97 Blazer Loss Engine Power after warm up.
#31
02-01-2008, 12:15 PM
RE: 97 Blazer Loss Engine Power after warm up.
I really am questioning if the PCM is working properly. Almost looks like it is dropping the reference to the O2 sensors when it is acting up. It is possible that there is a temperature (expansion) dependant fault in the PCM that is causing this and by shutting it off for a few minutes, the circuitry is cooling down to a point where it can once again function. Have you tried logging the O2 sensor data when it is acting appropriately and comparing that to the poor performance data?
The next step I would take would be a trip to a junkyard (or phone calls), attempting to locate a used PCM from a '97. You will want to know how many O2 sensors (3 or 4) you have as that is the only appreciable difference between the PCMs in '96-mid'97 and mid'97-'01.
The next step I would take would be a trip to a junkyard (or phone calls), attempting to locate a used PCM from a '97. You will want to know how many O2 sensors (3 or 4) you have as that is the only appreciable difference between the PCMs in '96-mid'97 and mid'97-'01.
#32
02-01-2008, 12:41 PM
RE: 97 Blazer Loss Engine Power after warm up.
Ok, that will be next. I did just now take apart the MAF and it had lots of carbon on the wires. I did do a short trip with the sensor disconnected and seemed like the engine had alot more power to it. (Burnt some rubber). It put the Check Engine light on. I cleaned off the carbon on the wirs and the three little sensors. Put it all back together but ran the vehicle but the CEL still stays on now. Maybe take a few starts before it goes out? I'll test this on the way home tonight see if it made any difference. After that, if don't work it's off to the junk yard.
Thanks,
Brian
Thanks,
Brian
#33
02-02-2008, 05:20 AM
RE: 97 Blazer Loss Engine Power after warm up.
Can i have it... I will replace the converter and have a great running truck..
http://www.ae92gts.com/ae92gts_cat_symptoms.html
http://www.sunjournal.com/specialsec....php?DirID=615
http://www.ae92gts.com/ae92gts_cat_symptoms.html
http://www.sunjournal.com/specialsec....php?DirID=615
#34
02-02-2008, 07:45 AM
RE: 97 Blazer Loss Engine Power after warm up.
Your point? The fact that this problem isn't always there leads me away from the cat as I have stated in this thread already. That and the fact that fuel trims wouldn't be pushed to all the way rich with a failed cat either. If anything, they would be trying to lean the mixture back out. This sounds like a sensor/pcm problem, not a cat problem.
#35
02-02-2008, 04:43 PM
RE: 97 Blazer Loss Engine Power after warm up.
I'm pretty sure it's not the cat at least right now.
Ok, here is what happend on my way home from work after claening off the MAF sensor. Maybe drove a good 10 miles then the engine just made a loud thud like noise. It's hard to explain the sound. My MIL(CEL) light went on. Had my scanner on as always, ready to capture data incase the something happened. Turned out I had preliminary codes at first that my 2 upstream O2 sensors (bank 1 & 2 sensors 1) had low circuit voltage. Then I guess the computer then ran a check on them again before throwing the actual codes and turning on my check engine light. I captured data with10 frames before the trigger from the CEL coming on, and9 from after the trigger, as well as the trigger frame. Well during the whole period20 frames my O2 sensors (all of them (4))had no output at all (were 0 volts or very near 0, and the computer was running in open loop mode the whole time.
So, something is a mess. Only my 2 upstream sensors bank 1 and 2 gave codes. The other 2 before cat and after cat did not. My short term and long term fuel trims were maxed at 50 and 25% before the CEL trigger and after the trigger went to Short 0 % and long 6.25 %.
I trigger in the middle as to capture 10frames before the event and 9 after it.
Today in the morning I started up the vehicle and watch everything. While the car is running code it's goes into open loop mode till it warms up. During open loop my 02 sensors were operating normally like the should, Fuel trims were changing like they should too. Car finally warmed up and switch into closed loop and still 02 sensors were switching as normal.
I don't exactly know what is happening but when the vehicle runs from awhile the o2 sensors lose their voltage and I guess the computer goes into open loop. But why do the fuel trims jump to 25 and 50%, then after the CEL came on they went down? This is crazy. The car then runs horrible with complete loss of any power.
I thought maybe grounds to the O2s could be a problem, But I can't find them. They are mentioned in Mitchell's (I have Mitchell's OnDemand for my Blazer) wiring diagrams that they (grounds for o2 sensors)are located behind "rear left and rear right of cylinder head". How the heck can someone see them there. I can even get my hands back there to feel around. The ground to the VCM is also located rear right cylinder head. Can't see it anywhere. But as I'm thinking if the VCM was acting up from a bad ground the thing would keep resetting itself (clearing codes).
Problem must lie in the VCM itself as it may not be providingthe .450 volts to my O2 sensors after awhile when hot.
My O2 sensor grounds are all tied together and suppose to be connected to the engine I take it (again rear of cylinder head).
They don't make this easy do they? Putting ground connections places were you can reach them or see them.
Brian
Edited: Just adding if the ECM/VCM supplies about .450 volts to all the O2 sensors (all 4 of them), and they all get that voltage from the same supply rail in the ECM/VCM what if one sensor starts to short out when it get really hot. Wouldn't that cause or make all 4 O2 sensors fail? Providing that they are all feed the same voltage from the same source. This is just a thought. I only replace my 2 upstream sensors. There are 2 others that are still original. Wondering if one of those going bad can affect all the others.
This is kinda along the same lines as if all the O2 sensors were grounded at the same point and that ground went bad then all sensors would not work.
The reason for this thinkingis because all my 02 sensors drop to 0 volts when the problem is occuring. So they must all be getting there supply voltage from the same source point. If one sensor is shorting to ground internally might it kill the supply to all the other sensors?
The ECM/VCM is only supplying about .5 volts to the s
Ok, here is what happend on my way home from work after claening off the MAF sensor. Maybe drove a good 10 miles then the engine just made a loud thud like noise. It's hard to explain the sound. My MIL(CEL) light went on. Had my scanner on as always, ready to capture data incase the something happened. Turned out I had preliminary codes at first that my 2 upstream O2 sensors (bank 1 & 2 sensors 1) had low circuit voltage. Then I guess the computer then ran a check on them again before throwing the actual codes and turning on my check engine light. I captured data with10 frames before the trigger from the CEL coming on, and9 from after the trigger, as well as the trigger frame. Well during the whole period20 frames my O2 sensors (all of them (4))had no output at all (were 0 volts or very near 0, and the computer was running in open loop mode the whole time.
So, something is a mess. Only my 2 upstream sensors bank 1 and 2 gave codes. The other 2 before cat and after cat did not. My short term and long term fuel trims were maxed at 50 and 25% before the CEL trigger and after the trigger went to Short 0 % and long 6.25 %.
I trigger in the middle as to capture 10frames before the event and 9 after it.
Today in the morning I started up the vehicle and watch everything. While the car is running code it's goes into open loop mode till it warms up. During open loop my 02 sensors were operating normally like the should, Fuel trims were changing like they should too. Car finally warmed up and switch into closed loop and still 02 sensors were switching as normal.
I don't exactly know what is happening but when the vehicle runs from awhile the o2 sensors lose their voltage and I guess the computer goes into open loop. But why do the fuel trims jump to 25 and 50%, then after the CEL came on they went down? This is crazy. The car then runs horrible with complete loss of any power.
I thought maybe grounds to the O2s could be a problem, But I can't find them. They are mentioned in Mitchell's (I have Mitchell's OnDemand for my Blazer) wiring diagrams that they (grounds for o2 sensors)are located behind "rear left and rear right of cylinder head". How the heck can someone see them there. I can even get my hands back there to feel around. The ground to the VCM is also located rear right cylinder head. Can't see it anywhere. But as I'm thinking if the VCM was acting up from a bad ground the thing would keep resetting itself (clearing codes).
Problem must lie in the VCM itself as it may not be providingthe .450 volts to my O2 sensors after awhile when hot.
My O2 sensor grounds are all tied together and suppose to be connected to the engine I take it (again rear of cylinder head).
They don't make this easy do they? Putting ground connections places were you can reach them or see them.
Brian
Edited: Just adding if the ECM/VCM supplies about .450 volts to all the O2 sensors (all 4 of them), and they all get that voltage from the same supply rail in the ECM/VCM what if one sensor starts to short out when it get really hot. Wouldn't that cause or make all 4 O2 sensors fail? Providing that they are all feed the same voltage from the same source. This is just a thought. I only replace my 2 upstream sensors. There are 2 others that are still original. Wondering if one of those going bad can affect all the others.
This is kinda along the same lines as if all the O2 sensors were grounded at the same point and that ground went bad then all sensors would not work.
The reason for this thinkingis because all my 02 sensors drop to 0 volts when the problem is occuring. So they must all be getting there supply voltage from the same source point. If one sensor is shorting to ground internally might it kill the supply to all the other sensors?
The ECM/VCM is only supplying about .5 volts to the s
#36
02-02-2008, 06:46 PM
RE: 97 Blazer Loss Engine Power after warm up.
You will find the O2 sensor schematic for your truck attached. The only thing that I would think would influence this in terms of a grounding problem would be the main PCM ground which should affect MANY other things as well. The ground for the O2 sensors only services the heater element. The PCM supplies ground to each individual sensor. It also reads the voltage generated by each O2 sensor (yep, the O2 will generate its own voltage based on O2 content of the exhaust).
Based on the schematic above and the fact that all 4 sensors are dropping out to nothing, I do believe this is a PCM failure.
Here is a link for ya: Oxygen (O2) Sensors: Diagnose and Replace
Based on the schematic above and the fact that all 4 sensors are dropping out to nothing, I do believe this is a PCM failure.
Here is a link for ya: Oxygen (O2) Sensors: Diagnose and Replace
#37
02-02-2008, 08:12 PM
RE: 97 Blazer Loss Engine Power after warm up.
OK, so this is maybe where I'm confused. The O2 sensors actually generate their own voltage? My belief was that they were fed about .5 volts from the PCM then the O2 sensor varied that voltage and send that back out to the PCM to read. Kind of like how the TPS sensor works. It is fed 10 volts in on one lead and ground on another, and a variable voltage out on another which is sent back to the PCM. Simple representation of a potentiometer in ASCII which is just what a TPS sensor is.
10v in---|
|
\
/
\<-----Out 0 - 10 volts
/
\
/
|
Gnd-----|
Brian
10v in---|
|
\
/
\<-----Out 0 - 10 volts
/
\
/
|
Gnd-----|
Brian
#38
02-02-2008, 08:28 PM
RE: 97 Blazer Loss Engine Power after warm up.
The O2 sensors do generate their own voltage. It is not a potentiometer like the TPS sensor.
From the link I posted above:
From the link I posted above:
HOW IT WORKS
The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.
The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.
The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading.
An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor output voltage will drop down to about 0.2 volts or less. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around .45 volts.
The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts.
The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail.
The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading.
An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor output voltage will drop down to about 0.2 volts or less. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around .45 volts.
#40
02-04-2008, 09:07 AM
RE: 97 Blazer Loss Engine Power after warm up.
swartlkk,
Latest update,
Ok, car is still losing power as always. This time I watch everything that was goingon and when. As I was driving to work I monitored my O2 sensors as well as my Fuel trims.I was about halfway to work about 7-10 miles of driving. I started noticing a sight loss of power going up hill. Saw my O2 sensors droping in voltage (about .030) and not switching. My Fuel trims jump up to 25 and 50%. As I made my way down hill every returned back to normal. O2 sensors were switching over there full range and fuel trims drop back down. Again, I hit another part of the highway going uphill and the same thing happened. Computer was still in closed looped operation. It was getting worse everytime I went up hill and put more load on the engine.
When I go home its always mainly an all uphill drive and that is when I have major loss of power and need to pull off the highway and sit it out till everything cools down.
Now I am just for the sake of it thinking about the cat. If it is being plugged and the exhaust is not flowing or is being restricted can that cause my O2 sensors to output very little voltage because they are not getting the exhaust the need to create the signals? Thereby sending my fuel trims way up. Maybe it's not a huge restriction in the cat but enough to cause this problem on heavy loads.
WhenI pulled the car over to the side of the road without turning it off and punch the gas to the floor I was able to see the same thing. O2s drop way down and fuell trims jump up. I thinkwhen this happens really bad for awhile then the computer goes into open loop operation but still exibits the power loss.
What do you think about this?
Brian
Latest update,
Ok, car is still losing power as always. This time I watch everything that was goingon and when. As I was driving to work I monitored my O2 sensors as well as my Fuel trims.I was about halfway to work about 7-10 miles of driving. I started noticing a sight loss of power going up hill. Saw my O2 sensors droping in voltage (about .030) and not switching. My Fuel trims jump up to 25 and 50%. As I made my way down hill every returned back to normal. O2 sensors were switching over there full range and fuel trims drop back down. Again, I hit another part of the highway going uphill and the same thing happened. Computer was still in closed looped operation. It was getting worse everytime I went up hill and put more load on the engine.
When I go home its always mainly an all uphill drive and that is when I have major loss of power and need to pull off the highway and sit it out till everything cools down.
Now I am just for the sake of it thinking about the cat. If it is being plugged and the exhaust is not flowing or is being restricted can that cause my O2 sensors to output very little voltage because they are not getting the exhaust the need to create the signals? Thereby sending my fuel trims way up. Maybe it's not a huge restriction in the cat but enough to cause this problem on heavy loads.
WhenI pulled the car over to the side of the road without turning it off and punch the gas to the floor I was able to see the same thing. O2s drop way down and fuell trims jump up. I thinkwhen this happens really bad for awhile then the computer goes into open loop operation but still exibits the power loss.
What do you think about this?
Brian