Vibration and knock retard

[pinellas50]

Long story short, I decided to do a DM pull last night. I hadn't done one since putting the rebuilt top end of the motor back together.

Up around 3900 rpm the motor got a vibration to it. I immediately lifted out of the throttle when I felt it. Truck ran fine after that. I don't yet have a wide band or in cab FP guage.

Brand new cap, rotor, wires, plugs. Some recently replaced sensors are on the truck. Fueling mods are in my sig. Stock motor and electronics.....even the chip in the ECU.

I looked at the DM file after this. KR went up to 4.4. What I found weird was that it was still showing KR as the rpms dropped. Like it was still knocking with no throttle. Is that normal? There was no audible sound to detonation. Would 4.7 KR be felt as a vibration? I have solid mounts. This felt more like a mechanical kind of thing to me.

Not sure where to start. A wideband won't be in the picture until at least Christmas.

 

[pinellas50]

Re: Vibration and knock retard

When I had the heads off the motor, I verified that the harmonic balancer had not slipped. Well I guess it is possible that it could have moved a degree or two without me being able to tell. All the pistons came up to the same height so I don't think there is a rod issue. Timing is set at zero. Fuel pump, fuel filter, and the fuel pump wiring harness are all relatively new additions. I have looked at the fuel lines from front to back and didn't find anything like a smashed or kinked fuel line.

Just to answer some of the things I found during searching. I never found anything talking about KR and a vibration such as this all in one post or being related to each other.

This should be the DM file: http://www.mediafire.com/?sharekey=916032f4082d64c2d2db6fb9a8902bda

 

[SCWolverine]

Re: Vibration and knock retard

You mentioned solid mounts, did you just put them in? Does the vibration and/or KR still occur if you rev it in P or N (no load)?

 

[pinellas50]

Re: Vibration and knock retard

The mounts have been in there for almost 2 years.

I didn't think to rev it all the way up in neutral with DM recording. So I don't know. I guess that is one of the first questions to get answered.

 

[jwaller]

Re: Vibration and knock retard

there is a lag time to the kr being removed. so when you see falling rpm's and still have KR it's only bc the computer hasn't yet restored all the timing it was pulling under load.

solid mounts will not cause KR. I use them in every truck I build and it's not an issue. if you felt a vibration you need to look elsewhere. ie driveshaft, wheel, tire, propshaft. your kr was propably not even due to the engine. your knock sensor was picking up the vibration of whatever was causing the vibration you felt.

 

[SCWolverine]

Re: Vibration and knock retard

solid mounts will not cause KR.

I should have been more clear, I was thinking if the mounts were just installed, the dp-firewall clearance may have disappeared, but only resonated (rattled) at certain rpms (btdt).

 

[pinellas50]

Re: Vibration and knock retard

there is a lag time to the kr being removed. so when you see falling rpm's and still have KR it's only bc the computer hasn't yet restored all the timing it was pulling under load.

solid mounts will not cause KR. I use them in every truck I build and it's not an issue. if you felt a vibration you need to look elsewhere. ie driveshaft, wheel, tire, propshaft. your kr was propably not even due to the engine. your knock sensor was picking up the vibration of whatever was causing the vibration you felt.

Thank you sir. This makes sense. I didn't suspect the solid mounts. I was just pointing that out as they will transmit vibration through the chasis easier than regular mounts.

I just can't think of anything in the driveline that would only show itself only under heave load at higher rpm like that. I have looked at the flexplate and there are no cracks there. Drive shaft and propshaft both look good with no slop to them when yanked on. I'm hesitant to pull the prop shaft and try WOT for fear of killing the viscious clutch.

Is there any other way to narrow this down? Would unplugging the electric to the tranny to prevent the converter from locking up tell me anything either way?

 

[pinellas50]

Re: Vibration and knock retard

I unpluged the electric to the turbo to take it out for a boost limited run to see what it did.

Before the run, I reved it up a few times while in park. The vibration was there up around 4200 and was enough to set off the knock sensor. That narrows things down quite a bit.

I ran it through the gears once on the way home just to do it. No knock on this boost limited run.

So I think I am looking at a problem with the harmonic balancer, flex plate, TC, or something internal like a bent rod(God I hope not). Anyone agree or disagree?

My thought is to go after the balancer first for obvious reasons. I looked at it tonight and didn't see any wobble or anything else weird about it. I'm also assuming that the flex plate and mabey even the TC have weights on them that I should check to make sure they didn't fly off or something. Actually I think I will start by pulling the serpentine belt to try and rule out front engine accessories.

Am I on the right track here?

Oh. Here is the latest DM file if anyone cares to look. http://www.mediafire.com/?sharekey=916032f4082d64c2d2db6fb9a8902bda

 

[MikeMcNair]

Re: Vibration and knock retard

have you pulled the plugs to see if there was oil on them? i apparently had a simiar issue, and it was due to the decrease in octane when under heavy load due to oil seepage. (sp)

just a thought, plus it is free to check

 

[sly dvl]

Re: Vibration and knock retard

Just another thought, are you still using the stock clutch fan? I've seen old worn clutch fans cause vibrations @ higher RPM.
I put an electric fan on an older 4.3 I had years ago, and I couldn't believe how much smoother it was when going through the gears.

 

[pinellas50]

Re: Vibration and knock retard

I haven't pulled plugs since getting this new top end of the motor together. I had them out a couple of months ago during the cylinder head swap and there was no trace of oil on them. I don't suspect anything like that from the bottom end. Though you are right, it's a free check so I'll keep that in mind.

The fan clutch is one of the things I tought of. That's a lot of metal flying around.

Thanks for the ideas. I'll know more once I get a chance to run it without the serpentine belt. It's just getting the time to mess with it.

I did take the intake tube from the box to the turbo off today. I found that it was cracked big time and just about to feed itself to the turbo. I got lucky finding that one! So now I have another thing to put on my to do list. It never ends.

 

[dgoodhue]

Re: Vibration and knock retard

Did you use Loctite on the flywheel bolts?

 

[pinellas50]

Re: Vibration and knock retard

I've never had the flex plate off. I have no idea what could have been done with it in the past.

Some time ago I was under there and grabbed the flex plate to see if it moved at all. It was solid as a rock with no cracks in it.

I've had this vibration since I got the truck and had started looking for it a long time ago. I got side tracked with a blown head gasket and three cylinder head swap jobs.....long story. I don't remember the vibration being as intense as it is now though. But it could have easily been a year ago since I was looking at the vibration issue.

So back to the question, loose flex plate bolts should show themselves if I try to move the flex plate around by hand, right? If I don't find the answer in the front of the motor, the flex plate/TC will be my next stop.

 

[dgoodhue]

Re: Vibration and knock retard

I've never had the flex plate off. I have no idea what could have been done with it in the past.

I had assume the motor had been out recently from quickly reading your post. From what I have seen, usually the flex plate bolt start to loosen within 1000 miles.

Have you tried manually locking to the torque converter (A to F on the ALDL) to see if it goes away.

 

[pinellas50]

Re: Vibration and knock retard

Well, good news I think. I got the motor up to operating temp and then took the belt off. No more vibration.

Before that I took the fan out and took it for a drive. There only seemed to be a hint of vibration at full rev in neutral......nothing like last night. Of course I didn't take it full throttle with no fan on it to see if the vibration was gone........that would have made too much sense. I don't know why I didn't think to do that. Oh well, I can try again soon with that idea.

The fan clutch appears old and crusty. I grabbed the fan and tried to rock it side to side. I did notice a little play in it but no much at all.

So now I guess the standard game of throwing parts at it begins. I guess I'll start with the fan as it makes the most sense to me at least.

And 2661. I know a new motor was put in back in 03 at unknown mileage. There was supposed to have been a rebuilt transmission put in at some point but I didn't get any documentation on that to know when that happened. I have put around 2500 miles on it since I got it 2 years ago. So I guess my point is the flex plate was off at the most 5 years ago and the least 2 years and 2500 miles ago.

I haven't tried locking the TC. If tonight's test turns out to be inaccurate and I need to start looking at the rear of the motor I will go there.

Thanks for eveyone's help so far.

 

[MikeMcNair]

Re: Vibration and knock retard

the fact that the heads were off, MAY JUST BE IT. if the valve seals are shot/improperly set, the oil will sneak in there.

i would pull a plug or two to see before throwing any parts at it.

oh, and the plugs i had were ~ 400 miles and ~ 1 month old, and were shot!! it can happen in minutes. just food for thought.

looks like you and i both have a long night of logging ahead of us

 

[Big Mike]

Re: Vibration and knock retard

Are you sure you have the correct flex plate from the 03 build, our v6 flex plates have a counter weight on it very noticeable (you said you always had a vibration) when the motor was rebuilt was it balanced?? Have you checked your balancer to see if it was loose and walking forward? Do a compression check maybe you have a cracked piston/ring land,check plug wires make sure you have the correct firing order and the wires are all connected properly on the plugs and cap maybe you are not running on all 6 cylinders. re check your rocker adjustment maybe one backed off since adjustment,maybe you have a bad injector not firing. Good luck and keep us posted.

 

[pinellas50]

Re: Vibration and knock retard

All good ideas guys. Thank you!

Mike. The heads are freshly rebuilt with only a couple hundred miles on them now. These are not high on my suspect list. I may pull a plug or two while I'm in there just for good measure.

Big Mike. All I know of the motor is that a new short block was put in at a dealership in Maryland. There in nothing on the recepit about a new or different flex plate. When I was looking at the flex plate awhile ago I was mainly looking for cracks and didn't pay attention to the counter weight or possible lack of one.

I have verified that the balancer is true to TDC. Real easy to do with the heads off the motor. It doesn't have any wobble to it when the motor is running. So it APPEARS ok to me. I have kicked around the idea of putting an after market balancer on it given the reputation of the stockers. That will probably be my next move if this fan idea doesn't pan out.

I did a compression test just a couple of months ago. It came back 150 across 5 cylinders and around 160 on the last cylinder.

It's running on all 6 cylinders. The motor is real smooth up to 4K rpm. That's when the vibration sets in. And it's consistent on a neutral rev as well as at WOT so I don't suspect spark blow out. I set the gap at .32 if memory serves.

I'm going to try and take it back out tonight without the fan on it again to see if the vibration is there at WOT without the fan.

 

[Big Mike]

Re: Vibration and knock retard

Try disconnecting your torque converter and push it twords the rear then start the truck to check if it may be the converter. While your at it you may want to look for the weight on the flexplate.

 

[pinellas50]

Re: Vibration and knock retard

I took it out last night with no fan. I got the same result as when I did the neutral rev. The vibration was still there but was only about 1/3 what it was with the fan on. KR dropped to 2.4 at WOT.

What I found to be real interesting was KR kicked in at 2.4 around 3700 to 3800 but then dropped as rpms climbed to 4200. This was the same rpm as the vibration started.

So I'm left scratching my head. The water pump shaft seems rock solid. None of the accessories have any noise to them what so ever. I'm still rather confident that it's something at the front of the motor doing this based upon the no serpentine belt test but I'm kind of at a loss now. I've never run across something like this before.

DM File: http://www.mediafire.com/?sharekey=916032f4082d64c2d2db6fb9a8902bda