Chevy. Posted March 20, 2008 Report Share Posted March 20, 2008 hey guys im havn a problem with my motor ok so here is my deal. i have a 98 chevy RCSB with a LQ9 in it that was installed at Nelson perofmance. allen finally finished everything up and was driving it around town and he started to notice a miss fire in the #4 cylinder. its not big, or noticeable when driving, only when idle. it kinda sounds like a loap from a big cam. the motor has never been opened up before, it had less then 17xxx miles on it. allen changed the pcm, coil, all the coils, injector, all the injectors, spark plugs, sp wires, checked the compression, it all came out a little above 10 to 1 in each cylinder. he did a compression leak down test, it all came out good. so after idling for a few minutes u can hear it miss fire, and u pull the plug out, its black from soot not oil, which to me seems like it is running rich. well the truck runs awesome except for this one little thing. anyone ever had this problem before?? we dont want to open the engine up because my budget is over as it is and that will defantly break my wallet here is allens post over at ls1truck.. #4 plug, second one on the passenger side, keeps fouling during idle.I can detect a misfire once in a while during cruising with the laptop. If the truck idles long enough, it will start to rock like the engine has a small cam. But during acceleration in fourth gear, everything is smooth and I don't feel a misfire or hesitation, like you would if a bad plug or wire exists. Here's what I've changed and done to troubleshoot this: replaced plug replaced injector replaced wire replaced coil replaced entire coil set confirmed harness is correct. Measured from pcm to coil and all terminals. replace pcm all sensors look good and are working. If I take the truck out for a spin, it seems the plug will clear up a bit. What I mean is, if the truck idles, the plug will get real black, if I go drive it, the plug starts to get cleaner. So that's why I say an idle misfire. I shook stuff while the truck was running too to see if the cause was a bad connection somewhere. Every once in a while, the engine seems like it clears up for a minute or two. The only cylinder giving me this issue is #4. I pulled the #4 injector connector and plugged in another injector, you can feel the injector firing, so I know the wiring is good and that injector is firing. I pull the plug wire, put a spare plug in it and laid it on the valvecover to see if I was actually getting fire, it is. The plug fires just like all the other ones, as far as spark intensity. Does anyone else have any suggestions on what to look for or replace? This is driving me nuts! I did a compression test and it looked ok, I haven't done a leak down test, which would show a valve seat, bent valve, blown head gaskets, etc. I wanted to add, I drove it some more tonight and it's definitely missing during cruising and semi aggressive acceleration, so pretty much all the time. keep them coming, just need to get this last issue taken care of. any ideas would help greatly thanks Quote Link to comment Share on other sites More sharing options...
Fireman31 Posted March 20, 2008 Report Share Posted March 20, 2008 (edited) Sounds to me like you have a bad plug wire or a bad injector. EDIT: I see you went that route already........ Edited March 20, 2008 by Fireman31 (see edit history) Quote Link to comment Share on other sites More sharing options...
SS_bnoon_SS Posted March 20, 2008 Report Share Posted March 20, 2008 Does anyone know if the injectors are batch fire, or sequential? I know in the batch fire systems, you can move one injector plug from one injector/cylinder to another to see if the problem follows the wiring or stays with the cylinder... Since you've already replaced everything else, it's all I can think of... Quote Link to comment Share on other sites More sharing options...
Chevy. Posted March 20, 2008 Author Report Share Posted March 20, 2008 yea its wierd guys, this one has me an nelson stumped! well i guess its good it only really happens after idling for a few mintues Quote Link to comment Share on other sites More sharing options...
desrtrat Posted March 20, 2008 Report Share Posted March 20, 2008 is there a way to check the voltage going to that injector? i would think there has to be a set voltage that it could be not getting Quote Link to comment Share on other sites More sharing options...
Chevy. Posted March 21, 2008 Author Report Share Posted March 21, 2008 is there a way to check the voltage going to that injector? i would think there has to be a set voltage that it could be not getting i have no idea, but i swaped injectors and even the hole fuel rail still same problem .. Quote Link to comment Share on other sites More sharing options...
detjoe Posted March 22, 2008 Report Share Posted March 22, 2008 what about an intake manifold leak? Quote Link to comment Share on other sites More sharing options...
Fireman31 Posted March 22, 2008 Report Share Posted March 22, 2008 what about an intake manifold leak? What if there is actually something stuck in the intake manifold? There was a thread here a while back when someone had rough running and knock sensor issues. There was actually leaves and all kinds of crap stuck in the intake manifold........ Quote Link to comment Share on other sites More sharing options...
Chevy. Posted March 22, 2008 Author Report Share Posted March 22, 2008 What if there is actually something stuck in the intake manifold? There was a thread here a while back when someone had rough running and knock sensor issues. There was actually leaves and all kinds of crap stuck in the intake manifold........ nope its all sealed up, nice an clean. pretty much brand new too.. just drove the truck about 100 miles an i think i found out what the problem is, a bent valve, im gunna get a new head slap it on see if it fixes it. Quote Link to comment Share on other sites More sharing options...
Tony-CA Posted March 22, 2008 Report Share Posted March 22, 2008 I'd want to know for damn sure I had a valve issue before I slapped on a head. You could do a running compression test on the #4 hole and compare it to good hole. Usually a lower reading will show up on the affected cylinder with respect to valve sealing problems. Another option would be to hook it up to a scope with a vacum/pressure transducer. If the #4 cylinder pulled less vacum then the rest you'd know you had a mechanical problem. Something like this would probably have to be taken to a good independent repair shop. Most dealers don't even have scopes. It's all about swaptronics to them. Quote Link to comment Share on other sites More sharing options...
Chevy. Posted March 23, 2008 Author Report Share Posted March 23, 2008 I'd want to know for damn sure I had a valve issue before I slapped on a head. You could do a running compression test on the #4 hole and compare it to good hole. Usually a lower reading will show up on the affected cylinder with respect to valve sealing problems. Another option would be to hook it up to a scope with a vacum/pressure transducer. If the #4 cylinder pulled less vacum then the rest you'd know you had a mechanical problem. Something like this would probably have to be taken to a good independent repair shop. Most dealers don't even have scopes. It's all about swaptronics to them. compression test ran fine, i can hear it making a tapping noise now that i have put about 200 miles on it. its deffantly something in the head. here is a vid, you cant really hear it here this was takn this morning.. after i did this vidoe i changed the plug out, it was soaked in gas. http://s70.photobucket.com/albums/i105/_Ch...=newvids001.flv Quote Link to comment Share on other sites More sharing options...
SS_bnoon_SS Posted March 24, 2008 Report Share Posted March 24, 2008 compression test ran fine, i can hear it making a tapping noise now that i have put about 200 miles on it. its deffantly something in the head. here is a vid, you cant really hear it here this was takn this morning.. after i did this vidoe i changed the plug out, it was soaked in gas. http://s70.photobucket.com/albums/i105/_Ch...=newvids001.flv Sounds like a lifter sticking to me, could be a sticky valve too, but I would replace a set of lifters first because it's a lot less work than the entire head. ...and, uh, your camera work about cost me my lunch. Quote Link to comment Share on other sites More sharing options...
misterp Posted March 24, 2008 Report Share Posted March 24, 2008 (edited) Yeah you got something clattering away in there, you can really hear it when you pop the throttle. I quickly scanned your posts and it sounds like you've already done this - but what you do is swap the ignition components on the #4 cylinder with a known good set of components. i.e. swap the coil, plug, and plug wire between #4 and say #2 cylinder, and if the problem is in the swapped components then you will see the misfire "move" to the #2 cylinder. If however the #4 continues to have an issue then you know it's not the ignition causing the problem. Likewise swap the #4 injector with another known good injector (say again #2) and see if the misfire moves to the #2 chamber. I believe in leakdown tests rather than compression tests. If you have done a leakdown test in the #4 hole and it's under 2-3% then the chamber is physically in good condition. So that would leave the valvetrain to be suspect, maybe a shot lifter? SS TRCK's idea to view running manifold vacuum is a good way to find a valvetrain issue but requires specialized equipment. So I would test "cheapest to most expensive" meaning swap ignition/injector components between cylinders first since it is cheap to do and rules out those components, then do a leakdown test to verify rings & valves, and assuming those results are fine then it's gotta be the valvetrain. My $1 is on a bad lifter. Mr. P. ps - I just had an old-school idea, get your hands on a cheap vacuum guage and watch the needle as you hear the clacking underhood - the needle should be dead smooth at steady RPM but if instead the needle is jumping or fluctuating then you've got a valvetrain problem. I'm sure there's gotta be a web page on google that illustrates diagnosing vacuum problems in a running motor. Edited March 24, 2008 by Mr. P. (see edit history) Quote Link to comment Share on other sites More sharing options...
Chevy. Posted March 25, 2008 Author Report Share Posted March 25, 2008 Yeah you got something clattering away in there, you can really hear it when you pop the throttle. I quickly scanned your posts and it sounds like you've already done this - but what you do is swap the ignition components on the #4 cylinder with a known good set of components. i.e. swap the coil, plug, and plug wire between #4 and say #2 cylinder, and if the problem is in the swapped components then you will see the misfire "move" to the #2 cylinder. If however the #4 continues to have an issue then you know it's not the ignition causing the problem. Likewise swap the #4 injector with another known good injector (say again #2) and see if the misfire moves to the #2 chamber. I believe in leakdown tests rather than compression tests. If you have done a leakdown test in the #4 hole and it's under 2-3% then the chamber is physically in good condition. So that would leave the valvetrain to be suspect, maybe a shot lifter? SS TRCK's idea to view running manifold vacuum is a good way to find a valvetrain issue but requires specialized equipment. So I would test "cheapest to most expensive" meaning swap ignition/injector components between cylinders first since it is cheap to do and rules out those components, then do a leakdown test to verify rings & valves, and assuming those results are fine then it's gotta be the valvetrain. My $1 is on a bad lifter. Mr. P. ps - I just had an old-school idea, get your hands on a cheap vacuum guage and watch the needle as you hear the clacking underhood - the needle should be dead smooth at steady RPM but if instead the needle is jumping or fluctuating then you've got a valvetrain problem. I'm sure there's gotta be a web page on google that illustrates diagnosing vacuum problems in a running motor. I did a compression test my self yesterday and here is what i came up with #'s 2, 6, and 8 are around 160 psi and # 4 is around 110 psi. so there is deffantly something going on in there, the problem has gotten a lot worse sence nelson performance had my truck, so maybe thats why the test came out bad this time.. i talked with the guy who i purchased my motor from, he is willing to send me a complete head that has about 28xxx miles on it, with a new head gasket and head bolts, free of charge. they should be here by thursday, so friday i will remove the head and take a look at it and see if those valves are messed up.. the only reason i am saying its not a bad lifter, is becasue of the back fire around 50+ mph. i think that ticking noise in the video is from massive exhaust leaks. i will have those fixed in a week when i take the truck back up to nelson to have him fix a few other things. haha sorry if i was that bad at using the camera i was just trying to get short video of everything.. Quote Link to comment Share on other sites More sharing options...
chpspecial Posted March 25, 2008 Report Share Posted March 25, 2008 it could be a cracked ring land. Mine had a cracked ring land and after a compression test I had similar results to your, and the same symptoms. Quote Link to comment Share on other sites More sharing options...
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