Knock sensor or dealer copout?
 

So, having my issues with number 8 misfiring at 4000+ RPM. Took to dealer after switching plug, wire, coil, injector, and still same issue.*

Went there today and went for a ride with the tech. He is trying to say that header is hitting frame at WOT and tripping knock sensor to pull timing from #8 only.*

Is this possible? *I know the clearances are tight with the pace setters but can knock sensor pull timing from only one cylinder? *

Or are they tryin to get out of digging deeper into it?

knock sensors don't do that

That's what I thought. Went for a ride with the tech with scanner hooked up and it read 0* knock retard the whole time but he is insisting that's what it is.

Just got off phone with tech, he's saying his log is showing knock on all cylinders. Once again, blaming it on headers. My Aeroforce shows 150+ misfires on #8 from 4000 through shift and NONE on any other cylinder.*

So pissed.

Crank sensor maybe? But I dont see that just randomly going out after the mods you did at all. What was the tech using to log the car? Is the mis-fire just a hiccup or constant after 4k? Look for possible drops in voltage.

On my first evo with the wrong downpipe, it hit the transfer case and pulled timing.

I have sigs and avatars turned of so excuse me for asking but Im curious what kind of car you are having issues with?

Do you have a tune for your headers?

Tbss

http://www.gmfullsize.com/forum/showthread.php?t=90314

possibly?

So when I talked to him, he says there are only 280 misfires in the history. I unhooked battery the other day, and it has only been driven to "failure" three times since. 2 of them were when he was driving and I was riding shotgun with GM TECH 2 scanner in my lap. It was set on knock retard monitor, and it NEVER showed any knock retard while I had it. He had it recording, and says now that he reviewed the data, it was detecting knock on all cylinders, not just #8.

280 misfires in three 3 second goes at WOT. But if I monitor with aeroforce gauge (can monitor misfires on each cylinder individually), it will hit 150+ on #8 ONLY from 4000RPM through 1-2 shift. So I don't know what to think.

I told him if he felt so strongly about it, to make some clearance....dimple the primary a little bit or dent the fucking framerail, whatever, but that I wasn't going to pick the truck up, do it myself, and then have to bring it back when that wasn't the problem.

I don't know much about knock sensors and retard and all that, but with only 2 sensors, I find it hard to believe that the sensor can sense that only 1 cylinder is knocking b/c of a harmonic "noise/vibration" in the header. Just doesn't make sense. I have heard some valvetrain noise a couple of times, and told them that.

BUT, it seems that he is hell-bent on blaming it on this instead of checking other things first.

Then, he says the "ticking" noise I heard in the valvetrain was water dripping from A/C onto collector....WTF? I'm not a fucking idiot. I told this guy that I wasn't Joe Blow off the street with a TBSS, I have been wrenching on cars all my life, and know what valve train noise is. There was this little plastic hose that comes out of firewall that routes condensation away from exhaust.....well I found the piece of hose in my driveway. Water drips directly on collector, and guess what it sounds like.......water dripping on something hot, UNDER the truck.



I have a feeling that I will be getting a call on Monday saying that they clearanced the header and still have problem. When they tell me it's a valve spring or something like I thought all along, and told them 20 times, I am going to laugh at this guy.

So I told them I wanted Martin, Doug, or Deon, and instead got some young kid named Kelly. We'll see I guess.

That is the bad thing about dealerships. They blame it on mods. If they can't fix it, you need to take it to a tuning shop that knows what they are doing.

But, of course, if he's right, I will thank him and admit "defeat".

This is a "mod friendly" dealership and this will be warrantied if it's internal.

its NOT the knock sensor......

tell him to disconnect the knock sensor harness (back of intake manifold), this will set a knock code and retard the shit out of the timing, but it wont cause a misfire.....

tell him he is a fucking moron and pick your truck up, then call GM directly, ask them where to take it for your warranty work because you do not want that service department working on it again.

sounds like the tech just doesnt know his shit, because false knock will not cause a misfire, real knock could possibly, but "if" he is blaming the headers causing false knock then whats up with the misfires? his story doesnt hold up.....

might i ask what dealership this is and what the tech's name was? i know quite a few people in the industry.

Yep Rick Hendrick chevy in west Ashley. Tech is Kelly as mentioned above.

My uncle worked there for 20+ years, wish he was still there.....



SO, might I ask, what do YOU think it could be? Weak/broken valve spring?

So their service department is just as fucking shitty as their sales department, nice! I'd never buy or take anything to those dickfaces at Rick Hendrick.

Hope you get the problem solved man.

Worst part is the rental car....a fucking HHR.

What a POS. Damn thing won't get out of it's own way and is uncomfortable as hell. I asked for a vette for a rental jokingly, he said he had one and walked me out to the HHR. Got me.

Fuckin ey. I had to drive a HHR for someone at work and I could barely fit. Slow as balls too.

Kelley is not a young kid. He is a team leader and is one of the more certified mechanics there. Has a nasty vette as well. I will swing in tomorrow since I will be in the area.

Thanks Matt.

Not sayin that he doesn't know what he's doing at all. Just that he seemed hell bent on sticking with the knock thing and that he acted like I had no clue what I was talking about.

I tried to tell him that I know everything because I have the Internet.

did you tell him you have read ls1tech? He would have listened than

This might be why Chris (service manager) went and got him personally to meet me in service drive. Chris looks out or me.

I'm not too smart on the electronic side of things, but can a PCM differentiate between "false" & "real" knock? How does the PCM know the difference between the two?

he is saying that knock in general should not cause a misfire. i dont feel that even if it did cause a misfire that it would single out one cylinder to misfire being that the ignition isnt controlled individually per cyl

exactly what i meant, the tech is claiming the headers are causing false knock, which i'm ASSuming he is blaming the false knock for the cylinder #8 misfire...... which isnt possible.

if its picking up false knock (like alot of GMs do anyways) then it would simply pull timing, not cause a noticeable misfire above XXXX rpm, loss of power, but definately not a SINGLE cylinder misfire.

even real knock (detonation or pre-ignition) shouldnt theoretically cause a misfire either, so using knock as the cause of a misfire is in my opinion a cop out (or just an uneducated technician) which in this case doesnt seem to be the case.

PAPABEAR, since it seems to be related to RPM i'd imagine its valvetrain related, but thats just an educated guess.

my question would be does it seem to be more noticeable in higher/lower gears, when the engine is cold/hot, and when did it start.....

a knock sensor will not cause one single cylinder to pull timing, this is a gm system not a big stuff 3, dont feel bad about the HHR, when i took my tbss in for work they gave me an aveo

it does it hot and cold an above 4000 rpm and in every gear.

I Forgot to add that he brought up my motor mounts. He said I could have a mount bad that is causing the header to e too close to frame rail.

This is the stuff I'm talking about. That just doesn't make sense to me. Really grabbing for things at this point instead of diggin in. A motor mount on a 3 year old vehicle with 50k miles isn't very common.

I just want my truck back.

Hey hey hey... My Uncle Les is a salesman there and he is no dickface sir.

Les Rogers has sold me 5 vehicles. Great guy. Used to live next door to my uncle Chris.

Les has sold us two. He is the ONLY person I would go to at Hendrick. Great guy.

Papabear why even think about false knock at this point whether its from headers a motor mount or anything else because its not causing your misfire. They do understand that's what you are trying to get fixed right?

Yes they do. I'm not worried.

I am actually looking forward to saying I TOLD U SO!

Diamond in the rough :).

I hate little quirks like that. Knock sensor can be a little tricky and pick up some intrerferance from time to time. But when they are activated it should pull timing and reduce some power not pop and misfire. JP might be the guy to help you, log some pulls turn some stuff on and off should help you isolate the problem.

I'm not paying Jamie $375 to tune my truck, sorry. This will be figured out by the dealer. All I know about knock sensors after all this and all the reading I've done is that I don't know shit about them!

Have you tried to isolate the latest mods you installed and slowly determine if any of them is causing this? i.e. plug wires and all?

heres another thing to think about, what if it actually is knocking? cylinders 7 and 8 are prone to it b/c they usually run about 20-30* hotter than the rest. why dont you just pull a valve cover off and see if the spring is broke?

Did they decide the injector wasn't causing it? If its not an injector then its most likely a valvetrain issue

it could be as deep of a problem as the reluctor wheel on the crank or cam having a small nick in it. start with the simple stuff instead of letting it sit at the dealership for days, i promise your truck is the least of their worries when they have easier money coming through the door. go get it back and swap the coil pack with another, swap the injector with another, pull the valve spring out and ckeck it, make sure the rocker is torqued down properly, make sure the pushrod isnt bent, swap the wires and plugs. thats a lot of simple stuff you could do yourself that doesnt take much time

I've already done all the simple stuff. Remember my other thread? Re read my first post. I have swapped EVERYTHING and done everything short of pulling the valve cover.

I have ruled out injector, plug, wire, coil pack, and tune.