problems have proven to be the most challenging, especially intermittent problems. Intermittent performance problems can be affected by connection-relate conditions and the presence of […]
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