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Good tests so far – have you checked for codes or history despite the lack of CEL? This may be able to do it quickly (well, it is quick if there are no codes):
What does a power balance test show? If I recall from my friend’s Honda engine of that era this should be quite simple to do. http://www.ericthecarguy.com/faq/solving-automotive-performance-issues?start=3
Just be careful during the power balance test – if for some reason the car loses power, be mindful to turn off the AC quickly. I have heard dreadful rumors that running the AC with the engine off for extended periods can damage it so I am very mindful of even a short duration.
Is it possible to test the fuel pressure? This may not help but if it is on your bucket list it would not hurt (I am never looking back, myself):
1. Is it within spec?
2. If you give it some gas, does the pressure raise momentarily then lower, or lower and struggle?
3. If the fuel pressure regulator runs off of vacuum, does disconnecting that have any difference?
4. Any other test your maintenance manual recommends.From what I know fuel pressure regulators which run off of vacuum can also be tested by disconnecting their vacuum line and seeing if they leak liquid out of the vacuum port within 1-3 minutes. No guarantee that a lack of fluid means it is good, but it could prove it is bad.
Is the fuel filter due to be replaced? If so, if you disconnect the outlet side (be careful of spilling gas – I think the filter is in the engine compartment!), THEN disconnect the inlet side, does the inlet side have pressure as if it were clogged? Is it cheap and easy to replace and need to be done every so often anyways?
If you give it some gas when it does this, does the idle even out or stay rough even with additional RPMs? If you shift into drive when it happens does that suddenly cure it or change it at all?
I am not sure that any of the above will help but they should not hurt to add to your list of tests and they are what I would do to start (in addition to a many you have already done, of course).
Good tests so far – have you checked for codes or history despite the lack of CEL? This may be able to do it quickly (well, it is quick if there are no codes):
What does a power balance test show? If I recall from my friend’s Honda engine of that era this should be quite simple to do. http://www.ericthecarguy.com/faq/solving-automotive-performance-issues?start=3
Just be careful during the power balance test – if for some reason the car loses power, be mindful to turn off the AC quickly. I have heard dreadful rumors that running the AC with the engine off for extended periods can damage it so I am very mindful of even a short duration.
Is it possible to test the fuel pressure? This may not help but if it is on your bucket list it would not hurt (I am never looking back, myself):
1. Is it within spec?
2. If you give it some gas, does the pressure raise momentarily then lower, or lower and struggle?
3. If the fuel pressure regulator runs off of vacuum, does disconnecting that have any difference?
4. Any other test your maintenance manual recommends.From what I know fuel pressure regulators which run off of vacuum can also be tested by disconnecting their vacuum line and seeing if they leak liquid out of the vacuum port within 1-3 minutes. No guarantee that a lack of fluid means it is good, but it could prove it is bad.
Is the fuel filter due to be replaced? If so, if you disconnect the outlet side (be careful of spilling gas – I think the filter is in the engine compartment!), THEN disconnect the inlet side, does the inlet side have pressure as if it were clogged? Is it cheap and easy to replace and need to be done every so often anyways?
If you give it some gas when it does this, does the idle even out or stay rough even with additional RPMs? If you shift into drive when it happens does that suddenly cure it or change it at all?
I am not sure that any of the above will help but they should not hurt to add to your list of tests and they are what I would do to start (in addition to a many you have already done, of course).
Good news, engine is running very smoothly with nice power – I still note a hint of lack of power at higher speeds but quite acceptable and nowhere near as bad as when #7 cylinder was misfiring. I think we are good!
I am going to repair or replace that EGR within a few weeks: if the EGR fixes the hint of lack of power at higher speeds I will post here again, otherwise just assume it had no impact or maybe fixed other unrelated things.
Once again, thank you both! 🙂 I will watch and see if I can contribute back to the forum. There is bound to be some low-hanging fruit I know enough about to help others with.
Good news, engine is running very smoothly with nice power – I still note a hint of lack of power at higher speeds but quite acceptable and nowhere near as bad as when #7 cylinder was misfiring. I think we are good!
I am going to repair or replace that EGR within a few weeks: if the EGR fixes the hint of lack of power at higher speeds I will post here again, otherwise just assume it had no impact or maybe fixed other unrelated things.
Once again, thank you both! 🙂 I will watch and see if I can contribute back to the forum. There is bound to be some low-hanging fruit I know enough about to help others with.
Nearly out of time so I am heading home on the final test drive of my vacation. Plug wire #7 was burnt badly (touching the exhaust) and nearly 1/4″ of it was exposed wire. For verification purposes I put a spark tester on it: good spark but that 1/4″ exposed part would jump to anything it could get near. Put the old wire back on and routed it 3″ away from the exhaust (no one tell GM :whistle: ).
Started it up, “exhaust sound” is still there but unless I am damned mistaken it is now on both sides of the engine and sounds healthy. Will listen more later to verify. No more excessive exhaust noise from the tail pipe…unless I disconnect the pesky #7 cylinder, then the excessive noise begins. The engine RPM is lower at idle and when I remove the #7 fuel injector the idle is now impacted like the other cylinders.
The EGR is obviously still a huge problem but will fight that fight next week unless the car drives very poorly…will report back once the trip home is complete.
Thanks again and hopefully if this does not resolve the issues it at least clears the way to diagnose things further.
Nearly out of time so I am heading home on the final test drive of my vacation. Plug wire #7 was burnt badly (touching the exhaust) and nearly 1/4″ of it was exposed wire. For verification purposes I put a spark tester on it: good spark but that 1/4″ exposed part would jump to anything it could get near. Put the old wire back on and routed it 3″ away from the exhaust (no one tell GM :whistle: ).
Started it up, “exhaust sound” is still there but unless I am damned mistaken it is now on both sides of the engine and sounds healthy. Will listen more later to verify. No more excessive exhaust noise from the tail pipe…unless I disconnect the pesky #7 cylinder, then the excessive noise begins. The engine RPM is lower at idle and when I remove the #7 fuel injector the idle is now impacted like the other cylinders.
The EGR is obviously still a huge problem but will fight that fight next week unless the car drives very poorly…will report back once the trip home is complete.
Thanks again and hopefully if this does not resolve the issues it at least clears the way to diagnose things further.
Disconnected each fuel injector twice (once while listening with my ear and once while listening with the stethoscope); all of them caused an RPM drop except for that pesky #7 again. It stayed above 700 RPM where the others caused dipping below 700 RPM. None of the cylinders when cancelled caused that exhaust noise to go away…going to examine plugs and spark next, starting with #7.
Disconnected each fuel injector twice (once while listening with my ear and once while listening with the stethoscope); all of them caused an RPM drop except for that pesky #7 again. It stayed above 700 RPM where the others caused dipping below 700 RPM. None of the cylinders when cancelled caused that exhaust noise to go away…going to examine plugs and spark next, starting with #7.
Switched that injector from the back of the engine to the front – definitely has more power. It is still rough but not rough as often. It still loses power when hot.
The exhaust sound did not relocate itself along with the injector – I am actually going for a power balance test before I examine plugs. Took me a bit but found Eric’s writeup here and going to follow that: http://www.ericthecarguy.com/faq/solving-automotive-performance-issues?start=3
Will cancel each cylinder and look for 1) an RPM loss which does not match the other cylinders and 2) listen for that “exhaust” sound to go away.
Switched that injector from the back of the engine to the front – definitely has more power. It is still rough but not rough as often. It still loses power when hot.
The exhaust sound did not relocate itself along with the injector – I am actually going for a power balance test before I examine plugs. Took me a bit but found Eric’s writeup here and going to follow that: http://www.ericthecarguy.com/faq/solving-automotive-performance-issues?start=3
Will cancel each cylinder and look for 1) an RPM loss which does not match the other cylinders and 2) listen for that “exhaust” sound to go away.
Progress! It drives much more smoothly with cleaned injectors (also, all ohm’d out within spec); when the engine was cold for a glorious 3 minutes I had clean power. 🙂 It only does one “I’m about to die” lope when coming to a stop now and most of the time it no longer tries to die or hesitate when taking off.
Roughness is still there and still gets worse as it gets hot but engine is quieter overall (I am using 200 fewer RPMs now to do the same acceleration, so I think that is why it is quieter). I made sure to put the injectors back in the order they were originally so that if they were at fault it would not change the sounds I hear.
Since the sound the engine makes is worse in drive I nosed it to another vehicle, left it in drive and listened. I was able to hear the #7 cylinder making a different sound than the others. It clicks the same at the fuel injector, but with the cone attachment on my stethoscope, that one is just…different near to the spark plug, more echoing and deep, hard to explain. Sticks out like a sore thumb, though.
I plan to move that #7 injector from the rear of the engine to the front and see if the sound follows. If it does not follow, I am going to swap the spark plugs. If it does not follow then, I am going to put the old spark plug wires back on. If that does not resolve I am going to assume that the engine just echoes differently in that cylinder…and maybe move the injector to the right side of engine and see if the exhaust noise follows to that side, just for good measure.
EGR – wow, more like “EGTar” – I had to push that rod hard to get even a bit of movement. If I shake it I hear fine rattling inside and black powder falls out and it is simply coated in black powder internally otherwise. Still focusing on that odd cylinder first but EGR seems in trouble too.
Code 44 came back, lean exhaust on left side. Same side as that odd-sounding cylinder, hmm. Letting engine cool then back at it…
Progress! It drives much more smoothly with cleaned injectors (also, all ohm’d out within spec); when the engine was cold for a glorious 3 minutes I had clean power. 🙂 It only does one “I’m about to die” lope when coming to a stop now and most of the time it no longer tries to die or hesitate when taking off.
Roughness is still there and still gets worse as it gets hot but engine is quieter overall (I am using 200 fewer RPMs now to do the same acceleration, so I think that is why it is quieter). I made sure to put the injectors back in the order they were originally so that if they were at fault it would not change the sounds I hear.
Since the sound the engine makes is worse in drive I nosed it to another vehicle, left it in drive and listened. I was able to hear the #7 cylinder making a different sound than the others. It clicks the same at the fuel injector, but with the cone attachment on my stethoscope, that one is just…different near to the spark plug, more echoing and deep, hard to explain. Sticks out like a sore thumb, though.
I plan to move that #7 injector from the rear of the engine to the front and see if the sound follows. If it does not follow, I am going to swap the spark plugs. If it does not follow then, I am going to put the old spark plug wires back on. If that does not resolve I am going to assume that the engine just echoes differently in that cylinder…and maybe move the injector to the right side of engine and see if the exhaust noise follows to that side, just for good measure.
EGR – wow, more like “EGTar” – I had to push that rod hard to get even a bit of movement. If I shake it I hear fine rattling inside and black powder falls out and it is simply coated in black powder internally otherwise. Still focusing on that odd cylinder first but EGR seems in trouble too.
Code 44 came back, lean exhaust on left side. Same side as that odd-sounding cylinder, hmm. Letting engine cool then back at it…
Thanks guys! I moved those two to the top of my list. Injectors clear the way for easy access to the EGR, but if I find any issue with the EGR I will test with just the injectors cleaned and do EGR after. That way we can avoid a “Wait, what fixed it?” situation…
One injector (passenger side of engine) seemed to spray in an unreliable pattern, sometimes just two streams. I had to run carb cleaner through it twice before it had a reliable pattern of gas spray…taking a short break now to get the fumes out of my system then back to it!
Thanks guys! I moved those two to the top of my list. Injectors clear the way for easy access to the EGR, but if I find any issue with the EGR I will test with just the injectors cleaned and do EGR after. That way we can avoid a “Wait, what fixed it?” situation…
One injector (passenger side of engine) seemed to spray in an unreliable pattern, sometimes just two streams. I had to run carb cleaner through it twice before it had a reliable pattern of gas spray…taking a short break now to get the fumes out of my system then back to it!