GM Training Tapes - Fuel Impact on Drivability - 1994 VHS Training

[00:00:00]Several of the recent GMC truck PPN releases have had references to fuel quality. So, this release is about just that, fuels.

[00:00:10]Now, one of the more recent PPN programs was on the CMFI, central multi-port fuel injection diagnosis program. Now, there was a statement in that video to the effect that if customers experienced repeat CMFI failures, well, the problem could be poor-quality fuel, and it should be suggested that they use a different brand or source of fuel.

[00:00:36]A couple of years ago, there was a complete PPN program devoted to fuel-related drivability problems. Now, that was release GMC TT-94-010.

[00:00:50]This program is not a duplication of that release. Rather, it builds upon that information and more recent developments.

[00:00:58]You may want to review that program if it's still available in your dealership.

[00:01:03]One thing that was covered in that release must be emphasized here. A fuel, either gasoline or diesel, is not a single hydrocarbon liquid. Let me show you what I mean.

[00:01:16]The crude oil from which we refine gasoline contains everything from methane, butane, and propane, which have high volatility but low heat or energy content, to tar and asphalt, which have low volatility but high heat content.

[00:01:34]Crude oil contains a lot of other compounds, too.

[00:01:38]Undesirable ones, such as sulfur, soluble metals, acidic corrosives, basic caustics, and even helium, which is sometimes removed and sold to fill balloons.

[00:01:51]Crude oil is indeed a very appropriate name for that witch's brew from which we get gasoline and diesel fuel.

[00:02:00]Petroleum refineries use several methods to refine the usable components from this brew. Now, the simplest method is distillation. And while the explanation I'm going to give you is simplified, it should help you understand how fuels are produced and how some fuel problems can occur. One way to distill or refine crude oil is to put it into a container and heat it to boiling. Now, the vapors of this brew travel up a temperature controlled condensation column.

[00:02:33]Different compounds then condense out of the vapor at specific temperatures where they are removed from the column. Now, starting at the base of the distilling column, we find asphalt. Now, asphalt has such a low volatility or ability to convert from liquid to gas that it won't even boil.

[00:02:53]It is ultimately removed from the bottom of the still container after all of the other components have boiled off.

[00:03:01]As we move up the column, our heated vapor begins to cool and the heavy components like grease and gear lube stocks condense out first.

[00:03:11]Continuing up the column, more stocks are removed. Engine oil, kerosene, diesel and jet fuel.

[00:03:19]A little further up and even cooler, the gasoline, naphtha and lighter fluid stocks appear.

[00:03:27]Finally, at the very top of the column are the components that tend to remain a vapor even after cooling. Components such as methane, butane, propane and other natural gases.

[00:03:40]You probably noticed that I referred to these components as stocks. Well, this is because they are not yet in their final form.

[00:03:48]At this point, we only have the basic building materials that now need more processing and blending. And many of the undesirable elements like sulfur and corrosives have yet to be removed from the stock.

[00:04:03]Not only will the refinery try to get the unwanted materials out, they'll mix or blend additives in.

[00:04:11]It's at this point that a fuel must be more clearly defined.

[00:04:16]Gasoline engines have different requirements than diesel engines, and therefore the additives must be different.

[00:04:23]Since GMC truck sells more gasoline than diesel engine powered trucks, we'll look at gasoline first.

[00:04:31]Now, before we get to gasoline additives, there's one point which needs to be understood about the gasoline stocks that were obtained from the distillation process we just saw.

[00:04:43]The heavier components that condensed first generally have a higher heat or BTU content with a lower octane rating.

[00:04:52]The lighter components that condensed last or didn't condense at all, but remain vapors, have a much higher octane rating but less heat content.

[00:05:03]While a higher octane rated fuel will resist spark knock better and is sold as super or premium, there is less heat available to produce power. Now, here's how that translates into the real world.

[00:05:17]If an engine doesn't exhibit spark knock at 89 octane rated fuel, using 94 octane will either reduce performance or reduce fuel mileage. Yeah. When you buy premium fuel, you are getting less heat per gallon, and heat is what makes trucks move, not octane.

[00:05:39]At this point, you may be saying, "Well, if that's the case, I'll run kerosene and get more power." And you would be correct. The only problem is that the very low octane rating of kerosene would limit the compression ratio to a maximum of about 4:1 to prevent spark knock.

[00:05:58]Any higher compression ratios would lead to such bad spark knock that the extra heat would be lost to the improper combustion of the fuel.

[00:06:08]In the '20s and '30s, 5:1 compression ratios were called high compression engines.

[00:06:14]Now, it was known that even higher compression ratios could improve the efficiency of the engines if only the spark knock problem could be overcome.

[00:06:25]While improvements in refining helped, the big boost was from an additive, tetraethyl lead. But, due to emissions and catalytic converters, as well as the health hazard from lead, it's no longer added to gasolines. However, 60 years of refinery developments and additive research have helped. Current gasoline additives include detergents and deposit control additives to prevent fuel system deposits and intake valve deposits, anti-icers to prevent fuel line freeze-up, fluidizer oils which help control intake port and valve deposits, corrosion inhibitors to minimize fuel system corrosion, metal deactivators to minimize the effect of metal-based compounds that can naturally occur in gasolines, antioxidants to minimize gum formation in storage or in the fuel system, and lead replacement additives to minimize exhaust valve recession. And that list of additives doesn't include things for oxygenated or reformulated gasoline.

[00:07:39]This list also lacks the blending of the various gasoline hydrocarbon components to meet Reid vapor pressure standards, ASTM volatility requirements, or distillation curve requirements.

[00:07:54]The vapor pressure, volatility, and distillation curve tests are distinctly different tests.

[00:08:02]Yet, they all pertain to gasoline vaporization.

[00:08:05]And vaporization will depend upon which fuel stocks and which additives are in the gasoline.

[00:08:13]Now, remember, gasoline must be a vapor before it will burn. So, when and how it vaporizes will have a direct impact on both drivability and emissions.

[00:08:24]It's primarily the impact on emissions that has led to the more recent changes in the regulations.

[00:08:32]Now, vapor pressure is the amount of pressure a known quantity of gasoline will produce when sealed in a container and then warmed to 100° Fahrenheit.

[00:08:43]It was first regulated in 1989.

[00:08:47]At that time, the vapor pressure had to be between 9 psi and 10.5 psi for gasoline sold between June 1st and September 15th.

[00:08:59]In 1992, the regulations changed to no more than 9 psi for gasoline sold between June 1st and September 15th.

[00:09:09]The exception to that requirement is gasoline blended with ethanol.

[00:09:14]Now, ethanol blends are allowed a vapor pressure of 10 psi.

[00:09:20]While the vapor pressure requirements are intended to reduce evaporative emissions, they also tend to decrease the hot drivability conditions, such as vapor lock.

[00:09:32]Unfortunately, cold starts and warm-up have been affected because the fuel doesn't vaporize as well. Now, you might think that an ethanol-blended gasoline, with its higher vapor pressure, might help this condition. But, remember the vapor pressure is checked at 100°.

[00:09:51]In the morning, even in the summer, the temperatures aren't that high.

[00:09:56]When the gasoline-ethanol blend starts evaporating in the intake, the evaporation cools things down even more.

[00:10:04]Also, because ethanol has a very low BTU content, it doesn't generate as much heat in the combustion chamber as unblended gasoline. So, the engine takes longer to warm up. The result is stalling, stumbling, and hesitation during cold starts and warm-up.

[00:10:25]Obviously, the vapor pressure test is inadequate.

[00:10:30]The distillation curve also deals with how gasoline evaporates, but not just at 100° like the vapor pressure test.

[00:10:40]The distillation curve shows the percent of evaporation and the temperature at which that percent of evaporation occurs.

[00:10:49]The American Society for Testing and Materials ASTM specification sets temperature ranges at which 10, 50, and 90% of the fuel must be evaporated.

[00:11:04]ASTM also specifies the temperature at which at least 98% of the gasoline must be evaporated.

[00:11:14]Since colder weather requires a higher volatility, cool or cold winter months require a gasoline that starts to go into a vapor state at cooler temperatures.

[00:11:26]ASTM recommends a different grade or volatility class by month and by state or area.

[00:11:35]Now, the exception is the EPA regulated time from June 1st to September 15th.

[00:11:41]During this time period, the EPA requires a volatility class A gasoline be sold.

[00:11:49]Well, let's look at a class A gasoline's distillation curve.

[00:11:54]At 158° Fahrenheit, 10% of the fuel should be evaporated.

[00:12:00]It should be 50% evaporated between 170 and 250°.

[00:12:07]By 374°, it should be 90% evaporated and there should be less than 2% of the gasoline left at 437°.

[00:12:21]The first 10% must be a vapor at a relatively low temperature for easy cold starting. But, if too much of the gasoline vaporizes at a low temperature, vapor lock and hot driveability will be a problem when the engine warms up.

[00:12:38]The 50% evaporated temperature is a range 170 to 250° Fahrenheit and it's necessary for proper warm-up and cool weather driveability.

[00:12:51]The 90% evaporated temperature, 374°, is low enough to prevent heavy hydrocarbon dilution of the engine oil, spark plug fouling, combustion chamber deposits, and crankcase deposits.

[00:13:08]But, it's also high enough to allow for higher heat content.

[00:13:13]The heavier hydrocarbons are the ones that give better fuel economy and power in an engine that's at operating temperature.

[00:13:22]Okay, there are all of these regulations and specifications. So, how does a truck customer get a tank full of bad gas?

[00:13:31]Well, first let's look at contamination.

[00:13:34]Contamination can occur accidentally or intentionally.

[00:13:38]Accidental contamination can happen in many different ways. Now, moisture condensation or water leaking into storage tanks can lead to water in the fuel as well as rust particles if it corrodes the storage tank. Some filling stations are concerned about the water and they check their tanks for it regularly.

[00:14:01]If they detect water, they'll put a neutralizer in their tanks. Usually, it's an alcohol-based additive because alcohol and water will mix and sort of burn in an engine.

[00:14:14]If they're having a problem with a lot of water in their tanks, well, they could add enough alcohol to affect the gasoline.

[00:14:22]Accidental contamination can also come from transporting gasoline in a semi-tanker or railroad tank car that had previously been filled with diesel fuel or heating oil and didn't get totally emptied.

[00:14:37]Unfortunately, there are some people that will intentionally contaminate or otherwise cheat with gasoline.

[00:14:44]200 gallons of less expensive kerosene can be mixed with 800 gallons of gasoline and be sold as 1,000 gallons of gas.

[00:14:55]It has also been documented that some filling stations will buy 87-octane regular gasoline and sell it as 89-octane mid-grade gas.

[00:15:07]In this area, that's about 10 cents of pure profit per gallon and a tank full of poor performance due to spark knock retarding the timing.

[00:15:18]Problems can also occur in the spring and fall transition periods. Now, this happens when a filling station still has some summer blend, low volatility fuel, and the weather turns unseasonably cold.

[00:15:32]The combination of cool temperature and low volatility fuel cause hard starting and poor warm-up operation.

[00:15:41]Of course, the opposite can also happen.

[00:15:44]The filling station just got its first load of winter blend, high volatility fuel, and the weather turns unseasonably hot.

[00:15:53]The hot temperature and high volatility can cause vapor lock conditions, even in fuel injection.

[00:16:00]More often, it causes poor performance and decreased fuel mileage.

[00:16:05]Now, there's one other group of additives that needs to be covered before we get to gasoline tests.

[00:16:11]It's the oxygen-bearing additives, or oxygenates as they're sometimes called.

[00:16:17]Primarily, they're alcohols and ethers.

[00:16:20]Why add oxygenates to gasoline? Well, the answer is emissions.

[00:16:25]Carbon monoxide emissions, and to a lesser degree, ozone.

[00:16:31]First, we'll cover geographical areas that exceed the federal carbon monoxide standards.

[00:16:37]Now, some of the more unlikely areas with carbon monoxide concerns are Anchorage, Alaska, Phoenix, Arizona, Greensboro, North Carolina, and there are 34 other areas nationwide.

[00:16:55]Reducing carbon monoxide levels can be fairly simple. All that's needed is to make sure there's sufficient oxygen present when combustion or burning occurs. So, carbon dioxide is formed instead of carbon monoxide.

[00:17:11]One method of doing this is to have the gasoline carry extra oxygen with it.

[00:17:16]Now, the problem with this is that oxygen is normally in a gaseous state.

[00:17:21]This means that liquid compounds which have oxygen in their chemical makeup must be used. Fortunately, alcohols and ethers have oxygen in them.

[00:17:32]Unfortunately, not all alcohols are compatible with truck fuel systems.

[00:17:38]Methanol, wood alcohol, is one alcohol that is corrosive to fuel systems unless mixed with other cosolvent alcohols and special corrosion inhibitors.

[00:17:51]Even with the cosolvents and other additives, only 5% methanol is allowed.

[00:17:58]Ethanol, grain alcohol, is compatible with the fuel system and should not present a problem as long as concentration does not exceed 10%.

[00:18:10]One ether that has oxygen in it and is being used currently is methyl tertiary butyl ether, MTBE.

[00:18:20]The maximum MTBE allowed is 15% of the fuel volume.

[00:18:26]It will also raise the octane rating of the fuel by about three numbers at the 15% level.

[00:18:33]However, it doesn't increase the volatility of most gasolines, nor is it as sensitive to water as alcohols.

[00:18:42]Two other ethers that are being researched and are seeing some use are tertiary amyl methyl ether, TAME, and ethyl tertiary butyl ether, ETBE.

[00:18:56]Now, the maximum amount of TAME allowed is 16.7% and ETBE can be up to 17% of the fuel volume.

[00:19:08]Both increase the octane about three numbers at their maximum allowed percentage and both actually reduce the volatility of the gasoline they're added to.

[00:19:19]Well, what happens when oxygenated gasoline burns? Well, the burning process releases the oxygen from the alcohol or the ethers.

[00:19:28]This allows the extra oxygen to combine with any carbon monoxide to form carbon dioxide. The end result being less carbon monoxide.

[00:19:39]Most technicians understand the dangers of carbon monoxide and recognize it as a pollutant.

[00:19:45]Ozone is a different matter. Now, many of you are involved in the reclaiming and recycling of CFC refrigerants in order to help protect the upper atmosphere ozone layer.

[00:19:58]Ozone is also a part of that brown haze or smog too many areas see on hot, windless, sunny, summer days and at ground level it's a respiratory irritant.

[00:20:10]Unfortunately, too many of you know what I'm referring to because the areas exceeding the federal ozone standards are very widespread. Some of the more unlikely areas are Salt Lake City, Utah, Baton Rouge, Louisiana, Louisville, Kentucky, Tampa, Florida, Portland, Maine, Kansas City, Kansas, Sheboygan, Wisconsin, El Paso, Texas, and well, there's a list of the 96 areas nationwide that have an ozone concern in your reference manual.

[00:20:44]The gasoline components that cause ground-level ozone are primarily the VOCs, volatile organic compounds.

[00:20:53]Now, these components, which include benzene, toluene, and xylene, are naturally occurring in crude oil and therefore in gasoline.

[00:21:03]They are lighter hydrocarbons and many have high octane ratings.

[00:21:08]Consequently, their concentration in gasoline went up to keep the octane rating up as lead was phased out.

[00:21:17]To reduce the undesirable compounds in gasoline, reformulated gasoline regulations have been put into place by the EPA.

[00:21:27]By limiting the amount of certain compounds, the EPA has forced the refiners to change their blending formula used to mix various stocks to make gasoline. Therefore, reformulated gasoline.

[00:21:42]The areas that were required to use reformulated gasoline during the summer months of 1995 did report a few problems. There were cold start and warm-up driveability concerns, as I mentioned earlier.

[00:21:58]With some of the more volatile components removed, there have been more additives put in the gasoline. Some of these additives are causing a no start condition. An engine will crank over, but sounds like it has no compression and won't start. Well, what's happening is the additives are forming a sticky substance on the valves.

[00:22:20]As the engine cools down overnight or after a long cold soak period, the valves stick in the position that they're in.

[00:22:28]If they're open, they stay open. If they're closed, well, they may stay closed to the point that the rocker studs may be pulled out of the head when the cam tries to open the valve.

[00:22:41]While this condition is not widespread, please let the GMC truck technical assistance people know about it if you run into it.

[00:22:50]Many times the valve sticking situation can be corrected by spraying choke cleaner or WD-40 on the valve stems to dissolve the substance.

[00:23:01]Also, the gas in the tank should be treated with GM injector cleaner, part number 12346291.

[00:23:12]At this time, no other fuel treatment can be recommended since it isn't known if they contain any of the substances which will prevent the sticky build-up.

[00:23:22]The GM cleaner does contain the necessary components to neutralize the build-up.

[00:23:28]Another thing that's caused some concerns is oxygenated gasoline. Now, please don't misunderstand me. If the ethanol is no more than 10% or the ethers don't exceed their allowable percentage, there's usually no concern.

[00:23:44]But, if the percentages are more because a filling station dumped alcohol in their storage tanks to take care of water in their tanks, or if a little more alcohol was added to the gasoline to increase the octane rating, well, things start to happen. Higher concentrations of oxygenates may start to deteriorate fuel line components such as rubber hoses and O-rings.

[00:24:10]Also, the oxygenates don't have the lubricating qualities that gasoline has.

[00:24:16]Now, this can lead to premature wear on moving components such as the fuel pump, injectors, and in CMFI or SCFI equipped engines, the poppet nozzles.

[00:24:30]Now, the big question is, is there any way to test gasoline in my dealership?

[00:24:35]Now, fortunately, the answer is maybe.

[00:24:38]There are tests which may help you, but there are none at the present time that will give a clear-cut yes, this is good gas, or no, this is bad gas answer.

[00:24:50]There are only a few gasoline tests available that can be performed in a and A Reid vapor pressure test can be performed using the Kent Moore test kit J-39383A.

[00:25:06]Now, since that was covered in the earlier release, I won't cover it here.

[00:25:10]Another test that can be performed easily in the dealership is the alcohol test.

[00:25:16]Now, there is a Kent Moore test kit available, part number J-34353A.

[00:25:24]Really, all that is needed is a 100 ml graduated cylinder with a stopper.

[00:25:31]The test is very simple.

[00:25:33]First, measure out 10 ml of water.

[00:25:43]Set the water aside and dry the cylinder.

[00:25:54]Next, measure out 100 ml of gasoline to be tested.

[00:26:15]Add the 10 ml of water to the gasoline.

[00:26:18]Now, we've added dye to the water, so it will show up for the camera.

[00:26:23]Put the stopper in the cylinder and shake thoroughly for 1 minute.

[00:26:33]Then, set it down for 2 minutes.

[00:26:37]Since alcohol and water will mix, they'll settle out to the bottom of the cylinder.

[00:26:42]If after setting for at least 2 minutes, there's only 10 ml of water at the bottom of the sample, there was no alcohol in the gasoline.

[00:26:53]If there's 10% alcohol in the gasoline, well, there should be 17 ml of alcohol and water settled out at the bottom.

[00:27:02]Anything more than 17 ml is above what GMC Truck recommends.

[00:27:08]There's a chart in your reference manual that gives the milliliter volume to percent of ethanol volume.

[00:27:16]Unfortunately, this test works only for alcohols, not for MTBE or any of the other ethers.

[00:27:24]Now, one other test that is available is a specific gravity test. Its results may vary depending upon the refinery blending. So, it's neither recommended nor disapproved by GMC Truck. There is an aftermarket kit available, and it consists of a graduated cylinder, a hydrometer, and temperature correction tables.

[00:27:48]One kit supplier says that gasoline with a specific gravity of less than 0.730 is more prone to driveability conditions that result from a gasoline that has high volatility.

[00:28:03]Now, generally speaking, a low specific gravity gasoline has high volatility, and a high specific gravity gas has a higher BTU content. But, specific gravity doesn't indicate vapor pressure or octane rating. That's about all that can be tested in your shop.

[00:28:23]Now, what can you do besides recommending a different brand of gas?

[00:28:27]Well, one thing would be to check with your state's Department of Weights and Measures to see if they have a petroleum inspection or testing division. If so, they may be able to test a fuel for compliance. Now, there's a list of agencies in your manual.

[00:28:44]Also, you may want to check with the Better Business Bureau to find out if a gasoline quality testing program is available in your area.

[00:28:54]Then, there's diesel fuel. Now, unlike gasoline, which must resist premature burning or spark knock, diesel fuel must burn easily when sprayed into hot compressed air.

[00:29:07]The cetane rating of diesel fuel is just the opposite of the gasoline octane rating.

[00:29:13]Where the higher octane is more resistant to burning, the higher cetane rating indicates the fuel is easier to burn, thus more desirable for a diesel engine.

[00:29:25]Like gasoline, there are different blends of diesel fuel for winter and summer use.

[00:29:31]Now, traditionally, number one diesel fuel was the winter grade, that will burn easier than number two diesel, the traditional summer grade.

[00:29:41]Currently, most fuel distributors seasonally adjust their blends for the anticipated temperatures.

[00:29:48]With cold weather adjusted fuel, less heat is generated during compression because of the cold weather. So, an easier burning fuel is needed for easy starting.

[00:30:00]As with the gasoline-powered engine, the lighter high volatility stocks help start a diesel, but the heavier low volatility stocks have more heat or energy content, and it's that heat that the diesel uses to produce power.

[00:30:17]Therefore, you can easily see that a low power complaint can be caused by using number one diesel or winter adjusted fuel in the summer.

[00:30:27]Another reason for low power is a restricted air intake. Now, this is usually accompanied by black smoke since the engine is not getting enough air to burn all of the fuel.

[00:30:39]Check the air filter and the intake air system. Intake deposits should not be a problem since there's no fuel in a diesel intake.

[00:30:49]Just be sure to check for other restrictions. Restrictions in the fuel system can also cause low power.

[00:30:56]Impurities in the fuel can support bacteria growth which form a slime that plugs up filters, fuel lines, and pump screens.

[00:31:06]Reduced fuel delivery and lower power are the result. This usually occurs after the truck has been standing for some time. To remove the slime, the fuel system must be disassembled and thoroughly cleaned.

[00:31:20]If the customer has their own fuel supply, the stored fuel will have to be treated with a biocide to stop the bacteria growth.

[00:31:29]Now, here's another drivability problem caused by fuel. This time, it's reduced or no fuel delivery. This condition will occur in cool weather if the fuel's cloud point is too high. The cloud point is the temperature at which the waxes and paraffins in the fuel begin to solidify.

[00:31:49]The semi-solid wax can plug up the entire diesel injection fuel system and the only way to clear the system is to warm it up to a temperature above the cloud point. The fuel will flow normally.

[00:32:04]Some poor grades of diesel, those with too much wax and paraffin, have been found with a cloud point of about 40° Fahrenheit.

[00:32:13]While the cetane rating of that fuel was within the number two diesel fuel range, the cloud point was what would be expected of number four fuel.

[00:32:24]Some fleets mix their used engine oil with their fuel to dispose of it and to keep from buying as much fuel.

[00:32:32]GM Truck recommends that this not be done for several reasons. Well, first, the heavier hydrocarbons may not burn completely and will carbon up the engine causing problems such as stuck piston rings.

[00:32:47]Second, even if the oil is carefully filtered, small metal particles can get into the injection pump and shorten its life due to wear.

[00:32:58]Both engine oil and poor fuel can cause carbon deposits both on and in the tips of the diesel fuel injectors.

[00:33:06]Now, this can lead to uneven spray patterns, leaking or dribbling, all of which will negatively affect combustion causing low power, smoke, and even misfiring.

[00:33:18]Another cause of poor combustion and low power is injector pop-off pressure.

[00:33:24]Over time, the injector pop-off pressure may become lower due to the loss of spring pressure. Too low a pop-off pressure will cause a change in the fuel spray patterns and generate a low power complaint.

[00:33:39]If you suspect pop-off pressure to be the cause of the problem, check the pressure by using nozzle tester J29075B.

[00:33:50]And replace the injector if the pressure falls below the specified poundage.

[00:33:56]Smoke concerns also bring diesel truck owners into your dealership, so let's quickly cover those. White smoke is normally from incomplete combustion and a little is to be expected during cold start-up and warm-up. The white smoke is diesel fuel that got hot enough to vaporize but not hot enough to burn.

[00:34:17]A change to number one diesel fuel in cold weather should help as well any type of engine heater.

[00:34:24]If the white smoke continues, there is a mechanical problem either with the thermostat and the engine is not warming up or coolant could be getting into the combustion chamber.

[00:34:36]Black smoke shows up when there's not enough oxygen to burn all of the fuel, but the fuel gets hot enough to burn off the hydrogen components while discharging the remaining carbon, black carbon, thus the black smoke.

[00:34:51]Too much fuel delivery due to a restricted return line or too high a pump housing pressure will also cause black smoke. Remove any restriction in the return lines and housing pressure control to correct the excessive fuel delivery.

[00:35:09]Blue smoke is usually not a fuel problem. It's caused by engine oil getting into the combustion chamber.

[00:35:17]Either the engine is consuming its own crankcase oil or someone mixed oil in with the fuel. Eliminate the oil and you will eliminate the blue smoke.

[00:35:28]There's really only one test for diesel fuel and that's the specific gravity test, but there are different ways of measuring the specific gravity. By different ways, I mean there's a specific gravity range for diesel fuels.

[00:35:43]There's also an American Petroleum Institute API gravity range.

[00:35:49]I'll start with specific gravity and an old friend, the diesel fuel hydrometer J34352.

[00:35:59]It's the easy one to use since it has from the top a yellow range, then a green, another yellow, and finally a red range.

[00:36:09]The upper yellow range is the least heat content, but the highest cetane value range.

[00:36:15]A reading in this range has a cetane rating of over 50 and usually indicates something like gasoline has diluted the fuel.

[00:36:25]The green range indicates a high quality and high cetane fuel. The approximate cetane range is from 46 at the low part to about 50 at the high part of the range.

[00:36:38]The next yellow range indicates a moderate quality fuel with a cetane range of about 45 at the high end to 41 at the lower part.

[00:36:49]A reading in the red area indicates a low quality fuel of about 38 to 40 cetane. It would have a high heat content but would be very hard to ignite. This would translate into a no start or excessive white smoke if the engine started. To help you understand the relationships, well, let's go back to the middle yellow and show specific gravity, cetane, heat content, and API gravity, and chart the values.

[00:37:22]Now, this moderate quality fuel range corresponds to a specific gravity of 0.8155 at the upper part and 0.8936 at the lower part of the range.

[00:37:38]A low specific gravity is a high cetane rating of about 45 at the high end of the range and a low cetane about 41 at the low end.

[00:37:49]The lower specific gravity at the high end of the range has less heat content, about 137,000 and a higher heat content, about 142,000 at the higher specific gravity at the low end of the range.

[00:38:09]The API gravity is related to heat content, so it goes from a low number, about 30 at the top of the range, to a high of about 37 near the bottom of the range.

[00:38:22]Now, what does all this mean?

[00:38:24]A high cetane, low heat content fuel will be easier starting in cold weather, but have low power in warm weather. A low cetane, high heat content fuel will be hard starting in cold weather, but produce more power in warm weather.

[00:38:42]Of course, the high heat fuel will contain heavier hydrocarbons and will be more prone to carbon build-up and black smoke.

[00:38:52]The one point I should make is that some things about diesel fuel that weren't covered in this video presentation were covered in the earlier release, GMC TT-94-010.

[00:39:06]Also, there's additional information in the reference manual.

[00:39:11]Whether it's diesel or gasoline, the use of the correct grade of quality fuel can make a big difference in the drivability of GMC trucks. Now, that applies to everything from the 2.2 L four-cylinder in the Sonoma to the 3116 CAT diesel that powers the Topkick.

[00:39:31]And remember, when you suspect the quality of the fuel your customer's putting in the tank is the cause of their drivability problems, be sure to get them into a good quality fuel. The problems just may go away. Oh, be sure they give the new fuel a real chance.

[00:39:49]Now, they need to burn at least three complete tankfuls of gasoline or 50 gallons of diesel fuel before you consider more serious action.

[00:39:59]Well, we discussed the drivability characteristics of diesel fuel, the cetane rating, heat content, specific gravity, and API gravity.

[00:40:09]Now, before we end this video, a word about the manual.

[00:40:13]You're going to find it very useful.

[00:40:16]Now, there's a full explanation of specific properties of gasoline including the anti-knock index, Reid vapor pressure, and the distillation curve. There's a thorough explanation of fuel additives and how they perform.

[00:40:31]There's a section on GM trucks position on oxygen bearing additives. And wrapping up the gasoline section, you'll note there's a glossary of over 40 gasoline terms. And finally, there's a section on diesel fuel. General considerations and be sure to reference your diagnosis charts and GM service bulletins.

[00:40:54]On that note, we'll wrap up this production on fuels and how they affect driveability. And we hope the information presented in this video production and manual will be useful to you when servicing GMC trucks.

[00:41:08]Thanks for your attention.