Horrible Gas Mileage and Misfires
#1
04-29-2018, 10:13 AM
Horrible Gas Mileage and Misfires
Alright i have been getting horrible gas mileage on my 2004 blazer since i purchased it. This morning, 35 degrees, while warming up the engine it was misfiring at idle. but after i started going it has not done it since. That has been the only time that it has misfired. It gave me the random cylinder misfire code. I have other P codes consisting of P0155(Bank 2 Sensor 1) P0449(EVAP valve solenoid) and P0463(Fuel Level Sensor Circuit high input) the last one has to do with my fuel gauge bouncing around.
Where do i need to start to fix my gas mileage, currently about 8-9 mpg, and to stop my misfiring issue. I would rather not just through a whole bunch of parts at it, but i do need to replace my plug wires because the PO only replaced a couple and they are not the correct length for the plug they are going to. Should i go ahead and replace my distributor cap as well. ACDelco is only 39.99?
Edit: Oh and after the blazer sits overnight in the cold, when is start it in the morning there is just a plume of water vapor from the tailpipe. There is at least one hole in the exhaust system located on the muffler. The white smoke/vapor is only there until it warms up or i go uphill and all of the water drains from the system
Where do i need to start to fix my gas mileage, currently about 8-9 mpg, and to stop my misfiring issue. I would rather not just through a whole bunch of parts at it, but i do need to replace my plug wires because the PO only replaced a couple and they are not the correct length for the plug they are going to. Should i go ahead and replace my distributor cap as well. ACDelco is only 39.99?
Edit: Oh and after the blazer sits overnight in the cold, when is start it in the morning there is just a plume of water vapor from the tailpipe. There is at least one hole in the exhaust system located on the muffler. The white smoke/vapor is only there until it warms up or i go uphill and all of the water drains from the system
Last edited by Eric Lewis; 04-29-2018 at 10:16 AM.
#3
05-01-2018, 02:59 PM
Without a scanner that can read live data it is just a guess, but possibly a coolant temp sensor telling the engine it is much colder outside than it really is...... Better get a capable scanner, or take it to someone who does (not the parts store). Also needed for the Fuel trims that George LG is speaking about.
#4
05-01-2018, 05:00 PM
A capable scanner will tell you a lot about what going on that will help you get to the bottom of you problem. Fuel trims, O2 sensor function, etc. If money is tight you can shop used on ebay from a reliable seller. Or you can follow Lesmyers suggestion and get a $20 BT dongle from amazon and put car gauge pro on your android. Its a very cost effective basic scanning capability. Even does graphing.
George
George
#5
05-02-2018, 07:21 PM
A capable scanner will tell you a lot about what going on that will help you get to the bottom of you problem. Fuel trims, O2 sensor function, etc. If money is tight you can shop used on ebay from a reliable seller. Or you can follow Lesmyers suggestion and get a $20 BT dongle from amazon and put car gauge pro on your android. Its a very cost effective basic scanning capability. Even does graphing.
George
George
Short term bounces from 0-3 I don' know how to read them but you guys asked for them, so maybe you'l be able to tell me more of what' going on with them.
#6
05-03-2018, 11:37 AM
I'll answer your question about your vehicles fuel management first:
Fuel delivery is first determined by the input from several sensors such as MAF and ECT. The PCM has hard coded data from engine development and dyno testing that determines the correct fuel delivery level based on the input from these sensors. The amount of fuel is varied by modifying the injector pulse width. When the engine is first started and cold this is the sole determining facor and a live data stream will show that the system is in open loop. As the engine warms up the engine transitions to closed loop. At this point the O2 sensors take over the job of fuel delivery by measuring the exhaust gases and then tell the PCM to modify injector pulse width to get the fuel/air ratio to the ideal proportions to create the lowest emissions. The system does not care about mileage or power, just emissions. The only exception once in closed loop is full throttle (useful in diagnosis) or a failure.
Fuel trims are a measure of how different the actual O2 sensor driven fuel delivery is from the theoretical values based on the PCM tables. A negative number indicates less fuel delivery than theoretical to compensate for a rich exhaust condition to get the actual air fuel ratio back in line. In this example something is creating a rich condition such as a leaky injector. A positive trim indicates that the system is adding fuel from the theoretical to compensate for a lean condition caused by say an air leak after the MAF sensor (extra air not measured). The long term trim is the running average. Short term trim is the immediate difference to theoretical. At any given time you always add the two numbers together for a given bank to get the difference in fuel delivery from the theoretical amount (on a new engine with no issues in ideal conditions). There will always be a fuel trim that is not zero because your engine is not brand new on a dyno testing machine. The question is if your fuel trims are out of bounds and indicate a problem.
The level thats turns on your CEL light is +/- 25% total on a given bank. Fuel trims less than that can cause significant problems and need to be investigated. Anything less than 10 total is generally considered good with more allowance for an older engine. Your fuel trims are quite good. Does this mean that your truck is OK? No, not if your getting 1/2 of your expected mileage so that means that the computer thinks that the O2 sensors and the PCM essentially agree on fuel delivery for that set of sensor conditions. So now what? This means that either you have a sensor problem, a PCM problem or a set of conditions that robs you of perfomance without creating an extremely rich or lean condition that must be compensated for.
So now what? The next thing that you should check are your O2 sensors. You need live data capability. Numerical values are OK but graphing is even better. Warm up the engine and watch each of your 4 O2 sensors (each bank has 2). You should see either a fairly constant voltage between zero and 1 (usually around 0.5) or constant switching between two values that are between zero and one (usually less tha 0.3 and greater than 0.7). This is because there are two types of sensors, narrow band (voltage cycling) and wide band (constant voltage). monitor them warm at idle, then highwat speed and finally full throttle (have help for this so you drive safely). This is a first order test of those sensors. We may do more like create a lean or rich condition and make sure that the system responds properly.
George
Fuel delivery is first determined by the input from several sensors such as MAF and ECT. The PCM has hard coded data from engine development and dyno testing that determines the correct fuel delivery level based on the input from these sensors. The amount of fuel is varied by modifying the injector pulse width. When the engine is first started and cold this is the sole determining facor and a live data stream will show that the system is in open loop. As the engine warms up the engine transitions to closed loop. At this point the O2 sensors take over the job of fuel delivery by measuring the exhaust gases and then tell the PCM to modify injector pulse width to get the fuel/air ratio to the ideal proportions to create the lowest emissions. The system does not care about mileage or power, just emissions. The only exception once in closed loop is full throttle (useful in diagnosis) or a failure.
Fuel trims are a measure of how different the actual O2 sensor driven fuel delivery is from the theoretical values based on the PCM tables. A negative number indicates less fuel delivery than theoretical to compensate for a rich exhaust condition to get the actual air fuel ratio back in line. In this example something is creating a rich condition such as a leaky injector. A positive trim indicates that the system is adding fuel from the theoretical to compensate for a lean condition caused by say an air leak after the MAF sensor (extra air not measured). The long term trim is the running average. Short term trim is the immediate difference to theoretical. At any given time you always add the two numbers together for a given bank to get the difference in fuel delivery from the theoretical amount (on a new engine with no issues in ideal conditions). There will always be a fuel trim that is not zero because your engine is not brand new on a dyno testing machine. The question is if your fuel trims are out of bounds and indicate a problem.
The level thats turns on your CEL light is +/- 25% total on a given bank. Fuel trims less than that can cause significant problems and need to be investigated. Anything less than 10 total is generally considered good with more allowance for an older engine. Your fuel trims are quite good. Does this mean that your truck is OK? No, not if your getting 1/2 of your expected mileage so that means that the computer thinks that the O2 sensors and the PCM essentially agree on fuel delivery for that set of sensor conditions. So now what? This means that either you have a sensor problem, a PCM problem or a set of conditions that robs you of perfomance without creating an extremely rich or lean condition that must be compensated for.
So now what? The next thing that you should check are your O2 sensors. You need live data capability. Numerical values are OK but graphing is even better. Warm up the engine and watch each of your 4 O2 sensors (each bank has 2). You should see either a fairly constant voltage between zero and 1 (usually around 0.5) or constant switching between two values that are between zero and one (usually less tha 0.3 and greater than 0.7). This is because there are two types of sensors, narrow band (voltage cycling) and wide band (constant voltage). monitor them warm at idle, then highwat speed and finally full throttle (have help for this so you drive safely). This is a first order test of those sensors. We may do more like create a lean or rich condition and make sure that the system responds properly.
George
Last edited by GeorgeLG; 05-03-2018 at 11:40 AM.
#7
05-10-2018, 12:11 PM
I'll answer your question about your vehicles fuel management first:
Fuel delivery is first determined by the input from several sensors such as MAF and ECT. The PCM has hard coded data from engine development and dyno testing that determines the correct fuel delivery level based on the input from these sensors. The amount of fuel is varied by modifying the injector pulse width. When the engine is first started and cold this is the sole determining facor and a live data stream will show that the system is in open loop. As the engine warms up the engine transitions to closed loop. At this point the O2 sensors take over the job of fuel delivery by measuring the exhaust gases and then tell the PCM to modify injector pulse width to get the fuel/air ratio to the ideal proportions to create the lowest emissions. The system does not care about mileage or power, just emissions. The only exception once in closed loop is full throttle (useful in diagnosis) or a failure.
Fuel trims are a measure of how different the actual O2 sensor driven fuel delivery is from the theoretical values based on the PCM tables. A negative number indicates less fuel delivery than theoretical to compensate for a rich exhaust condition to get the actual air fuel ratio back in line. In this example something is creating a rich condition such as a leaky injector. A positive trim indicates that the system is adding fuel from the theoretical to compensate for a lean condition caused by say an air leak after the MAF sensor (extra air not measured). The long term trim is the running average. Short term trim is the immediate difference to theoretical. At any given time you always add the two numbers together for a given bank to get the difference in fuel delivery from the theoretical amount (on a new engine with no issues in ideal conditions). There will always be a fuel trim that is not zero because your engine is not brand new on a dyno testing machine. The question is if your fuel trims are out of bounds and indicate a problem.
The level thats turns on your CEL light is +/- 25% total on a given bank. Fuel trims less than that can cause significant problems and need to be investigated. Anything less than 10 total is generally considered good with more allowance for an older engine. Your fuel trims are quite good. Does this mean that your truck is OK? No, not if your getting 1/2 of your expected mileage so that means that the computer thinks that the O2 sensors and the PCM essentially agree on fuel delivery for that set of sensor conditions. So now what? This means that either you have a sensor problem, a PCM problem or a set of conditions that robs you of perfomance without creating an extremely rich or lean condition that must be compensated for.
So now what? The next thing that you should check are your O2 sensors. You need live data capability. Numerical values are OK but graphing is even better. Warm up the engine and watch each of your 4 O2 sensors (each bank has 2). You should see either a fairly constant voltage between zero and 1 (usually around 0.5) or constant switching between two values that are between zero and one (usually less tha 0.3 and greater than 0.7). This is because there are two types of sensors, narrow band (voltage cycling) and wide band (constant voltage). monitor them warm at idle, then highwat speed and finally full throttle (have help for this so you drive safely). This is a first order test of those sensors. We may do more like create a lean or rich condition and make sure that the system responds properly.
George
Fuel delivery is first determined by the input from several sensors such as MAF and ECT. The PCM has hard coded data from engine development and dyno testing that determines the correct fuel delivery level based on the input from these sensors. The amount of fuel is varied by modifying the injector pulse width. When the engine is first started and cold this is the sole determining facor and a live data stream will show that the system is in open loop. As the engine warms up the engine transitions to closed loop. At this point the O2 sensors take over the job of fuel delivery by measuring the exhaust gases and then tell the PCM to modify injector pulse width to get the fuel/air ratio to the ideal proportions to create the lowest emissions. The system does not care about mileage or power, just emissions. The only exception once in closed loop is full throttle (useful in diagnosis) or a failure.
Fuel trims are a measure of how different the actual O2 sensor driven fuel delivery is from the theoretical values based on the PCM tables. A negative number indicates less fuel delivery than theoretical to compensate for a rich exhaust condition to get the actual air fuel ratio back in line. In this example something is creating a rich condition such as a leaky injector. A positive trim indicates that the system is adding fuel from the theoretical to compensate for a lean condition caused by say an air leak after the MAF sensor (extra air not measured). The long term trim is the running average. Short term trim is the immediate difference to theoretical. At any given time you always add the two numbers together for a given bank to get the difference in fuel delivery from the theoretical amount (on a new engine with no issues in ideal conditions). There will always be a fuel trim that is not zero because your engine is not brand new on a dyno testing machine. The question is if your fuel trims are out of bounds and indicate a problem.
The level thats turns on your CEL light is +/- 25% total on a given bank. Fuel trims less than that can cause significant problems and need to be investigated. Anything less than 10 total is generally considered good with more allowance for an older engine. Your fuel trims are quite good. Does this mean that your truck is OK? No, not if your getting 1/2 of your expected mileage so that means that the computer thinks that the O2 sensors and the PCM essentially agree on fuel delivery for that set of sensor conditions. So now what? This means that either you have a sensor problem, a PCM problem or a set of conditions that robs you of perfomance without creating an extremely rich or lean condition that must be compensated for.
So now what? The next thing that you should check are your O2 sensors. You need live data capability. Numerical values are OK but graphing is even better. Warm up the engine and watch each of your 4 O2 sensors (each bank has 2). You should see either a fairly constant voltage between zero and 1 (usually around 0.5) or constant switching between two values that are between zero and one (usually less tha 0.3 and greater than 0.7). This is because there are two types of sensors, narrow band (voltage cycling) and wide band (constant voltage). monitor them warm at idle, then highwat speed and finally full throttle (have help for this so you drive safely). This is a first order test of those sensors. We may do more like create a lean or rich condition and make sure that the system responds properly.
George
#9
05-10-2018, 06:52 PM
I don' believe I need to do a leak down test.. I opened the throttle with my hand and was met with an overwhelming smell of gas. And the inside of the intake is nearly completely clean unlike the underside of the throttle which is completely black. I am not sure where to begin to check which one is leaking. This is my daily as well so I can only check up on things either when I work mornings or when I'm off
#10
05-11-2018, 08:45 AM
Well, you've got a number of places you can have a leak. I don't know if you have the older or newer style spider, but you'e got six lines going to six injectors or poppets and any one of the lines can be leaking. Or more than one. Each solenoid is housed in a plastic housing which could be cracked. There is a fuel pressure regulator on the back of this housing under the upper intake manifold. That could be leaking too. Since it sounds like the entire upper side of your lower intake manifold is clean (and it should be dirty black) so you have a massive leak or multiple leaks. I've got several used spiders that I know are leaking, but I cannot find the leaks. If you could pressurize your spider off the vehicle with fuel to 60psi, you might be able to find it. You might be able to get a fuel rail out of a junkyard and pressurize it somehow. I wound up just putting in the up dated spider and it solved all my problems.