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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #1 ·
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?
 

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Premium Member
07 TrailblazerSS Imp
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9,389 Posts
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?
How would he know unless he is under the hood while you drive it or has a cam under there to watch. Speculation is not analysis.
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #4 ·
The question is, will the sensor pull timing from only one cylinder?
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #6 ·
no


did you try changing the, plug,wire,coil and injector on number 8?
Re read first post. Yes I did.

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.
 

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Premium Member
Trailblazer SS
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15,616 Posts
What a joke of a excuse. I guess there doin alright cause they don't get paid if they don't work
 

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Premium Member
2008 TB SS AWD 3SS
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3,288 Posts
Hmmm, anyone local have EFILive/HPTuners so you can get a good log of it? If its JUST #8 (sounds like it), then you might have a bigger issue here than just knock. Do a compression/leakdown test on it? Check the injector?
 

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Premium Member
TrailblazerSS 3SS
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1,226 Posts
Take it to another dealer
 

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Old but not Dead Yet!
TrailblazerSS
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9,572 Posts
I agree man to take it to another dealer. They would have to show me some printouts verifying what he claims. Sounds like he is just blowing smoke to me
 

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Registered
2007 TBSS 3SS
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525 Posts
I agree man to take it to another dealer. They would have to show me some printouts verifying what he claims. Sounds like he is just blowing smoke to me
Ask him for print outs and that you are going to get a second opinion. If he doesn't give them to you call GM complaint line in front of him.
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #13 ·
I don't want to take it to another dealer. I have been dealing with these guys for 15 years. Hell, my sister has worked there for 15 years, and they have done nothing but look out for me and my family. I want them to investigate this, and not to try and blame it on something that in my mind has nothing to do with it.

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.
 

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Philanthropist
Trailblazer SS
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346 Posts
If you can, wtite down every answer or "theory" he has to your questions or complaints. If the person askes what you are doing....the B.S. usually stops right then and there.
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #15 ·
Need some advice guys.........

Service manager called me, and says that they can't figure out what's going on. He now wants money to change plugs/wires out to stock, and go from there. Not only that, he's asking if i'm gonna "help him out" with the work they've already done?

His specific quote "We can't find anything NON-OEM that could be causing this."

YET THEY STILL HAVEN"T PULLED THE VALVE COVER? WTF?

I called the other local dealership (they are new) and the guy was a total tool on the phone, couldn't even understand him, and gave me the dealership rhetoric about processes and things I already knew.

What am I supposed to do? Let them put plugs/wires on it? Problem is, clearance issues with LT headers and stock wires, #2 and #7 primaries will melt the wires. And they want to charge me?

HELP
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #16 ·
So fed up right now and want to call them back, someone offer up some advice will ya?
 

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Premium Member
'08 TrailblazerSS
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4,146 Posts
Tell them if the parts they suggest don't fix it, then you won't be paying for it. If they do, then you'll be glad to pay for it. Tell them you pay your diagnostic fee to them because they are professionals with the latest tools and equipment to get the job done. Because you payed them diagnostic fees, you won't be paying for guesses.

I'd be looking hard at the valve springs if your truck was in my stall.

Besides it's pretty standard practice to move components around to find misfires, like if the misfire is on #6, relocate the plug to cyl #3, the wire to cyl #2 and the coil to cyl #7. The misfire will move with the defective part to the new cylinder. No need to start slinging new parts at it on a wild ass guess.
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #18 ·
Thanks jay, thats pretty much what i told them.

I don't know why the guy is dead set that it's not a mechanical issue. Once he rules out ignition, it's into the valve cover he goes.

And I already told them that I have swapped injector, plug, wire, coil, and all that yet they insisted on pulling fuel rail and now doing ignition.

At this point I really hope it's not something with the plugs or wires, but if it fixes it then so be it.
 

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stupid white guy
TrailblazerSS
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4,887 Posts
Discussion Starter · #19 ·
Jay what happens if it is mechanical. Will they still charge me diagnostic fee?
 

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Registered
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398 Posts
BTW, although it doesn't sound like this is YOUR problem, but it IS possible to pull timing (and adjust fueling) per cylinder with just a couple knock sensors.

We used to do it with the Mercury/Mototron controllers (on SeaRay ECUs). You know which cylinder is knocking based on the knock sensor with the most signal and the position of the crank. The crank acceleration is affected by knock and a misfire (which is how it detects a misfire on a particular cylinder). The ECU predicts the rate of change of the crank and watches the encoder to see if it matches the prediction or not. If not, it is probably a misfire, if no knock signature is present.
 
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