Bad knocking... still having truble
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Bad knocking... still having truble
Hey guys,
My friends Vette is still having problems with bad knocking when any load over about 25% is quickly put on the engine. I changed the spark plugs and wires because they were sparking at night, but the problem still persists...
I dont know how to diagnose this any further and I am looking for advice...
Vette Info:
1994 Automatic LT1
60k miles
NO check engine lights
you can hear the miss/knock here:
http://www.youtube.com/watch?v=SOjOsgow2bY
Thanks!
My friends Vette is still having problems with bad knocking when any load over about 25% is quickly put on the engine. I changed the spark plugs and wires because they were sparking at night, but the problem still persists...
I dont know how to diagnose this any further and I am looking for advice...
Vette Info:
1994 Automatic LT1
60k miles
NO check engine lights
you can hear the miss/knock here:
http://www.youtube.com/watch?v=SOjOsgow2bY
Thanks!
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Sounds like its misfiring.
Make sure you got all the plug wires on good and the plugs are tight.
Then check spark out of the coil to be even and consistent. It is best to have a inline checker and an HEI type checker.
I prefer this one for when the engine is running off the coil to cap wire.
http://www.harborfreight.com/inline-...ker-69014.html
This one for testing spark output during cranking both coil and plug wires.
Can check plug wires while engine is running but not coil, duh.
http://easyautodiagnostics.com/HEI-S...k_tester_1.php
Make sure you got all the plug wires on good and the plugs are tight.
Then check spark out of the coil to be even and consistent. It is best to have a inline checker and an HEI type checker.
I prefer this one for when the engine is running off the coil to cap wire.
http://www.harborfreight.com/inline-...ker-69014.html
This one for testing spark output during cranking both coil and plug wires.
Can check plug wires while engine is running but not coil, duh.
http://easyautodiagnostics.com/HEI-S...k_tester_1.php
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Sounds like its misfiring.
Make sure you got all the plug wires on good and the plugs are tight.
Then check spark out of the coil to be even and consistent. It is best to have a inline checker and an HEI type checker.
I prefer this one for when the engine is running off the coil to cap wire.
http://www.harborfreight.com/inline-...ker-69014.html
This one for testing spark output during cranking both coil and plug wires.
Can check plug wires while engine is running but not coil, duh.
http://easyautodiagnostics.com/HEI-S...k_tester_1.php
Make sure you got all the plug wires on good and the plugs are tight.
Then check spark out of the coil to be even and consistent. It is best to have a inline checker and an HEI type checker.
I prefer this one for when the engine is running off the coil to cap wire.
http://www.harborfreight.com/inline-...ker-69014.html
This one for testing spark output during cranking both coil and plug wires.
Can check plug wires while engine is running but not coil, duh.
http://easyautodiagnostics.com/HEI-S...k_tester_1.php
I 3x made sure all of the wires were on the plugs and opti tight so I think that is covered! How do you get to the coil?
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
I personally did the wires and plugs and I am sure they are not crossed... If they were, the car would have trouble idling and driving under soft load conditions right?
I checked the fuel pressure and it is good... It is good at idle, while driving at different rpms, and holds when the car is off... I am not sure if that weeds-out the injector problem...
As for Compression, I am not sure because I dont have a compression tester.
I checked the fuel pressure and it is good... It is good at idle, while driving at different rpms, and holds when the car is off... I am not sure if that weeds-out the injector problem...
As for Compression, I am not sure because I dont have a compression tester.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Fuel pressure won't weed out an injector issue. You didn't mention what "good" was. What was the pressure? Did it rise to spec and hold at WOT?
Do you have a test light? Some dielectric grease? Hook the test light to ground. Lube the probe and with the engine running, slip the probe into the back of the plug boots until you short out that cyl. OR, pull injector plugs one at a time.
Either way, you're killing a cylinder (w/o risk of getting shocked). When you get to the cylinder that is dead (not contributing) you'll notice that there is no change or very little change to the way the engine runs.
Yes, the engine can run quite well on only 7 cylinders.
Once you have confirmed that there IS a weak or dead cylinder, THEN you'll need to buy a compression tester. At that point you'll want to confirm three things on the suspect cylinder; compression, spark, and fuel.
EDIT: JUst listened to the vid; I completely agree that it's missing a cylinder during some (most) of the rev-up events.
Do you have a test light? Some dielectric grease? Hook the test light to ground. Lube the probe and with the engine running, slip the probe into the back of the plug boots until you short out that cyl. OR, pull injector plugs one at a time.
Either way, you're killing a cylinder (w/o risk of getting shocked). When you get to the cylinder that is dead (not contributing) you'll notice that there is no change or very little change to the way the engine runs.
Yes, the engine can run quite well on only 7 cylinders.
Once you have confirmed that there IS a weak or dead cylinder, THEN you'll need to buy a compression tester. At that point you'll want to confirm three things on the suspect cylinder; compression, spark, and fuel.
EDIT: JUst listened to the vid; I completely agree that it's missing a cylinder during some (most) of the rev-up events.
Last edited by Tom400CFI; Nov 26, 2012 at 08:48 PM.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
I'd go thru each cyl as suggested and then pull plugs to inspect each one for color, deposits and insulator condition. Even IF they are brand new the spark plug color is a picture of combustion in that cylinder. There WILL be one thats odd...darker or spotted...something. Once that cyl is identified, then confirm the basics as suggested...air, fuel and spark.
You can also pull inj wires to do the same thing....essentially killing the fuel supply to that cyl to see if it makes ANY difference in the idle and/or as throttle is applied. When you pull one that changes nothing...thats your hole.
and yes, it will run pretty well with certain plug wires crossed or d/c.
The definitions are always confusing...what one guy calls knocking is misfiring to others. Knocking makes me want to look at specific things first...while a misfire is more generic. Basics always first...fuel pressure,. numbers are good to know, timing set by the FSM, and inj ohms tested and leak down done. Compression when none of the above yeild results.
Whats your FSM say as far as following the flow chart for engine misfire?
You can also pull inj wires to do the same thing....essentially killing the fuel supply to that cyl to see if it makes ANY difference in the idle and/or as throttle is applied. When you pull one that changes nothing...thats your hole.
and yes, it will run pretty well with certain plug wires crossed or d/c.
The definitions are always confusing...what one guy calls knocking is misfiring to others. Knocking makes me want to look at specific things first...while a misfire is more generic. Basics always first...fuel pressure,. numbers are good to know, timing set by the FSM, and inj ohms tested and leak down done. Compression when none of the above yeild results.
Whats your FSM say as far as following the flow chart for engine misfire?
Last edited by leesvet; Nov 26, 2012 at 09:03 PM.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
I'd go thru each cyl as suggested and then pull plugs to inspect each one for color, deposits and insulator condition. Even IF they are brand new the spark plug color is a picture of combustion in that cylinder. There WILL be one thats odd...darker or spotted...something. Once that cyl is identified, then confirm the basics as suggested...air, fuel and spark.
You can also pull inj wires to do the same thing....essentially killing the fuel supply to that cyl to see if it makes ANY difference in the idle and/or as throttle is applied. When you pull one that changes nothing...thats your hole.
and yes, it will run pretty well with certain plug wires crossed or d/c.
The definitions are always confusing...what one guy calls knocking is misfiring to others. Knocking makes me want to look at specific things first...while a misfire is more generic. Basics always first...fuel pressure,. numbers are good to know, timing set by the FSM, and inj ohms tested and leak down done. Compression when none of the above yeild results.
Whats your FSM say as far as following the flow chart for engine misfire?
You can also pull inj wires to do the same thing....essentially killing the fuel supply to that cyl to see if it makes ANY difference in the idle and/or as throttle is applied. When you pull one that changes nothing...thats your hole.
and yes, it will run pretty well with certain plug wires crossed or d/c.
The definitions are always confusing...what one guy calls knocking is misfiring to others. Knocking makes me want to look at specific things first...while a misfire is more generic. Basics always first...fuel pressure,. numbers are good to know, timing set by the FSM, and inj ohms tested and leak down done. Compression when none of the above yeild results.
Whats your FSM say as far as following the flow chart for engine misfire?
Fuel pressure won't weed out an injector issue. You didn't mention what "good" was. What was the pressure? Did it rise to spec and hold at WOT?
Do you have a test light? Some dielectric grease? Hook the test light to ground. Lube the probe and with the engine running, slip the probe into the back of the plug boots until you short out that cyl. OR, pull injector plugs one at a time.
Either way, you're killing a cylinder (w/o risk of getting shocked). When you get to the cylinder that is dead (not contributing) you'll notice that there is no change or very little change to the way the engine runs.
Yes, the engine can run quite well on only 7 cylinders.
Once you have confirmed that there IS a weak or dead cylinder, THEN you'll need to buy a compression tester. At that point you'll want to confirm three things on the suspect cylinder; compression, spark, and fuel.
EDIT: JUst listened to the vid; I completely agree that it's missing a cylinder during some (most) of the rev-up events.
Do you have a test light? Some dielectric grease? Hook the test light to ground. Lube the probe and with the engine running, slip the probe into the back of the plug boots until you short out that cyl. OR, pull injector plugs one at a time.
Either way, you're killing a cylinder (w/o risk of getting shocked). When you get to the cylinder that is dead (not contributing) you'll notice that there is no change or very little change to the way the engine runs.
Yes, the engine can run quite well on only 7 cylinders.
Once you have confirmed that there IS a weak or dead cylinder, THEN you'll need to buy a compression tester. At that point you'll want to confirm three things on the suspect cylinder; compression, spark, and fuel.
EDIT: JUst listened to the vid; I completely agree that it's missing a cylinder during some (most) of the rev-up events.
Thanks for the info...
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Joined: Apr 2000
Posts: 15,344
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From: Texas
Knock is a constant "tap tap tap tap....". It will clearly emanate from the lower half of the engine since it's typically a rod bearing (although a bad dual-mass flywheel can knock as well). Misfiring is a dead cylinder that you can hear as a popping through the exhaust.
Personally I'd remove/replace the fuel injector connectors one at a time. When there's no change, you will have found the dead cylinder. Then you can start trouble-shooting it.
Probably a dead injector since it was doing it before the plug/plug wire swap. A noid light will verify a signal to the injector. An ohm test may show a bad injector.
You can also buy a spark tester. You simply place it against each plug wire and it'll light up when that cylinder fires. No light = no spark to that cylinder.
Personally I'd remove/replace the fuel injector connectors one at a time. When there's no change, you will have found the dead cylinder. Then you can start trouble-shooting it.
Probably a dead injector since it was doing it before the plug/plug wire swap. A noid light will verify a signal to the injector. An ohm test may show a bad injector.
You can also buy a spark tester. You simply place it against each plug wire and it'll light up when that cylinder fires. No light = no spark to that cylinder.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Knock is a constant "tap tap tap tap....". It will clearly emanate from the lower half of the engine since it's typically a rod bearing (although a bad dual-mass flywheel can knock as well). Misfiring is a dead cylinder that you can hear as a popping through the exhaust.
Personally I'd remove/replace the fuel injector connectors one at a time. When there's no change, you will have found the dead cylinder. Then you can start trouble-shooting it.
Probably a dead injector since it was doing it before the plug/plug wire swap. A noid light will verify a signal to the injector. An ohm test may show a bad injector.
You can also buy a spark tester. You simply place it against each plug wire and it'll light up when that cylinder fires. No light = no spark to that cylinder.
Personally I'd remove/replace the fuel injector connectors one at a time. When there's no change, you will have found the dead cylinder. Then you can start trouble-shooting it.
Probably a dead injector since it was doing it before the plug/plug wire swap. A noid light will verify a signal to the injector. An ohm test may show a bad injector.
You can also buy a spark tester. You simply place it against each plug wire and it'll light up when that cylinder fires. No light = no spark to that cylinder.
Does anyone think this is a coil problem???
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
He's asking what the fuel pressure was. 43 lbs, 50 lbs, 22lbs, what was the number? What was the pressure when the ignition key was turned to the ON position but the engine not started?
As for a bad coil, it doesn't really sound like it. From the video, the engine seem to run smoothly after the initial stumble. I'm also thinking bad injectors that may be dumping fuel into a cylinder and fouling plugs.
As for a bad coil, it doesn't really sound like it. From the video, the engine seem to run smoothly after the initial stumble. I'm also thinking bad injectors that may be dumping fuel into a cylinder and fouling plugs.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Absolutely not. What makes you think that it's the coil??
Good advice has been given in this thread. Lets stop GUESSING and lets start DIAGNOSING.
1. Identify the clyinder with the miss, using one of the several techniques discribed above.
2. Figure out what is missing from that cylinder; fuel, air (compression) or spark.
3. Report back. GOOD data helps here. For example, "43 PSI" is much better than, "Fuel Pressure is 'good'." We don't know if you know, what "good" IS. Ya don't know how to identify a cylinder misfire...ya don't know "how to get to the coil" (sits right on top of the front of the motor in plain view), so what DO you know? You're here for help...help us, help YOU.
Last edited by Tom400CFI; Nov 27, 2012 at 10:52 AM.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
He's asking what the fuel pressure was. 43 lbs, 50 lbs, 22lbs, what was the number? What was the pressure when the ignition key was turned to the ON position but the engine not started?
As for a bad coil, it doesn't really sound like it. From the video, the engine seem to run smoothly after the initial stumble. I'm also thinking bad injectors that may be dumping fuel into a cylinder and fouling plugs.
As for a bad coil, it doesn't really sound like it. From the video, the engine seem to run smoothly after the initial stumble. I'm also thinking bad injectors that may be dumping fuel into a cylinder and fouling plugs.
No. That's not what most people think. In fact, I don't think a single person has said, "It's probably an injector". What people HAVE said is to unplug injectors, one at a time, for the purposes of isolating/identifying the problem (missfiring) cylinder. Someone did suggest Ohm'ing the injectors, but thats not a suggestion that it's "a bad injector".
Absolutely not. What makes you think that it's the coil??
Good advice has been given in this thread. Lets stop GUESSING and lets start DIAGNOSING.
1. Identify the clyinder with the miss, using one of the several techniques discribed above.
2. Figure out what is missing from that cylinder; fuel, air (compression) or spark.
3. Report back. GOOD data helps here. For example, "43 PSI" is much better than, "Fuel Pressure is 'good'." We don't know if you know, what "good" IS. Ya don't know how to identify a cylinder misfire...ya don't know "how to get to the coil" (sits right on top of the front of the motor in plain view), so what DO you know? You're here for help...help us, help YOU.
Absolutely not. What makes you think that it's the coil??
Good advice has been given in this thread. Lets stop GUESSING and lets start DIAGNOSING.
1. Identify the clyinder with the miss, using one of the several techniques discribed above.
2. Figure out what is missing from that cylinder; fuel, air (compression) or spark.
3. Report back. GOOD data helps here. For example, "43 PSI" is much better than, "Fuel Pressure is 'good'." We don't know if you know, what "good" IS. Ya don't know how to identify a cylinder misfire...ya don't know "how to get to the coil" (sits right on top of the front of the motor in plain view), so what DO you know? You're here for help...help us, help YOU.
Also, if most people are saying to test the injectors, they are thinking that it could be a bad injector... That is what I mean by what I said...
Thanks for all of the help...
I am going to test each injector as stated and report back... I dont have a compression tester so I might purchase one if I cant figure it out any other way.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Copy that. In the interest of saving you and your friend money, pull the injector plugs (this is not a test of the injector), or ground the spark at each cylinder one at a time, to identify the problematic cylinder. Report back.
NOTE: In your vid (could be hard to tell) but I don't notice the misfire during idle. it would be harder to hear during idle than accel, my point being, you MAY have to ground spark/disconnect injector, and then throttle it just like you did in the video. As stated earlier, good cylinders that are disabled will make a noticeable difference, especially under acceleration. THe offending cylinder, won't make a difference at all.
NOTE: In your vid (could be hard to tell) but I don't notice the misfire during idle. it would be harder to hear during idle than accel, my point being, you MAY have to ground spark/disconnect injector, and then throttle it just like you did in the video. As stated earlier, good cylinders that are disabled will make a noticeable difference, especially under acceleration. THe offending cylinder, won't make a difference at all.
Thread Starter
Safety Car
Joined: Dec 2008
Posts: 3,588
Likes: 10
From: North New Jersey
Copy that. In the interest of saving you and your friend money, pull the injector plugs (this is not a test of the injector), or ground the spark at each cylinder one at a time, to identify the problematic cylinder. Report back.
NOTE: In your vid (could be hard to tell) but I don't notice the misfire during idle. it would be harder to hear during idle than accel, my point being, you MAY have to ground spark/disconnect injector, and then throttle it just like you did in the video. As stated earlier, good cylinders that are disabled will make a noticeable difference, especially under acceleration. THe offending cylinder, won't make a difference at all.
NOTE: In your vid (could be hard to tell) but I don't notice the misfire during idle. it would be harder to hear during idle than accel, my point being, you MAY have to ground spark/disconnect injector, and then throttle it just like you did in the video. As stated earlier, good cylinders that are disabled will make a noticeable difference, especially under acceleration. THe offending cylinder, won't make a difference at all.
I will see if I can isolate the cylinder that might have the problem!
