Please read, need help, crappy running LQ4 in 03 Silverado.
02-04-2013, 10:36 PM
#23
TECH Senior Member
1 and 6 are firing order companions (they're at the same position in their cylinders as each other)...
the common thing here is they share the same position on the reluctor wheel.
02-04-2013, 11:07 PM
#25
Engine coolant temp sensor. It's the sensor in the cylinder head that tells the PCM what temp the coolant is.
If its bad, let say it thinks its colder than what the engine temp actually is, it will dump extra fuel into the engine because it thinks it needs it. The ECT is one of the most important sensors the PCM uses to decide fuel delivery.
Look through the PID's, ECT should be there.
If its bad, let say it thinks its colder than what the engine temp actually is, it will dump extra fuel into the engine because it thinks it needs it. The ECT is one of the most important sensors the PCM uses to decide fuel delivery.
Look through the PID's, ECT should be there.
02-04-2013, 11:58 PM
#26
Weak broken bent anything and everything. Doing a leak down test will tell you exactly where to look. With comp in the 120 range you have multiple problems in various cylinders. Only reason I suggested looking at the valve train 1st is sometimes problems there are easy to spot.
03-05-2013, 04:49 PM
#28
Sorry, nothing new, still runs like crap. Dont remember if I reported, but I changed pluts/wires/coil and engine temp sensor, no difference. Have been told that the ticking is exhaust leak & may be throwing off O2 readings.
120 lb range not good?
Other think I have noticed recently is I keep hearing what sounds like a fan belt squeeling, but its not. Told it may be exhaust leak, plugged cat possibly. So some of you had mentioned the cats. So I guess I will be checking/replacing them.
Weak broken bent anything and everything. Doing a leak down test will tell you exactly where to look. With comp in the 120 range you have multiple problems in various cylinders. Only reason I suggested looking at the valve train 1st is sometimes problems there are easy to spot.
Other think I have noticed recently is I keep hearing what sounds like a fan belt squeeling, but its not. Told it may be exhaust leak, plugged cat possibly. So some of you had mentioned the cats. So I guess I will be checking/replacing them.
03-10-2013, 04:16 PM
#29
So I have spent the past 2 days taking off the cats on my truck because they are plugged. I had to floor it to go up a small hill. I had hoped that this was the cause of my miss when cold, instead it is the cause of it. So I am still back to the same situation with a miss from hell when cold, once something gets hot (past when the water temp is hot), then it runs fine.
I am about to give up, I don't know what to do.
Timing chain?
Crank target wheel? What could it do that might cause this?
I haven't take the valve covers off yet to look for anything peculiar.
I am about to give up, I don't know what to do.
Timing chain?
Crank target wheel? What could it do that might cause this?
I haven't take the valve covers off yet to look for anything peculiar.
11-21-2014, 05:08 PM
#31
So recently my truck was at a shop near my house (not dealership), they had it for 3 weeks. & replaced the following:
fuel pump
fuel pressure regulator
one injector
O2 sensors
cam & crank position sensors
intake gaskets
Also cut the exhaust before the mufflers in case they were plugged.
And still could not figure it out. They did the smoke test on the intake, that is why they changed the intake gaskets.
He gave up, charged me $400 for the fuel pump, nothing else, but would have been almost $2000.
So I decided to try another ECM. Same results, still misses.
Any other thoughts?
fuel pump
fuel pressure regulator
one injector
O2 sensors
cam & crank position sensors
intake gaskets
Also cut the exhaust before the mufflers in case they were plugged.
And still could not figure it out. They did the smoke test on the intake, that is why they changed the intake gaskets.
He gave up, charged me $400 for the fuel pump, nothing else, but would have been almost $2000.
So I decided to try another ECM. Same results, still misses.
Any other thoughts?
11-24-2014, 12:10 PM
#32
post all the general info you can think of...
- year, make, model, options on the truck
- mileage
- general description of history of truck, are you original owner?
- was the truck ever modified, if so how?
- was the PCM ever tuned/modified in any way shape or form?
- anything else you feel like typing
- * obd2 readings see below, what are your long/short term fuel trims?
from what was said so far i would conclude you might have a bad PCM, but you said you replaced that.
other thing that comes to mind which i know from experience, is you might have a wiring harness problem. jeep i had the wire harness was routed over a valve cover stud by factory, after 60k miles the stud wore into harness and chaffed at least 3 wires shorting them to ground. they were fuel injector or coil wires and by shorting them to ground caused a engine computer to fault and do a hard reset where it would shut the engine off while driving at 40mph (like you turned the key off) and never resulted in a stored DTC.
regarding crank and cam sensors, they really don't work in such a way to give erroneous signals to then cause a misfire. that's wishful thinking at best. and they can be monitored/recorded with a tech2 or software... or at least the dealer can use the big scope machine to observe the waveforms and make sure they are good.
** systematically look at data being provided to you from engine sensors, don't guess.
you have a maf, map, short and long term fuel trims, engine coolant, intake air temp, system voltage and so on. everything should make sense. don't forget there are 2 modes of operation: open loop and closed loop. generally speaking, you should be able to operate in open loop not relying on feedback from MAF and O2 sensors and the engine should run well without misfire and have power. so take those out extra pieces of equipment of the equation to troubleshoot and make life simpler. either disconnect MAF and/or use software to force PCM into open loop for troubleshooting. start engine cold and observe all engine parameters and make sure they make sense... coolant temp should be less than 100°F, MAP sensor pressure should be low, MAF should make sense, throttle position sensor and idle air control if relevant should all make sense... and so on. and after you run it and it misses and runs like crap, park it and check spark plug condition. if all plugs are clean and normal looking except one... then troubleshoot from there you might have a failing ignition coil or bad wiring to one.
your compression numbers looked ok, nothing to suggest piston rings are the issue. one other thing i would not overlook is auto trans issues where you think it might be engine misfiring/sputtering but it's transmission problems. transmission data seen by a transmission computer or PCM can affect engine performance.
- year, make, model, options on the truck
- mileage
- general description of history of truck, are you original owner?
- was the truck ever modified, if so how?
- was the PCM ever tuned/modified in any way shape or form?
- anything else you feel like typing
- * obd2 readings see below, what are your long/short term fuel trims?
from what was said so far i would conclude you might have a bad PCM, but you said you replaced that.
other thing that comes to mind which i know from experience, is you might have a wiring harness problem. jeep i had the wire harness was routed over a valve cover stud by factory, after 60k miles the stud wore into harness and chaffed at least 3 wires shorting them to ground. they were fuel injector or coil wires and by shorting them to ground caused a engine computer to fault and do a hard reset where it would shut the engine off while driving at 40mph (like you turned the key off) and never resulted in a stored DTC.
regarding crank and cam sensors, they really don't work in such a way to give erroneous signals to then cause a misfire. that's wishful thinking at best. and they can be monitored/recorded with a tech2 or software... or at least the dealer can use the big scope machine to observe the waveforms and make sure they are good.
** systematically look at data being provided to you from engine sensors, don't guess.
you have a maf, map, short and long term fuel trims, engine coolant, intake air temp, system voltage and so on. everything should make sense. don't forget there are 2 modes of operation: open loop and closed loop. generally speaking, you should be able to operate in open loop not relying on feedback from MAF and O2 sensors and the engine should run well without misfire and have power. so take those out extra pieces of equipment of the equation to troubleshoot and make life simpler. either disconnect MAF and/or use software to force PCM into open loop for troubleshooting. start engine cold and observe all engine parameters and make sure they make sense... coolant temp should be less than 100°F, MAP sensor pressure should be low, MAF should make sense, throttle position sensor and idle air control if relevant should all make sense... and so on. and after you run it and it misses and runs like crap, park it and check spark plug condition. if all plugs are clean and normal looking except one... then troubleshoot from there you might have a failing ignition coil or bad wiring to one.
your compression numbers looked ok, nothing to suggest piston rings are the issue. one other thing i would not overlook is auto trans issues where you think it might be engine misfiring/sputtering but it's transmission problems. transmission data seen by a transmission computer or PCM can affect engine performance.
11-24-2014, 12:47 PM
#33
i would think not otherwise you would have had a DTC set specifically for that.
the OBD2 system is designed around providing sensor data to identify, troubleshoot, and fix problems.
forgot to mention, if truck is parked outside in area where there are rodents, i would not overlook a mouse problem somewhere where wires have been chewed. pull your underhood fuse box apart and check and look over the entire wire harness.
11-24-2014, 05:11 PM
#34
post all the general info you can think of...
- year, make, model, options on the truck
2003 Chevy Silverrado 1500 HD crew cab 4WD. 6.0L LQ4, automatic transmission.
- mileage
167,xxx
- general description of history of truck, are you original owner?
I am original owner, used it a couple of winters in indiana for plowing snow. Not commercial, just driveways.
- was the truck ever modified, if so how?
Changed wheels/tires to 16x8, 285/75/16
- was the PCM ever tuned/modified in any way shape or form?
Just for the change of tire size so speedo is correct.
- anything else you feel like typing
Been a great truck. Years ago driving from Indianapolis the check engine light would flash, but could not tell any difference in how it ran. It was still under warranty then. Took it to the dealer, & they said they updated the tune in the ECM & didnt see the blinking check engine light for a long time. Years later, when it was hooked to a Tech II to change the tire size, guy was leaning on the truck while it was running & said he felt it missing. Checked it & tect II said it was a general missfire. Missfire was all over the place. I changed plugs/wires. I didnt notice it missfiring, so left it. 2010 truck started acting funny, every once in a while it would say "Reduced Engine Power" on the DIC, and would have to turn it off for 20 seconds or so before it would give me anything more than an idle. Moved to Virginia, this reduced engine power issue kept appearing. Found out the throttle body was bad. Had it replaced, fixed. June 2012 fuel pump went out, changed it, back on the road. Then noticed it started missing. Only when cold, once hot it ran decent. Missfire kept getting worse, to the point that when cold, it will not go 5mph with pedal floored. Once something gets hot, it runs fairly decent. Around August of 2013 I noticed it having less & less power. Because the the cats were plugged because of the raw fuel being dumped into the exhaust.
I dont have HP Tuners yet, but about the buy it to check these logs you are asking for.
Also somewhere along the line I tried removing the MAF to keep it from going into closed loop. No difference.
It is definetly a missfire. I have tested cylinder 1 coil wire to ground & there is no spark. I tried different coils, and a whole set of coils so that part of the harness is different. May be in the harness between coil harness & ecm.
Thanks for your input.
- * obd2 readings see below, what are your long/short term fuel trims?
- year, make, model, options on the truck
2003 Chevy Silverrado 1500 HD crew cab 4WD. 6.0L LQ4, automatic transmission.
- mileage
167,xxx
- general description of history of truck, are you original owner?
I am original owner, used it a couple of winters in indiana for plowing snow. Not commercial, just driveways.
- was the truck ever modified, if so how?
Changed wheels/tires to 16x8, 285/75/16
- was the PCM ever tuned/modified in any way shape or form?
Just for the change of tire size so speedo is correct.
- anything else you feel like typing
Been a great truck. Years ago driving from Indianapolis the check engine light would flash, but could not tell any difference in how it ran. It was still under warranty then. Took it to the dealer, & they said they updated the tune in the ECM & didnt see the blinking check engine light for a long time. Years later, when it was hooked to a Tech II to change the tire size, guy was leaning on the truck while it was running & said he felt it missing. Checked it & tect II said it was a general missfire. Missfire was all over the place. I changed plugs/wires. I didnt notice it missfiring, so left it. 2010 truck started acting funny, every once in a while it would say "Reduced Engine Power" on the DIC, and would have to turn it off for 20 seconds or so before it would give me anything more than an idle. Moved to Virginia, this reduced engine power issue kept appearing. Found out the throttle body was bad. Had it replaced, fixed. June 2012 fuel pump went out, changed it, back on the road. Then noticed it started missing. Only when cold, once hot it ran decent. Missfire kept getting worse, to the point that when cold, it will not go 5mph with pedal floored. Once something gets hot, it runs fairly decent. Around August of 2013 I noticed it having less & less power. Because the the cats were plugged because of the raw fuel being dumped into the exhaust.
I dont have HP Tuners yet, but about the buy it to check these logs you are asking for.
Also somewhere along the line I tried removing the MAF to keep it from going into closed loop. No difference.
It is definetly a missfire. I have tested cylinder 1 coil wire to ground & there is no spark. I tried different coils, and a whole set of coils so that part of the harness is different. May be in the harness between coil harness & ecm.
Thanks for your input.
- * obd2 readings see below, what are your long/short term fuel trims?
from what was said so far i would conclude you might have a bad PCM, but you said you replaced that.
other thing that comes to mind which i know from experience, is you might have a wiring harness problem. jeep i had the wire harness was routed over a valve cover stud by factory, after 60k miles the stud wore into harness and chaffed at least 3 wires shorting them to ground. they were fuel injector or coil wires and by shorting them to ground caused a engine computer to fault and do a hard reset where it would shut the engine off while driving at 40mph (like you turned the key off) and never resulted in a stored DTC.
regarding crank and cam sensors, they really don't work in such a way to give erroneous signals to then cause a misfire. that's wishful thinking at best. and they can be monitored/recorded with a tech2 or software... or at least the dealer can use the big scope machine to observe the waveforms and make sure they are good.
** systematically look at data being provided to you from engine sensors, don't guess.
you have a maf, map, short and long term fuel trims, engine coolant, intake air temp, system voltage and so on. everything should make sense. don't forget there are 2 modes of operation: open loop and closed loop. generally speaking, you should be able to operate in open loop not relying on feedback from MAF and O2 sensors and the engine should run well without misfire and have power. so take those out extra pieces of equipment of the equation to troubleshoot and make life simpler. either disconnect MAF and/or use software to force PCM into open loop for troubleshooting. start engine cold and observe all engine parameters and make sure they make sense... coolant temp should be less than 100°F, MAP sensor pressure should be low, MAF should make sense, throttle position sensor and idle air control if relevant should all make sense... and so on. and after you run it and it misses and runs like crap, park it and check spark plug condition. if all plugs are clean and normal looking except one... then troubleshoot from there you might have a failing ignition coil or bad wiring to one.
your compression numbers looked ok, nothing to suggest piston rings are the issue. one other thing i would not overlook is auto trans issues where you think it might be engine misfiring/sputtering but it's transmission problems. transmission data seen by a transmission computer or PCM can affect engine performance.
other thing that comes to mind which i know from experience, is you might have a wiring harness problem. jeep i had the wire harness was routed over a valve cover stud by factory, after 60k miles the stud wore into harness and chaffed at least 3 wires shorting them to ground. they were fuel injector or coil wires and by shorting them to ground caused a engine computer to fault and do a hard reset where it would shut the engine off while driving at 40mph (like you turned the key off) and never resulted in a stored DTC.
regarding crank and cam sensors, they really don't work in such a way to give erroneous signals to then cause a misfire. that's wishful thinking at best. and they can be monitored/recorded with a tech2 or software... or at least the dealer can use the big scope machine to observe the waveforms and make sure they are good.
** systematically look at data being provided to you from engine sensors, don't guess.
you have a maf, map, short and long term fuel trims, engine coolant, intake air temp, system voltage and so on. everything should make sense. don't forget there are 2 modes of operation: open loop and closed loop. generally speaking, you should be able to operate in open loop not relying on feedback from MAF and O2 sensors and the engine should run well without misfire and have power. so take those out extra pieces of equipment of the equation to troubleshoot and make life simpler. either disconnect MAF and/or use software to force PCM into open loop for troubleshooting. start engine cold and observe all engine parameters and make sure they make sense... coolant temp should be less than 100°F, MAP sensor pressure should be low, MAF should make sense, throttle position sensor and idle air control if relevant should all make sense... and so on. and after you run it and it misses and runs like crap, park it and check spark plug condition. if all plugs are clean and normal looking except one... then troubleshoot from there you might have a failing ignition coil or bad wiring to one.
your compression numbers looked ok, nothing to suggest piston rings are the issue. one other thing i would not overlook is auto trans issues where you think it might be engine misfiring/sputtering but it's transmission problems. transmission data seen by a transmission computer or PCM can affect engine performance.
11-24-2014, 05:13 PM
#35
what does this mean, were catalytic converters a problem?
i would think not otherwise you would have had a DTC set specifically for that.
the OBD2 system is designed around providing sensor data to identify, troubleshoot, and fix problems.
forgot to mention, if truck is parked outside in area where there are rodents, i would not overlook a mouse problem somewhere where wires have been chewed. pull your underhood fuse box apart and check and look over the entire wire harness.
i would think not otherwise you would have had a DTC set specifically for that.
the OBD2 system is designed around providing sensor data to identify, troubleshoot, and fix problems.
forgot to mention, if truck is parked outside in area where there are rodents, i would not overlook a mouse problem somewhere where wires have been chewed. pull your underhood fuse box apart and check and look over the entire wire harness.
I checked for mice nests, none found.
11-24-2014, 08:29 PM
#38
forgot to ask, does this motor have cylinder deactivation to save fuel, or variable valve timing or any crap like that? and is the throttle body drive by wire?
if you've never done fuel injectors, i guess consider doing them. one way to do it which i recommend if you can do the work yourself, is to pull the intake and injector rail and get all 8 injectors out. mail them out or find local place that will do professional injector cleaning. I did this on my 2006 2500hd with 8.1L, and had injectors done by marren in wallingford, CT which is local to me. 8 injectors will cost you $200-220. it certainly won't make things worse.
however i still maintain the answer is there in the obd2 data. getting a reduced engine power scenario and with pedal floored not going more than 5mph... something is causing that. and based on that you have an electronic drive-by-wire throttle body?
you or someone needs to log engine data before the event occurs then look at all the parameters to diagnose what's causing it. a competent dealership should be able to do this, and if the problem happens often or every time you drive the truck then they should have the answer within a day and a $100 diagnostic charge. i would go that route for $100 but be up front with a dealer you want an answer not some excuse we test drove it and we 'think' it's the fuel pump/fuel filter bullshit (you go to autozone for those kind of answers). the dealer should also put it on the big engine analyzer and verify crank and cam sensor signals are good and ignition coils are firing properly. tell them you've been around the block with various shops and want the problem diagnosed properly and you want them to present their findings to you and convince you their diagnosis is correct based on hard data. tell the service manager if they **** around you're not paying the diagnostic charge.
if you've never done fuel injectors, i guess consider doing them. one way to do it which i recommend if you can do the work yourself, is to pull the intake and injector rail and get all 8 injectors out. mail them out or find local place that will do professional injector cleaning. I did this on my 2006 2500hd with 8.1L, and had injectors done by marren in wallingford, CT which is local to me. 8 injectors will cost you $200-220. it certainly won't make things worse.
however i still maintain the answer is there in the obd2 data. getting a reduced engine power scenario and with pedal floored not going more than 5mph... something is causing that. and based on that you have an electronic drive-by-wire throttle body?
you or someone needs to log engine data before the event occurs then look at all the parameters to diagnose what's causing it. a competent dealership should be able to do this, and if the problem happens often or every time you drive the truck then they should have the answer within a day and a $100 diagnostic charge. i would go that route for $100 but be up front with a dealer you want an answer not some excuse we test drove it and we 'think' it's the fuel pump/fuel filter bullshit (you go to autozone for those kind of answers). the dealer should also put it on the big engine analyzer and verify crank and cam sensor signals are good and ignition coils are firing properly. tell them you've been around the block with various shops and want the problem diagnosed properly and you want them to present their findings to you and convince you their diagnosis is correct based on hard data. tell the service manager if they **** around you're not paying the diagnostic charge.
12-07-2014, 04:49 PM
#39
forgot to ask, does this motor have cylinder deactivation to save fuel, or variable valve timing or any crap like that? and is the throttle body drive by wire?
if you've never done fuel injectors, i guess consider doing them. one way to do it which i recommend if you can do the work yourself, is to pull the intake and injector rail and get all 8 injectors out. mail them out or find local place that will do professional injector cleaning. I did this on my 2006 2500hd with 8.1L, and had injectors done by marren in wallingford, CT which is local to me. 8 injectors will cost you $200-220. it certainly won't make things worse.
however i still maintain the answer is there in the obd2 data. getting a reduced engine power scenario and with pedal floored not going more than 5mph... something is causing that. and based on that you have an electronic drive-by-wire throttle body?
you or someone needs to log engine data before the event occurs then look at all the parameters to diagnose what's causing it. a competent dealership should be able to do this, and if the problem happens often or every time you drive the truck then they should have the answer within a day and a $100 diagnostic charge. i would go that route for $100 but be up front with a dealer you want an answer not some excuse we test drove it and we 'think' it's the fuel pump/fuel filter bullshit (you go to autozone for those kind of answers). the dealer should also put it on the big engine analyzer and verify crank and cam sensor signals are good and ignition coils are firing properly. tell them you've been around the block with various shops and want the problem diagnosed properly and you want them to present their findings to you and convince you their diagnosis is correct based on hard data. tell the service manager if they **** around you're not paying the diagnostic charge.
if you've never done fuel injectors, i guess consider doing them. one way to do it which i recommend if you can do the work yourself, is to pull the intake and injector rail and get all 8 injectors out. mail them out or find local place that will do professional injector cleaning. I did this on my 2006 2500hd with 8.1L, and had injectors done by marren in wallingford, CT which is local to me. 8 injectors will cost you $200-220. it certainly won't make things worse.
however i still maintain the answer is there in the obd2 data. getting a reduced engine power scenario and with pedal floored not going more than 5mph... something is causing that. and based on that you have an electronic drive-by-wire throttle body?
you or someone needs to log engine data before the event occurs then look at all the parameters to diagnose what's causing it. a competent dealership should be able to do this, and if the problem happens often or every time you drive the truck then they should have the answer within a day and a $100 diagnostic charge. i would go that route for $100 but be up front with a dealer you want an answer not some excuse we test drove it and we 'think' it's the fuel pump/fuel filter bullshit (you go to autozone for those kind of answers). the dealer should also put it on the big engine analyzer and verify crank and cam sensor signals are good and ignition coils are firing properly. tell them you've been around the block with various shops and want the problem diagnosed properly and you want them to present their findings to you and convince you their diagnosis is correct based on hard data. tell the service manager if they **** around you're not paying the diagnostic charge.
I am going to take it to the dealer soon. I bought HPTuners & recorded it from first start this morning. I can't make heads or tails of it. Truck does not have DOD or variable valve timing. And is drive by wire. I tried a different set of injectors. I took plug 1 wire off the plug & it isnt sparking at all to ground.
Hmmm, I guess I can't attach the log file. 1 FMF, PM me your email & I will send it to you if you want to look at it.
THanks,
Scot
12-30-2014, 12:58 PM
#40
Got my truck back today from its 4th visit to 3 different shops. And it's fixed. Problem was a rusty crank sensor mounting surface. That hole is a stepped bore hole and the inner surface had rust on it that caused the gap between sensor and reluctant wheel to bee too big and throw off the signal.