new 383 build backfire help
10-10-2009, 09:55 AM
#17
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Speedy- Thanks I will try getting it to go into open loop and see if it does not backfire. I thought I was chasing some very strange hot temp mechanical/ gasket faliure even though it made no sense and goes against everything I had been taught. But since chasing a ghost, I thought I would ask. I'll also try to get my hands on a scanner that monitors sensors in real time. My scanner only reports codes but doesn't monitor o2 readings. I am relieved(kind of) that you are saying what I was thinking and that it is not a ghost as much as it is a sensor problem. Thanks again
Injuneer- The fuel pressure at idle is now holding at 39-40 psi and WOT 40-45 psi. It has lasted longer than the factory style replacements at this point and the original factory one was blown reading 50 psi at idle before the build which no doubt caused the initial injectors to blow open. But I will tell him to keep an eye on it and head your warning.
Injuneer- The fuel pressure at idle is now holding at 39-40 psi and WOT 40-45 psi. It has lasted longer than the factory style replacements at this point and the original factory one was blown reading 50 psi at idle before the build which no doubt caused the initial injectors to blow open. But I will tell him to keep an eye on it and head your warning.
10-10-2009, 11:22 PM
#18
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Which plugs are/were fouled? If they're all on the same side of the engine, that gives you a clue.
Here's my thinking: If the cylinders on one side of the engine aren't firing properly, the unburned fuel would partially wash oil from the cylinder wall, thus lessening the pressure readings you've been getting.
Also, if the engine seems to run well in OPEN Loop but only begins to backfire when it goes into Closed Loop, that's another clue.
So ask yourself, what are the differences between Open Loop operation and Closed Loop operation? One of the several things is that in Open Loop, the PCM system ignores 02 feedback, but in Closed Loop 02 feedback is one of the most important bits of info the PCM needs.
The only time my son's 96 ran badly and fouled all four plugs on the same side (passenger) of the engine was when the 02 on that side of the engine failed.
Easiest way to check for that is to scan the engine idling real time and see what the 02 readings are. Absent a scanner, the 02 sensors can be swapped from one side to the other and see if the problem follows the 02. If, for example, all the fouled plugs are now/were on the passenger side of the engine but the one's on the driver's side looked good, swap the 02s. Then if the driver's side plugs foul, you can strongly suspect it's the 02 as the cause.
Back-firing in the exhaust can be caused by unburned fuel being ignitied in the exhaust system. An overly rich condition, where all the fuel is not burning during the power stroke, the unburned portion can ignite farther down the exhaust system.
An old trick was to race the engine in neutral to high RPMs, then cut the igntion key off but quickly turn it back on. That'll cause a really nice back-fire. Some guys use to clear out the muffler baffleing that way. The results could be similiar to what you're experiencing.
Another possible cause could be the lifter preload being set too tight, which would hold open the exhaust valve. Doesn't take much. This would cause low cranking pressures and backfires in the exhaust.
Just my thoughts.
Jake
West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!
Here's my thinking: If the cylinders on one side of the engine aren't firing properly, the unburned fuel would partially wash oil from the cylinder wall, thus lessening the pressure readings you've been getting.
Also, if the engine seems to run well in OPEN Loop but only begins to backfire when it goes into Closed Loop, that's another clue.
So ask yourself, what are the differences between Open Loop operation and Closed Loop operation? One of the several things is that in Open Loop, the PCM system ignores 02 feedback, but in Closed Loop 02 feedback is one of the most important bits of info the PCM needs.
The only time my son's 96 ran badly and fouled all four plugs on the same side (passenger) of the engine was when the 02 on that side of the engine failed.
Easiest way to check for that is to scan the engine idling real time and see what the 02 readings are. Absent a scanner, the 02 sensors can be swapped from one side to the other and see if the problem follows the 02. If, for example, all the fouled plugs are now/were on the passenger side of the engine but the one's on the driver's side looked good, swap the 02s. Then if the driver's side plugs foul, you can strongly suspect it's the 02 as the cause.
Back-firing in the exhaust can be caused by unburned fuel being ignitied in the exhaust system. An overly rich condition, where all the fuel is not burning during the power stroke, the unburned portion can ignite farther down the exhaust system.
An old trick was to race the engine in neutral to high RPMs, then cut the igntion key off but quickly turn it back on. That'll cause a really nice back-fire. Some guys use to clear out the muffler baffleing that way. The results could be similiar to what you're experiencing.
Another possible cause could be the lifter preload being set too tight, which would hold open the exhaust valve. Doesn't take much. This would cause low cranking pressures and backfires in the exhaust.
Just my thoughts.
Jake
West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!
10-11-2009, 03:56 PM
#19
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The fouled plugs WERE all on the passanger side, but have since been replaced. After only 5 minutes of run time, number 6 and 8 looked more dirty than 2 and 4 but none were fouled. But 2 and 4 looked perfectly clean still. And the 02 sensors both fronts are brand new. I had thought of the pre-load issue, but that has been set many times using the same method (one valve open, set other valve) without issue on any other engine or even the other head on this one. But we have to set again to put the head back on anyway obviously so we will see. The lifters are new as stated in first post also.
10-12-2009, 07:04 AM
#20
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You proved with the readings that the valve/head/gasket is not the cause of the problem. Once it's back together who knows.
If what your saying about the 2 plugs in question is they are slightly fouled, Then you have either a fuel problem or ignition problem. Since you only have a problem with 2 of the 4 on one side, that leaves out a control problem since all 4 should show evidence of a control problem.
So now you have limited it down to either an injector issue or ignition. Injectors themselves are highly doubtful so that leaves wiring. That means either crossed injector wiring or bad wiring/contacts. All of the injector questions can be answered by simply pulling up the fuel rail and observing the injectors for proper spray pattern and timing. Be sure to disable the coil by any of several methods available to you before doing this.
While cranking you will see the spray pattern and simply compare them to each other. Obviously they should all appear the same.
now look for timing. Depending on which cylinder is ready to fire at the time you start cranking the engine, will determine which one you see first. The order from the begining on that side is 8 - 4 - 6 - 2. So you could also see 4 - 6 - 2 - 8 repeat. Or 6 - 2 - 8 - 4 repeat. Or 2 - 8 - 4 - 6 and repeat. Understand.
Once that's taken care of. You could move on to ignition. Since you have a new opti, that is not likely the cause. Here is where you should focus on the wiring. Check again for crossed wires. Check for white or black spots on the sides of the wire.
If what your saying about the 2 plugs in question is they are slightly fouled, Then you have either a fuel problem or ignition problem. Since you only have a problem with 2 of the 4 on one side, that leaves out a control problem since all 4 should show evidence of a control problem.
So now you have limited it down to either an injector issue or ignition. Injectors themselves are highly doubtful so that leaves wiring. That means either crossed injector wiring or bad wiring/contacts. All of the injector questions can be answered by simply pulling up the fuel rail and observing the injectors for proper spray pattern and timing. Be sure to disable the coil by any of several methods available to you before doing this.
While cranking you will see the spray pattern and simply compare them to each other. Obviously they should all appear the same.
now look for timing. Depending on which cylinder is ready to fire at the time you start cranking the engine, will determine which one you see first. The order from the begining on that side is 8 - 4 - 6 - 2. So you could also see 4 - 6 - 2 - 8 repeat. Or 6 - 2 - 8 - 4 repeat. Or 2 - 8 - 4 - 6 and repeat. Understand.
Once that's taken care of. You could move on to ignition. Since you have a new opti, that is not likely the cause. Here is where you should focus on the wiring. Check again for crossed wires. Check for white or black spots on the sides of the wire.
10-12-2009, 08:39 AM
#21
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I appreciate the help Speedy and this is why I posted in the first place. Sometimes you just get frustrated and need to step back and ask for advice, and hope for someone to remind you of a line of thinking that works, which you have.
The car in question only has 56k on it and the harness has never been touched to my knowledge anyway. So we will inspect it along the injectors for wear but I doubt cross wiring since never seen any splices. Will also pull the fuel rails and look at the spray pattern and look for abnormalities between injectors.
The car in question only has 56k on it and the harness has never been touched to my knowledge anyway. So we will inspect it along the injectors for wear but I doubt cross wiring since never seen any splices. Will also pull the fuel rails and look at the spray pattern and look for abnormalities between injectors.
10-12-2009, 12:16 PM
#22
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Since they're all on the same side I suspect the 02 on that side.
I next recommend you monitor the voltage readings on the passenger side 02 sensor. Depending on his widely and quickly the voiltage changes you can next try either swapping sides on the 02s or replacing the passenger side 02.
Remember, when my son's engine fouled four plugs on the same side the cause was a bad 02 on that side.
Keep us posted.
Jake
West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!
I next recommend you monitor the voltage readings on the passenger side 02 sensor. Depending on his widely and quickly the voiltage changes you can next try either swapping sides on the 02s or replacing the passenger side 02.
Remember, when my son's engine fouled four plugs on the same side the cause was a bad 02 on that side.
Keep us posted.
Jake
West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!
Last edited by JAKEJR; 10-12-2009 at 12:18 PM.
12-22-2009, 05:31 PM
#23
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This car is still acting up so coming here for help again for my buddy. He sent a copy of a run file to Brian at pcmforless (after checking injector pulse and everything that has been suggest in this thread.all were opperating correctly). He said intake leak, exhaust lead, or still bad opti even though that was the first thing replaced. No intake leak or exhaust leak, so it was pulled apart and another opti was used.
Success!!! The car is no longer back firing. But it does not want to start either. Takes a minute or two of cranking before it will start. Runs great for about 15min then dies and will not restart for a couple of hours. The last part of that to me sounds like a heat issue.
But why the hard start? And tach gauge not working.
I put the new opti on for him but he put everything back together. I got time today to go over there for a little while and look at it with him. There is no spark coming from the coil and this is after him replacing ICM and coil. Now eventually it does get spark as I stated I did hear it start just took a while, but for the most part, 95% of time, no spark. The ICM is getting 12 volts though. He said he checked resistance in the opti pig tail and non of the wires are blown open.
There has to be some connection between the tach not working and this hard start/ die after 15min run time issue. Thoughts?
Success!!! The car is no longer back firing. But it does not want to start either. Takes a minute or two of cranking before it will start. Runs great for about 15min then dies and will not restart for a couple of hours. The last part of that to me sounds like a heat issue.
But why the hard start? And tach gauge not working.
I put the new opti on for him but he put everything back together. I got time today to go over there for a little while and look at it with him. There is no spark coming from the coil and this is after him replacing ICM and coil. Now eventually it does get spark as I stated I did hear it start just took a while, but for the most part, 95% of time, no spark. The ICM is getting 12 volts though. He said he checked resistance in the opti pig tail and non of the wires are blown open.
There has to be some connection between the tach not working and this hard start/ die after 15min run time issue. Thoughts?
Last edited by texas97z; 12-22-2009 at 05:32 PM. Reason: can't spell
12-23-2009, 09:18 AM
#25
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I agree. It's time to see if a sensor is operating out of range.
I looked in my 96 FSM for the listing of causes for "Hard Start" and "No Spark" conditions and there are a while host of possible causes. Just wondeirng if you have a FSM to review of would you like me to list some of the causes.
Jake
West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!
I looked in my 96 FSM for the listing of causes for "Hard Start" and "No Spark" conditions and there are a while host of possible causes. Just wondeirng if you have a FSM to review of would you like me to list some of the causes.
Jake
West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!
12-23-2009, 09:47 AM
#26
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The cods that came up were P1351, and P0372. I am familiar with the 1351 but not the other. Sorry I forgot to mention the codes last night.
And pardon my ignorance but what is a FSM? If it is a chilton's or something like that, I have one of those but otherwise I am not really sure what you are asking.
Edit: So i had time tonight after game to do search on 0372 code and sent him an email with results. If I am understanding other threads with this code, main causes are either harness or bad opti. i would hate to think three bad brand new opti's in three months, but it is what it is. He already checked the pigtail for ohms resistance and none of the wires are bad. We'll see what happens. When this gets resolved I will post or if we have anymore questions.
Josh
And pardon my ignorance but what is a FSM? If it is a chilton's or something like that, I have one of those but otherwise I am not really sure what you are asking.
Edit: So i had time tonight after game to do search on 0372 code and sent him an email with results. If I am understanding other threads with this code, main causes are either harness or bad opti. i would hate to think three bad brand new opti's in three months, but it is what it is. He already checked the pigtail for ohms resistance and none of the wires are bad. We'll see what happens. When this gets resolved I will post or if we have anymore questions.
Josh
Last edited by texas97z; 12-24-2009 at 12:47 AM. Reason: did a search on code.
12-24-2009, 08:16 AM
#27
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Doubt you've had 3 defects in 3 months
Have you ever probed the cable at the opti for voltage and ground? Or probed the 2 feedback signals? Even though someone measured the resistance of the cable from one end to the other, does not mean the cable is making a good connection at the pins of the 2 mating connectors.
The only way to know what the cause is 100% is back probe the connector at the OPTI and look at the actual signal. But that is going to require a scope to do so.
This signal in question is the hi-res feedback signal from the opti. In OBDII apparently this has an influence on the running of the engine. On one page of the GM shop manual it describes problems with this signal as causing surging and lack of power.
On the actual DTC description page it says that a 372 will shut down the injector.
Now for the most important thing that I read in the GM shop manual is this:
If a DTC1351 is set with the DTC372. And no external fault can be found, replace the PCM.
The only way to know what the cause is 100% is back probe the connector at the OPTI and look at the actual signal. But that is going to require a scope to do so.
This signal in question is the hi-res feedback signal from the opti. In OBDII apparently this has an influence on the running of the engine. On one page of the GM shop manual it describes problems with this signal as causing surging and lack of power.
On the actual DTC description page it says that a 372 will shut down the injector.
Now for the most important thing that I read in the GM shop manual is this:
If a DTC1351 is set with the DTC372. And no external fault can be found, replace the PCM.
12-24-2009, 09:02 AM
#28
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I think speedy might be on to something here. I would swap your ECM into that car and try it . Also you said you ohmed the harness to the opti , I have had to shake and twist the harness around some before i found it open.
Good luck, I know what a pain these kind of problems can be.
Good luck, I know what a pain these kind of problems can be.
12-24-2009, 10:10 AM
#29
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Shouldn't take much to find the codes - Shoebox has a list of LT1-specific codes. OBD-II codes are reached via the tabs at the bottom of the page:
http://shbox.com/1/Dtcs.htm
The high res pulse is used to "fine tune" the injector and ignition timing. The PCM knows where the cam is located from the low resolution pulses, then uses the high res pulse to keep track of the 90-crank degrees between the low res pulses.
http://shbox.com/1/Dtcs.htm
The high res pulse is used to "fine tune" the injector and ignition timing. The PCM knows where the cam is located from the low resolution pulses, then uses the high res pulse to keep track of the 90-crank degrees between the low res pulses.
12-24-2009, 02:27 PM
#30
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I just got an email from him and he ordered the pigtail to opti, but to answer your question Speedy I do not think he tested the signal wires but he is going ti replace with new so that will eliminate harness as cause.
That is interesting about those two codes in conjunction possibly meaning pcm is bad. I wouldn't mind using mine as test to see if helps but am a little worried about that because...what fried his???? And would it fry mine????
If his computer is no good though how would the car be able to start? Granted it takes several minutes of cranking, but it does start and runs well till it dies?
That is interesting about those two codes in conjunction possibly meaning pcm is bad. I wouldn't mind using mine as test to see if helps but am a little worried about that because...what fried his???? And would it fry mine????
If his computer is no good though how would the car be able to start? Granted it takes several minutes of cranking, but it does start and runs well till it dies?